Journey By Starlight

Albert’s lost secret revealed. What is the one thing that can travel faster than light?

2007-12-31T23:59:00.000-08:00

The time has come, as the Walrus never said, to think of many things: of light and life and quantum cats, of planets and their rings and why the sun can shine so hot and give imagination wings.

By now Albert and his travelling companion are lost somewhere inside your head which just leaves me to finish off the story. Albert 2.0, like an imaginary friend, is only the palest imitation of the real thing. But then what sequel ever matched the original? I hope having first imagined this journey over a hundred years ago Einstein would have enjoyed finally completing it.

This journey was a thought experiment, the real Albert’s favourite type of experiment. A thought experiment that allowed us to imagine travelling across huge distances of space and time. When we started out 3000 years ago humans didn’t understand much about how things worked. Almost everything humanity knows about light, the universe, life and just about everything else about science was discovered during our travels. From a distant star called Deneb this journey has covered everything from how the sun shines and atom bombs to quantum mechanics and black holes. By ending up being seen we even managed to get inside one of the most the mysterious places in the universe, the human mind.

Different parts of this journey connect in surprising ways. People that made big discoveries in one area often made just as big a discovery in another. Newton worked out gravity and the basics of what light is all about. Kepler worked out planetary movement and was the first to properly explain how the human eye works. Albert himself, famous for his theories of relativity and E=Mc², received his Nobel prize not for that but for showing that light comes in little packets or photons as they were later named. The total eclipse of the sun that shot Einstein to fame happened at a place and time that was predicted using Newton’s and Kepler’s laws.

Erwin Schrödinger who made the breakthrough in quantum mechanics went onto write a little book in 1944, called ‘What is Life?’ based on three lectures he gave in Trinity College Dublin in early 1943. He predicted that life needed some genetic code in the form of what he called an aperiodic crystal. James Watson read this book and this set him on the path to discover the structure of DNA with Francis Crick in 1953. As Watson himself put it, “Up until then, I was interested in birds. But then I thought, well, if the gene is the essence of life, I want to know more about it. And that was fateful because, otherwise, I would have spent my life studying birds and no one would have heard of me".

The discovery of the structure of DNA relied on a technique that involved using the scattering of X-ray photons to work out the internal shape of crystals. Linking all these discoveries together is light. Light and other forms of electromagnetic radiation, like x-rays and microwaves, crop up in almost every aspect of science from physics to understanding the climate, possibly even in the origin of life itself.

Not bad progress in 3000 years, even if humanity didn’t leave the planet for the first time until 40 years ago. Humans haven’t travelled far in galactic terms but our understanding of what’s going on out there now stretches across the galaxy and the whole universe. In just 500 years since the renaissance, human knowledge and awareness of the universe has spread from one little planet to distant galaxies billions of light years away. So human understanding has travelled far faster than light ever could - the one thing in the universe that breaks Einstein’s rule about nothing going faster than the speed of light, apart from imagination of course.

The big question that no-one can answer is ‘why are all these laws here in the first place?’ Did they just happen by chance? Some of the laws seem so simple and elegant it’s hard to imagine they were just the random results of a huge cosmic accident. To mathematicians and physicists these equations even appear beautiful. The question of how it all started is still unanswered. Did God invent the rules and then just sit back let the universe unfold for the next fifteen billion years? Is it all some huge cosmic experiment by a super advanced race, so powerful they might as well be God? Or are we really inside The Matrix, a huge computer simulation? It’s always worth remembering that despite everything that all the smartest people on Earth do know, there is much more that they don’t know.

With all this progress humans tend to think that all the big discoveries have been made. Does that mean there’s nothing much left to discover nowadays? People thought the same thing a hundred years ago. It wasn’t true then and it almost certainly isn’t now. One of the most successful scientists of the 19th century and one of the contributors to the second law of thermodynamics, Lord Kelvin, proved this point. In 1895 he said that “heavier-than-air flying machines are impossible”, just 8 years before the Wright brothers flew the Kitty Hawk on December 17 1903 - the world’s first heavier-than-air flying machine or aeroplane as they are now called. He also came up with the now famous line in 1900 –

“There is nothing new to be discovered in physics now. All that remains is more and more precise measurement.”

This was just a few years before Einstein’s theory of relativity, quantum mechanics and the discovery of radioactivity completely changed science. So being a world famous scientist doesn’t guarantee you’ll always be right.

The science fiction writer Arthur C Clarke, the man that wrote ‘2001: A Space Odyssey’, invented three laws about progress.

First law: When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.

Second law: The only way of discovering the limits of the possible is to venture a little way past them into the impossible.

Third law: Any sufficiently advanced technology is indistinguishable from magic.

Imagine how the things you take for granted would look like to Lord Kelvin if we could take him on a 100 year journey forward through time. Supersonic aeroplanes, space travel, microwave ovens and computers would all look like some form of magic. What seems like science fiction now could, with the help of the next generation of scientists, be just as real as all these things. Sometime it takes a leap of imagination to start believing that there are things still to be discovered.

So how much more is still to be discovered? Of all the things that seem impossible now, how many will become possible in your lifetime? Maybe someone reading this will go on to prove the impossible really is possible. Remember Einstein was only working in the patent office as a clerk when in a single year he changed the world. May be it could be you that’ll make the next great breakthrough and produce hover cars and space ships that can cover huge distances to finally let humans travel more than a light second into the galaxy. Admittedly there are only a few Albert Einsteins and Isaac Newtons ever born, but for every one of them there are thousands of scientists and inventors who have imagined the impossible and proved it’s possible. Like Alice said, in Through the Looking Glass:

So every second your brain is working flat out to make sense of the pattern of light reaching your eyes. Scanning across this page a jumble of black and white arrives at the retina in the back of your eyes. At the back of your head edges are picked out by individual brain cells. Lines of light and dark put together to make up the letters of the alphabet, the shapes programmed into your brain from nursery school. The letters are effortlessly pieced together into words. Words into sentences and sentences into meaning. The meaning lingers on in your memory, slowly fading over time.

So we will last within you for as long as the memory of this journey remains with you. I hope that some of what you’ve read will stay with you forever and you will try to imagine at least one impossible thing everyday before breakfast. I know we were only a minute fraction of the light reaching your eyes at the moment we arrived. But we can still say we were there, we were seen. Not immortality perhaps, but far better than never being seen at all.

After travelling so far it would have been a dreadful pity to have arrived just as you were blinking.

What happens in your brain and what happened to Albert's brain

2007-12-26T05:24:00.001-08:00

So we’ve finally arrived. The end of our 19 quadrillion mile journey, and here we are inside your brain. In your visual cortex to be precise, under that bony lump you just felt at the back of your head. The pattern of light has been carried from your eyes to your brain and is now a pattern of flickering activity in billions of brain cells. This pattern still has to be decoded and put together before we can really claim to have been seen. This is probably one of the most difficult things your brain does.

"What's difficult about seeing?"

Seeing looks easy but is a lot more complicated than it seems. So complicated that it’s one of the things computers can’t do well. If computers could be smug, they would boast about being able to calculate millions of times faster than humans or being able to beat anyone on the planet in a game of chess. They couldn't boast about being able to see.

"Seeing doesn’t feel hard. I can certainly see better than I can play chess.”

That because human brains are built for seeing not playing chess. A four year old human will see better than the best supercomputer on the planet. A computer can certainly be programmed to recognise particular shapes but ‘seeing’ properly needs understanding of what an image means, and that requires an ability to think. Understanding and thinking are things that can’t easily be broken into little steps. So computers are great at some things but they can’t yet think for themselves or see for themselves.

“How much of our brains is involved in seeing?”

Almost half of your brain is working on vision in one way or another. If half of your brain was dedicated solely to playing chess then chess would be pretty effortless too. When you are sitting still, like now reading this blog, your brain is using just under a third of all the oxygen you breathe and burning about a third of the calories. So with half your brain working on vision, that means that a sixth of what you eat is used by your brain just to see or roughly half your lunch every day. Things like speech are done by tiny areas on just one side of the brain. Hearing is done by parts of the brain that are about one tenth of the size of the visual areas. The vision areas are just as big if not bigger than the areas using for thinking and what are called ‘higher mental functions’ - the things that make you humans clever and different to other animals. Even the brain areas involved in moving arms and legs (or anything else) are also surprisingly small. So compared to anything else you do, the fact that so much brain power is needed for seeing proves the point that seeing must be very complicated indeed.

“Does the brain just work like a really fast computer?”

Your brain works in a very different way to a computer which helps in vision and lets you do lots of things at the same time. In a computer there usually just one central chip, reasonably enough called a central processor unit or CPU, that does one thing at a time and does all the actual computing. Even though you might feel that you can only think about one thing at a time, your brain is actually made of trillions of little CPU’s called brain cells. Each of them can be working on one small part of whatever you are doing. So you can walk, see, talk and listen all at the same time. It’s what computer scientists call parallel processing, with lots of little computers sharing out one big problem.

“Do we understand anything about how the brain helps us to see?”

We know quite a lot but much more we still have to work out. The main challenges of seeing can be broken down into a few stages. First the pattern of light has to be separated to pick out different objects. This is the ‘What’ part of vision. For this the brain looks at edges, sudden changes in the pattern of light. As soon as an image reaches the visual part of the brain, the position and angle of any edges are picked out first. Colour and how things are moving can also help to ‘glue’ patterns of light together into an object. This gives the brain a basic sketch of what’s there.

“It sounds like creating a cartoon in reverse. You start with line drawings and make a simple story board with just a few of the details.”

Is seeing like drawing a cartoon in reverse? I suppose it is a bit. Well the next step is for this outline sketch or story board to be sent to next level of brain cells that start adding understanding by recognising different features.

“That would be where the cartoonist adds facial expression.”

Well your brain does this in a special area of the brain, the inferior temporal cortex that helps to recognise faces. You can find the inferior temporal cortex easily enough. Find the bony lump behind your ear and it’s just above that on the inside of your head. In this area there are brain cells that are good at finding bits of faces noses, eyes and mouths. These brain cells then lead onto the next level where the pattern of recognised features, like a police identikit picture, leads you to realise that the pink thing over there is your grandmother. You can still recognise this shape as your granny even if her legs are hidden from view by the suitcase, she is wearing new clothes you have never seen before and is perhaps even looking a little older since she last visited. That’s the real trick of recognition to be able to pick out something familiar in an unfamiliar setting, something brain scientists call invariance.

“Hmm. Do we have a brain cell for everyone we know?”

There was an idea, first suggested by Jerry Lettvin in the 1970’s that people might have a single grandmother cell (and one for everything else they recognise); a brain cell that fires when your granny appears. This master brain cell has billions of cells working for it sifting visual information. The granny cell sits on the top of the pile like a queen and makes the final decision if that person really is your granny. It is a nice idea in some ways but it seems the brain works a little differently. Rather than a single brain cell for each memory, scientists now think that recognition and memory are coded as patterns in large groups of brain cells. Otherwise one small knock on the head and your granny could vanish before your eyes.

“So is that the secret of seeing, being able to recognise what you see?”

Recognising things is important, but knowing where they are is just as important. The image your brain receives from the eye is, like the image made by any camera, flat or two dimensional. In this flat image light from all the objects in view is superimposed. Distance disappears and the only difference between objects is the pattern of light. Looking at a photograph none of this is very obvious to you of course. Your brain works this out for you so that you can tell effortlessly where one object stops and the next begins. Even in a two dimensional photograph your brain seems to instantly recreate some sense of depth, a notion of where things are in relation to one another and puts a label on what all these objects are. So it looks simple enough to work out to how far things are away, but it’s not as simple as it looks.

“How does our brain do that?”

The brain uses lots of tricks for working out how far away things really are. Cover one of your own eyes and then the other. The world will look slightly different in the two eyes, things close up seem to jump from side to side compared to the background as you change from one eye to the other. The brain has learnt to use these differences between the two eyes to work out where things are in depth. Your brain takes the two slightly different images from your two eyes and combines them into the one image that you see. The differences that seem to be lost in the process are converted by your brain into a sense of depth that is called stereopsis. You can also judge depth with just one eye. Move your head from side to side with one eye shut. Nearby objects move from side to side, but further away things seem to move less.

"That's why pigeons keep nodding their heads as they walk in the park! You told me about that earlier."

Well remembered. A pigeon’s eyes are on opposite sides of the head so they can’t use stereopsis because the two eyes are always looking in opposite directions. The final part of vision to understand what you are looking at and how all the different objects at different distances relate to each other. To do that you often need to understand how the world is put together and what sorts of things are likely and unlikely. That’s how some visual illusions work. If you have a drawing where there are two possibilities that are both equally likely, your brain can't make up its mind and you see things first one way and then the other. Take a look at these drawing of a cubes.

“What about them?”

The middle one, number 2, is a famous cube called a Necker cube. Look at it and decide whether it is sitting in the same orientation as cube 1 or cube 3.

“It’s the same as 1, no number 3. It’s impossible it keeps changing.”

Exactly, because it is ambiguous the brain can see it both ways. In this case the image in your head flips between the two possible real world shapes because the brain can’t decide which is correct. Your brain tries to take what your eyes see and work out what object is out there making that pattern of light. Sometimes it will create lines that don’t exist.

“What do you mean?”

Look at this picture, a Kanizsa triangle, what do you see?

“A black triangle sitting on three dots on top of another triangle.”

There is no black triangle there.

“Yes there is.”

No it just looks like a real triangle even though it doesn’t have sides because to your brain it looks more likely to have a triangle sitting on three sound dots than to have three dots with wedges out of them that line up so perfectly. The white triangle behind makes the effect stronger but it works even without that. The sides of the imaginary black triangle are called an illusory contours. The other thing that helps us to make sense of what we see is our memory. If there is an hidden image in a visual illusion it can takes ages to see it. But once you’ve see and remembered you can look at the same picture 10 years later and see the hidden image straight away. Take a look at this picture. Can you see the dog in the picture?

“No, where is it?”

Put the mouse over the picture and you’ll see. Now whenever you see that picture you brain will see the dog straight away. Without memory seeing the dog is very hard. Once the memory is in your head it is impossible not to see the dog.

So seeing is not as simple as it looks. The whole process of seeing and perceiving merges into almost every other aspect of what your brain is doing. Remembering, thinking, learning and interpreting are all part of seeing. How humans actually manage this part of vision is still mysterious. Crack this and you’re close to unravelling what it is to be human.

“We still don’t know how our brains see?”

Three hundred years ago William Molyneux said it’s not the eyes that see ‘it is the soul’. And three hundred years later he’s still not far from the truth. A lot has been learnt about seeing but there is a lot more we don’t know. The secret of seeing is there somewhere in your brain which is getting a stream of images through your eyes, from the moment you open your eyes first thing in the morning until they close in sleep at night. Even though you don’t think you are working that hard, parts of your brain are working flat out. For every second of your waking hours your brain is untangling the patterns of light reaching your eyes to make sense of them. Continually trying to work out the shape of the world and what is happening ‘out there’. You see things, wonder about them, and learn about them, seeing merges into thinking. What you are doing right now, reading, is from a vision point of view quite simple, but the patterns of light and dark on the page get transferred almost directly to ideas, thoughts and memories.

“Albert, this may be a bit of sore point, but do you know what happened to your brain when you died?”

At the time no, because I wasn’t using it any more. But since I’ve come back I read that story. It is not a happy one for me nor, it seems, for Dr Harvey who stole my brain in the first place.

“I read about that. He lost his job because he wouldn’t give your brain back to the university of Princeton.”

It seems that my brain was chopped into pieces and left in a two jugs for decades. They even published pictures of my brain in a medical journal. When scientists eventually got around to studying the brain they found my brain had a few unusual features but was smaller than most brains. Sperm whales have brains five times the size of the average human. Does that make them five times smarter than us?

"No, they just have bigger bodies so they have bigger brains too."

So the size of the brain as a percentage of our weight would be a better way to work out how smart we are.

“I would think so.”

So on that basis mice are 50% smarter than humans.

“So I guess brain size is not that important.”

It is much more important what you do with your brain than what shape or size it is. One of the largest preserved brains is in a pot at Cornell University. It used to belong to a man called Edward Rolloff who was a self taught expert in languages but also a murderer. When he was being hanged for his crimes his last words were; ‘Hurry up I want to be in Hell in time for dinner.’

What were your last words?

“I told them to the nurse who was with me as I passed away. Sadly she didn’t speak German so she just look blankly back at me. That was my last memory, a sadness not at dying but that those last words would be forgotten forever. Do you speak German?”

“Sorry, apart from ‘auf Wiedersehen’, barely a word.”

That’s a shame, so there is no point in telling you either. If I say so myself, as last words go they were rather good.

“Tell me in English then.”

It wouldn’t be the same. So much would be lost in translation.

Being seen from the perspective of a glass of water being drunk

2007-12-22T15:11:00.000-08:00

“So when do we actually get seen?”

We start getting seen in about 70 billionths of a second. That is how long it will take us to get through the clear jelly-like stuff in the middle of the eye to reach the retina.

“What exactly is the retina?”

Like the film in a camera, the retina is the part of the eye that actually detects photons, a job done by cells called photoreceptors. When we get to the retina we’ll have to pass through a few blood vessels and nerves before we reach the photoreceptors.

“That’s a bit daft why aren’t the photoreceptors at the front of the retina?”

A lot of people have spent a lot of time arguing about that.

“Well it doesn’t make sense to me but if that’s the way God built the retina what is there to argue about?”

That is just the point. Did God design it that way or did evolution come up with that design? Creationists and believers in “Intelligent Design” think that the eye is too perfect to have been made by evolution and must have been made by God or by the hand of a super-intelligent being of some kind.

“But if it isn’t designed very well doesn’t that mean God isn’t as clever as he is made out to be?”

That is just the argument that evolutionists make, the existence of “stupid designs” in nature disprove the idea of “intelligent design”.

“What do you think?”

I don’t think that God or a being capable of designing all living creatures would have felt the need to create creationists to argue on his/her/its behalf. On the other hand evolution needs to create a few blind alleys to achieve progress. So the fact that creationists and scientists coexist makes me believe in evolution.

“So are human eyes badly designed?”

Not at all. By being at the back of the retina these photoreceptors line up against a layer of pigmented cells that help them recover from the effects of bright light.

“Recover?”

Oh yes. Light can be very damaging. Just think of sunburn. These other cells the retinal pigment epithelium keep the photoreceptors functioning normally. There are other animals that have eyes designed the other way around like squid but they live in a very different worlds. Underwater there is much less light, particularly deep in ocean where most squid live, so it makes sense for them to have their photoreceptors at the front of the retina so they can capture as many photons as possible.

“So where does that leave the argument between evolutionary scientists and creationists?”

Whichever side has more children will ultimately win the argument, assuming of course that their children share their views.

“Huh?”

Well I doubt either side will convince the other just by talking. So in evolutionary terms reproductive success determines what the next generations look like. Of course, if either side wins by producing more children that share their beliefs then evolution must be true. So ultimately Darwin will win either way.

“The problem for me is that the eye seems so amazing it’s hard to believe evolution could have created eyes by tiny changes over millions of years.”

It may be hard to believe, but there are clues that it happened.

“Where?”

In the genes. Remember we talked about DNA and the genetic code?

“Yeah, I remember that.”

Well in humans, squids and even flies there are genes that are involved in shaping the eye. If complex eyes developed from a simple ability to detect light then different animals should have some genes in common. There is a gene in humans called “Pax 6” which is very similar in man, squid and flies where the gene is called eyeless.

“So?”

Well if a fruit fly is missing this type of gene they don’t develop eyes and neither will any of their baby flies. Now remember that flies eyes are very different to ours. But if the human or squid gene is put back into the fly then they will recover the ability to grow eyes.

“Do they grow human eyes or fly eyes?”

That’s the amazing thing, a human gene can help a fly grow a fly’s eye. So these same genes have been preserved over hundreds of millions years while the animals have evolved to have very different eyes. The protein used in a fly’s eye is closely related to one of the pigments used in the human eye, rhodopsin. That looks like good evidence for evolution to me.

“Maybe God is lazy and decided to recycle spare genes to make different type of eyes.”

That is why physics makes much more sense to me. Creationionists and intelligent design enthusiasts are more slippery than a giant squid.

"OK, I can see why no-one has won this argument. Let’s get back to the important issue of being seen. How do the photoreceptors detect light?"

With special pigments that absorb the light.

"When is this all going to happen?"

I should say about abouuutt.......now.

Well, as I was saying before we ceased to exist, we’ve just been absorbed by this photoreceptor.

"How can you finish what you were saying if we have just ceased to exist?"

We’ve stopped being photons, but we haven't died so much as passed into the quantum afterlife. Like all the photons that never made it past the dot above the “i” a few posts ago , we changed into a different form of energy. You can thank the first law of thermodynamics again. Energy may change from one form to another but it can’t be made or destroyed.

“So we’re immortal?”

In a way, rather than being little bundles of photon shaped energy, we are now energy trapped in the shape of this pigment molecule, in the same way energy can be stored in a spring. The energy we had as photons was used to change the shape of a small molecule called retinal that’s part of a large protein molecule called an opsin. Retinal is made from another compound called beta-carotene.

“Is that why carrots help you see at night by any chance?”

Humans do get beta carotene from food like carrots, but you won’t see better by eating carrots unless your body is very short of this substance. Changing the shape of this retinal molecule and the protein it is attached to is the first step in being seen. This first shape change starts a whole series of events inside the photoreceptor like a line of domino’s falling over, each molecule changing shape of the next in line.

“What is the point of that?”

All these changes are about converting light into an electrical signal, just like in a digital camera, but they also boost the signal from each photon. So much that humans can detect the arrival of even a couple of photons.

“So are we seen yet?”

We have been detected but not seen. There are 100 million of these photoreceptor cells across the retina, each "looking" at one tiny area of a visual scene, the pattern of light reaching an eye is captured as a chemical and then an electrical pattern amongst all these photoreceptors. Another twist in all this is that not all photoreceptors are the same, there two types. There are rods which are used in very dim light and about 6 million cones which are used in brighter light for colour vision and fine detail.

“Why are they called rods and cones?”

Because that’s their shape. The rods are long and thin and rod like and the cones…

“Are cone shaped.”

Exactly. There are also different types of cones, three to be precise that respond to light of different wavelengths or colour. There’s a different type of cone for reds, greens and blues.

“Why three colours?”

Any colour can be made from a mixture of other colours. Artists and colour printers worked out ages ago that you don't need paints or inks of every possible colour. In fact colour printing uses only three coloured inks. The eye does the same sort of thing in reverse; taking a colour and breaking it down into three different components. Thomas Young, the man who did the two slit experiments that showed photons could behave like waves, worked this out. So Thomas Young managed to explain both what we are and how we’re seen.

“So what does being colour blind mean?”

People who are colour blind are missing one or more of the three types of colour detectors called cones. Usually the red or green one is missing, much more rarely the blue pigment. If you are missing one pigment then you can still see a huge range in colours but you will confuse certain shades that to a normal person are hugely different. Most commonly pale reds and pale greens are confused. But ask a red-green colour blind person what colour grass is they will always say green. How come? Because they see grass as a particular colour and are told from the time they are knee high that colour is green. It wouldn't look the same colour as it does to a person with normal colour vision but they don't notice because they have never seen it in the way you can. That's why most colour blind people don't suspect it until someone tells them. If any of these images look the same you are probably colour blind.

"So explain to me why we haven’t been seen yet?"

The picture of this page is still divided over these millions of cells. It is like dividing a 100 best-selling novels into their individual words and then giving one letter from all the words to 100 million different people. Although all the information is there, if you got all these people together in a big room and asked them all what the book was about, no-one would have a clue.

“So who makes sense of it all?”

Not who but what. The making sense of vision happens in the brain, but before the brain can do that the information needs to get there. Photoreceptors are like tiny batteries and light changes their voltage. The next hurdle is the first synapse - a gap, a few millionths of a metre across, that separates photoreceptor cells from the next type of cell in the chain, the bipolar cell. This gap is bridged by a chemical messenger which is released by photoreceptors. It drifts the short distance, a few millionths of millimetre, across to the surface of a bipolar cell. When enough of these chemicals arrive the bipolar cell changes its voltage, just like the photoreceptor did when we arrived. This is the internal language of the brain, electrical signals within cells and chemical signals between them. These chemicals are the neurotransmitters, over forty different types of molecule that can excite other cells, inhibit them or change their behaviour in more subtle ways. Synapses are how the billions of cells in the brain communicate with one another. Helping, among other things, to convert a pattern of light into a meaningful message. Within the eye we have one further synapse to cross to reach a ganglion cell, the cells that will help us on the first part of our journey to your brain. These cells have long fibres, over two inches long that carry signals from the eye into the brain. These fibres are collected into a bundle called the optic nerve which looks like a rather thick piece of spaghetti around 3 millimetres or 1/8th of an inch thick. Everything you have seen in your entire life, every word you have ever read has passed down these unimpressive looking cables that connect your eyes to your brain. Going down these cables takes an agonisingly long time compared with the speed of most of our journey. It is only a couple of inches from your eyes to your brain but it will take a tenth of a second to get there. In open space we could have travelled over 18 thousand miles in the same time.

So which part of your brain do you think helps you see.

“The front part I’d guess, just behind the eyes?”

Strangely enough this bit of the brain, the visual cortex, is right at the back. To find the visual part of your own brain put your fingers at the very top of your head. Now run them straight backwards feeling the lumps and bumps of your skull. At the back of your skull, near the top of your neck, is a big bony ridge running side to side. Inside your skull at this point is a thin pink wrinkly film only a few millimetres thick. This is your primary visual cortex, where billions upon billions of neurons are trying to make some sense of what you are seeing – linking the shapes of these black marks called letters into words and ideas. That’s where we are now. In YOUR brain.

Love, lies and Pupils

2007-12-12T15:35:00.000-08:00

“Was that the pupil we just went through? There was nothing there apart from more watery stuff.”

That’s right the pupil is just a hole in the iris, the coloured part of the eye.

“Not very exciting things then, these pupils.”

Their main job is the important but unexciting task of controlling how much light gets into the eye. When it’s bright they can constrict down with tiny little muscles around the edge of the pupil to let less light in. In the dark they get big to let in as much light as possible. But pupils can be very interesting things. They are emotional, responsive and sensitive. Humans look through them and sometimes stare lovingly into them. They can also give away what you are thinking.

“That’s daft. You can’t really tell what someone is thinking from their eyes.”

Well not exactly but you can get some good clues. Your pupils get bigger when you are stressed. Some new lie detectors even measure pupil size along with other things like voice pitch, sweating and heart rate. Large pupils can also be a sign that you find whoever you are looking at very attractive. Years ago young ladies would put an extract of the poisonous plant Deadly Nightshade in their eyes to make their pupils bigger and themselves more attractive.

"What has being attractive or attracted to someone else got to do with pupils?"

Do you want the whole birds and bees thing explained or just the pupil size thing.

"The pupil size thing will do fine thanks."

That’s a relief. When you find someone attractive, or when you are happy and relaxed, your pupils dilate. There are two systems in the body that control all this and they are wired into the emotional parts of the brain; the sympathetic and para-sympathetic nervous system. The sympathetic is the pupil dilating system - the positive, let’s get going system. The parasympathetic is the let’s sit down, do nothing and digest lunch system. The sympathetic system also gets going in other ‘lets get going’ situations, such as an ‘I'm terrified lets get out of here situation.’ That’s the system that gives you away in a lie detector.

"That doesn't explain it at all. Taking deadly nightshade to make your pupils bigger will make it look as though you are either afraid of or attracted to the other person. Why should that make you attractive?"

I'll admit courtship is complicated, but it's a little bit of subconscious flattery. Someone else finding you attractive, is very attractive.

"I think relativity is easier to understand that this human relation stuff.”

I agree completely.

“One thing I don’t get. If pupils are black, shouldn’t they be absorbing light rather than letting light through?

It’s black because not much light comes out of the eye. Most the light that gets in is absorbed at the back of the eye. Of course if you shine enough light in some escapes. That’s what happens in a flash photo when your pupils are red.

"But if the pupil's get smaller in bright light won't that stop most of the light from the flash from getting in the eye."

Yes, but human brains are slower than cameras. By the time the brain has worked out that the flash has happened the photo has been taken. A fraction of a second later the pupils constrict. That’s why some camera’s flash blinks for a few time before taking the picture. This gives humans rather slow brains time to make the pupils smaller and so stops red-eyed photographs. For humans the red eye look from flash photos is a nuisance, but some animals have eyes that use the ‘red eye’ effect to see better when it’s dark. Cat’s eyes, the ones with four legs rather than the ones in the road, have a special reflective layer called the tapetum in the back of the eyes so much more of the light that gets into the eye is reflected back.

“How does that help?”

This helps them see in dim light because it gives them two bites at the cherry. The light that isn't absorbed or seen on the way into the eye is reflected back and some of it will be seen on its way out of the eye. So the eye has a second chance to see the photons it missed first time around. Scoring on the rebound so to speak.

Just behind the pupil is the lens. This is the part of the eye that allows the eye to focus on fine detail at different distances. It is just like a magnifying lens but rather than being made of glass is a springy glob of transparent protein. This glob is very elastic and constantly wants to be ball shaped but is pulled into the proper lens shape by a ring of fine fibres called the Zonules of Zinn.

"Wasn't he the mad Spanish swordsman who slashed the letter Z in everything and everyone?"

No that was Zoro. Johann Gottfried Zinn was the man who found these zonules in the first place over 200 years ago. These zonules can change the lens’ shape by being attached to small ring of muscle in the eye, the ciliary muscle. Every time you look from a far away object, like a star, to something up close, like this book, this muscle contracts and in a fraction of a second changes the focusing power of your eye so the pages of the book are clear and in focus. Unfortunately as your eyes get older the lens becomes stiffer and stiffer and so cannot round up so much to allow you to read close up. So you hold books further and further away. Then one day you find your arms aren't long enough.

“What happens then?”

You have to admit you are getting old and get reading glasses or start carrying heavy weights in the hope that your arms get a little longer.
“Hmm, how about we get back to this lens thing.”

Well, going back a few thousand years to the start of our journey the understanding of how eyes worked was a little primitive. Back then, people thought it was the lens that detected light and made people see.

“How can something transparent be the place where light is detected? The light should go straight through it.”

Exactly. Also what do all the bits of the eye behind the lens do if seeing is done by the lens near the front of the eye? The man who sorted all this out was Johannes Kepler.

"Wasn't he the man that..."

Worked out the orbits of the planets and the three laws of planetary motion? Yes, the very same man. In his spare time he invented the modern science of optics and worked out the optics of the eye in 1604. He worked out that the cornea and the lens of the eye work like a normal glass lens and the whole eye acts like a small camera.

“They had cameras back then?”

There was a type of primitive camera back called the camera obscura. The only problem was that it wasn’t until 1888 that John Corbett, an Englishman living in America invented film.

“What use is a camera without film?”

Well camera obscura means ‘dark room’ in Latin and that explains what they did without film. A camera obscura was a dark room with one small peep-hole into the outside world with lens in it, just like the lens in a magnifying glass. The picture from the camera lens was projected on a screen or a far wall and it had to be dark to be able to see this faint image. People paid just to see this strange upside down image because at the time this looked almost like magic to most people. Some artists even used this to help them paint. To get all the sizes and shapes right they just had to trace around the outline of the upside down image and then turn the picture right way up.

At the time people really didn’t believe Kepler. If he was right that meant that the image of the world inside the eye was upside down just like the image in a camera obscura. That seemed just as unlikely as feeling rays coming out of the eye. But Kepler was right. This very sentence is being focused upside down on the inside of your eye as you read. Kepler was proved right a few years later by the French philosopher Renee Descartes, who is most famous for his statement, ‘I think therefore I am’. He published a book on optics that showed the picture of an experiment first done by Christophe Scheiner In this macabre experiment, the outer layers are peeled off the back of an eye taken from a dead ox. This leaves the thin, almost transparent innermost lining at the back of the eye. Sitting in a darkened room with this eye pointing out a small hole into the world outside, Scheiner saw a faint upside down image of the world - just like a tiny camera obscura. It’s a bit eerie that the last thing that had seen through that eye was the ox itself.

"So why doesn't the world look upside down?"

It is almost impossible to imagine how the brain does it, but as babies start to seeing things and learning about the world through the images captured by the eyes, the sense of ‘rightway upness’ is learnt along with everything else about the world. This seems hard to believe but even adults can un-learn this and then learn it again in a few weeks. In the interests of science back in 1976, two scientists Gonshor and Melville Jones recruited volunteers to wear special glasses that made the work look upside down. After a few very bad days they started to cope. After a week they had adapted to an upside down world and could go out and ride a bike with no problems. They learnt so well that taking the glasses off was almost as hard as when they first put them on. They had to learn again to ignore the fact that the world really is upside down in your eyes.

The Power of Tears to the Quantum Mechanics of Colour

2007-12-08T06:02:00.000-08:00

“Is it my imagination or is has it suddenly got wet?”

No you’re not imagining it, we’ve just hit the front of an eye ball. These are tears.

“We travelled quadrillions of miles through space, just to arrive as someone is crying? What is so sad?”

I don’t think they are sad. There is a thin layer of tears in your eyes all the time. Have you noticed we’ve changed direction again and slowed down?

“Tears can slow down light as well?”

Oh yes, and change our direction much more than the gravity of the sun managed according to the theory of special relativity. Remember the total eclipse of 1919 that we talked about before? Well, the sun changes the direction of starlight that just skims the surface by only 5 ten thousandth’s of a degree.

“But we’ve just slowed down by a quarter and turned about five degrees. Are you telling me that tears can bend light ten thousand times more than the sun?”

I am because it is true, in the words of Washington Irving tears ‘are not the mark of weakness, but of power. They speak more eloquently than ten thousand tongues.’ In this case tears are indeed ten thousand times more powerful than the theory of general relativity. These tears are sitting on the equivalent of the windscreen of the eye, a curved structure called the cornea that you have probably never seen.

“I can look at my eyes in a mirror so of course I can see my cornea even if I didn’t know what it was called.”

When you look in the mirror you can see your eye lashes, the colour of your eyes and the black pupil. You can be looking directly at the cornea but you can’t see it. The cornea is transparent when you try to look at it you literally see straight through it.

“I'm very glad that this cornea thing we're going through is transparent but how can anything solid be transparent. I can see how outer space is easy to fly through, but how do we get through this solid stuff?”

Anything can be transparent provided it doesn't reflect, scatter or absorb light. Even glass can be hard to see through if the surface is bumpy, like in a bathroom window. Bumpy glass scatters light because light is refracted in all sorts of directions by the bumps. Although light still gets through you can't see any details of what is on the other side of the window because all the rays of light are jumbled up.

“Clouds scatter light too. You told me that a little while back. That’s why they are white.”

Very good. But sometime even transparent materials can scatter light.

“How is that possible?”

It only works in materials where the atoms and molecules are arranged in a very regular pattern. When we talked about light as a type of wave, I told you about constructive and destructive interference.

“Remind me about that.”

In destructive interference the peak of one wave exactly meets the trough of another and they cancel each other out. In constructive interference both peaks meet making a new wave that is twice the size. If the spacing of the atoms or molecules is just right any scattered light is canceled out by other scattered light rays. So it looks like there is no scattering at all and the material seems transparent. That’s how the cornea manages to be see-through but there is one more thing a substance needs to be transparent.

“What’s that?”

It must not absorb light. Remember the dot of the “i" last time. Things look black if they absorb most of the light that hits them. To get to the bottom of absorption you need to go back to the nuts and bolts of how matter is made up. We talked about it a few million billion miles back, right at the start of our journey. Matter is made up of atoms and these atoms are made up of protons, neutrons and electrons.

“I just about remember that.”

Good, now in the middle of an atom is the nucleus where protons and neutrons are all packed together. The electrons are almost two thousand times smaller than protons or neutrons but are much more important for photons. As they fly around the nucleus in clouds they take up most of the space of an atom. So a photon is far more likely to hit the electron clouds than the nucleus. When light is absorbed it is electrons that do the absorbing.

“OK, so far so good.”

The way electrons absorb the energy of a photon explains how objects appear and even what colour they are. If an atom or molecule absorbs all colours equally it will look white, grey or black depending on how much of the light is absorbed. If different colours are absorbed to different degrees then the substance will be coloured.

"So grass is green because it absorbs all the green light."

Sorry, it’s just the opposite.

"Uh?"

If it absorbed all the green light there wouldn't be any green light to see. If white light hits grass and green light comes off, then everything except the green must be absorbed.

"Oh I see. So why do some things absorb light of a certain colour?"

Electrons, like photons, follow the strange rules of quantum mechanics and are only allowed to have certain amounts of energy. If a photon is absorbed it has to be completely absorbed. An electron is only "allowed" to absorb a photon if it will end up with an acceptable amount of energy. This aspect of quantum mechanics of electrons always sounds like it was invented by a bureaucrat but it seems to be true. An electron can also lose energy in certain fixed amounts and create a photon out of thin air so to speak, that’s how things make light from light bulbs to TV’s.

“So, if an electron falls to a lower energy level a photon is released and that photon contains all the energy that the electron loses.”

Exactly and the amount of energy the photon has determines its colour. Short wavelength or blue photons have more energy than long wavelength or red photons. More importantly every blue photon has exactly the same amount of energy as any other blue photon, provided it is exactly the same blue. When light is absorbed by an atom the same rules apply. Only a photon of exactly the right energy can be absorbed. So what colour light is absorbed depends on what energy levels are allowable in a certain atom or a molecule. Remember, a molecule is simply a collection of atoms that are held together by sharing electrons. In terms of this quantum-electron-photon idea molecules are like atoms but just more complicated. If an atom or molecule has only a few energy levels for absorbing light, it will only absorb certain colours of light and so will look coloured itself. If it can absorb light at lots of energy levels it will be white or grey. How the electrons and atoms are arranged can make the difference between jet black or brilliantly transparent. Take carbon for example.

“As in carbon dioxide the gas?”

That’s right, but carbon dioxide is two different atoms stuck together, carbon and oxygen. Pure carbon is solid and it also comes in different forms. Charcoal for a barbecue is almost pure carbon and is jet black. Diamonds are also pure carbon and transparent. The atoms are the same in both, but the electrons and atoms are in a different pattern and the quantum rules for the electrons are different.

“So quantum mechanics can make the same stuff either jet black or transparent?”

That’s right, atomic physics and quantum mechanics in action in front of your eyes.

“Wow.”

We spent about 2 trillionths of second negotiating the cornea which is only half a millimetre thick in the centre. With a slight increase in speed we slosh through a few millimetres of salty water towards another black hole.

“A real one this time?”

No, the type of black holes that we call pupils.

Black Holes and Grey Holes - All very strange.

2007-11-23T06:57:00.001-08:00

That black hole you were worrying about is only the dot above an ‘i’ on the page of the book we are about to hit.

“So are we going to disappear?”

We haven’t finished our journey yet so I imagine not.

“OK, talk me through this one. Black means no light, therefore if we hit that dot we'll never be seen again. End of story.”

No, luckily for us black doesn’t mean no light at all. The letters on a page will always look black as long as there is a lot less light coming off the black letters than the white part of the page. It’s all about contrast, the difference between the brightest thing you can see and the darkest. This page will look much the same read at night by torchlight or in full sunlight even though sunlight might be a hundred thousand times brighter. There will be more light coming from the black letters in bright sunshine than is coming the white page by torchlight. So exactly the same amount of light can look white or black at different times. Sometimes the same amount of light can look a different colour at the same time.

“How can that make sense?”

Look at this picture. The two squares marked 'A' and 'B' are the same brightness.

“No they’re not.”

'A' just looks darker because of the way we see contrast. Take a piece of paper and poke two holes so that you can only see the 'A' and 'B' but nothing else of the picture. You will be surprised to see two grey holes of the same colour and brightness.

"Whooaaaaaahhh! What just happened?"

Can I say I told you so?

“You can if you explain what just happened.”

We just bounced of that black dot and lived to tell the tale. The dot is black, so lots of photons were absorbed, but as I said even black things reflect some light and we were some of the lucky ones that made it.

"What happened to the ones that didn't make it?"

Well, they were absorbed by the black ink on that dot. They stopped being photons but they didn’t just vanish. They changed to a different form of energy, mostly heat. In sunlight the letters in an open book will be slightly hotter than the white page because the black ink will absorb more of the sun rays. It’s just the same as sitting in the sun yourself; you get hot because you are absorbing photons. Along with all the others laws that universe follows, there are laws of thermodynamics that explain how energy in the universe behaves. Light is a form of energy and so has to obey first law of thermodynamics. This law says that energy can change from one form to another but can’t disappear or be made.

“How about power stations they make power, isn’t that energy?”

A power station is a perfect example of this first law. Whatever type of power station you think of, they all just change some other form of energy into electricity. It could be wind powered, burning coals which like all the other types of fossil fuel is really stored sunlight from long dead plants, even directly solar powered. But every power station is converting energy not making it.

“OK Albert how abour your E=Mc²? Didn’t you say you can convert matter into energy? So how about nuclear power stations?”

Excellent, so you have been listening. That equation just means that matter is really a special type of energy. So a nuclear power station is a real world proof of Einstein’s equations and the first law of thermodynamics.

"What's going on now? I'm being bent. I've travelled in a straight line for hundreds of years from a distant star and in a few fractions of a second I’ve narrowly escaped dying and been twisted in a very unnatural angle and to top it all we just slowed down."

I think we've just been refracted. We just hit one of the lenses of a pair of glasses.

“Hang on, we can travel through thousands of billions of miles of space at highest speed the universe allows but we can be slowed down by a pair of glasses?”

I’m afraid so, that’s how glasses work. Glass is transparent so light travels through it easily enough, but only at about two thirds of our normal speed. So you see light doesn't always travel at the speed of light. The speed of light, the ‘c’ in E=Mc², is more like a speed limit than a law.

“So what does refracted mean?”

When light hits something at an angle that it makes it go slower (or faster) it gets bent. That’s refraction.

“Is that the same type of bending of light that black holes or even stars do?”

No, refraction is quite different and I’m happy to say a lot easier to explain than relativity. Imagine a car, if you drive straight onto some surface that slowed you down like gravel you would still be going in a straight line, just slower. If you drove onto it at an angle then one front wheel, say the left, would hit it first and that side of the car would slow down. The other front wheel, the one on the right, would still be gripping the road and would keep going at the normal speed for a moment until it hit the slow stuff.

“What happens to the car?”

It gets pulled over to the left until all the wheels are in the slow stuff and then it goes in a straight line in a new direction but at a lower speed. That’s exactly how light gets bent by glasses.

“So how do glasses work?”

Lenses in glasses are curved so that they can focus light. Hit a different part of the glass and light is bent a different direction. If you are long sighted your glasses will bend light rays inwards and if you are short sighted your glasses bend light rays outwards.

“How does that help?”

The eye is like a camera and must bring rays of light to a single focus inside the eye. If the focusing isn’t quite right, then glasses can help the eye bring things into proper focus. If you are long sighted then the focussing power of your eyes isn’t strong enough to bring all the rays of light into focus. So glasses for long-sightedness do some of the bending for you. If you are short sighted the eye focuses light too much so by the time it reaches the back of the eye it is blurred. Glasses for short-sightedness bend light away from a focus point to counteract the effect of overly strong eyes. But now it is time to be refracted again, this time by going out the back of the lens and into air again.

"That's much better, almost back to our normal speed 'c'. By the way Albert, why is the speed of light called 'c' ?"

Nowadays people seem to that 'c' comes from the latin word celeritas which means swiftness, but in my day it was because it was a constant. If fact back in 1905, I wrote the equation that everyone now recognises as m = L / V² because I used V for the speed of light and L for energy, it was a few years later that I re-wrote it as E=Mc².

Blue Skies, Red Sunsets.

2007-11-12T15:05:00.000-08:00

"Hmm, nice colour. Where are we now Albert?"

We're entering the bottom layer of the atmosphere called the troposphere. This is the part of the atmosphere that you would normally think of as the sky, the part that is breathable and is affected by the weather. This nice blue is the colour of the sky seen from the Earth.

"Why is it blue?"

Because of the sunlight passing through it.

"But sunlight isn't blue."

No, but as Isaac Newton showed with his prisms, sunlight contains all colours of light including blue. As sunlight passes through the atmosphere the blue light is much more likely to be knocked off course by gases in the atmosphere like oxygen and nitrogen. It is this scattering of blue light, called Rayleigh scattering, that makes the sky look blue.

"Hmmm"

I see I'll have to try a bit harder than that. Now consider all the light coming from the Sun.

"Okay."

Now most of the light goes in a straight line so that on a clear day you can see the Sun.

"So far so good."

The light from Sun that makes the sun look like, well… the sun, is heading straight towards you. But there is much more light that misses your eyes and speeds on through the atmosphere. Now, the light that isn't going towards you should be invisible because it can't reach your eyes. However, a small fraction of this light is visible because the sun's rays are knocked off course by air molecules. Because of their size, air molecules scatter ten times more blue light than red. So wherever you look in the sky your eyes will be hit by some of this scattered mostly blue light that comes from sunlight passing through the atmosphere.

“I thought it was something to do with light reflected off the sea?”

It’s nothing to do with light from sea. The sky looks the same colour in the middle of an ocean or in the middle of the Sahara desert. This same effect is why the Sun looks redder at sunrise and sunset. When the Sun is near the horizon, the rays of light have to pass through more of the atmosphere.

"So more of the blue is scattered leaving yellow and red light."

Very good. The light that is left instead of being yellowy-white becomes red because the blue is missing. It goes back to Newton and white light being a mixture of all the colours of a rainbow. Subtract a colour and what's left isn't white any more.

"So what's that white thing then?"

It's a cloud.

"We went past loads of clouds of dust and gas in space and none them looked like that."

That’s an Earth cloud. It's made up lots of tiny water droplets. Air contains a lot of water as a colourless gas known as water vapour. This is what is meant by humidity. If there is too much water or the temperature drops then this water stops being a gas and becomes droplets of a fine liquid. If it happens on the ground it's called dew. Just above the ground it's called fog. At twenty thousand feet it's called a cloud.

"So why isn't it blue like the sky?"

The water droplets are much much bigger than the air molecules that make the sky blue. Big things like water droplets scatter light of all wavelengths completely equally. So the light that you see scattered from a cloud is white because it contains an equal mixture of all the colours contained in sunlight. If clouds are very thick then not much light gets through at all, so rather than looking a nice bright white colour they look grey. From white to black via grey just involves less and less light. In light terms, grey is just a dim white. Clouds can, of course, be pink at sunrise and sunsets. Clouds can only scatter what reaches them. At sunrise and sunset the blue light in the sun's rays have all been scattered so all the clouds can do is scatter what is left, and that's pinky red light.

"One last question."

Fire away.

"Where do we fit in? I mean the sky's blue so it must be daytime, but stars disappear in the daytime, so how can we be here at all?"

Just because something can't be seen doesn't mean that it doesn't exist. We're here along with all the rest of the photons from stars and other galaxies. It's just that we are outnumbered by all the scattered light from the sun. On those very rare occasions when the moon happens to block out the sun, in a total eclipse of the sun, suddenly all the stars will appear in the middle of the day. All the stars you can see in the sky at night during the winter are up there in blue sky during the day in summer. A star like ours which is in the night sky in summer is up there during the day in winter. So stars don't come out at night, they just become more visible. If you watch carefully as the sun sets on a clear day you start to see first the very brightest few stars and then as it gets darker slowly all the other stars start to be visible or in other words stand out from the background.

"But we're invisible, and you said we were going to be seen."

We can be seen just as easily as any other photon. It's just that eyes can't pick out where we've come from in the middle of the day because of all the other photons. We're not invisible, it's just our star that's invisible at the moment. Every scene needs almost uncountable numbers of photons to be seen. So every photon makes its own very tiny contribution.

“So I’m tiny and insignificant?”

No just tiny, and you’ve seen more of the galaxy than any of those earthlings down there so I think that makes you pretty significant.

"Wait a minute. Look ahead, look ahead, it's a black hole."

I think that’s a bit unlikely in someone's back garden.

"But it's round, black, straight ahead and we're about to hit it."

It is also flat, a tenth of a millimetre across and has no gravitational field.

"So what, it's black, that means there is no light coming out of it. That means we're about to disappear."

Perhaps.

"Perhaps? Is that all you can say Albert!"

Where space stops and Earth begins

2007-11-03T16:31:00.000-07:00

"So Albert when do we reach this chaotic planet?"

That depends on where you decide the Earth begins.

"Don't be daft, there is space and then there is this great lump of rock. I'm sure we'll notice when we reach it."

Around the Earth is a very unsolid atmosphere and that’s a very important part of the Earth. That’s where all this weather and climate stuff happens.

"OK, when do we reach the edge of the atmosphere then?"

The atmosphere only has one well defined edge and that's where it meets solid ground or the ocean.

"The outer edge I mean. Everything that has a beginning must have an end."

Not everything. The Earth's atmosphere is one of those fading away sort of things. It gets thinner and thinner and then eventually blends in with the solar wind over a thousand miles above the surface.

“The winds from the sun reach the earth?”

Solar wind is the rather romantic name given to the stream of particles like electrons and protons coming out of the sun. The outermost layer of the atmosphere is called the magnetosphere. This is really a portion of the solar wind trapped by the Earth’s magnetic field rather than anything you would think of as an atmosphere. The magnetosphere sits around the Earth like a giant ring doughnut. Near the north and south poles some of the charged particles from the solar wind can get through this magnetic field. As they fall earthwards they produce an eerie swirling light; the aurora borealis or northern lights.

“Wow, one day I’ll see that for real.”

One of the many things on this planet, everyone should try and see once.

“Excuse me for asking but is the atmosphere a dangerous place for photons?"

Why do you ask?

"Because some of our fellow photons seem to be disappearing as we speak."

Don't worry about them, they are just ultraviolet photons. They’re the high energy photons that are like an invisible type of very blue light. Most of them don’t get past the first bit of atmosphere they meet. The outer atmosphere has a thin smattering of a particularly nasty type of oxygen called ozone.

"I thought things that destroyed ozone were 'environmentally unfriendly'. That should make ozone environmentally friendly and nice rather than nasty."

It rather depends where it is. Ozone or O₃, is just three oxygen atoms stuck together. When photons from the sun collide with normal oxygen molecules, which are two oxygen atoms stuck together or O2, they can be split up into single oxygen atoms. Some of these free oxygen atoms join back up with other oxygen atoms to remake normal oxygen gas and others stick together in a different way to make ozone. Ozone absorbs ultraviolet photons and prevents most of the ultraviolet photons from the sun from reaching the Earth's surface which is a good thing as these ultraviolet photons can cause a lot of damage.

"Ultraviolent?"

Well yes, but more high energy than violent. UV light is certainly ultraviolent to one thing that is very important to living things, DNA. You remember the stuff that contains all the genetic codes or instructions about how everything works in living things. If you are a single celled organism then damaging your DNA is a death sentence. If, like humans, you are composed of trillions of cells then it is only the cells on the outside that are damaged. This is less drastic, but as any sunburn sufferer will tell you, it's no fun. More serious damage to the DNA in human skin can produce something far more dangerous than sunburn - skin cancer. Cancer is a type of disease where cells start to grow out of control. Damage to the DNA from things like ultraviolet light can cause random changes, or mutations, to some of the letters in the genetic code. Some of these mutations don’t cause any problems, but some affect how a cell grows and behaves. Without the normal brakes on their growth these mutated cells keep on growing and spread into other parts of the body causing damage as they go.

“So ozone is like sunscreen for the planet?”

I suppose it is but for all the talk about ozone, there is surprisingly little of it in the atmosphere. Ozone is found high up in atmosphere, in a layer called the stratosphere about 15 miles up. At this height the atmosphere is very thin and wispy. Down at ground level, where the atmosphere is much thicker than in the stratosphere, all the ozone that exists would only make a layer a few centimetres thick. Although ozone is being made all the time in the upper atmosphere, chemicals that used to be used in aerosol cans and old fridges can spread up to the stratosphere and destroy ozone. Each of these molecules which are called Chloroflurocarbons or CFC’s can destroy thousands and thousands of molecules of ozone. Pollution like this has created a hole in the ozone layer that appears every spring at the South Pole. It was first recognised in 1984 but looking back it was happening in the 1970’s.

“Why does it appear only in the south pole?”

Ozone is only destroyed when the temperature gets below minus 80^oC. At that temperature clouds form high in the atmosphere with ice crystals covered in nitric acid. It’s the combination of these clouds and CFC’s that destroy ozone. Ozone at the North Pole hasn’t had the same problem because it’s a little warmer than the South Pole so only a small dimple in ozone appears in the artic spring at the North Pole.

“And why in spring? It is surely colder in the middle of winter at the South Pole?”

“It is colder in winter, but the damage to ozone needs light from the sun. Remember we talked about how the Earth is tilted? Well because of that tilt the sun doesn’t rise at all in the South Pole in winter. It is only when the sun reappears in spring that ozone starts to be destroyed.

“Is anyone doing anything about it?”

This is one time when countries have managed to agree to do something together. Twenty years ago the Montreal protocol was agreed and the use of these CFC chemicals has been reduced dramatically. Unfortunately as these chemicals can last 50 years or more in the atmosphere it will be a long time before they are gone.

“And the ozone hole?”

Well it stopped getting bigger. 2003 was a very bad year but overall things have stopped getting worse which is a good thing. But ozone is not always a good thing. Ozone can also be made closer to the surface where it is not such a pleasant thing to have around. Environmentalists may not like CFC's because they are bad for the ozone layer but that doesn't mean that they like ozone everywhere. Photochemical smog, the kind that Los Angeles is famous for, is caused by the effect of sunlight on the pollution coming out of car exhausts, contains ozone. Ozone near the ground is very nasty stuff. Even at minuscule concentrations it can start to kill plants. At even lower concentrations it can cause breathing problem for some people. Ozone is also produced by electric sparks. It is that slightly sharp, acrid smell that comes off electric train sets. Fortunately there aren't that many electric train sets in the world and they are not all turned on at the same time. The only truly ecologically safe pastime left seems to be sitting on your compost heap and slowly decomposing. But I don't suppose that is as much fun as pretending to be the Flying Scotsman.

“What would happen if all the ozone was destroyed?”

If the ozone layer was seriously damaged it would be disastrous for life on Earth. If all the ozone disappeared overnight I'm afraid it would be dinosaur time all over again for most creatures. Humans can wear sunscreen but the food supply would start to arrive pre-cooked and then would disappear altogether. The good news for us is that being a nice, non controversial, middle of the road sort of wavelength, ozone doesn't really bother us. Since we are part of the band of visible light, we should breeze through.

"It's lucky for us that the atmosphere lets visible light through."

Well it’s a sort of the other way around. If a certain type of light didn't get through the atmosphere, then there wouldn't be any point in life forms evolving eyes that could see that wavelength. And if there aren't any eyes that can see it then...

"It isn't visible light."

Precisely.

Climate Change Made Simple

2007-10-27T10:45:00.000-07:00

“OK Albert, give it to me straight about climate change. Is the world getting warmer?”

I think the answer to that question is a definite yes.

“So why are some people saying global warming is a liberal conspiracy by the makers of wind generators and the like?”

You are confusing something that a lot of other people are confusing too. There are two questions about climate change not just one. The first is the one you have just asked, ‘Is the world getting warmer?’ The second question is what is causing that change. It will be impossible to be absolutely sure about the cause of any temperature change until it is too late. Trying to prove that one thing causes another is surprisingly difficult when it comes to anything as big as the planet. People who seem to be arguing against climate change are usually arguing against the cause of climate change.

“So the world is definitely getting warmer?”

Here is a graph of the world temperature over the last 150 years. The last ten years have been the warmest for a very long time, almost 1^oC warmer than back in 1860.

“Only a degree? That’s not much. The temperature can change that much from one day to the next.”

True but that is just the average so in some places it may be hotter and other places cooler. What is also certain is that glaciers and ice at the North Pole are disappearing.

“Does that really matter?”

What happens to the ice that melts?

“It goes into the sea.”

So the sea level rises and low lying cities will be flooded. The sea level has been rising for the last hundred years as the temperature has risen. Ice is also shiny and so ice helps to reflect a lot of the sun’s heat back into space. The worry is that once the ice starts to go, the world will heat up faster and faster as more of the sun’s heat is absorbed rather than reflected.

“So what is all this talk about carbon foot prints and CO₂?”

Since humans invented factories and engines we have been pumping huge quantities of CO₂ into the atmosphere by burning fossil fuels like coal, oil and gas.

“Why are coal, oil and gas called fossil fuels?”

Oil, coal and gas are all made from fossilized sunlight.

“Huh?”

Millions of years ago carbon dioxide, water and light were converted into sugar and various other molecules, by photosynthesis in plants. When the plants died some of them ended up being buried and over millions of years these prehistoric compost heaps were buried deeper and deeper. Cooked by the heat of the rocks deep in the Earth and squeezed by millions of tons of rock above, the compost was converted in oil or coal and sometimes gas as well. This is why oil and coal are called fossil fuels; they are a type of fossilized compost. When they are burnt to release energy, the carbon dioxide and water that was trapped by photosynthesis millions of years ago is released again. And as we know, carbon dioxide is a greenhouse gas. So even though you could say that most power stations and cars are already solar powered because it took sunshine to make the fossil fuels in the first place, this isn’t any help to the planet. At the moment CO₂ makes up only a tiny proportion of the Earth's atmosphere, around three ten thousandth's of it. But all this extra CO₂ from cars and factories could double the amount of CO₂ in the atmosphere in the next few decades.

“Won’t some of the plants and trees today end up buried and eventually turn into oil?”

I suppose they will.

“So what is the problem? We burn some fossil fuels now but if more are being made there shouldn’t be any problem should there?”

Good thinking but the fossil fuels being burnt at the moment have taken millions of years to form and will be used up in a few hundred years. So CO₂ is being released far faster than it can be turned back into oil and coal. The question is can the Earth cope with millions of years of CO2 being released all in one go?

“Can it?”

Well the only way to be sure is to burn it all and see what happens. We’ve been doing that and the world has been getting warmer and warmer. So if we are worried about CO₂ we need to stop burning fossil fuels and find other ways of powering our cars and factories. If we made fuel directly from plants, biofuel, the CO₂ released as we drive around would be the same CO₂ which was captured from the atmosphere a few months earlier. That way the amount of CO₂ wouldn’t increase.

“That’s a good idea isn’t it?”

It is as long as it doesn’t take too much energy to make fuel from plants like corn in the first place. The other problem is that rich countries with enough food might buy up so much corn that poor countries will find it even harder to feed all their people.

“Oh, I’d never thought of that.”

It’s not even a new idea. When the diesel engine was first invented it was designed to use peanut oil and when cars were being made popular for the first time by Henry Ford back in 1903 he designed his Model T Ford to use alcohol as a biofuel.

“Wow, so he knew about climate change back then?”

Not at all, he was no environmental angel. He thought it would be cheaper.

“So why didn’t he build the Model-T Ford to run on alcohol?

Oh, the usual reasons, politics. In 1919 alcohol was banned in North America during the prohibition era and powerful oil interests pushed for gasoline to be used on its own, but imagine how different the world would be if cars had been burning ethanol for 90 years not fossil fuels. The Middle East would be a very different place and world politics would be completely different. Better? Who knows, but certainly they’d be less CO₂ in the atmosphere.

“So are humans and all this extra CO₂ really responsible for this increase in temperature? Last time we spoke you said that the climate on Earth has had all sort of crises over the last few hundred million years. Ice ages, mini-ice ages and all sorts. If cars were only invented a hundred years ago and the climate has been doing wild things for millions of years it’s not necessarily the fault of humans releasing too much CO₂.”

No, but it could be. If there’s any more than a reasonable chance that humans are damaging the planet then they should probably do something about it before it’s too late, don’t you think?

“I was hoping that scientists could give me a more definitive answer. It seems like a simple question to me.”

Well, it’s a question you would have to ask just a single scientist who only has one hand if you want a definite answer.

“Why?”

Because, if you find two scientists they will always disagree about some detail because that is their job. After all, if you accept everything you read you without questioning it you are not a proper scientist.

“OK, but why only a one handed scientist? What’s that got to do with it?”

If a scientist has two hands then he or she can always say, ‘well, on the one hand CO₂ is the most likely cause, but on the other hand we can’t completely disprove other theories.’

“Not bad Albert, not exactly funny but not bad for you. Jokes aside why can't scientists just work out what will happen to the world’s climate with a computer so we can stop talking about it and do something about it?"

Nice idea but that assumes that scientists can predict the weather and politicians around the planet can agree what to do about it. Humans seem very bad at both these things. Weathermen have some of the fastest and most expensive computers in the world to help tell them what the weather will be like tomorrow. Initially the calculations took so long that by the time they had got the answer for tomorrow's weather, the weather had already happened. By the time computers got fast enough, the predictions were still not perfect. Then came along a bunch of mathematicians would told them they were wasting their time even trying. This was the birth of Chaos Theory and for a time weathermen, or meteorologists as they call themselves which is a bit odd as they don’t study meteors, were a bit depressed as predicting the weather accurately seemed impossible.

“What is Chaos Theory?”

Chaos theory says that even in systems that seem to have well defined mathematical rules for what should happen next, minute variations can, over time, lead to completely different results. Take a pendulum swinging back and forward, what could be more predictable? But add a little pendulum on the end of the pendulum and it starts to swing very strangely. Add just one more little pendulum on the end and it will swing so chaotically that it is impossible to predict the pattern. Now the climate of the whole Earth is a lot more complicated than a triple pendulum, but it can behave just as unpredictably. We can’t predict whether it’s going to be a good or bad summer next year because of this unpredictability, so predicting the effects of climate change or reducing our production of CO₂ is at best and educated guess.

“So Albert, what do you, as a no-handed computer recreation of a famous scientist, say about climate change?”

Imagine you are sitting in your house as a forest fire gets nearer and nearer. What are you going to do?

“What’s that got to do with it?”

Trust me, it will make sense.

“OK. When I got really worried about the flames getting too close I’d eventually leave to go somewhere safer.”

Now imagine the Earth is that house. There is nowhere else for us to go. All we have is this one little planet. Anyway would you really just sit in your house and do nothing until you could see the flames?

“Of course not, I’d phone the fire brigade.”

Would you expect the fire brigade to do anything as the flames continued to spread?

“Of course, I would.”

Imagine they said, ‘We didn’t cause the fire. It was caused by the sun being too hot and drying out the forest too much, so we don’t have to do anything about it.’ What would think then?

“I’d be furious, they should try and do what they could. They could drop water on the flames from helicopters, that would help whatever caused the fires in the first place.”

Exactly. So even if most scientists are wrong and humans aren’t the most important cause of global warming, it doesn’t make sense to do nothing. We know CO₂ can act as a greenhouse gas, so reducing human release of CO₂ might be the only sensible thing we can do to try and stop the Earth getting hotter and hotter. If there is something you can do which could help isn’t it worth a try? If that something would also avoid polluting the planet, what do we have to loose? At worst, if we are wrong about humans causing global warming and wrong that reducing our CO₂ will help, we’ll have a warmer planet that is less polluted.

“Seems simple when you say it like that?”

Everything should be made as simple as possible, but no simpler.

Seasons, Ice ages and why greenhouse gases are good for the planet.

2007-10-20T22:26:00.000-07:00

“So that’s Earth close up?”

That’s it. Pretty isn’t it. Nothing quite like it as far as the eye can see.

“Is it my imagination or is the earth titled over?”

No you are quite right it is leaning over. With maps showing north being straight up people usually think the earth spins upright, but without that tilt life on earth would be very different.

“In what way?”

Well, no seasons. There would just be hot places and cold places. The hot ones would stay hot all year around and the cold ones stay cold.

“Just because the earth is tilted a little?”

All because the Earth is tilted and by more than just a little. The most famous leaning thing on Earth, the leaning tower of Pisa, only leans over by 5.5^o. The earth leans over by more than four times as much, 23^o.

“So could the Earth fall over?”

Well it wobbles at bit, but it’ll never fall over. It’s like a spinning top; as long as it keeps spinning it will stay upright.

“But spinning tops fall over eventually?”

What makes a spinning top fall over is the fact that the bottom is rubbing on the table slowing it a fraction at every turn. The Earth is floating space, not touching anything so there is nothing to slow it down. It’s been spinning for 4 billion years which sort of proves the point. If it wasn’t tilted tree’s wouldn’t need to loose their leaves in winter in colder countries, there’d be no such things as summer holidays and swallows would only bother flying south if the north bored them.

“Hold on, you’ll have to explain that one. How can the earth’s spin cause all that?”

Well, because the Earth is tilted over as it circuits the sun every year then for half the year the top half of the earth is leaning towards the sun and for the other six months the bottom half. When the top half of the Earth is sloping towards the sun, it’s hotter because it’s a bit nearer the sun but more importantly the sun's rays hit the Earth head on. That’s why in summer the sun is higher in the sky. In winter the suns rays hit the earth at an angle and are spread over a bigger area, so it’s much colder. Of course whatever happens in the top half of the world, the northern hemisphere, is opposite to the what happens in the bottom half or southern hemisphere. When it’s winter in Europe, its summer down south in places like Australia. That's why in Australia they celebrate Christmas in shorts on the beach, at least for the time being.

“The time being? Is Australia going to move somewhere else?”

No but the seasons can change because the Earth wobbles as it spins. The bad news for Australia is that over the next 12,882 years the direction of the Earth’s tilt will change. That will make it winter at Christmas in Australia in the year 14,889, but everything should be back to normal by the year 27,772.

“Could that explain global warming?”

The earth’s temperature doesn’t seem to change in synchrony with that particular wobble, so, if the earth is getting hotter as it seems to be, then we have to look at other causes. The problem is that the earth’s temperature is a very fine balance of gaining heat from the sun and loosing to space. All the weather on Earth, even life itself depends on the fact that the Earth is in almost in perfect temperature balance. For all the energy arriving on Earth from the Sun, exactly the same amount has to be lost back into space. If a fraction more arrives than leaves then the Earth heats up. If more is lost than arrives then the Earth starts to freeze over.

“How can a planet loose heat?”

Some of the heat from the sun is reflected by clouds and the ice at the north and south poles. Some of it is sent back into space as infra-red rays. These are the type of invisible photon that carries heat - the same sort of photons that night vision goggles use. By turning infra-red photons into normal visible light, night vision goggles let you see the heat from anybody or anything even in complete darkness. How much infra-red escapes from the Earth depends on the greenhouse effect.

"You told me a while back that it’s the greenhouse effect that keeps Venus so hot. So it must be a bad thing?"

Well it depends. On Venus the greenhouse effect traps so much heat that it is horribly hot but Mars is so cold because there isn’t enough of a greenhouse effect. On Earth the greenhouse effect is there, but not to the same devastating degree as on Venus. You might read about how the carbon dioxide from cars, factories and airplanes is putting the world in danger, but without any greenhouse gases the Earth would be frozen solid and probably lifeless. The most important greenhouse gases for Earth are water in clouds and carbon dioxide gas (or CO₂). Clouds and CO₂ both absorb infra-red rays leaving the earth and heading off into space. Because the energy is absorbed the earth doesn’t cool down as much. If there was no greenhouse effect on Earth from the water vapour in clouds and CO₂ in the atmosphere, the world would be 40^oC cooler and most of it would be frozen solid. In all the recent global warming the Earth’s temperature has risen by less than a degree in the last hundred years.

"So what's the problem?"

The problem is that if the greenhouse effect is changed even a little bit that could put the Earth out of energy balance. What happens if you are leaning to ride a bicycle and you loose your balance?

“You fall over.”

Exactly, humanity is like a small child learning to ride but rather than getting the hang of bicycle it has to learn to keep a whole planet in balance. When things on earth get out of balance animals and plants start dying off so it is an important lesson for humanity to learn. The asteroid that hit the Earth 60 million years ago and caused the dinosaurs to die out didn’t kill them by blowing them up, but by changing the temperature balance from all the dust that was blasted into the atmosphere. Dinosaurs couldn’t keep up with the climate change that this dust caused. 245 million years there was an even bigger life wipe-out with 90% of all sea species dying out and that was probably climate related too.

“But that was millions of years ago, things have been pretty stable recently haven’t they?”

Well, not really. There have been major freezes or ice ages throughout the last few million years, following a pattern of an ice age every 40,000 years or so. But it’s not got any better recently. It’s only 10,000 years ago since the last proper ice age, with ice covering most of Europe for thousands of years. There was a mini chill just a few hundred years ago. Between the years 1645 and 1715 winters were so cold that it was called the little ice age, the River Thames in London froze so solid Londoners had winter fairs on the ice.

“What causes ice ages?”

There is a pattern in when ice ages happen and a mathematician Milutin Milankovitch from Serbia, in the 1930’s suggested that it was all to do with the wobbles in the Earth’s spin. But ice ages could be caused by lots of other reasons like changes in how brightly the sun shines, sudden shifts in ocean currents or volcano’s. The bottom line is that no-one is quite sure what causes ice ages. The worrying thing about the ice ages is that as scientists are not absolutely sure why they happened in the past, they can’t predict when they might happen in the future.

“Well, if the earth is warming up we could do with another mini-ice age right now.”

I’m not sure the earth can wait 30,000 years until the next one, but let’s talk more about global warming next time.

The Meaning of Life (according to Albert 2.0)

2007-10-10T05:50:00.000-07:00

“Hey Albert, have you noticed this is the 42nd post on your blog?”

So?

“So now you’ve covered every other angle on life, how about telling me the meaning of life?”

Well, I could try but what does that have to do with the number 42?

“In Douglas Adam’s book The Hitch-Hikers Guide to the Galaxy, it’s the answer to life, the universe and everything. A race of hyper-intelligent pan-dimensional beings built a monster computer called Deep Thought that took seven and a half million years to work out the answer which was… 42. I know it was after your time but haven’t you come across that yet?”

No, but a hitch-hiker’s guide to the galaxy would be fun. What I don’t understand is that if the answer was 42 what was the question?

“Exactly, so you have read it.”

Not at all, I just couldn’t imagine trying to find the answer without knowing what the question was.

“That was the funny bit. They asked for the answer but forgot to be precise about the question.”

Why was that funny?

“Ok Albert, we’ll work on your humour programming later, but if you are so smart and the answer is 42, what could the question be?”

Do you mean what is the right question to ask if you want to find the answer to life, the universe and everything?

“Well I was more thinking of why the answer to life, the universe and everything might be 42.”

What if it isn’t?

“You’re the one that said imagination is more important than knowledge, so imagine for a moment the answer is 42. What could the question be?”

Hmmm, a tricky one….I know. What is the secret of a rainbow?

“Brilliantly random, but what are you talking about?”

42 degrees is the angle that light is reflected inside a raindrop to make a rainbow.

“Are you serious?”

Absolutely, that’s the only important question I know about the universe that has the answer 42.

“So how does that explain how a rainbow works?”

A rainbow forms because a raindrop can act just like the prism that Isaac Newton used to split light into different colours. When ray of sunlight hits a raindrop it is bent and split into colours as it passes through the middle of the drop in the same way as a prism. It then reflects off the back of the raindrop like a mirror and comes back out of the from of the raindrop, bent round by 42 degrees. In fact it is not always exactly 42 degrees because each colour or wavelength of light is bent by a different amount, blue more than red, which is why the colours are spread out into a rainbow in the first place. The laws of optics tell us there has to be a fixed angle between the sun, the raindrops and you the observer. That’s why a rainbow will move away as you move towards it – you can never reach the end of a rainbow which is why it is such a good place to hide pots of gold.

“I always knew those leprechauns were clever.”

Clever indeed, but let me ask you a question, and this question will help explain the meaning of life. What is more important, knowing how the reflection angle of light inside a raindrop forms a rainbow or looking at a rainbow in wonder in the first place?

“Oh, well I suppose knowing how a rainbow is formed is better than just gawping at it.”

I wasn’t thinking of gawping at a rainbow but looking at it in wonder. That is more important than knowing how it works.

“Why?”

Because without a sense of wonder you won’t be able to appreciate the beauty of a rainbow or anything else. If humanity lacked wonder then who would have bothered to find out the secrets of rainbow?

“But what does knowing the secrets of a rainbow have to do with the meaning of life?”

The most remarkable thing about the universe is that it is understandable at all. The journey of discovery towards understanding starts with wonder. A famous Jewish theologian Rabbi Abraham Joshua Heschel said a very wise thing back in 1951, ‘life without wonder is not worth living.’ I remember as a child being given a compass and being completely fascinated by what invisible force could keep it pointing north. That gift helped ignite a sense of wonder in the physical world that I’ve never lost.

“I’m still not clear what that has to do with the meaning of life?”

Do you really want to know?

“Of course.”

Well to capture the meaning of life in one sentence I’d rephrase Abraham Heschel’s words and add the missing final link. Life without wonder has no meaning, so the meaning of life must be wonder itself.

“Life without wonder has no meaning, so the meaning of life must be wonder itself…..mmm…. deep.…but cool all the same…..and 42?”

Next time you see a rainbow, stop what you are doing and just sit and watch it. Then you’ll find out the real importance of 42…. and of being alive as well.

P.S. More on Heschel, Adams and Einstein.

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Are we Alone? Listening for extra-terrestrial life

2007-10-06T15:53:00.000-07:00

“Is that the Earth straight ahead?”

That's the Earth, in all its glory. Only five seconds and the best part of a million miles to go.

“Pretty place, with all those bluey, greeny whitey bits. A bit small though.”

At this distance it certainly looks small. Amazingly no earthling has ever seen the Earth from this distance with their own eyes. The farthest humans have been is the moon which is only a quarter of a million miles away, just over a light second.

“We’ve been 3000 light years across space on this journey and human astronauts have only travelled one light second! That’s a bit pathetic isn’t it?”

Well, earthlings are only just starting to explore space. NASA is back talking about going to Mars which is at least a planet away.

“And how far is Mars?”

At its nearest a few light minutes.

“A few light minutes? And they’re still only talking about that? I guess it’ll be a while before humans make the return visit to our star.”

They have sent machines, or space probes as they call them, off into the outer solar system to Saturn and beyond. Remember we talked about voyager and the golden disc a while back?

“Not exactly Star Trek is it? Will humanity ever travel into space and meet aliens?”

We might but it is more likely they will visit us than the other way around.

“Why is that?”

Well, we have only just started wondering about life on other planets in the last hundred years – a mere blink of the eye in terms of the age of the universe. Humans only discovered the first planet around another star ten years ago. If there are other civilisations out there asking the same question as us, the chances are they are more advanced.

“I don’t see why?”

If there are lots of intelligent civilisations who know that planets exist around other stars and we have only just discovered this, then we must be the newest member of the galactic civilisations club. So it stands to reason that the other members have been in the club for longer and so will be more technologically advanced.

“Unless we are the only member of the club.”

True, but that is the real question - are we alone?

“How can we answer that question without just waiting for someone to visit.

We can try and listen for their signals. When we talked about this last time, I explained how radio and TV signals from earth can’t have travelled very far into the galaxy because we’ve haven’t been transmitting for that long. The signals from other planets, if they are more advanced and using radio waves for thousands of years, should have been travelling for far longer so could have spread out across the whole galaxy by now. This is what the organisation SETI, which stands for Search for Extra-Terrestrial Intelligence, does – listen for radio signals from space.

“Have they found anything yet?”

Not yet but there is a lot of space out there. They have been getting ordinary people to help by using their own computers, almost 3 million people are helping in the search.

“But if they have found nothing so far is there any point in keeping trying?”

Heavens above, what a question, of course. Scientists have tried to calculate the chances of there being other civilisations in our galaxy and it seems unlikely that we are completely on our own.

“How can they know that?”

One of the founders and now president of SETI, Dr. Frank Drake, came up with a way of came up with a way of caculating the chances of finding intelligent life in our galaxy by listening to radiowaves from space – The Drake Equation. To work it out you need to first answer seven questions. I’ll take you through a slightly simplified version of the Drake Equation and we can answer them together as they are tricky enough. First, we need to know how many stars there are in the galaxy. Any ideas?

“A hundred million?”

Oh, a lot more than that, perhaps a hundred billion or more. Now the next question is how many stars have planets around them. When Dr Drake thought up his equation in 1961 astronomers had no idea how to answer that question. With all the planets discovered in the last few years we now know planets are common so it might be as much as half of all stars.

“Just what I was about to say.”

The next question is how many planets are capable of supporting life, with a temperature that is not too hot or cold and an atmosphere. If there are lots of planets around these stars then the chances of one in the right zone goes up. So there might be one suitable planet around every one or two stars that have planets. So can you guess what’s the next thing we need to know?

“How often life starts on these planets?”

Exactly, well done. Even though it seems remarkable that life could start out of nothing, if it could start on earth then there is no reason that it couldn’t start anywhere else. So life might be very common, so common that some form of life might start whenever there is a suitable planet.

“But would it be intelligent life?”

Good question. On earth chimpanzees and dolphins undoubtedly have some form of intelligence. So if there are at least three intelligent species on earth then given enough time evolution should be able to create intelligent life anywhere. The sixth question is the chance that this intelligent life could build machines to send radio signals into space. This could be difficult for dolphins even if they evolved to be ten times smarter than humans because they only have flippers, so not every intelligent life form may be able to send radio waves or want to.

“How about 10% of intelligent life being able to send radio waves?”

Not a bad guess. Now the seventh and last question is how long an intelligent alien species would use radio waves for.

“Once they discover radio waves, why would they stop?”

They might blow themselves up in a war if they are like humans, or die from an asteroid hitting the planets like the dinosaurs. The other reason is that there are probably much better ways of sending signals across space that we haven’t even discovered yet. Imagine how advanced human civilisation might be in a thousand or a hundred thousand or even a millions years? A really advanced civilisation would probably have stopped using radio waves and TV-like signals thousands of years ago, in the same way that we’ve moved on from painting pictures on cave walls. They could be sending signals to us right now and we wouldn’t know because we aren’t advanced enough to know what to listen for.

“How long will humans be using radio waves for?”

We discovered them about a hundred years ago, but I can’t imagine we won’t have discovered something better than radio waves in another thousand years. So earth might be sending out radio waves for only 1000 years. For a planet that will exist in total for 10 billion years this means that there is only a one in a ten million chance of anyone listening in with a radio telescope of catching us at the right moment in our evolution. So that’s the last number we need - the number of years a civilisation sends radio signals into space.

“So what’s the answer? How many planets in the galaxy have intelligent life?”

At least one.

“That’s’ a daft answer, of course there’s at least one, the earth.”

Well you can put in your own numbers and calculate it yourself, but before you do have a wild guess.
When you are ready CLICK HERE.

p.s. If you are interested in helping SETI in the search for extra-terrestrial life please visit http://setiathome.berkeley.edu/

p.p.s If you are an extra-terrestrial life form please leave a message in the comment section.

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Light of my Life (and almost every other living thing)

2007-09-29T15:18:00.000-07:00

Of course, wherever life came from there wouldn’t be much point in being alive if it wasn’t for us.

“That’s a bit dramatic isn’t it Albert?”

I mean us as light coming from a star, rather than you and me. Nearly every living thing on earth depends on the light from its nearest star, the sun.

“Nearly?”

Well I would have said all life until I read that deep in the oceans there are bacteria that live around vents in the ocean floor where hot volcanic water and gas bubble up. They live off the chemical hydrogen sulphide that comes out of these vents. So they are living off chemical energy not light energy and strange giant worms live off them. Mind you, as hydrogen sulphide has the smell of rotten eggs and is just as poisonous as hydrogen cyanide to most life forms, you can hardly call it living.

“Hold on Albert, the rotten egg smell chemical is also in stink bombs isn’t it? It can’t be that poisonous?”

It really is that poisonous, it’s just that it is so smelly that it only takes a miniscule amount to make a good stink. Even 600 molecules of hydrogen sulphide for every million molecules of air could kill you and at that concentration your sense of smell is paralysed so you can’t even smell it. So all in all I’d rather not live near one of the underwater vents. For all rest of life on earth sunlight is the power source. Plants trap the energy from light and with the gas CO2 from the atmosphere and water make sugars.

"But humans don't eat sunlight."

No, but they do eat plants that grow using the sugars they make out of sunlight. Even pure meat eaters like lions eat other animals, that might eat other animals, that might eat even smaller animals, but at some stage the smallest forms of life are ether green or eat something green.

“How do plants use sunlight if we can’t?”

The process that plants use to trap the energy from the sun into a chemical form is called photosynthesis, literally making things (the ‘synthesis’ bit) out of light (the ‘photo’ bit). A special molecule called chlorophyll captures photons and uses the energy to make water and CO2 stick together to make sugars and other more complicated molecules. This pigment is green which is why plants are green. The sugars can be converted into all the other things that plants are made of. In potato plants all the excess sugar that is manufactured in the leaves and other green parts of the potato plant is moved underground and stored as starch.

“So a potato is like bottled sunshine.”

That’s right and french fries are deep fried sunshine. When you eat a potato, you release the energy trapped in the sugar and turn sugars back into water and carbon dioxide.

"If animals reverse the process that makes sugar by photosynthesis, why don't they glow when they eat vegetables?"

What a great thought, but animals don't exactly reverse photosynthesis. If they did they would have to give back all the energy as light and so wouldn’t be any better off. Instead they have their own specialised pigments that break down sugar back into water and carbon dioxide but trap the released the energy in the form of a chemical called ATP (adenosine triphosphate) which is the energy currency used in cells. This whole process is called metabolism. The idea that animals might glow when eating is not as odd an idea as it seems. Some bacteria and fungi that live by digesting dead plants and animals do actually glow as they eat. Rotting wood or meat infested with certain bugs can give off a faint bluish light.

"What about fireflies, they glow don't they?"

Yes but when they're mating, not when they are eating. Animals like fireflies have evolved such amazing tricks to produce light that it leaves you wondering how evolution alone could have done it. Fireflies mate at night and use flashes of light to attract one another. Each species of firefly has its own code of flashes so that they can avoid an embarrassing meeting in the dark with the wrong sort of firefly.

“So light is important for reproduction too?”

Of course, light helps you to find food, avoid predators and to attract or even find a mate. The beautiful plumage of birds is only there to be seen by potential mates. Most humans choose clothes because of how they look in them. If there was no light, evolution wouldn't have evolved eyes and no-one would care what they looked like. So photons drive the entire fashion industry. Of course some animals live where there is no light or very little light and so they have little vision. There’s an old saying ‘beauty is in the eye of the beholder’, and if there is no-one to do the beholding (or seeing) then why should evolution bother to make you beautiful? This is probably why you don't see many beautiful moles, bats or deep sea fishes. But apart from these creatures that live in very dark places, nearly all animals from the very simplest can react to light. Not all can ‘see’ as you might understand it, but even tiny microscopic organisms can detect light and move towards or away from it.

"So what do you need to be able to see?"

An eye, a brain and a bit of light. A fancy eye is useless if it is attached to a brain the size of a pinhead and any eye is useless if you live somewhere without light. Simple animals only need simple eyes because they are too dumb to need anything better. The simplest eye of all is something that can just tell light from dark, what’s called a light receptor. Next step up is an eye that can tell which direction light is coming from. Simple creatures like flies have compound eyes made up of lots of receptor cells that can tell light from dark. Each receptor points in a different direction so that the pattern of light can be used to see what things are and where they are.

“What about our eyes?”

Human eyes have evolved to a spectacular level of precision. But before you get too proud of your own visual apparatus, you should know that some animals can see things that you can't see. Birds like hawks and eagles can see better than humans. When lunch depends on spotting a mouse while hovering at a hundred feet, good eyesight becomes essential. Lunch for many humans seems to involve reading the label on a sandwich and then guiding it towards the mouth. Not too challenging after all. In many ways it is surprising that humans can see as well as we do. But then, there is more to life than finding the next meal. Seeing better than humans is one thing, but some animals can see the invisible.

“How can you see the invisible? That doesn’t make any sense.”

This might seem impossible until you realise that invisible only means invisible to humans. It's just one of the many perks of being the dominant life form on the planet. You get to name everything and decide what is and isn’t invisible. Bees can see into the ultraviolet spectrum. Ultraviolet is where light gets bluer and bluer and after that seems to disappear. Some flowers, which look boring and white to us, are spectacular in ultraviolet light. Bees might be rather impressed if they knew that humans could ‘see’ red light that was invisible to them. Some snakes, like vipers can see even redder light than humans, what humans call the infrared. This allows vipers to see in the dark. They perform this neat trick with special pits next to their mouths. Handy for vipers, but I don’t suppose the mice they eat are that impressed.

"So are we infrared or ultraviolet or what type of light?"

We’re good old fashioned visible type of light.

“So will we be seen?”

Perhaps, if anyone is looking this way when we finally reach earth in the next few minutes. I guess we’ll just have to wait and see.

Enjoyed it? Then Digg it.

HOW DID LIFE BEGIN (questions just don't get any bigger)

2007-09-22T14:56:00.000-07:00

“So where did all this life come from?”

Excellent question and like all the best questions is very hard to answer. We do know that there has been life on earth for a very long time. The earth is around 4,500 million years old and the first forms of life are thought to have been primitive bacteria that appeared around 3,500 million years ago.

“How can anyone know that?”

These bacteria left fossilized rocks called stromatolites, scientists know these rocks were made by simple bacteria because they are still alive today in parts of Australia. Here's a picture of them.

“They look like rocks.”

Well spotted, but they are rocks made by the bacteria as they grow.

“So everything came from these rock-making bugs?”

Well not necessarily those exact bacteria but something very similar. The fact that all living things use DNA, the stuff we talked about last time, suggests all life on Earth came from a some simple original life form. That life-form changed and more complicated versions appeared. Over millions of years new life-forms and creatures developed from this very simple start. That’s what evolution is all about.

“The thing that Charles Darwin discovered?”

That’s the one. One of the strongest pieces of evidence for evolution is that DNA alphabet I told you about is shared by every living creature. But Charles Darwin didn’t know about DNA, he developed his theory of evolution by examining the different types of animals on a tiny set of islands in the Pacific Ocean, the Galapagos Islands. He found that birds on different islands had changed so they were best suited to eating particular types of food. From these little changes he suggested that if you string together lots of little changes over millions of years you can explain how any living creature could evolve from a simple common ancestor.

“I can just about believe that all the different forms of life evolved from one very simple creature, with a lot of imagination. But where did that first creature come from?”

Hmm, I thought I might have got away with not answering that question. Where life first came from must rate as one of the universe's really big questions. It’s one of the universe’s big questions exactly because no-one has answered it yet. For most scientists, life came by random chemical reactions over millions of years suddenly kick-starting life.

“Life just started out of the blue by chance? That seems a little unlikely.”

There are plenty of scientists who’d agree and suggest life just happening would be like a hurricane passing through a junk yard and creating a pristine Boeing 747. Or a million chimpanzees randomly hitting keys on a million keyboards and suddenly one of them writes one of Shakespeare’s plays. So some people have suggested that life came from space and landed on Earth from a comet or asteroid. There is another idea that was put put forward by Francis Crick, one of the scientists who discovered the shape of DNA. He suggested that life was deliberately put here on Earth by intelligent space travelling aliens.

“What? Was he mad?”

No, I think it was a well thought out idea if a little unusual. After all our galaxy has been around for billions of years before the Earth even formed, so if life could start once it could start many times.

“So?”

So if it possible for life to start by chance, then it is likely to have happened more than once. As the universe has been in existence about 9 billion years longer than the Earth, it is likely that life started somewhere else first. Crick and his colleague Leslie Orgel pointed out that living things need a very rare element called Molybdenum to stay healthy. This is very rare on Earth but seems much more common in other star systems. So they argued that it was more likely that life started on a planet with lots of molybdenum. This theory has wonderful name of 'Directed Panspermia'.

“Life reaching earth from outer space sounds a bit weird but it doesn’t really answer the question. Even if I believe that, how did life start in outer space?”

You’re absolutely right, life has to come from somewhere and saying life on earth came from another planet doesn’t answer the real question. The real answer is that no-one really knows where life came from. What makes it a bit more believable that life could have developed out of the blue is that some of the molecules that really important for living creatures, like amino acids, have been detected in space dust. There is even alcohol floating around between clouds.

“Couldn’t that just be bits left over from a pub on some planet that blew itself up or got blown up?”

It could be, but these amino acid molecules can be created out of the simple gases found in space. There are 20 different type of amino acid in living things on earth and they are the building blocks of proteins. All those words in the DNA alphabet are instructions to make proteins. Proteins are strings of amino acids and each three letter word in the DNA alphabet tell which amino acid goes where. Proteins are the second most important molecule in living things after DNA. DNA has the instructions, but proteins are the molecules that do all the important jobs in living things.

“Like the musicians in your ‘life as an orchestra idea’.”

Just so. With radio-telescopes, astronomers have found these amino acids in space. The right combination of gases and light can just make atoms combine into these building blocks of life. So at least some of the raw materials are out there in space. Even more interesting was a shower of meteorites that landed in Australia on September 28, 1969. These were collected and investigated by NASA. Remarkably these meteorites contained 90 different types of amino acid including 19 of the amino acid found in living things on earth. So the other 71 types of amino acids that don’t exist naturally on earth can only have come from outer space.

“Alien amino acids?”

Possibly. Another meteorite ALH84001 was found hidden in snow in Antarctica in December 1984. Scientists believe this meteorite was originally blown off the surface of Mars by another large meteorite collision. It became famous when Dr. David McKay from NASA claimed in 1996 that it contained microfossils of tiny bugs showing life on early Mars, but not everyone if convinced about that. The other view is that life is so implausibly and fantastically complicated that it shows someone, like God, must have been involved.

“Could that be true?”

It all comes down to what you believe. Any of the possible explanations of where life came from needs a leap faith, so at the end of the day it depends which way you want to jump.

“Couldn't it be proved one way or another?”

Well logically there are only two ways of proving it. Finding God and asking him or showing that life really can be created out of a soup of simple chemicals that can be found in space or on planets. Back in 1953 Stanley Miller and Harold Urey showed that these important amino acid molecules might have been made here on Earth. They passed lightning through a mixture of gases that were probably around when the Earth was formed- methane, ammonia and hydrogen. The same gases that are found on lots of planets in the solar system. They showed that the simple building blocks of life could be formed in a single week– amino acids, sugars even the building blocks of DNA. It is a long way from building blocks to people but a billion years is lot longer than a week.

“So going back to my question of how life started.”

To be truthful, I don't know.

“Finally I've got you on something.”

True but to be fair I’m a physicist not a biologist and I am dead, so you have to give me a little credit for that.

WHAT IS LIFE? (big questions need big letters)

2007-09-15T04:57:00.001-07:00

“So Albert, what's next?”

Next is that little planet called Earth.

“Where is it?”

It's that little gleaming dot ahead of us.

“But it's tiny.”

We're still eight minutes away, about 90 million miles. At this distance the Earth looks like a tiny bright pearl lost in a sea of darkness.

“Don't get poetic on me, Albert. Tell me what makes the Earth so special?”

Life. The Earth’s special because it’s full of life. It’s just the right distance from the sun so that it is not too hot and not too cold. It’s also the right size to have enough gravity to keep a breathable atmosphere. Remember Mars, it’s a bit smaller and has been losing it atmosphere for billions of years. The huge planets like Jupiter and Saturn have so much gravity they have a huge, dense atmosphere that isn’t very friendly to life. So the Earth is just in the right place and is just the right size. Right in the middle of that goldilocks zone we talked about before.

"I know this is a silly question…..”

Some of the best questions are, so go on.

“But what is life? How can you tell that something is alive?"

Hmmm…now that is an interesting question. Let’s think about that. Well, most living things move, but not all of them and anyway cars move. So movement can't be the key. Living things grow but then so can stalactites in caves and volcanoes. How about reproducing. That's it; living things reproduce and make new living things.

"So anything that's not reproducing isn't alive?"

Well, you don't have to be always in a constant reproductive frenzy to be alive. I suppose it's the ability or potential to reproduce that's the key to life?

“So if someone couldn’t have babies for some medical reason they wouldn’t be alive?”

Of course humans or any creature can be unable to have children and be alive. I guess reproductive potential is out. What does that leave? Evolution, living things evolve getting better each generation.

"So do soap powders."

They need energy.

"So does an iPod."

They can think and react to things.

“I don’t think grass thinks and that’s alive.”

Hmmm. When you think about, it's surprising tricky to define what life is. It’s easy to say that humans are alive and trees are alive in a different sort of way. To describe life in a simple way that includes everything we think of living but doesn’t include any machines or anything else is surprising difficult.

“What about DNA? Isn't that in all living things?”

That is true and it is amazing that, on Earth at least, all forms of life use this chemical DNA, which is short for DeoxyriboNucleic Acid. But on its own DNA is just a molecule, a whole load of atoms arranged in this long spiral shape – the famous double helix. DNA contains all the instructions about to how make a living thing and keep it working. There is a very simple sort of alphabet stored in DNA, so simple that it only has four types of letters A, C, G and T. These letters stand for Adenosine, Cytosine, Guanine and Thymidine which are the names of the molecules that DNA is made from. These letters make up three letters words which stores all the information in the DNA. There are only 64 word combinations of these letters so the DNA language is very simple compared to most human languages. The Oxford English Dictionary has 290,000 words. But every bug, person and blade of grass on Earth uses the same DNA language of just 64 words and three of those are ‘stop’.

“So is life DNA?”

It’s used by life on Earth but there could be life on other planets that uses something other than DNA. Even on Earth DNA isn’t alive. You could take the DNA from any living creature and have it in a test-tube but it wouldn’t be alive. When an animal dies you could still extract the same DNA as was there when the animal was alive. So life has to be more than just DNA. DNA is like music printed on a page. All the instructions are there to make a beautiful sound but it needs an orchestra to play the notes. Life is the whole thing, the instructions, the musicians, and the music.

“So if you just record the music on a CD would that be life?”

No because the sound of the music is just the end result. A CD of music is just a copy of what the music sounds like, just like a DVD of a film shows living actors but isn’t alive. The whole complex process of actually making the music is more what life is about. One extra twist is that the printed music in the form of DNA also includes the instructions about how to make the instruments, musicians and everything else needed to make music. Part of the problem in defining life is that there are lots of type of life and so lots of different ways of living.

“What do you mean?”

Well if we start with the smallest living things, there are bacteria. These are tiny little balls of life, so small, about a millionth of a metre across, they can only been seen with powerful microscopes. They have DNA, can move, and can make new baby bacteria. They live almost everywhere. Some bacteria when they start growing inside humans cause disease or infections, but there are lots, literally billions, that live quite happily inside every earthling. But most bacteria live in soil. There is an even simpler form of life that is smaller than bacteria, some are only a few billionths of a metre across and not everyone even thinks they are actually alive. These are viruses that can only live inside other living things. There are even viruses that live inside bacteria.

“So what is the difference between a virus and a bacteria?”

A virus is just a package of DNA (or its first cousin called RNA, ribonucleic acid) surrounded by a capsule usually made of protein. On their own they can’t do anything. They can’t grow, move, reproduce or anything else. All they can do is get inside other living things. The virus then takes them over from the inside and makes new copies of itself.

“Is that all they do?”

That’s it. Going back to my orchestra example, it’s like someone sneaking in and changing the music on the music stands without the musicians noticing so they all start playing a different tune. Sometimes viruses don’t cause much harm to the thing they invade but often they can kill the cell and can cause diseases from the common cold and the Flu to and HIV and the deadly Ebola which is probably the nastiest virus on the planet for humans.

“Why do they exist? What’s the point of just being DNA and making copies of yourself if you don’t do anything else?”

I suppose they exist just because they can. A scientist called Richard Dawkins has come up with the idea of the ‘Selfish Gene’. A gene is set of instructions coded in DNA. His idea is that all living things are just very complicated ways for genes to spread themselves around the earth.

“So viruses are one of the best ways of doing just that.”

That’s right so the real question is why bother with great big complicated animals like humans. It takes humans 30 or so years just to make a few new humans in the form of kids. Then they have to grow up and go through 13 years of school just so they can make some more copies of their DNA by having more kids. During that time they even have lessons on how to avoid making new humans.

“I guess it’s more fun being human than being a virus, but I’m not sure how this fits into the selfish gene theory. Anyway what about all the other living things?”

One up from bacteria in size and complexity is a whole range of living things made up of things called cells, which are still tiny but much bigger than bacteria at a few tens of millionths of a metre. There are three types of these cells; animals, plants and fungi. Even single celled animals (like an amoeba), single celled plants (like algae) and single celled fungi (like yeast in bread) are different enough to tell apart. Single cell plants are green, single animal cells can have little hair-like things on their surface called cilia which lets them move. Fungi are in the middle, not quite an animal but not a plant. From tiny single cell versions, much more complicated living things have been made just by putting together lots of different types of cells. The cells then become specialised so you have brain cells, skin cells and cells that help make bones. That is all humans are, collections of lots of cells working together like a massive city.

“So we're not really all that different from other forms of life. What’s the best type of life to be?”

It depends on how you judge it. For the health and safety of planet then definitely trees; they’re good for the environment and trees have never started a war or created toxic waste dumps. For cleverness humans win, but you would wonder how clever it is pollute the planet you live in. The biggest life form is a fungus. Most earthlings would say the blue whale is the biggest living thing on Earth but they’d be wrong. A fungus has been discovered that lives in the forests of Oregon in North America. This monster fungus, Armillaria ostoyae or the Honey Mushroom, lives mostly underground and is over 3 miles across and could cover more than 1,500 football pitches. A blue whale is only about the quarter of the length of one football pitch.

“So do bigger things have more DNA?”

Surprisingly not. Humans have 3 billion letters in their genetic code but onions have 17 billion. The animal with the largest amount of DNA is the marbled lung fish. This is the sort of thing we are supposed to have evolved from when life left the sea and started living on land. This fish has 130 billion letters in its DNA. But the record so far is a single celled amoeba, so small that you need a microscope to see it, it has 670 billion letters.

“Why?”

There is a lot we don't understand about DNA, like why some creatures have so much and what most of it does. We have a better idea of how the universe started than we do about why a lungfish and an amoeba have so much more DNA than us.

The close encounter that made Albert famous, by the skin of his teeth.

2007-09-08T13:06:00.000-07:00

“Ahem, aren't we getting a little close to the sun for comfort?”

What's wrong with stars, we came from one remember.

“Yes, but it seems a bit pointless to travel so far just to end our days back in star.”

We're not going to hit the Sun, just skim past it.

“If this is skimming why are we changing direction, I thought we always travelled in straight lines. We've been doing just that for quadrillions of miles?”

Don't worry it's just a minor deformation in space-time due to the gravitational force of the sun. It was a moment just like this that made me famous in 1919. Physicists would say we are following a geodesic within curvilinear deformations of the space-time continuum.

“You’ve got to be kidding!”

Let’s just call it bending of light.

“Why didn’t you just say that? And couldn't you just tell me about it rather than make me relive it?”

Well seeing is believing and I thought you might enjoy the experience, I certainly am. Anyway remember when I was explaining about relativity. I told you about my theory of gravity about how it tested during an eclipse of the sun.

“Of course....but remind me of the details.”

Well in my theory of general relativity, gravity is created by objects changing the shape of space. The sun is like a small canon ball sitting on a trampoline.

“I remember the trampoline bit.”

Good. Now gravity only has a large effect close up, so at the edge of the trampoline it is almost flat so a beam of light or a ball bearing seems to travel in a straight line. But if a beam of light goes across the middle of the trampoline just missing the sun it won't go in a straight line but curve around the sun. That's what we are doing.

“How does that work?”

On a flat surface the shortest distance between two points is straight line.

“Yes, but that doesn't answer my question.”

In fact it does. On a curved surface the shortest distance between two points is never straight but curved. So when light is bending around the sun, or when a ball bearing is travelling across a curved trampoline, they are both travelling the shortest possible distance between where they start and where they finish. That is what that wonderful word geodesic means, it's just the equivalent of a straight line in curved space.

“Hold on, I'm not sure I'm getting all this.”

Let's take an example closer to home. Have a look at a map between London and New York. What is the shortest distance between them?

“A straight line across the Atlantic of course.”

So, why do aeroplanes leaving London on their way to New York fly in a curve starting off almost in the direction of Greenland before coming in over Canada?

“They do? Oh, I've no idea.”

Because it is the shortest distance.

“Huh?”

Change your map for a globe and hold a piece of string as tight as you can with one end on London and the other on New York and you'll see the same curved line that aeroplanes take. That is a geodesic, the equivalent of a straight line in curved space. It's just that we humans aren't good at thinking in curved space.

“So by bending we are travelling in the nearest thing to a straight line because space around the sun is curved?”

Exactly. This was the reason anyone has ever heard the name Albert Einstein. When a man called Arthur Eddington first showed that light could be bent this way in 1919, it made headlines all over the world. Suddenly I was famous, but it could have been so different.

“What do you mean?”

If it hadn't been cloudy in 1912 or the first world war had started a few weeks later you might never have heard of my name.

“Why?”

Well, the only way to check my theory about bending light back then was to look at the position of stars during a total eclipse of the sun, when the moon blocks out the sun completely. A solar eclipse is the most extraordinary thing you'll ever see. The sky goes black in the middle of the day and the stars appear. Around the sun a beautiful halo appears, the corona. Scientists realised that if the sun could bend light, stars close to the sun would appear in the wrong positions and the only time you can see stars close to the sun is during an eclipse.

“So what was the problem with that?”

Well back in 1911, before I had completed my theory of general relativity, I had made a prediction about the sun being able to bend starlight. The problem was I had made a mistake, back then I thought the bending would be only half as big as it really was. If it hadn't been cloudy in Argentina for the eclipse in 1912, everyone would have though I was wrong and I would never have been famous outside the world of physics. Luckily for me, it was cloudy all day in the place where the expedition had their telescopes. The first world war meant the German expedition to the eclipse in 1914 was also abandoned. The astronomers were in Russia when Germany declared war on Russia three weeks before the eclipse, so they were all arrested. Strangely enough it was also the same war that made the 1919 expedition happen.

“Go on, tell me about 1919.”

Arthur Eddington, was like me, opposed to war. Back then it wasn't the thing to be, and Arthur's friends made a deal with the military that he would spared being sent to war if he arranged an expedition to the 1919 eclipse. But this deal only held if the war was over by then.

“Wow, kind of weird.”

But apparently that's how it happened. So two expeditions were sent. One to an island off the coast of Africa called Principe, the other to Sobral in Brazil in case it was cloudy in Principe island. On the day of the eclipse there was a storm raging in Principe but it was sunny in Sobral. It cleared a little later on but Eddington only got two good photographs from Principe island because of the clouds. It was sunny in Brazil but the sun made the telescopes heat up so much that most of the photographs were out of focus and they only got seven good photographs.

“Bit of a disaster then.”

Looking back it was but at the time, with the confidence of youth, I never doubted that my theories were true, so I didn't take too much notice. I received a telegram saying my theories had been proved, so I was happy. When the expeditions returned they analysed the pictures and found the star shift was close to what I had predicted from my new calculations. The 6th of November 1919 was the day that changed my life.

“What happened then?”

That was when they announced the results of the eclipse at a meeting in London. Normally a scientific discovery only gets a small mention in the newspapers. This meeting made the front pages of newspapers in London and New York. The London Times had 'Revolution in Science. New Theories of the Universe' on the front page and the New York Times had the headline 'Lights all askew in the heavens'.

“Wow, quite a splash.”

That is just the point. Looking back now almost a hundred years later and dead it seems all the more surprising that the world was so excited. I think it was just lucky timing. Straight after the bloodiest war in history between England and Germany, an Englishman was proving the theory of an unknown German scientist and it caught people's imagination. Funnily the results weren't even that clear cut.

“What do you mean?”

Everyone kept writing that the 1919 eclipse in Principe proved my theories, that's what all the text books say. I was delighted, but it turns out that Eddington chose the best plates and ignored pictures that seemed to give the wrong answer. It wasn't really until another eclipse in 1922 that astronomers really believed the results, but by then it was already fact for the newspapers and most ordinary people. Arthur Eddington even wrote a poem about it.

Oh leave the Wise our measures to collate
One thing at least is certain, light has weight
One thing is certain and the rest debate
Light rays, when near the Sun, do not go straight.

“Hold on, I thought you said it was because space was curved, not because light has weight. If light has weight then it should be affected by gravity like everything else.”

Well done, I think you are really getting this. Eddington was wrong in this poem. If light did have weight, it would bend with gravity but not as much as happens with my theories.

“So did Eddington really understand your theories?”

Oh, I think he did, but 'weight' rhymes with 'straight' and geodesic doesn't really rhyme with anything.

“How about amnesic?”

Very good, but try and write a verse about relativity using those two words.

[If this has whetted your appetite then try this article by astronomer Peter Coles, it's a bit heavy on mathematics but otherwise a brilliant in-depth review of this whole story.

p.s. Any verses on amnesic and geodesic gladly received by email to albert AT journeybystarlight.com]

Rocky IV: The inner planets which are made of errr...rock

2007-09-01T10:03:00.000-07:00

“So we must be getting close to Earth now Albert.”

Down to the last few hundred million miles.

“Oh, still that much?”

Don't worry, it will only take us thirty more minutes. After seeing these last few planets we'll go right past the sun. From there it is only another eight minutes to planet Earth.

“So what's next.”

The small inner planets. There are four of them Mars, Venus, Mercury and of course Earth. They are very different to the giant gas planets like Jupiter and made of the stuff we usually think planets are made of, rock.

“We could call them Rocky IV.”

Why?

“It's another film Albert, and like you said there are four inner planets and they're all rocky”

True, is Rocky IV another space film?

“No it's about a boxer, but perhaps we should get back to talking about Mars.”

Good idea. Well, see for yourself.

“Those white bits at the north and south poles of Mars, are they ice?”

Of sorts. There is probably water ice under the surface but ice caps on Mars are dry ice, frozen carbon dioxide, CO₂.

“Carbon dioxide. Isn't that the stuff causing global warming on earth?”

Well, rising CO₂ is a one of the things that might be making the earth warmer because it is a greenhouse gas.

"What's a greenhouse gas?"

A greenhouse gas is any gas that makes planets hotter by trapping the heat from the sun. Normally a lot of the heat that reaches a planet’s surface is lost back into space as infra-red radiation, effectively heat waves. Greenhouse gases absorb the infra-red radiation so the heat stays in the atmosphere rather than escaping into space. This means that more and more of the sun's heat is trapped so the planet warms up.

“So is Mars hot with all that CO₂?”

No, Mars is very cold, the hottest places are just about at freezing point, zero degrees Celsius, and the coldest more than minus 100oC. There is a lot of trapped CO₂ but it won't work as a greenhouse gas when it is frozen it would have to be in the atmosphere.

“So to make Mars a nicer place to live all you'd have to do is melt all that trapped frozen CO₂.”

That could work. As the the martian ice caps melted, carbon dioxide levels would increase. When there was enough carbon dioxide in the atmosphere the greenhouse effect would take over making Mars warmer and warmer. The frozen water that scientists think is under the surface would melt too. Wait a few hundred years for things to settle down and there you have it - a nice new world with an atmosphere, reasonable climate, ripe for exploitation. Mind you there'd be no oxygen to breath so they would have to find some way making that. Perhaps they could use solar energy to break down some of the water into hydrogen and oxygen.

“You are not really being serious are you Albert?”

Well, it's not beyond the power of imagination, but then to my way of thinking very little is. I've discovered that there is even a new word for this - ‘Terraforming’, sounds so much nicer than polluting doesn't it?

“So is there is life on Mars now?”

An interesting question and the short answer is we don't know. Back in the 1920’s when I was still in my prime an American astronomer, Percival Lowell, had the world convinced of an advanced civilisation on Mars with a large system of canals to bring water from the ice caps. When he looked through the best telescopes of the day, he could see these canals criss-crossing Mars. Most other people only saw red blobs, but some people started believing Lovell and started seeing canals too.

“People were really convinced there were little green men on Mars?”

Oh yes. So much so that on August 23rd 1924 when Mars and the Earth were closer than they had been for over 100 years, groups of people set up powerful radio receivers to try and hear any messages from Mars and send messages back to Mars.

“Any one call?”

Not a peep, I’m afraid. As telescopes got better it became clear these canals were only in Percival Lovell’s imagination. By the time space probes were sent to Mars they didn't find canals but what looked like empty river beds. So Mars may have been a friendlier place for life a few billion years ago. Back in 1976 the two Viking space probes landed on the surface with equipment to look for life. Even though they weren't expecting Martians but there might still be Martian bacteria in the soil.

“Did they find anything?”

The results didn't definitely prove there wasn't life, but some of the experiments had unusual results which could just be caused by an unusual form of bacteria.

“Why isn't that bigger news?”

Well they decided overall that they didn't find life, but some scientists are still not so sure. The man who designed one of the experiments, Gilbert Levin, still claims the results could have been caused by simple bacteria. Later on NASA claimed to have found what looked like fossilised bacteria in a meteorite that came from Mars. If life did start on Mars, it would probably survive under gound so they will have to go back and start drilling some holes.

“If there are dry river beds, where did all the water and air go?”

The water probably sank underground and got trapped as ice. Most of the air drifted off into space because there is less gravity on Mars than on the Earth.

“You need gravity to hold the air onto a planet?”

Gravity is the only thing holding the atmosphere and all the air and clouds onto a planet. Mar's problem is really that it was just a little too far from the sun and a little too small. It has only a very thin atmosphere now, but smaller places like the moon have so little gravity that they have no atmosphere at all. Now the next planet on our tour has plenty of atmosphere, Venus.

“That would make it a more likely place for life then?”

Like all things in life, too much of a good thing is bad for you. The main problem with Venus is that its atmosphere is too full of greenhouse gases. It is also closer to the Sun than the Earth or Mars. Although the planet is named after the Goddess of Love, there is nothing lovely about Venus apart from brightly it shines.

“It is beautiful shining planet, you have to admit.”

True, from Earth it is brighter than any star apart from the Sun of course. Venus is called the morning or evening star as it is only seen just before dawn and just after sunset. It’s so bright it is hard to imagine that Venus has no light of its own but just reflects sunlight. Before you get too attached to this shining pearl in your skies, just remember that all that light is reflecting from clouds of sulphuric acid and the temperature on the surface is 450^oC, hot enough to melt some metals.

“Has anyone sent probes to the surface of Venus?”

The Russians had the most success with Venus, though lots of probes were lost. They sent a whole series of Venera probes but the longest any of the survived was about two hours before the heat and pressure destroyed them. Here's a picture of the surface. Apart from the atmosphere it's really all rocks, just like Mars and the next planet on our journey Mercury.

“Is that Mercury? Is it just me or does it look a lot like the Earth's moon?”

That's Mercury and you are right it doesn't look very different to the moon. No atmosphere and lots of craters. The only problem is the temperature. It is so near the Sun that the days are very hot, around 400^oC even without any greenhouse gases. The days are also very long so the sun doesn't set for 88 days at a stretch. As the scenery is much the same as the moon, all things being considered you might as well go to the moon for your holidays as travel all the way to Mercury. Having said that I am rather fond of this little planet.

“Why?”

For a long time there was a small wobble in its orbit that couldn't be explained by Newton's theory of gravity.

“And your theory of relativity explained it?”

Exactly. That little quirk of astronomy was the first evidence that my theories might really be true.

“How about the last planet, Earth? Aren't you going to tell me about that?”

There's plenty of time for that, first I want to demonstrate something very close to my heart.

“What?”

You'll find out in a few minutes. Hold onto your hat.

More Planets: Tiny but dangerous ones.

2007-08-25T16:10:00.000-07:00

“So Albert, what's next on this tour of the solar system?”

Well, we're just passing through the asteroid fields between Jupiter and the next planet we'll come to which is Mars.

“So where are all the asteroids? On Star Wars when they went into an asteroid field they were dipping and diving to miss them.”

One day I'll have to see this Star Wars film you keep talking about, but I'm not sure it gives you a very accurate picture of the universe. There are certainly plenty of asteroids it's just that space is very big.

“So how many asteroids are out here?”

I just looked up the number, by last month they had found 378,546 asteroids but they are finding thousands more every month so there may be a million or more out there. The biggest Ceres is much smaller than the earth's moon, around 600 miles across, and that single one contains a third of all the rock and ice in the asteroid belt. Here's a picture showing the Earth's moon and Ceres together.

“Is Ceres another Greek or Roman God?”

Well guessed, Ceres is the Roman God of agriculture. Ceres was the first asteroid they found and initially astronomers thought it was a new planet, until they started finding more and more of them in the same area. For a while they kept giving them names of minor Gods and Goddesses, like Pallas, Juno and Vesta.

“Then what happened?”

They were finding so many that they were running out of names, so the the discoverers starting naming them after their country, family members and even pets.
Now there are so many that most have only numbers or a scientific code. Have a look at THIS PAGE to see if anyone you know has an asteroid named after them .

“OK Albert, back in a minute...”

“Back again. I don't believe it. There are asteroids called Smiley, Doctor Watson and Asterix! Isaac Newton has his own one, but I'm afraid there's no Albert Einstein, just one called Albert.”

I think you missed one. I checked earlier and there is also an asteroid called just Einstein so that means I have two, one more than Newton.

“Oops, sorry, but guess what asteroid number 9007 is called?”

I'm not sure I know that one, sorry.

“James Bond!”

Why?

“James Bond? Double 'O' 7, get it?”

Is this a Star Wars thing again?

“No he's a secret agent, but he is in films too. Once this trip is over Albert I need to sit you down and show you all the great films you missed since you died. Oh, was that an asteroid we just went past?”

That was a fairly typical small lumpy looking asteroid yes.

“Hmm, not very exciting are they? How about getting onto the next proper planet?”

Not so fast young man, patience. They may be small but asteroids can have much more effect on the Earth than any of the monster planets we were talking about earlier.

“Such as?”

Such as killing half the living creatures on Earth for a start.

“Now you're the one talking about the nonsense from films.”

No, it really happened. That's how the dinosaurs died off and it wasn't just them. In the seas even more species were lost than on land.

“This sounds like science fiction.”

No just science but like a lot of science it started with a crazy idea that people found hard to believe. Luis Alvarez and his son Walter Alvarez made the suggestion in 1980 that an asteroid about 6 miles across crashed into the Earth 65 million years ago and caused the dinosaurs to die out.

“How could they possibly prove that?”

All over the world in rocks that were 65 million years old they found a thin layer of clay that had lots of an element called Iridium.

“What does that prove?”

Well there is very little Iridium in most rocks but there is a lot of Iridium in asteroids and meteorites.

“OK, but where's the big hole?”

They found a crater in Mexico that is now buried under the sea that dates from just the right time. They've even found a few other possible craters from around the same time in India and in the North Sea near England, so something big could have broken up and landed in several pieces.

“Oh, so people think it really happened. It's not just a crazy idea?”

No, now it's a considered the most likely reason for how the dinosaurs died out.

“Could it happen again?”

Yes it could. There was an even bigger extinction 251 million years ago when 90% of sea and 70% of land species died out. That might have been an asteroid too. The Earth is always being hit by small things, a hundred tons arrives from space every day but most are tiny particles or dust that burn up as they arrive. But there are bigger asteroids that come near the Earth and could possibly hit it one day.

“Any time soon?”

There seems to be no immediate risk, but I read that a few years ago it was predicted an asteroid called 1997 XF11 might hit Earth October 26 2028. Don't panic, they made a slight error in their calculations so it will miss by a safe margin.

“Phew. So the Earth is safe for now.”

Well...an asteroid called Apophis, the Egyptian god of evil and destruction who lives in the darkness might just cause a problem. On April 13, 2036 this asteroid has 0.0022% chance of hitting the Earth or a 1 in 45,000 chance, but on the bright side there is a 99.9978% chance the asteroid it will just miss us.

“Apophis destroying the Earth. That's straight out of Stargate, now I know you are joking.”

No, straight out of Nasa. Take a look for yourself. http://neo.jpl.nasa.gov/risk/a99942.html

“So we may have to work out how to blow up asteroids after all to save the world.”

We might.

“Is that 13th of April in 20..whatever a Friday by any chance?”

No I think it's a Sunday.

“Phew.”

Now it's time to get some practice blowing up a few asteroids. Have a go at this great Asteroids game I found.

Planets of the solar system: Big ones.

2007-08-21T13:04:00.000-07:00

“Albert, that big planet ahead looks blue, is that water?”

Those pretty clouds may contain a bit of water but there is a lot of other poisonous stuff like methane.

“What's that?”

A gas that comes from rotting things and cow dung, amongst other things.

“Oh how did it get out here then?”

It was here when the planets were first made from the gas and dust from blown up stars and bits left over the from big bang.

“Still it's a pretty impressive compared to poor Pluto. What's that planet called?”

That's Neptune, the first real planet we've met in this solar system, but the astronomers have made such a mess with their new definition of a planet that Neptune might not be a planet either.

“But it's huge!”

That's right four times bigger than Earth but one of the definitions of a planet is that it has to have cleared its orbit.

“What does that mean?”

It is supposed to mean that it should be the only thing in its orbit. Any decent sized planet's gravity with make any smaller mini-planet in the same orbit crash into it or get captured as a moon. The problem is that as Pluto cross Neptune's orbit, Neptune seems to fail that test.

“So it's not a planet?”

Oh, it's definitely a planet, scientists just need to get their words straight on defining a planet.

“They're meant to be the smart ones aren't they?”

Scientists are usually smart but often foolish and you can nearly always find something they can't agree on. Even something that seems quite simple can get scientists vexed, but Neptune has been here far long than scientists have been on Earth and Neptune will still be here when that definition is long forgotten.

“So tell me something interesting about Neptune. Is it outside that Goldilocks zone you were talking about last time?”

Oh definitely not, at almost three billion miles from the Sun it's always cold out here. One of Neptune's 11 moons, Triton, is famous for being one of the coldest places in the solar system at -240oC and having a crinkled surface like a cantaloupe melon. Apart from the poisonous atmosphere on Neptune there is also the problem with the weather which seems to be pretty awful too. One the space probes that have been sent to explore out here found a hurricane bigger than the whole Earth and the winds get up to 700 miles per hour.

“So there is not chance of any life down there?”

Well, even though the sun doesn't warm up the surface, the inside of Neptune might be quite hot and people have even suggested there might be vast oceans of water deep down. If there was any life in those seas it would have to be very different to us, the combination of gravity and heat from the centre would make the ocean more like a pressure cooker with a temperature of several thousand degrees centigrade.

“What's the strangest thing about Neptune?”

The wildest idea, possibly in the whole solar system, came from scientists in America in 1999. They recreated the high pressure and high temperature atmosphere of Neptune in a laboratory and found that the methane gas could be turned in diamond dust.

“Diamonds? Are you serious?”

Methane contains atoms of carbon, and diamonds are a form of pure compressed carbon so it makes sense. So the scientists, Benedetti and Raymond Jeanloz, suggested that it might be literally raining diamonds on Neptune and on Uranus too which that is big lump of a planet over there.

“Uranus looks a bit like Neptune, just a bit greener.”

They are almost like twins and made of the same stuff with lots of methane. Uranus most definitely wins the prize for the moons with the best collections of names. If you think what poets on earth achieved with just one moon called "the moon", imagine how lyrically they would have waxed with five moons called Ariel, Umbriel, Titania, Oberon and Miranda.

“Do all these big planets out here have loads of moons? They all seem to have loads.”

The Earth is unusual with only have one moon, these big planets also have rings but the rings on Uranus and Neptune are pretty small.

“Now that planet has really nice rings.”

That’s Saturn, it’s mostly made up of gases, but has sixty moons at the last count, and the most amazing set of rings that are more than 170,000 miles across.

“Impressive. What are they made of?"

They're made up of lumps of ice, dust and rocks. For all their size they are very thin, only a few miles thick or even less in places.

“Where do they come from?”

Well, they may be collections of small rocks that never made it to be moon sized, or they might have once been moons that were destroyed by colliding with each other or by the gravity of their planet pulling them apart. Now how about this for a strange fact. Although Saturn is the second largest planet in the solar system and weighs almost one hundred times more than the Earth (a mere 50,000 billion billion tonnes), it would float if you could find a big enough bath to float it in.

"How can a planet that weighs 50,000 billion billion tonnes float?"

All it means is that, like ice or wood or anything else that floats, the density of Saturn is less than water. An iceberg can be very heavy, but as long it weighs less than an equal volume of water it will float.

"And Saturn weighs less than an equal volume of water?"

Precisely. Archimedes, another of the ancient Greeks and one of their best mathematicians, worked all this out and it is still called the Archimedes Principle.

“How could he have worked out that Saturn would float? I thought they didn't know what the planets really were?”

That's right but he worked out the principle that applies to all floating or sinking things. It all started when he was asked to work out if a goldsmith had cheated King Hieron II of Syracuse when making a crown. When the idea came to him in the bath, he is supposed to have run naked down the street shouting Eureka – or I’ve got it. Once the cheating goldsmith had been sorted out, Archimedes developed the idea to explain how things float. Unlike some other ideas dating from ancient Greece, the Archimedes Principle has stood the test of time and is as valid today as when Archimedes leapt out of his bath dripping with water and enthusiasm.

“Now that is one massive planet over there.”

This next one is Jupiter is huge, the biggest planet in the solar system

“What’s that big red spot?”

That swirling red area, reasonably enough called the ‘Red Spot’, is a storm that is more than twice the size of the earth and it’s been there for at least 100 years. So you earthlings shouldn’t complain too much about your weather.

In some ways Jupiter is like a mini solar system. The planet itself is very similar to the sun being mostly hydrogen (about 85%) and most of the rest being helium. It is encircled by four large moons and twelve medium sized ones. In total Jupiter has over 60 moons if you count the very small ones too. The only small thing about Jupiter is its ring; a rather puny affair compared with Saturn or even Uranus.

"If Jupiter is big and made of the same stuff as the sun why doesn't it glow?"

Jupiter is almost as big as the smallest star but it doesn't have enough gravity to make the centre hot enough for nuclear reactions to start. In stars the gravitational forces compress the gases in the centre raising the temperature to the required 10 million degrees or so. Jupiter hasn't got enough gravity to do that.

“What would have happened if Jupiter had been big enough to become a star?”

In many solar systems that's exactly what did happen, there are lots of stars that have companion stars and they rotate around each other. If that had happened in our solar system, I doubt the Earth would be such as a nice place to live in terms of temperature. It might get a bit hot with two suns but it would make for interesting sunsets.

“Like in Star Wars.”

When did the star wars happen, while I was dead?

“Don't worry Albert, it's just a film.”

Planets, planets everywhere but not a drop to drink....until now

2007-08-14T09:25:00.001-07:00

“Albert, this solar system we're about to explore, is this the only one?”

Well there was a time when some people thought so. Even the nearest stars are so far off that seeing a planet around another star seemed impossible.

“But you told me that I should try to believe in the impossible.”

Exactly, and that's what astronomers did when they went searching for planets circling far off stars.

“Did they just build bigger telescopes?”

No, they had to think how they could detect something that they couldn't see and they worked out the answer a long time before they found the first planet.

“How did they manage it?”

Well the first way they discovered was to look tiny wobbles in the position of a star?

“How does that help?”

Imagine an ice-skater spinning on the ice. On their own he or she can spin on just one spot.

“So?”

Well, what happens if two skaters are hold hands and spinning. They can't both spin on the same spot can they?

“No, but I'm not sure where you are going with this Albert.”

It will become clear don't worry. Two skaters holding hands will spin in a circle, with the middle of the circle between them. So imagine one very large, fat skater and a tiny little one, if they held hands they would spin in a circle too, but the centre of that circle would be close to the fat skater.

“OK, but we are talking about discovering planets aren't we?”

Of course we are and that is how they discovered the first planets outside our solar system. Imagine you are looking at the fat and tiny skater from a distance, you might only be able to see the fat one but you could tell there had to be another skater there because they would be wobbling slightly. So that is what astronomers did, they looked for stars that seemed to be wobbling from side to side in space. Some people claimed to have found wobbling stars that must have planets going around them as long ago as 1855, but it wasn't until 1988 that three Canadian astronomers, Bruce Campbell, G. A. H. Walker, and S. Yang found the first definite star with a planet in the constellation Cepheus.

“Where's that?”

It's a constellation that looks like a house up near the pole star. This famous star with the first detected planet is the called Alrai (or gamma Cephei) and in terms of the constellation it makes up the top of the roof. It is one brighter stars near the pole star so in Autumn and Winter if you live in the northern hemisphere look up above and a little bit north and you'll see it.

“Will I be able to see it wobbling?”

It might be twinkling like any other star but the wobble is so tiny it can only be detected in photographs taken by the largest telescopes on earth.

“Is that the only planet they've found so far?”

Not at all, once they found the first one other astronomers started looking more seriously. There are now over two hundred planets detected and they are finding 40 or more every year now. The fact they are finding so many planets tells us that the universe is probably full of stars with planets.

“So where do they all come from these planets?”

Come from? The view these days is that both the sun and the planets formed at a similar time from a swirling disc of gas and interstellar debris. As things started to cool down gravity helped to collect most of the gas into the centre which became the sun. Gravity also collected the left overs and debris into planetoids and then planets.

“Are they aliens on these planets?”

No-one knows, but most of the planets that have been discovered so far are huge planets very different to earth so it's unlikely they have anyone like us on them. But they have just discovered a planet in the Goldilocks zone, where earth-like life could exist.

“The Goldilocks zone?”

From Goldilocks and the three bears, where Goldilocks found a porridge that was just right, not too hot and not too cold. If a planet is too close to its star it will be too hot and if it is too far away from the star it will be too cold. So there is a zone around every star that is now called the Goldilocks zone where the temperature would be just right for life, somewhere between 0 and 40 degrees Celsius. The planet they have just discovered around a star called Gliese 581, is in just the right place and seems to be a rocky planet like earth and only a little bit bigger.

“What's the planet called?”

It's scientific name is Gliese 581c, but it has been given the name Ymir. It also has two other planets, so it is really like another solar system.

“So the aliens would be called Ymirians then?”

You and your aliens! Well, we don't know for sure that there is any water on Ymir, but as Xavier Delfosse, one of the team that discovered it said, “on the treasure map of the universe one would be tempted to mark this planet with an X.”

“So is anyone sending a space ship there?”

It's still 20.5 light years away so there is no way humans could get there at the moment, but a radio or TV signal could get there in 20.5 years. So the TV pictures from the moon landings would have reached them in about 1990. Perhaps if they exist and are impressed by our first attempts at space travel they might send us a message back.

“When could that message reach us?”

If they didn't spend too long thinking about it, a message could get back to us by about the year 2010..

“Are you serious?”

Not very often, but it is nice to think that it is at least possible.

Seeing the invisible, from the largest to the strangest telescope on Earth.

2007-08-09T08:50:00.000-07:00

Of course, astronomers now make telescopes that can see the invisible.

“How can a telescope see things that aren't visible?”

Light is just a small part of a much larger spectrum, the electromagnetic spectrum.

“Why is it called that?”

It's called the electromagnetic spectrum because a Scotsman, called James Clerk Maxwell, in 1873 discovered that magnetic and electrical fields both behave as waves and travel at precisely the same speed as light. Maxwell then went on to produce a theory that encompassed light, electrical waves and magnetic waves: hence electromagnetic. The range of all electromagnetic waves is huge; from x-rays and gamma rays with wavelengths of one hundred trillionth of a metre to radio waves with wavelengths of hundreds of miles. Do you remember what a wavelength is?

“I think so, it's the distance between the peaks a wave.”

That’s right. For light, the whole range of colours is squeezed into a surprisingly small range of wavelengths. Even though light and sound are completely different types of waves, if you think of light in musical terms, the whole range of visible light, every colour, would fit into a single octave. Do you know what an octave is?

“An octave is the eight notes of a scale isn’t it? Doe a deer a female deer, Ray a drop of golden sun, Me a name I call myself and all that stuff until you get back to Doe.”

Exactly. Now from one end of an octave to another the wavelength of sound changes by a factor of two. Going up it halves and going down in doubles. . If you think of a piano keyboard, which only covers a fraction of the range of possible pitches of musical notes, then this can give you a range of frequencies for sound which is eight times bigger than that for the whole of visible light. In other words, if you could construct a light keyboard the long wavelength light on this keyboard would look red and be like the low pitched notes in sound terms. The short wavelength light would be blue and be like the high pitched sounds with the whole of the rainbow in between. But all the light you can see would only cover eight white keys or thirteen if you count the black ones too.

“Every colour would fit into thirteen keys on a light piano? But that's impossible there are millions of different colours.”

To a completely colour blind man there are only three.

“What are you talking about Albert?”

You may see million of colours but someone with no colour vision at all will see only white, black and gray. There appears to be so many colours because our eyes is much better at detecting fine variations in light than our ears are at detecting differences in the pitch of a sound. If we were bats we might have decided to put a thousand notes in an octave and thirteen keys for light might be too many to describe all the colours a bat can see.

“OK. So where does this electromagnetic stuff fit in?”

If there was an electromagnetic piano its keyboard would be almost eight times longer than a normal keyboard and would have over 750 keys. Visible light would still represent only thirteen of these keys (that's counting the black ones as well), spanning only one octave in a range of over 63 octaves. A normal piano keyboard covers only 7 octaves or so.

“So what does this have to do with telescopes?”

Astronomers can now make telescopes that can detect the whole of this electromagnetic spectrum from x-ray telescopes which are good for detecting black holes and exploding stars in distant galaxies to radio telescopes which can detect pulsars. The biggest single telescope in the world is a radio telescope.

“How big is it?”

It is 305 metres across and in Arecibo, Puerto Rico. The most interesting thing about this telescope is that it was made inside the crater left by a meteorite.

“There are craters on Earth? I thought they only existed on the moon?”

Oh they exist here too but most meteorites burn up in the atmosphere. There is one in Arizona, the Barringer Crater, which is almost a mile across. It looks just like a crater on the moon.

“So why are there so few craters on Earth?”

There have been lots of craters on Earth but the atmosphere burns up smaller meteorites and the weather hides evidence of the rest. The moon doesn't have an atmosphere or any weather so all the craters for the last few billion years are piled one on top of the other. Remember the voyager probes and their golden discs with information about Earth? Well when the Arecibo telescope was upgraded in 1974 a radio message was sent into space towards a tightly packed group of stars in the constellation Hercules. This message, that included coded information about the structure of DNA, the shape of human beings and the solar system.

“Are these scientists crazy, giving away all our secrets to aliens?”

Well even though radio waves travel at the speed of light, the message won't reach its intended target until the year 26,000. So it will be a little while yet before anyone hears the message and decides to pay us a visit. But that's not the most unusual type of telescope. The strangest telescopes look particles called neutrinos which are nothing to do with light or the electromagnetic spectrum.

“Neutrinos? Never heard of them."
Well you have now. There are more neutrinos in the universe than any other particle, knocking us photons into second place. A neutrino could not only pass straight through your body but go through the whole earth. A neutrino telescope has to be the strangest type of telescope in the world. In 1964 a man called Raymond Davis junior decided to go in search of neutrinos.

"Why? Just because they exist?”

When he started no one was sure if they existed or not. They had been invented by theoretical physicists who worked out that they ought to exist before anyone had even detected one.

“So why bother try to find particles that someone has made up?"

They are important because scientists' best theory of how nuclear fusion works inside the sun predicted that the sun should produce a lot of them.

"I thought you said that Earth scientists had already worked all that out, even if they were a bit slow about it."

Well they had come up with what seemed like the right idea, but in science you need to start with the right theory, or hypothesis, and then do experiments or observations to check that the theory is correct. If they could measure that the sun was releasing the right amount of neutrinos is would help to show their theories were right. The problem with neutrinos is that they will fly straight through a normal telescope, through the head of the astronomer and nearly all of them will even pass straight through the earth

"So how do you detect something that can do that?"

It's not easy but this was Raymond Davis's approach. He found a deserted gold mine almost a mile underground and built a huge tank filled with 400,000 litres of dry cleaning fluid. The sun is thought to pump out almost 20 million trillion trillion trillion neutrinos every day and of these only one neutrino a day was expected to interact with one of the chlorine atoms in the fluid and change it into an atom of the gas argon. Having pumped the best part of a million dollars into this old gold mine they only found one neutrino every two or three days. Finding one argon atom in tank of 400,000 litres should have impressed most people, but theoretical physicists aren't impressed by any experiment that gives an answer that disagrees with their theories like this one did. Allowing for the difficulty in detecting neutrinos, this machine and others like it only found a third of the expected amounts of neutrinos. Lots of neutrino detectors have been built but most of the neutrinos are still missing.

“What happened to them?”

Well once they realised it was a problem with current ideas about neutrinos rather than the telescopes they changed their theory. The new theory is that the sun makes the expected amount of neutrinos but on their way to earth they change type to a sort that can't be detected by neutrino detectors.

“Is that cheating?”

No, it's science. You start with a theory that predicts that you ought to find a particular thing. You go looking for that thing and if you find it you start believing that theory but if you find something different it is time to create a new theory.

How the least read book in history changed our view of the universe forever

2007-08-03T20:47:00.000-07:00

“So when did people work out that the sun was in the middle of the solar system and the earth moved around it?”

Oh, that took a while, about two thousand years from the time that the ancient Greeks decided that everything moved around the earth.

“Two thousand years?”

Not a long time in terms of the age of the universe. It wasn't that no one had suggested an alternative. Back in the time ancient Greece, Aristarchus of Samos suggested that the earth moved around the sun around 270 BC. Even before him the ancient Indian astronomers put the sun at the centre of the universe in around 900BC. A man called Nikolaus Krebs said it in the 1400’s, but it was another hundred years before the the idea really started to catch on.

“What happened then?”

A polish astronomer called Niklaus Koppernigk published a book that changed people's view of the universe for good.

“How come I've never heard of him?”

Perhaps because people usually call him by the Latin version of his name,
Copernicus.

“I think I've heard of him. So what did he say about the universe?”

He put the Sun in the centre and then worked out a system to explain the movements of all the planets. The fancy word for this is Heliocentric and Geocentric is where the Earth is at the centre. He didn't get it exactly right but it was an important move in the right direction.

“So there must have been a big splash when he discovered that.”

Not really. Nothing happened for thirty years because he was too scared to announce it.

“Scared of what?”

The Church. At that time the Church was very powerful and totally opposed to anyone disagreeing with their view of the universe. The real problem was that he was in the Church and had the post of Canon.

“Tricky one. I can see why he looked so worried in this picture.”

So tricky that he only published his theory that placed the sun at the centre of things when he was almost on his death bed.

“So he didn’t have much time to enjoy the glory after it was published.”

True but it caused such a stir with the Church that he was probably right to wait until just before he died. Very few people actually read the book because it was banned by the Church just after its publication until 1835. By the time it could be published everyone believed the ideas anyway so no-one really bothered to read the book De Revolutionibus Orbium Coelestium which in English means On the Revolution of the Celestial Spheres. So it would probably rate as the world’s most famous and least read book.

“So how did the idea spread if the book was banned so fast?”

There is nothing like banning a book to make people seek out the few copies that were printed. One of the most important turning points was that Copernicus's ideas were taken up by greatest minds of the times, men like Galileo.

“The same man who tried to measure the speed of light with the two lamps and two assistants that you told me about earlier?”

That’s him. Galileo almost single handedly overturned the classical Greek view of the universe. Aristotle and Ptolemy represented the unquestionable truth to most people at this time. This truth required the existence of perfect, unchanging crystalline spheres, with the Earth at the centre and everything revolving in perfect circles. Galileo charged through this peaceful image of perfection like a bull in a renaissance china shop and disprove some of the most cherished ancient beliefs about the universe.

“How did he manage to do all that?”

He heard of man in Holland who had made an instrument that could far away things much clearer.

“What kind of instrument?”

A telescope. It was just a simple tube with two hand polished lenses and Galileo being good at almost everything made himself one. As soon as he did, he pointed it at the night sky. He became expert at designing telescopes and made an amazing series of discoveries about the skies above. The Greeks said the sun was this perfect glowing ball, but he discovered spots on the sun so that showed that idea was wrong. Though of course believers in the old ideas said the problem was with his telescopes.

“Was it?”

Not at all, the Sun really does have spots but that wasn't all Galileo discovered. He found that the moon had mountains and craters that cast shadows, so the moon wasn't a perfect sphere. He found that they were far more stars than can be seen with the naked eye and the milky way, the local galaxy, is in fact made up of thousands of faint stars. He also found that Jupiter had four moons revolving around it.

“Why was that important?”

Well one of the arguments that the Earth had to be at the centre was that if it were moving through space then the moon would be left behind. So when Galileo found moons around Jupiter that removed this argument, even if the Earth did stay still how could they explain how Jupiter's moons could move with it?

“But didn't they know about gravity?”

They knew things fell if you dropped them but Isaac Newton hadn't been born yet so there was no understanding that things like the moon would be affected by gravity.

“So they accepted the idea of the Sun being at the centre of the Universe then?”

Oh they didn't give up that easily. Believers in the old established ways of thinking soon invented answers for Galileo's findings, but these were a little far fetched. Ahah, they said, yes there may appear be mountains and valleys on the moon, but the valleys are filled with a pure, transparent crystal material so the moon is really a perfect sphere.

“That's a daft idea.”

People will often jump through hoops rather than change their minds. But as the new astronomy revealed ever more about the universe, the authorities adopted a different tack. They took to the pulpits and denounced the dangerous and heretical views of these renaissance madmen. Galileo was hauled up before the ecclesiastical courts and forced to renounce his dangerously mistaken views. To save his neck he stood up and declared that the Earth remained still and everything else moved.

“Why did he change his mind?”

Oh, he didn't. In true schoolboy tradition, no sooner had he said the words than he famously muttered under his breath at the end of his trial,. ‘..but it does move’.

“So what happened to him?”

Galileo was placed under house arrest for the last years of his life but that didn't stop him writing and while he was locked up at home he produced his last book - Dialogue Concerning the Two Chief World Systems. Galileo’s book was written as conversation just like this blog. After that the idea of a telling people about science with imaginary conversations fell out of fashion for five hundred years.

“So did Galileo and Copernicus get it all right, was there anything else to discover about the movements of the planets?”

No matter how much we think we know there is always more to discover. Copernicus finally made the world believe that the Earth spun on it is axis like a top and moved around the Sun, which is quite an achievement, if you watch a sunrise or sunset it is much easier to believe the sun is really rising or falling than the ground underneath you is spinning. But he didn't get it all right, he was still attached to the ancient Greek love of circles and ended up with a very complicated system. To explain the movements of the planets the ancient Greek plan needed the planets to rotate around the Earth and do little circles in space too called epicycles. Copernicus's system was just as complicated and in fact the only thing he really got right was putting the sun at the centre of the solar system.

“Who worked out how the planets moved properly then?”

A man called Johannes Kepler who was born in 1571 in Württemberg, Germany. Worked out that the planets don't move in circles but ellipses, sort of egg shaped orbits. From this he created his three laws of planetary motion even though he didn't know why these laws were true. He just worked them from studying the movements of the planets.

“So who did that bit?”

Isaac Newton. Remember his law of gravity? Well when Newton worked out gravity it turned out that his equations could be used to show why Kepler's laws were true.

“So they got it all right?”

Not even then, there was a wobble in the planet Mercury that still couldn't be completely explained.

“So who worked that one out?”

Oh, someone not a million miles from here.

“You!”

Naming the planets, a story stranger than the Sopranos

2007-07-28T20:44:00.000-07:00

“Where do all these names come from, like Neptune, Pluto and Charon?”

Most of the planets and moons are named after ancient Greek and Roman gods and goddesses. Pluto was the king of the underworld or Hell and Charon was, and perhaps still is, the boatman who ferried dead bodies across the river Styx in Greek mythology to bring them into the underworld.

“I thought you said Pluto was discovered in 1930, so why was it named after a 2,500 year old Greek god?”

The Greek hell was cold and dark, rather than hot and that pretty well describes this part of the solar system. The other reason is that he was one of the last of the Titans not to have a planet named after him, so it seemed only fair. Charon was only discovered in 1978, but astronomers like to keep the traditions going.

“Who were the Titans?”

The Titans were a family of ancient Greek and Roman gods and outer five planets are named after them, Pluto, Neptune, Uranus, Saturn and Jupiter. The family squabbles of the Titans would stretch the belief of the most hardened soap opera fan. In the ancient myths Uranus was the father of this clan. Worried about what the rest of his family were plotting, he hid his children in a cave. His wife, guided by her maternal instincts, let the youngest, Saturn, free who of course immediately attacked his dad Uranus. He then promptly claimed the throne and married his sister. Knowing what children of gods can do he decided to swallow his newborn children rather than take any risks. Saturn’s wife, like her mother decided to protect the youngest. This spared child was called Zeus by the Greeks and Jupiter by the Romans. He bided his time, grew big and strong and returned as leader of the Olympians to take his father on. So he came back, killed Saturn his father and cut his brothers Neptune and Pluto from their father's body where they had been ever since being swallowed shortly after birth. Jupiter gave his brothers jobs to keep them busy. Neptune got the sea and Pluto got the not so great job of governor of hell. After this they all lived happily ever after until Christianity came along.

“Wow, mixed up family. What about the rest of the planets are they part of this story?”

The family saga of the outer planets is maintained even here. Mars, Venus and Mercury are all children of Jupiter in the myths. That just leaves Earth which was where the Romans and Greeks lived so couldn't really be named after a god.

“So they must have known these planets existed back in the times of the ancient Greeks and Romans?”

They knew the planets that you can see by looking up in the sky were different from stars but they had no idea they were solid round planets out in space.

“How did they know they were different?”

They could tell they were different because they moved across the sky whereas all the other stars stayed in fixed patterns. This is where the word planet comes from. The greeks called them planetai which means wanderers. They also learnt that these planets didn't wander anywhere but in definite patterns within a belt of stars called the Zodiac.

“The thing that astrologers go on about?”

The very same. Astrology is bunkum and the ancient Greek view of how the planets moved was pretty odd too even if it did provide an explanation for how these wandering planets could move among the stars. The Greek universe was centred on the Earth and had everything else revolving around it in perfect circles. Aristotle set this particular ball rolling with 55 spheres made from a perfect transparent substance that moved all the planets around. A bit later another Greek astronomer-philosopher, Ptolemy, fine tuned this clockwork universe and his ideas were considered to be the way the universe was for well over a thousand years. Ptolemy placed the Earth at the centre of the universe. But I'm being a bit unfair on the early Greeks, not all of them got it wrong.

“It doesn’t sound like they got much right to me.”

At around the same time as Aristotle, Aristarchus suggested that the sun was at the centre of the universe, but like the better theories of light around at the time, this was largely ignored and later swept carefully under the scholastic carpets of European monasteries. This was at a time when men were either killing each other or copying out pages from of ancient books over and over again back in the dark ages. Then came the renaissance in the 1500’s and some very clever people who were not afraid to stick their necks out a bit, even at the risk of getting them cut off.

“What was wrong with thinking the earth moved around the sun?”

Nothing at all, apart from the curious fact that the Christian Church at the time was supporting the theories developed by an ancient pagan civilisation. Perhaps this was because this theory gave the most important position in the universe to the Earth and since the church was on Earth that seemed appropriate to the leaders of the Church at the time.

“Since the bible says God made the universe, shouldn't heaven be at the centre?”

People have been burned at the stake for less heretical suggestions. Remember what happened to Anaxagoras after he suggested his hot rock idea for the Sun back at the start of this journey.

To be or not to be, is that a planet I see before me?

2007-07-25T18:52:00.001-07:00

“So how much further is there to go?”

We’re almost there, only 4 billion miles to go.

“Another 4 billion miles?”

But the good news is that it will only take us 7 hours.

“That’s not so bad then.”

Just long enough for a good look at these planets. Where we are now is just at the edge of the solar system. This very cold and very dark place is a bit like the Oort cloud in that it was invented before it was seen. Just a year after Jan Oort named his cloud in 1951, Gerard Kuiper proposed there should be lots of small planets or bits of rubble on the edge of the solar system.

“This is a different lot of rubble to the Oort cloud?”

This is much closer to the sun than the Oort cloud. The other difference is that no-one, well no human, has ever seen the Oort cloud but just a few years ago in 1992 the first object was spotted with powerful telescopes in just the place that the Kuiper belt was meant to be.

“What was it called?”

1992QB1.

“That’s a bit of a boring name isn’t it?”

Things in space seem to get either strange names or boring names made up of letters and numbers. Astronomers think there are up 70,000 more of these things flying around out here and a few have been given proper but odd names, like Quaoar (which has a boring name - 2002 LM60) and Varuna. Sedna is the most remote object in the solar system ever seen by telescope and seems to be going around the sun between the Kuiper belt and Oort cloud, almost 4 billion miles from the Sun.

“So are these objects really planets?”

No they’re too tiny, much smaller than the earth’s moon so they aren’t proper planets. The big ones are sometimes called planetoids, the medium to small ones planetesimals and the tiny ones asteroids. The first proper planet in the solar system is Pluto, though some people starting saying that it was too small to be a planet as it is only two third’s the size of the earths moon.

“So how can you tell the difference between a moon and a planet?”

Moons are little planets but they are in orbit around a proper planet rather than around the sun.

“So even though Pluto is smaller than the Earth’s moon, Pluto is a planet and the moon is just a moon?”

Well Pluto’s been called a planet since it was first discovered in 1930 but that has just changed. Astronomers have come up with a rather complicated way of deciding if a planet really is a planet. In 2006 the International Astronomical Union decided that to be called a 'planet' you have to go around the Sun, being round (or nearly round) and have 'cleared the neighbourhood' around your orbit. They decided poor Pluto has met only two of these conditions. As it crosses the orbit of the next planet Neptune it hasn’t cleared its neighbourhood, so it is now officially a dwarf planet.

“And Neptune is a planet even though Pluto crosses its orbit? That’s not fair.”

I totally agree. It isn’t fair at all, but I don’t think we heard the end of this planet story just yet. I’m sure the International Astronomical Union might change their minds again. In the mean time Pluto has been given a number 134340.

“What if a dwarf planet had a moon going around it, what would that be called?”

Well they still can still call that a moon because no one has defined that yet but technically both would be dwarf planets. That’s just what Pluto has. Look there’s Pluto over there.

“There’s two of them or am I seeing double?”

The bigger one’s Pluto and the smaller one is Charon its moon which isn’t much smaller than Pluto. There are two other much smaller moons too, Hydra and Nix. We've got a much better view than they get from earth. Even the Hubble space telescope pictures of Pluto are fuzzy, but you can still see Charon. A space probe was launched in 2006, the New Horizons probe, but that won't reach Pluto until 2015.

“Nine years just to reach Pluto?”

It is a still long way away, on average 4 billion miles from the sun or about 5 light hours. Plutelings, if they existed, would have a slightly different view of the sun to earthlings. Firstly at minus 213oC in broad daylight sunbathing takes on a different complexion. Also the sun looks about 40 times bigger on earth than on Pluto, so rather than a nice golden disc the sun will look more like a bright point of light. The size of the sun as seen on Pluto actually changes during the Pluton year, about 248 earth years, almost doubling in size in what I suppose you would call the Pluton summer.

“How can the sun get bigger?”

The sun doesn't but Pluto has a very eccentric orbit so that it changes from being 2.8 billion miles from the sun to a very chilly 4.6 billion miles. A sun 2.8 billion miles away looks bigger than the same sun 4.6 billion miles away. This eccentricity helped it to sneak inside the orbit of Neptune in 1979, so for a few years it wasn’t the most distant planet. This was a short lived change in the solar system’s natural order; after February 1999 it was back to being the most distant planet for another 220 years or so.

“Not quite.”

Why?

“Well, you just said in 2006 Pluto became a dwarf planet so Neptune will always be the most distant planet from now on.”

You really are getting the hang of this space stuff you know.

The Cloud that Oort to exist and sending a message to ET

2007-07-21T16:02:00.000-07:00

You might like to know that we will be nearing the outermost limits of the solar system soon. Around a light years or four trillion miles from the sun are the first traces of the solar system, the Oort cloud.

"Are we really going to go through a cloud?"

Well, a sort of cloud, named after Professor Jan Oort.

"So why can't I see anything?"

No-one has ever seen the Oort cloud, but if it didn't exist someone would have had to invent it.

"So did Mr Oort invent it?"

Not exactly, he theoretically deduced its existence in 1950.

“So what is so special about this cloud?”

Well it's really just a collection of lumps of ice and rock, which never formed into a proper planet and drift around just about under the control of the sun's gravity.

“The gravity of the sun can be felt at this distance?”

Well, gravity is pretty weak out here but still strong enough to stop this space junk from drifting off into intergalactic space. What makes this cloud interesting is that every now and then a slight change in the balance of the sun's gravity and gravity from the rest of the galaxy gently nudges one lump onto a new path towards the sun. It picks up speed and heads off into the inner solar system.

“What happens then?”

When it gets nearer the sun the lump starts to evaporate and give off gases and dust that stream behind it. This is what comets are. This tail begins to glow and can reach millions of miles in length. Then it starts the slow journey back away from the sun and it starts to fade away again. Sometimes a comet is caught in an orbit so that it can go back again and again, like Halley's Comet which appears every 75 years or so. This was one of the important tests for Newton's theory of gravity. Edmund Halley, a friend of Isaac Newton, became famous for correctly predicting that a comet, which became known as Halley's Comet, would return in 1758.

“You said before that Newton almost never smiled, that must have pleased him.”

Sadly both he and Halley were dead by the time the comet came back, but at least Halley's name was remembered as the comet was named after him. His prediction showed that rather than being signs from God, comets were just another part of the solar system. But they are still very impressive.

“So what exactly is a comet made from?”

Well no-one really knew for certain until twenty years when the European Space Agency sent a probe called Giotto into space in 1986 that flew past and took photographs of Halley's Comet.

“What did it look like close up?”

Here's one of the pictures, there are a bit fuzzy but they showed that Halley's comet was a 10 mile long peanut shaped ball of ice and dust covered in soot.

“A great big dirty snowball?”

Basically yes, but as it heats up near the sun some of the contents get heated up and burst through the outer layer and that makes the tail of the comet as it escapes into space.

“Did I miss something, or did you forget to explain how Mr Oort worked out that his invisible cloud existed?”

Oh, sorry. Mr Oort deduced that this cloud had to exist otherwise there wouldn't be any comets left by now. Every time a comet comes by the some a lot of it melts. They lose so much of themselves on each pass by the sun that any comets that existed when the Earth and the rest of the planets were made, at least 4.5 billion years ago, would have long since evaporated into space. So there needs to be a place where comets can have stayed hidden away for a few billion years and that place is the Oort cloud.

“But no-one has ever been out this far?”

Not at all but there is one man made thing that is rushing out of the solar system, even though it has only gone 9 billion miles from the sun so far.

“Nine billion miles isn't bad.”

Not at all and it's now travelling at a million miles a day.

“Is this a space ship?”

More of a space probe than a space ship, Voyager 1, has been travelling through space for thirty years now powered by small nuclear power supplies and will head on out of the solar system eventually.

“When will it reach the nearest star?”

It might be 40 or 50 thousand years before it could reaches another star with planets. But if it ever does reach an alien civilisation they will certainly know a lot about us before they arrive.

“Just by examining Voyager?”

Well the space probe itself will hardly impress them. By the time it arrives the radioactive power sources will be all dead but it will be like a message in a bottle. They also included a 12 inch gold plated record with lots of information about earth.

“Like an LP record? NASA sent an LP into space?”

They certainly did, along with a needle to play it and instructions.

“They will think we are primitive cretins”

Well this was 1977, and nothing electronic would survive tens or hundreds of thousands of years like gold covered metal disc. The technology is primitive but the information if they play it will tell them a lot more. It is a bit odd that it uses a speed that no record player on earth uses, 16 and 2/3 revolutions per minute.

“What sorts of information was on this record?”

Well, a greeting in 55 languages.

“Will anyone one understand it?”

Well they are a few languages that no-one one Earth speaks like Akkadian which died out about 4000 BC. There are also the sounds of different animals, babies crying and a tractor. There are also 115 different pictures. Surprisingly detailed pictures of how humans reproduce. You can look at all these sounds and images at http://re-lab.net/welcome/images.html. Before you rush off to explore that here is the speech that US President Jimmy Carter recorded for the Voyager recordings.

“Of the 200 million stars in the Milky Way galaxy, some—perhaps many—may have inhabited planets and spacefaring civilizations. If one such civilization intercepts Voyager and can understand these recorded contents, here is our message: This is a present from a small, distant world, a token of our sounds, our science, our images, our music, our thoughts and our feelings. We are attempting to survive our time so we may live into yours. We hope someday, having solved the problems we face, to join a community of galactic civilizations. This record represents our hope and our determination and our goodwill in a vast and awesome universe."

Oh, and they also included a map to help any aliens find the sun and our planet in case they like the look and sound of us and decide to visit.

“Do you think aliens will ever find it and come to see us?”

If aliens do and find us first then that will mean they are a much more advanced species than we are, so I hope they will treat us lowly humans better than we have treated a lot of species that we consider simple. They might regard us as not much better or more interesting than pets if we are lucky.

“And if we are unlucky?”

If we are unlucky they will treat us in the same way that humans have treated of a lot of other species, they will either eat us or destroy us. That golden record contains anatomy pictures of what the insides of our bodies look like and even the structure of DNA, so they will certainly know if we look tasty.

[p.s. Voyager has featured in a lot of Sci-Fi films and most recently in the Futurama episode called Parasites Lost where Voyager ends up like a celestial space bug smashing into the Planet Express spaceship only to be cleaned off the windscreen by Leela.]

Life in the Galactic Suburbs (and what a pigeon can teach an astronomer)

2007-07-18T10:56:00.000-07:00

“So can we see the earth from here?”

We're still too far away to see the earth, but we're heading toward that yellow star straight ahead. That's the sun.

"It doesn't look very special, just a normal looking star."

That's because it isn't really special, other than being home to us humans. It's just a nice, ordinary, stable star. Just the sort you’d want to live near. Not too big and not too small. Not a bad place to live around.

“Good neighbourhood?”

Not really, a typical quiet galactic suburb only thirty thousand light years from the centre of the galaxy.

“It's not as impressive as the star we came from.”

No, it's tiny compared to Deneb, but remember that big stars burn their nuclear fuel much faster. If the sun wasn't so average star we wouldn't be here talking about.

“How come?”

The sun's been burning for over four billion years and it took one and a half billion years for the earth to cool down and primitive life to start. Deneb will have blown up before life could possibly start. Even though the sun's not huge it's still brighter than most of the stars in this neighbourhood. Here is a map of this part of the galaxy from www.atlasoftheuniverse.com. We're just over 12 light years away now and this shows all the stars that are around the sun. If we humans ever get to travel into the galaxy these are the first stars they will reach.

“So which is the closest star?”

That little brown one over there, called Proxima Centauri. That's just over four light years from the sun but a rather dull little star. The one just near it called Alpha Centauri is almost a twin of the sun, it is exactly the same type of star.

“They still all just looks like dots of lights. When will the sun stop looking like star and start looking like the sun?"

Well, if you only had a pair of human eyes then you'd need to be within 5 billion miles.

"That's nothing. It’s...it’s...less than a thousandth of a light year."

Very good, just under 8 light hours. That's why from Earth all the other stars look like points of light, they are simply too far away. See those two stars up ahead.

“The two little dim ones, I see them.”

Those two stars are a binary system, so they are going around each other. A lot of stars form that way. That system is called Cygnus 61 as it was originally thought of as one star which is the 61st brightest star in our constellation Cygnus.

“How can they be in our constellation if we have been travelling through three thousand light years of space to get here?”

The constellations are not real groups of stars but just appear close when we look into space from earth. Because all stars look like dots of light, when we look at them we can't tell how far they really are away. So our constellation Cyngus is made up stars that are scatted all the way from here back to where we started.

“Is that the same for all constellations?”

Nearly all of them. One of the most recognisable constellations Orion, the hunter, is spread out over a huge distance too. This picture show what the constellation looks like from earth and how the stars are really spread out in space.

“If all the stars look the same no matter how far they are away, how can you measure their real distance?”

Scientists have a few tricks for that but one of the best is called parallax. Move your head from side to side. What happens?

“Not much.”

Don't things close up seem to move?

“Yes but that's because I'm moving my head.”

I know, but things close up seem to move more than things far away don't they?

“Yes, I suppose they do.”

Well the same thing can work for stars but rather than move your head you have to look from two different places millions of miles apart.

“Oh, that sound's very simple.”

Of course it is. You just have to wait 6 months for the earth to go half way around the sun and you will be looking from a position that over 160 million miles different. The most distant stars, like things on the horizon when you shake your head, will appear to stay still, but nearer stars will seem to move position over six months. From measuring that movement, which is called parallax, scientists can measure the distance of nearer stars very accurately. It's not just scientists that use parallax to judge distance, pigeons do too. That's one of the reasons they nod their heads.

“Wow, Albert. That's a bit random even for you. Explain that one to me.”

Well a pigeon has an eye on each side of its head which makes judging depth difficult. So by bobbing their heads as they walk they can judge how far things are away from them with parallax.

“I suppose I did ask.”

The Praying Mantis, a large insect does the same thing.....but perhaps we should come back to that some other time.

“I think so Albert.”

Space the final Frontier (and how many aliens know we are here)

2007-07-14T03:56:00.000-07:00

“So where are we now?”

Looks like space to me, about fifty two liight years from earth.

"Not much going on around here is there?"

Of course not, that's why they call this place space. If space wasn't empty it wouldn't be called space, would it?

“I thought we were meant to be in the middle of a galaxy?"

We are in the galaxy but not quite the middle of it. We’re flying along one of the spiral arm of a galaxy. Like most galaxies, this galaxy that the earthlings call the Milky Way, has a central glob of stars surrounded by spiral arms because the whole galaxy is spinning.

"So shouldn't space be stuffed with stars if we’re inside a galaxy? There seems to be lots of stars but not many of them are near here.”

That's the way space is. The stars are spaced out by huge distances but because space is so large there are a lot of them. Thinking in terms of the size of people will make it easier to imagine the distances. The earth's sun is just under a million miles across but imagine the sun as a person of normal height. At this scale the whole earth would be the size of a marble. How far away do you think the nearest star would be?

“I'll guess a million miles.”

Not quite that much, just over thirty thousand miles.

"That's not far."

It's far enough. One person every thirty thousand miles hardly makes a crowd does it? It would take you four hundred and fifty days to walk that far even if you never stopped or slept. The stars in a galaxy only fill up one thousand billion billionth of a percent of the space. The other 99.9999999999999999999999% is empty.

“OK, I see now why this place is called space. But there are still lots of stars out there. How many stars are there in total?”

All the stars you can see are located in this galaxy, the milky way. Looking out you can see only a few thousand stars but there are a 100 billion stars in this galaxy alone. There are probably as many galaxies in the universe as there are stars in our own galaxy so that would make about 10,000,000,000,000,000,000,000 stars.

“That makes the little marble sized earth I was thinking about seem pretty insignificant.”

Small but because you live there it is significant and precious to you and everyone who lives there.

“So what's happening on Earth right now?”

That's a very interesting question.

“It seems a simple question to me.”

Yes but the simplest questions are often the most interesting and far from simple.

“But simple would be good right now, I've only just recovered from thinking about relativity.”

Well here is one last thought for you on relativity. At this very moment everyone on earth is in the year 2007 but as far as we are concerned they are still back in 1955. Also if earthlings were looking for us in a powerful telescope then they wouldn't be able to see where we are now until the year 2059.

“Sorry, I'm not getting this Albert. Is this because we are travelling so fast again?”

It comes back to the speed of light but it is just because we are so far away. If nothing can travel faster than light, then events happening a long way away can only happen in the past. Imagine we were standing where we are now fifty two light years from earth and the world suddenly blew up. What would we see?

“The explosion I suppose.”

But as we are fifty two light years away from Earth, we wouldn't see the explosion for fifty two years. So if the Earth had blown up five minutes ago we wouldn't know or care because there is no way it would affect us.

“I think I'd care if I called home and discovered they were all dead.”

Yes but it would take 50 years for the message to reach earth, no radio signal or telephone call can travel faster than light remember. Imagine it was just a bad dream and the Earth hadn't blown up. It would also take another fifty years for any message to travel back, so if we stayed here it would be a 100 years before you would know for certain that the Earth was still there.

“OK. I think I get that.”

So at this distance anything that happens now on Earth can't affect us for fifty years and anything we do here can't affect earth for fifty years. When an event happens anywhere in the universe any possible consequences start spreading out like ripples through space at the speed of light. Until light or any signal from that event reaches a certain point in time and space, it is as if it never happened. This is perhaps the most important lesson from relativity. Don't worry about things that can't affect you or things you can't influence.

“So has anything from Earth had any impact out here?”

For most of human history, nothing man has done has had any impact on the cosmos but that is changing. As soon as radio and television were invented and the signals were strong enough to be broadcast around the world, news that humans existed has been rippling out through the galaxy at the speed of light. About fifty years ago the Earth would have lit up like a light bulb in terms of radio and television broadcasts leaking into space.

“Wait a minute wasn't that flying saucer at Roswell discovered fifty years ago?”

A little bit more than fifty years ago, that was in 1947, if it happened at all.

“You don't believe in UFO's?”

If it was an alien space ship it must have been lost because it's very unlikely they were looking for us. Even if there are aliens in the galaxy, most of them wouldn't yet know that we exist. The bubble of radio and television signals from Earth will only have reached the few thousand stars that are within fifty light years. Of the 100 billion stars in the universe only 0.000002% could possibly know we exist. It will take another 150,000 years for the whole galaxy to be able to detect the earth's radio signals, so in the next half million years or so aliens might coming knocking on the door. What has just reached us in this part of space is the news of the death of a famous scientist back on earth.

“Who?”

You may have heard of him, Albert Einstein.

“You've just died?”

On the Earth of 1955 I have, but death has a very bad reputation. I have always felt that the fear of death is the most unjustified of all fears. After all, once you are dead it can't get any worse so logically things can only stay the same or get better.

“So you're not dead?”

If the character in a novel, who has never lived, can be brought to life just by the imagination of the reader, how much easier must it be to keep a real person alive through remembering their words and deeds.

“Are you sure about that?”

Dead certain. I'm here talking to you aren't I?

To Relativity and Beyond

2007-07-10T13:12:00.000-07:00

“So what happened when you first proposed your theory of relativity.”

A deafening silence. I was still working at the patent office when my special relativity paper was published in 1905 and no-one seemed particularly interested at the time.

“You weren’t immediately famous?”

Not at all, I wasn’t even an established scientist at the time. I was a poor patent clerk trying to claim that the greatest mathematical genius of the world Isaac Newton was wrong. It was lucky I wasn’t locked up for being crazy. But a few well known scientists did take an interest. Max Planck and one of my university mathematics teachers, Hermann Minkowski, did believe in my ideas. I am ashamed to say that I skipped a lot of Minkowski’s lectures, but it was he who helped transform a lot of my ideas into solid mathematics in a paper he published in 1908.

“Three years later? Had nothing happened before that?”

Oh there was a little bit of interest. I tried to use my relativity paper to get a university job in 1907 but they wouldn’t accept it. I ended up using a paper that helped prove the existence of atoms and molecules.

“You invented relativity, started quantum mechanics and discovered atoms? When did you find time to do all that?”

All in the same year, 1905.

“Wow. But they knew about atoms before then surely?”

As an idea yes, but a lot of people doubted atoms were real. How can you believe in something that is too small to see?

“How can you believe in things you can’t see?”

By looking very hard at things you can see and using a little imagination. Eighty years earlier botanist called Robert Brown who was looking at grains of pollen in water through a microscope.

“The things that cause hay fever?”

That’s right they are so small they almost float in the air but in water Robert Brown saw that they seem to jump and jiggle around like they are possessed. This is called Brownian motion. Well I looked at the pattern of the jiggling and showed mathematically it made sense if the pollen grains were being constantly bombarded by smaller particles. If you put the pollen in pure distilled water, what else could those smaller invisible things be?

“Water atoms?”

Water molecules, which are made up of three atoms two hydrogen H and one oxygen atom O which is why water is called H2O.

“Neat. So go on, tell me when did you get famous?”

Does that really matter? A lot of people are famous for nothing at all these days. Isn’t if better to be not famous but have achieved something truly important?

“I suppose, but you did both. Isn’t that why you are here explaining all this? So what made you world famous?”

What made the world really take notice was when other people started showing that my crazy ideas seemed to right.

“Wasn’t that your job, to prove your theories?”

I could have but I was a much better thinker than a doer. But before I tell you what happened to make the world really take notice, I have to tell you about general relativity, the full version.

“Oh no, I was enjoying just chatting. Will this be harder than the special relativity you told me about last time?”

It won’t be harder for you, but it was much harder for me.

“Why?”

Because I was trying to bring together my ideas of relativity and create a new theory of gravity all at the same time. The mathematics of general relativity is very tricky and took me more than ten years to get right, but the ideas aren’t too scary. The basis of my idea of gravity should be known to anyone who’s ever been in a lift.

“A lift? How come?”

When a lift moves up suddenly you feel heavier and when it starts to fall you feel lighter. Now what happens if you are in a lift and the cable breaks?

“You fall and die!”

Eventually but while you are falling you will be weightless. Where has gravity gone?

“I don’t understand.”

If you are in free fall you feel weightless, until you land of course. So I realised gravity is just the same as acceleration. Imagine you were floating in empty space without gravity but trapped inside a lift and a passing spaceship grabbed the lift cable and starting accelerating. You wouldn’t be weightless anymore, you could stand on the lift floor. You would feel that up was the direction you were being pulled in.

“OK, but why is that such a big thing?”

It was a huge realisation because it allowed me to create a new theory of gravity. Isaac Newton worked out a mathematical law but it didn’t explain how gravity worked. When I worked out all the details I realised that gravity works because objects, any object bends space. The bigger the object the more space gets bent.

“Here we go again.”

It’s not that hard I promise. Imagine space as not as some solid thing but a stretchy rubbery thing.

“OK.”

When there is an object big enough to create a strong gravitational pull, it bends space just like a heavy metal ball on a trampoline or you on a trampoline. Now if you put a marble on the edge of a completely flat trampoline what would it do?

“Just sit there I suppose.”

Exactly. Now if gently lowered you onto the centre of that trampoline what would happen.

“I’d dent in the middle bit.”

And….

“The marble would roll in to the middle?”

Now you’ve got the idea and that’s how I thought gravity works.

“So does it?”

Well that’s what got me famous. Gravity is supposed to pull together things that have mass, physical things. Light doesn’t have mass, it doesn’t weigh anything so it shouldn’t be affected by gravity, but if gravity bends space then a light beam should get bent with it. I predicted that gravity from the Sun should make light bend by a certain amount.

“How can you show that?”

Well it needs the light beam to be going right past the sun. When the Sun is blocked out by the moon in a total eclipse, the sky goes dark and the stars are visible for a few minutes. This is the only time you can see light from a distant star skim past the edge of the sun. If my theory was right then the stars nearest the Sun should appear to be shifted from their normal position because the gravity of the sun had distorted the bit of space the starlight was coming through. In 1919 an expedition led by an Englishman Arthur Eddington travelled off to Principe Island to study an eclipse the results seemed to agree with my theory. If I've planned things right we might I be able to demonstrate how this really happens.

“How about the ideas about time changing as you speed up? Has anyone shown that really happens?”

That has been tested too but that took a lot longer. It is not easy to find clocks travelling close to the speed of light after all. But fortunately there are natural clocks in the universe. The decay of radioactive atoms, where unstable atoms breakdown usually into smaller ones, is one of them. This is the sort of clock used to work out the age of objects in carbon dating because radioactive decay is like the tick of a clock. The carbon-14 clock ticks very slowly if a bit randomly over thousands of years as it decays into a different atom nitrogen-14, in 5,730 years half of it decays. Carbon-14 in the air is taken up by leafs and gets made into wood in trees and anything else that plants make. By measuring how much of that carbon-14 has decayed scientists can work out how old a piece of wood is, even if it is tens of thousands of years old. Another sort of natural clock is seen in unstable subatomic particles called Mu mesons which last only a millionth of a second or so before breaking down. This is a super fast clock. These particles are made in the top of the Earth's atmosphere by collisions between cosmic rays and atoms in the air.

"What are cosmic rays?"

They are particles like us that come from stars and fly across the galaxy at huge speeds until they collide with something. When they hit the atmosphere of a planet they smash into atoms in the air and produce a shower of particles and atomic remnants. Meson particles are created by these collisions at the edge of the Earth's atmosphere then they shoot onwards to the Earth's surface at 99.5% the speed of light. Even at this speed a millionth of second shouldn’t be long enough to reach the ground before they break up or decay.

"So they never reach the ground?"

That’s the interesting bit, so many mesons reach the ground that they must be surviving roughly ten times longer than they should. At 99.5% of the speed of light how fast do you think time passes?

"At a guess I'd say about ten times slower."

Exactly. Relativity may seem bizarre but it also seems to be true. It’s not just speed that slows down time. In general relativity I discovered that gravity slows down time as well. I was very excited to read that in 1971, sixteen years after I died, J. C. Hafele and Richard E. Keating proved the effects of speed and gravity and time by flying four atomic clocks in opposite directions around the earth and comparing it with a clock on the ground.

“How much did the clocks change by?”

It was only a difference of three hundred billionths of second but the planes weren’t going very fast and it was almost exactly what relativity predicted. To get big effects you need a lot of gravity. Remember we talked about black holes a while back?

“Oh yeah, where gravity is so strong that light can’t escape.”

Well if you saw someone fall into a blackhole from a safe distance they would seem to hover forever at the point of falling in, just before they disappeared from the universe, because time was slowed down so much by the intense gravity.

“What would they see looking out?”

They would be able to see the rest of the universe seeming to speed up. Rather than seeing their lives flash before their eyes, they would see the whole future of the universe unfold in fast forward.

“Wow, that’s freaky….Albert, I hope you don’t mind me saying this, but the Internet is full of nutters who claim you were wrong. I know you’ve explained to me how relativity explains lots of things but is relativity the final answer?”

Isaac Newton’s theories lasted twice as long as mine have so far. Who knows how long my theory will last, perhaps one of those nutters as you call them might be right. A hundred years ago I was just like them, trying to overturn hundred’s of years of tradition and convince people who thought that the answers to all the big questions had already been discovered.

“Have all the big answers been discovered?”

Not at all, not then and not even now. I spent almost forty years of my life trying to work out how quantum mechanics, gravity and relativity could all work together into one great theory of everything and failed. But I died convinced there was a way of tying everything together, God’s blueprint for the universe. So I’m certain a better theory will be discovered one day.

Relatively Weird. How to get younger, thinner and fatter all at the same time.

2007-07-07T23:30:00.000-07:00

“OK, Albert. Go on hit me with the weird stuff from your relativity theory”

You’ve got the idea that movement is relative from our last conversation?

“That bit’s fine.”

Good. The rest of the theory is based on the simple idea that the speed of light in space is constant. It doesn’t matter how fast the source of light is moving, or the speed of someone looking at that beam of light. Also nothing can go faster than the speed of light.

"If I came out of the headlights of a car that was flying through space at half the speed of light, I'd end up going one and a half times faster than you, wouldn't I?"

Unfortunately not, but a good question. Light from the headlights of a car isn't travelling at the speed of light plus the car's speed, but simply at the speed of light.

“How can that happen?”

It’s simple enough really you just have to change a few other rules to make sure that the speed of light is always the same. If the speed of light is always going to be the same, it just means that time slows down as you get faster. The good news is you stay younger longer. The bad news is you get squashed and get heavier and heavier. I’m afraid this next part will sound more like something out of Alice in Wonderland than science so I hope you are ready for this. And you people reading out there, if you are a bit sensitive it might be better to read on with your eyes closed.

“So basically you invented the idea that clocks slow down just to make your theory about the speed of light work?”

Well not exactly, I just started imagining how the universe would work if the speed of light was constant. The rest, slowing down clocks and even E=Mc² followed from that.

“OK Albert, start by explaining to me why fixing the speed of light makes you convinced that clocks can change speed.”

Imagine someone leaning out of a train travelling at 100 miles per hour and another person standing beside the track. Both of them throw an apple in the direction the train is moving. Which apple will be moving faster?

“The one from the train. It’s starting at 100 miles per hour so it must be moving faster than the one thrown from a standing start.”

Exactly. So change the apple for a torch. Does the light leave the torch faster if the torch is moving?

“I would think so, but you just told me I’m wrong.”

Yes, you are wrong. Even stranger is that to the person on the train and the person beside the track the same beam of light will appear to be going the same speed.

“How can that be true? If I am following a beam of light at half its speed it will move away from me at only half the speed of light.”

Unless time slows down, of course. There is a fairly simple formula that tells you how much time must slow down to make sure that the speed of light will always be the same no matter how fast you are moving.

“Of course, why didn’t I think of that? Albert are you crazy? Why would time slow down?”

To make the universe work properly, time has to slow down as you speed up.

“So why had no-one noticed this slowing down of speeding clocks before you?”

Because it doesn’t happen until you are going very fast.

“How fast is very fast?”

A reasonable fraction of the speed of light, which is something no human has ever done except in their imagination.

“What’s the fastest speed a human has ever travelled at?”

The fastest humans are astronauts. They have to reach a speed of more than 25,000 miles per hour to escape the earth’s gravity. But that’s a tiny fraction of the speed of light, only 0.004%.

“So go on explain what happens at almost the speed of light.”

If you could buy a ticket for a space ship going at 99% of the speed of light, time would go seven times slower than on Earth. If you tried just to spend your sleeping hours whizzing around the moon at 99% of the speed of light, you would face a slight problem. Everything in your body would, from an Earth point of view, slow down. From your point of view, if you could see what was happening on Earth, it would be like watching a video on fast forward. So if you go to sleep on your spaceship for eight hours sleep on Monday evening and came back to Earth the next morning it wouldn't be Tuesday but Thursday morning.

“Is that like time travel?”

It is a sort of time travel but it only lets you go into the future, you can't go back in time with this trick. If you slow down even a bit the effects gets much less. At 10% of the speed of light, a mere 67 million miles per hour, you’d gain less than two days if you spent a whole year travelling. At the end of the day it is easier, cheaper and more effective just to lie about your age like everyone else does than use relativity to stay young.

“How fast is time travelling for us then?”

We are travelling at the speed of light, so for us it is passing normally but compared to earth our clocks are ticking infinitely slowly.

“Infinitely slowly?”

Well when we started out, earth was back in 1223 BC and it’s now 1905 the year I published my theory of special relativity. Does it feel like we’ve been travelling for three thousand years?

“No, but…”

Well there you have it. We could travel the entire universe in no time. We can travel as fast as imagination. You can imagine yourself anywhere in the blink of an eye.

“If we went faster than the speed of light would time go backwards?”

We'll never know because nothing can go faster than the speed of light.

“Why not?”

Because as you get near to the speed of light your mass increases very rapidly. At half the speed of light, a space ship would have a mass 15% more than parked in a space dock. At 99% of the speed of light the mass would have increased sevenfold. At 99.99999% of the speed of light the mass would have increased by over two thousand times. As the mass of a space ship increased it would need more and more energy to accelerate. If it ever reached the speed of light, its mass would be infinite and it would require an infinite amount of energy to accelerate it to a speed greater than the speed of light. Since that would take more energy than is in the whole universe, it can't happen.

“Talking about energy, where does E=Mc² fit in?”

There are some other laws of the universe about conserving energy or momentum that I needed to tweak to work with relativity. These formula were worked out for moving objects but it turned that at rest, there was one part of the formula still needed. That leftover bit was E=Mc² which showed that mass and energy are related to each other.

“Tweak? The atomic bomb exists because you worked out how to tweak a mathematical formula. Is there anything else you are going to tell me changes?”

The other thing that changes as you approach the speed of light is your length. In fact everything you try to measure in the direction you are travelling, including distances, shrinks. Everything travelling with you shrinks by the same amount, so you could never measure this shrinkage because anything you tried to measure yourself with would also have shrunk. But someone else travelling slower than you, in relative terms of course, would see you as squashed. Since squashing sounds a little unscientific, scientists call this squashing the Fitzgerald Contraction, named after an Irishman George Francis Fitzgerald who invented it in 1889 more than fifteen years before I worked out special relativity in 1905.

“So Fitzgerald discovered relativity before you?”

No he was trying to explain how ether could exist even if we couldn’t detect it in experiments. He was changing the rules of physics to make old theories work, I was changing them to make my new theory work.

“So what’s to say you are right and he is wrong?”

I kept the strangest fact about relativity until now. When scientists have tested some of these crazy relativity ideas, like time slowing down, they have turned out to be true. Perhaps we’ll talk about that next time, just to prove to you that even though I may be dead I’m not dead crazy.

Enjoyed it? Then Digg it.

[Note. The limericks used here are attributed to that famous author Anonymous, if anyone knows their origin I will give their creator(s) the belated fame they deserve.]

Relatively simple. An easy guide to relativity

2007-07-03T15:44:00.001-07:00

“Albert, do you think you can really explain the Theory of Relativity to me?”

Of course but don’t worry if it seems confusing. It is. It’s not until you start thinking about things and getting confused that you can really start stretching your brain. Thinking is like exercise, if it hurts it must be good for you.

“As long as my brain doesn’t implode, I don’t mind a bit of an ache for a good cause.”

Good. Now, the first thing you need to know is that there are two theories of relativity.

“Two? That means it must be twice as hard to understand as I thought.”

Not at all. The two types of relativity are special relativity and general relativity. The special version was the first one I came up and is a little a simpler than general relativity.

“What’s the difference?”

Special relativity deals with things moving at a constant speed, like light or trains or cars. General relativity was much harder to sort out and took me another ten years to get right. This general theory explains how gravity works.

“How about starting by explaining what the word relativity means.”

It’s called the theory of relativity because it is based around the idea that there is no such thing as moving or staying still. All movement is relative to something else so you can never really know if you are moving or not. There is no such thing as absolute movement.

"But we're moving."

Or are the stars just coming towards us? In a station when the train next to yours starts to move, you might be convinced for a while that you are moving when you are not. That is relative movement or relativity.

“But I know a train really moves because it ends up somewhere else.”

True, but what else is happening during your train journey?

“I don’t understand what you are getting at.”

It is not just the train that is moving. The track and station are moving too.

“No they’re not.”

Of course they are. The earth is rotating and does one complete spin everyday.

“But that isn’t real movement because you can’t feel it.”

You can’t feel the movement but can see the effect, that is why the sun rises and sets. The important thing about relativity is that you need measure your movement against some fixed point. What scientists call a frame of reference.

“What’s the frame of reference on a train?”

Usually the track. The problem is that the track is moving as the world spins. If you were on a train near the equator, say in the middle of Africa, the track itself would be moving at almost a thousand miles an hour around the centre of the earth.

“So the centre of the earth must be a fixed point.”

No the whole Earth is going around the sun, that is where the seasons come from but that’s another conversation. Around the sun your train track would be moving over 60,000 miles per hour.

"Wow…so the Sun is a fixed frame of reference?"

Sorry, the Earth's Sun and the whole solar system are rotating around the centre of the galaxy. Your train track is travelling at a speed of almost a million miles per hour around the centre of the galaxy.

"Is the centre...."

Sorry again, all galaxies are moving away from each other; remember the Big Bang and everything moving apart.

"Doesn't the universe have a centre?"

I'm afraid not. My theories also showed that space is curved. If you travel far enough in a straight line you end up back in the same place. So how can something that has no edge have a centre?

"Hmmm, so what can you rely on?"

Much less than you think. If movement is relative, there can be no such thing as a fixed place because you could never know if you were still or moving. The other important thing I realised in developing the theory of relativity is that there is no such thing as absolute time.

“You are saying time is relative? Relative to what?”

Movement and position can affect the time things seem to happen at. Imagine an explosion seen by two people, one is very close and the other a hundred miles away and both have synchronised watches. Who will see it first?

“The light will reach the closest person first so they will see it a fraction before the person who is further away.”

So they won’t agree on the time of the explosion.

“No but if there were in the same place they would.”

So if two people at the same place they will always agree on timing.

“Yes. I think so”

OK, now imagine two explosives joined by long wires to one detonator placed exactly in the middle. What happens if you push the detonator.

“Both explosives will explode at the same time.”

Good. So what if at the exact moment of the explosion there is another person driving in a fast car past the detonator towards one of the explosives.

“He’ll see the two things explode at the same time if he can manage to look in two directions at the same time.”

As this is a thought experiment will give him the power to see in opposite directions at the same time, but he won’t see the explosions happening at the same time.

“Why not?”

He’ll see the explosion he is heading towards first because in the time it takes the light from both explosions to reach the detonator he will have moved a bit himself towards that explosion. Just like you agreed before as he’s nearer to one explosion he’ll see that explosion first and then other explosion later. So the moving person sees the explosions at slightly different times but they will look simultaneous to someone standing by the detonator. If you can’t get people to agree that things happen simultaneously how can you rely on time?

“Hold on Albert, that’s a trick. If the moving man reaches the detonator at the same time as the light from the two explosions they’ll look simultaneous. Ahah, got you!”

I’m afraid not. The light takes a little bit of time to get to the detonator so if the car is at the detonator just as the light reaches it, then at the time of the explosion the car would have to be a little bit away from the detonator. You already agreed that things will only appear to happen at the same time if people are in the same place. So the time things seem to happen at is different for two people if one is moving relative to the other. There is no such thing as absolute time.

“My brain is definitely about to implode.”

Hold on, you might need your brain for a bit longer. We’ve still a long way to go and lots of things to talk about. The good news is that there is one fixed thing in the universe.

“What’s that?”

The speed of light. That is the heart of my theory of relativity. After convincing myself that time and movement have no fixed meaning, I decided to see what would happen if God had decided the speed of light was the one fixed thing in the universe.

“So what does happen?”

Some very strange but real things. But I think it might be safer to let your brain cool down for a bit before I start telling you about that.

Enjoyed it? Then Digg it.

Faster than a speeding bullet or how to measure the speed of a beam of light.

2007-06-30T14:32:00.000-07:00

Do you remember how fast we are travelling? I did tell you back at the start of this journey.

“Well that was a while ago Albert, but as we’re travelling on a beam of light we must be going at the speed of light.”

If I told you we’d covered 18,382,965,104,070,000 miles in just over three thousand years could you work it out from that?

“I guess that means we must be going very fast.”

186,000 miles every second. Light moves so fast that it seems to arrive without any delay at all. Light could get from London to New York in just two hundredths of a second. That's faster than a human blink.

“So what’s our speed in miles per hour, I can’t really imagine a speed in miles per second.”

Oh, let’s see. Almost 671 million miles per hour.

“Wow, how could you measure something going that fast?”

It’s difficult but not impossible. How would you do it?

“I don’t suppose we have a speedometer with us do we? Would a stop watch work?”

Not a bad idea. You can measure the speed of anything if you can record how far it goes in a second. That idea works fine for checking the speed of people running or even cars but as light goes 186,000 miles in a second it gets a bit difficult. Can you think why?

“Because I couldn’t see that far? I’d have to be able to see the start and the finish line to see when the light beam started and finished.”

Of course you can see that far. The moon is further away than that. The furthest object in the sky you can see, the Andromeda galaxy, is 2.5 million light years away. The real problem is that the light coming from the starting line would take exactly the amount of time to reach you as the beam of light you were trying to measure. So by the time you saw it leaving it would have arrived at your position and appear to arrive with no delay at all.

“That’s weird.”

But true. Imagine a bullet being shot at you and travelling faster than sound. You would be hit by the bullet and dead even before you the sound of the gun being fired reached you.

“Kind of unfair, but I can picture that.”

So if the bullet was travelling at exactly the same speed of sound you would hear the bullet at the same moment it hit you. It would seem to have arrived without delay. It would be the same if the gun was two feet away. The sound and the bullet would always arrive at the same time.

“I could look for the flash from the gun. That would arrive faster and use that to measure the speed of the bullet.”

True but for measuring light you would need something much faster than light.

“How about radio signals?”

No, radio waves travel at the speed of light because they are part of the same electromagnetic spectrum as light. That is the one of the starting points of my theory of relativity, nothing travels faster than light.

“So just by knowing that nothing travels faster than light, I can understand a little bit of your theory of relativity?”

Not just a little bit, a very important part of relativity. Thinking about the speed of light and when things seem to happen is the heart of special relativity. I told you earlier that one of my scientific heroes, Galileo, was the first person to start thinking about relativity almost four hundred years ago. Galileo was also the first person to challenge the ancient Greek ideas about how light travelled by measuring the speed of light. It was clear to the ancient Greeks that light and sound don't travel at the same speed. The delay between lightning and thunder when a storm isn't overhead showed that light travels much faster than sound but they thought it just arrived without any delay.

“How did Galileo do it. I thought you just explained that you couldn’t measure the speed of light?”

Not at all. I was trying to show that it is difficult but not impossible. Galileo managed to solve the problem we were talking about by being at the starting line and finishing line at the same time.

“How can you be in two places at the same time?”

It happens all the time in a lap race. The start and finish are usually at the same place aren’t they?

“Yes, but light travels in straight lines”

Usually yes, but you can reflect it back or get someone to send another light beam back, like a relay race. That’s what Galileo tried. He sent an assistant to a hill a mile or so away and positioned himself on another hill so there was nothing blocking their view of each other. Galileo had sorted out lamps for himself and his helper and the plan was for Galileo to switch his lamp on and start a clock. As soon as the assistant saw the first lamp light go on, he would turn his lamp on. By measuring how long it took before the light from the second lamp to get back, Galileo hoped to work out how fast light was travelling. Unfortunately even a remarkable man like Galileo couldn't spot the 5 millionths of a second delay while the light travelled from one hill to another a mile away.

"So he just needed a better clock."

Well a better clock would have helped but that kind of accuracy was centuries away, but a much bigger distance for the light to travel would help. With a little thought a Danish astronomer by the name of Ole Rømer had a go at measuring the speed of light in 1676 and came up with a speed of 133,000 miles per second.

"But he got the wrong answer?"

OK, so he got the wrong answer by 50,000 miles a second or so, but back then that was a pretty impressive achievement. But he did show that light took time to get places, it didn’t just arrive.

"Better than a million miles off I suppose. So how did he measure the speed of light?"

He used a clock but didn't need to measure millionths of a second because the light he was measuring wasn’t coming from a nearby hill but from the planet Jupiter which is 400 million miles away at its nearest point to Earth. Rømer carefully measured the time it took for Jupiter's moons to circuit the planet. He noticed that the times when the planet Jupiter's moons disappeared from view behind the planet, like an eclipse, seemed to be different at different times of the year. Since the Earth's moon is regular as clockwork this seemed odd. It only made sense if light from Jupiter's moons took some time to reach the Earth. At those times of year when the Earth was nearer to Jupiter, the light had a shorter distance to travel so the eclipses of Jupiter's moon seemed to happen earlier. Later on when Jupiter was getting further away, the light had further to go so it arrived later. It looked as though the moon had disappeared behind Jupiter later than it should have done.

“So how did scientists come up with the answer of 186,000 miles per second?”

A Frenchman called Leon Foucault used an updated version of Galileo's idea in 1862 but rather than use an Italian servant to open the shutter on a lamp, he used a rotating mirror.

"How does that help?"

If the light beam is reflected off a spinning mirror before being sent off to another mirror some distance away, then by the time the light gets reflected back to the spinning mirror it will have rotated a fraction.

“So?”

So the reflected light beam doesn’t get back to where it started but ends up a small distance away because by the time it gets back the rotated mirror….

“…rotated.”

Exactly so the light beam is reflected off at an angle. It's easy to measure the distance the light beam has moved with a ruler and how fast the mirror is spinning than it is to measure a few millionths of a second. So much easier that Foucault only needed to bounce light from a mirror sixty feet away. He got an answer pretty close to the actual figure but was finally beaten by an American in 1879. Albert Michelson improved on the Frenchman's machine by borrowing $2,000 from his father-in-law to built a bigger better version. This was no mean feat as $2,000 was a huge sum in those days and would be the same as almost a million dollars today. Michelson’s final answer was a speed of light of 186,355 miles per second which is impressively close to the figure accepted today of 186,282 miles per second or 299,792,458 metres per second.

“Impressive but does measuring the speed of light that accurately really help anyone?”

It was an important step for physics. A few years later in 1887 Albert Michelson also helped finally to bury the idea that light needed a strange substance called ether to carry it through space.

"Who's Ether?"

Ether, or aether, is a non-existent substance invented because no one could imagine waves without water.

"I don't follow."

Remember I explained that light can act like a wave.

"Like a sound wave or a wave on the ocean?"

Precisely, but what is left of an ocean wave if all the water is taken away?

"The fish?"

Very funny, the real answer is absolutely nothing. When you take away air and make a vacuum, sound waves disappear like ocean waves without water. A Mexican wave in a football stadium is carried by the spectators, with an empty stadium there is no conceivable way of having a Mexican wave. So if space is empty then how can light waves cross it? Some people were so attached to light being a wave that they said – ‘Simple, space isn't empty, it is full of ether and that's the stuff that carries light waves’.

Proving ether didn't exist rested on the simple idea that swimming in a river with the current is faster than swimming against the current. As the Earth rotates around the sun each year then it must be sweeping through the ether if it exists, effectively producing a flow of ether in the same way as wind whistles past a moving car even on a windless day. Light travelling in the same direction as the movement of the Earth will be travelling into this ‘headwind’ and so get slowed down. Light travelling sideways compared to the Earth won't face any extra resistance. In 1887 Michelson and Morley measured light travelling in these two directions and showed there is no difference in the speed of light. Discounting the remote possibility that all the ether in the universe was rotating around the sun in exact unison with their laboratory on Earth, this showed that light can't be travelling in anything like ether.

“So what difference did that make?”

With ether gone, the time was right for a complete rethink about how the universe works. That rethink was my theory of relativity. Now give your brain a rest for a while. Next time I’m going to throw some really strange ideas at you.

Quantum mechanics for cat lovers – Newton strikes back.

2007-06-28T04:33:00.000-07:00

Let me you ask you a question. If you close your eyes does the world still exist?

“Of course it does. What a daft question.”

How do you know?

“Well, I can feel the chair I am sitting on. I can hear noise from the street outside.”

Yes but what if a tree falls in the middle of a forest and no-one sees or hears it falling?

“It still happens because the world exists, we are just part of it.”

You believe that the world is a physical reality?

“Of course, why are you asking these crazy questions?”

To show why I had such a hard time believing in Quantum mechanics. At the start of all this back in the 1920’s all of us theoretical physicists were excited by what we discovered about light and atoms. Then some people like my friend Niels Bohr took quantum mechanics to an extreme and claimed that nothing exists until it is measured. A tree wouldn’t really have fallen until someone went to see.

“So the big bang didn’t happen until someone came along and could measure it?”

Crazy idea, huh?

“Raving. If the universe couldn’t have been born until someone checked it had happened where did that person come from?”

Brilliant, now you’re thinking. Do you know what we call that? A paradox, where something contradicts itself or common sense. Quantum mechanics is full of them and I spent a lot of time tormenting Niels Bohr with paradoxes but he still believed in quantum mechanics. The crazier it got the more he believed in it. Niels Bohr once said if quantum mechanics hasn't profoundly shocked you, you haven't understood it yet.

“Well I’m shocked and I’m still not sure I understand it. How did they even start to believe this?”

In quantum mechanics any situation is a blend of every possible option of what might happen and this blend is called a wave function. This seems to work for light. Sometimes light can act as a particle and sometimes as a wave. Niels Bohr and his friends showed that atoms seem to follow the same rules. As the world is made of atoms, the world must follow the rules of quantum mechanics. Obviously in the real world doesn't spend its life sitting on the fence, things just happen. But in quantum mechanics things happen only when this wave function collapses and only one possibility is left.

"What on earth does that mean?"

Sorry that’s the sort of jargon quantum mechanics use all the time. It means that at some point a situation has to stop having every possible outcome. When an event is observed then all the other possibilities suddenly disappear.

"Hmmm. Still not sure I get this at all."

It's like saying that the universe is based on chance. One enormous casino. What happens next is based on chance not on an absolute certainty. Imagine the universe as a horse race with lots of evenly matched horses. Until the race is over you can't tell which horse is going to win. With quantum mechanics the idea is that the race isn't over until someone decides to check on the result. This is where the science fiction idea of ‘parallel universes’ comes from. If every possible outcome is waiting to happen perhaps it really does happen in another quantum universe. Every horse wins in some reality.

“Gamblers must love quantum mechanics, but it seems too weird to be true.”

That’s what I started to think. But it wasn’t just me. A friend of mine Erwin Schrödinger was the man who first discovered the equations that quantum mechanics relies on. Even he couldn’t believe the idea that nothing happens until someone looks to check it. He invented the most famous cat in science - Schrödinger's cat. If nothing happens until it is observed then imagine the following. A cat is put in a box with a small gadget that will release poison.

"A real cat?"

No this is just an imaginary cat, so whatever happens the cat doesn't really get harmed. Like this journey, it's what is called a ‘thought experiment’ as you have to imagine it happening.

“OK, I’m sure I want to even imagine poisoning a cat but let’s hear where this is going.”

This poison will be released by something that is controlled by the laws of quantum mechanics, for example radioactive decay. Radioactive atoms are ones that are unstable and spontaneously break down into smaller atoms. So there is a lump of radioactive material and a device to detect if an atom has broken down. This atomic break-up has a 50:50 chance of happening in one hour. According to quantum mechanics, until the box is opened an hour later both outcomes should co-exist. The cat should be both dead and alive at the same time until someone observes the result.

"Can't the cat tell if it's dead or not?"

Only if it's alive.

"Hmmm. That’s as daft as the ancient Greeks thinking that seeing involved feeling rays coming out of the eyes."

Well despite what some people think, this story was meant to show how Niels Bohr’s interpretation of quantum mechanics was wrong. It was just an interpretation. I think there is an easier way of thinking about this. Quantum mechanics does seem to explain a lot of things about atoms and light. This craziness of a cat that is both dead and alive only applies if you stick to the idea that everything happens until it is measured by a person. There is no paradox if you just change to the idea that a quantum event happens when the result interacts with anything. When the radioactive atom in the box decays, the cat will only die when the radioactivity detector in the box detects it. When a particle that follows quantum mechanics interacts with anything it has to commit to being one thing or another. So a quantum mechanic event can set up a sequence of events that end up with a cat that is dead or alive without needing it be both at the same time.

“I thought you didn’t believe in quantum mechanics?”

Well I didn’t believe the extreme version, but perhaps in my re-creation inside this computer I’ve mellowed a bit. All this cat really tells us about quantum mechanics is that trying to use quantum mechanics to explain normal day-to-day life doesn't work. Understanding atoms doesn't help you understand a whole cat, but then again understanding cats doesn't help you understand atoms, so it works both ways. At the end of the day quantum mechanics does make sense in its own realm and offers explanations for strange effects that have no other explanation. My problem with quantum mechanics was summed in the my idea that 'God doesn't play dice'. Everyone seems to remember that but do you know not what Niels Bohr said in reply?

“No.”

It is not the job of scientists to prescribe to God how he should run the world. Not a bad reply I think. My real problem with quantum mechanics was that I couldn’t see why the universe would have one set of rules for big objects and another set of rules for the particles inside atoms. I spent most of the second half of my life trying to join this all together into one beautiful theory of everything.

“Did you get there?”

No. Once or twice I thought I was close but it slipped away, like sand through my fingers. Someone out there will solve it I’m sure one day.

“The world needs another Albert Einstein or Isaac Newton to solve that.”

Well the world needs a lot of things more than another Einstein or Newton. Peace, kindness and fewer weapons would be a good start. Mind you, I don't suppose Isaac Newton would have been too happy with the Schrödinger's cat experiment either. One of Newton's less well known claims to fame is as the inventor of the cat flap. In the simple understandable universe that Newton described, the cat would have got bored and left out of the flap at the back, leaving the quantum mechanics scratching their heads and wondering where the cat had gone.

(No cats were harmed in the writing of this blog post. In fact one was fed, let out of the kitchen door, let back in and back out again. I don't have a cat flap.)

CHAT WITH ALBERT 2.0's CAT MIMI

Why you should never trust a Quantum mechanic

2007-06-23T12:11:00.001-07:00

“Albert, that stuff you were saying last time. I’m still not sure how a light can be a wave and a particle at the same time.”

Well light can be different things at different times. William Bragg who won a Nobel prize for physics said ‘On Mondays, Wednesdays and Fridays light behaves like waves, on Tuesdays, Thursdays and Saturdays like particles, and like nothing at all on Sundays.’

“He got a Nobel prize for saying that?”

No. He got the prize for work that would end up revealing the secret of DNA but, smart as he was, he found light baffling too. A whole new science called Quantum Mechanics was invented a hundred years ago to explain how light can be two things at once. Before that nearly all scientists thought like was a wave because of the experiments I told you about last time. Then came along some pesky young man working in a government Patent office in Switzerland with proof that light came in little bits he called Quanta.

“Who was that?”

Oh some man who couldn’t get a job in university called…what was his name?...oh yes Albert Einstein.

“You?”

Yes me, well the real me that is, back when I was a person not just an idea in a computer.

“You didn’t have a job at a university?”

No-one would have me. I wasn’t the best of students back then and some of my professors did all they could to stop me getting a job in a university so I ended up working in the patent office in Bern. It wasn’t so bad as I had plenty of time to read and think because the work wasn’t too hard. A hundred years ago I was reading about a new discovery called the photoelectric effect.

“What’s that?”

When light shines onto a metal surface it's not just light that is reflected but also a stream of electrons, the small charged particles that make up atoms.

“Why is that so interesting?”

The odd thing is that the speed of these electrons depends on the colour of light but not on how bright the light is. There are more electrons given off in bright light but they all come off at the same speed. The first of my big ideas was that this would happen if light arrived in small packets of a fixed energy. The speed of the electrons depends on how much energy was in each packet, so the electrons all fly off at the same speed. The brighter the light the more packets there would be to knock electrons from the surface of the metal. I worked out that different coloured light contained packets of different amounts of energy, with blue being the highest energy packets and red the lowest. So in blue light the electrons would be knocked with more energy and so move faster.

“And this proved that light wasn’t a wave?”

It showed that light had to come in little packets. Just before that a great German scientist called Max Planck had seen a similar effect by looking at the light emitted by glowing metal. Light energy was only emitted in multiples of a certain value. These small packets of energy were called quanta. He thought it was something about the metal that made it happen, I said it must be that light comes in packets.

“Photons.”

Well, we discovered them before we called them that. The name ‘photon’ was invented 20 years later in 1926 by a scientist called Gilbert Lewis. Best of all was that this could be described by an equation so simple it is beautiful; E=hf, where E is the energy in each quantum of light, h is Planck's constant (a very small number) and f is the frequency of light or how fast it is vibrating.

“How can an equation be beautiful?”

It’s not the equation as much as the natural law behind it. If there is a God his handiwork should be visible in the natural laws that shape the universe. This is so beautifully simple it could only make God smile. It certainly made me smile.

“I’m glad to hear it made you happy but you promised me there'd only be one equation on this trip, your E=MC²?”

Did I? Well that was a very long time ago, but if you prefer it described in words this equation just means that as the frequency of light increases from red to blue, photons carry more energy.

"OK. I can understand that explanation, but how can these particles behave like waves?"

This is where things start to get a strange. A whole science called quantum mechanics has been invented to explain what simply doesn’t make sense. Even though I was in part responsible for starting quantum mechanics I could never really believe it could be true.

“You didn’t believe you own theories?”

No, I believed my theories but some of my friends and colleagues starting making discoveries that would make your brain implode. For a start it turns out that to be able to a particle and a wave means that a photon can be two places at the same time. Remember Young's experiment with the two slits?

"The one where light is shone through two narrow slits?"

That's the one and remember it is constructive and destructive interference that produces the fringes of light, where the peaks of two waves meet to make a bigger wave or the peak and trough of two waves meet and destroy each other. In 1909, almost a hundred years after Young's first experiments, that experiment was repeated by Geoffrey Taylor with very faint light and using photographic film to record the shadows and fringes. The light source was so dim that only a single photon was released at a time and so these individual photons could only go through one slit or the other but not both at the same time. It took 3 months to get enough photons through to produce a picture on the film. So what happens with two slits when a single photon can only pass through one or the other?

"There can't be any interference pattern because there is only one photon at a time going through the slits so they can't interfere with other photons because there aren't any others there at the same time. It can only go through one slit or the other."

That is the common sense answer. But it turns out that an interference pattern is still produced. So single photons can interfere with themselves or be in two places at once.

“I can’t believe that.”

Strange isn’t it. But it doesn’t stop there. This quantum mechanics seems to apply to all the particles that make up atoms. Quantum mechanics was developed to explain what happens inside atoms. Atoms behave more according to the laws of probability or chance and have more in common with a casino than a physics book. In the quantum world, the question of whether light is a particle or a wave doesn't really matter since everything can act as a particle or a wave. At an atomic scale objects stop being solid and dependable objects. Instead they become very slippery creatures. The more you try to work out where a particle is inside an atom, the less well you can tell how fast it is moving. The better you know how fast it is moving then the less sure you can be of its location. You can never tell where anything is, all you can know is the probability of it being somewhere. This is called Heisenberg's Uncertainty Principle.

“There’s a scientific theory called the Uncertainty Principle?”

Probably but then again perhaps there’s not.

“Is there anything certain about quantum mechanics?”

Certainly, never buy a used car from a quantum mechanic because you can't believe a word they say.

What am I? The confused life of a light particle

2007-06-22T11:12:00.000-07:00

Remember I told you about Isaac Newton when we were talking about gravity?

“The apple man and his laws of motion. I remember him.”

Well he is just as famous for working out where the colours from a rainbow come from. He discovered that white light was made up of lots of different colours.

“How did he do that?”

Well the strange thing was that everyone in the local town market knew it already. They sold triangular bits of glass, as novelties. This is what Newton wrote in one of his books – ‘I procured me a triangular glass prism to try therewith the celebrated phenomena of colours’.

“Strange way of talking. What does that mean?”

This was how they spoke three hundred years ago. It means he bought a prism to look at the colours it makes. He worked out that raindrops must act in the same way to turn sunlight into a range of colours.

"So if everyone knew about these colours why is Newton famous rather than the person who first made these prisms?”

He did something much more important than discovering about prisms and colours, he examined it and worked out why a prism makes colours. By experimenting with these prisms Newton worked out a set of rules for how light could be split up into different colours and recombined again. He started by showing how light could be split up by a prism into different colours.

“But we knew that already”

Yes but people thought it was something magical about the glass not a feature of light. He also showed that these individual colours couldn't be split any more by passing the light through another prism. So the prism must separate light into its individual components like unravelling a rope made from lots of different coloured threads. What no-one suspected was you make white light from mixing all the colours back together again.

“Was that an important discovery? It doesn’t seem as big an issue as gravity.”

Not on a galactic scale but closer to home colour televisions use Newton’s discovery.

“Really?”

Oh yes. Go up close to an old fashioned television and you’ll see that all the colours including white are made up from coloured dots. You can’t see the individual dots on some modern televisions but every colour is still made up of a mix of three single colours. But what was much more important than television was that all this inspired Newton to produce an idea or theory about what light is.

"And the answer was?"

Newton concluded that light was made up of little particles, corpuscles as he called us, of different types. Each different type represents a different colour across the rainbow, or spectrum as scientists call it, from red to violet. White light is an equal mixture of all the different types. Every hue imaginable can be made by mixing the different types in varying proportions.

“But you said from the start that we were light particles or photons.”

I did because on this point I agreed with Newton. But for the next two hundred years, this was one thing that people thought Newton got wrong. Christiaan Huygens a Dutch man and French man Augustin Fresnel, argued that light was entirely wave-like spreading like ripples across water and most scientists started to believe that light was a wave.

“But you said near the start that we couldn’t be waves because if we were we couldn’t get through empty space.”

Very true but all that took a lot of working out and it just shows that scientists spend as much time getting things wrong as they do getting them right. The wave idea seems odd to most people because light casts shadows and so appears to always travel in straight lines. Waves on the sea spread a little around objects like boats, rocks and harbour walls. Sound waves carry sounds around corners.

“I can hear around corners but I can’t see around corners. So light and sound must be different.”

Yes, but in fact light does go around corners.

“No, it doesn’t.”

It does but only by a tiny amount and you have look carefully to see it. Just after Newton died another clever Englishman Thomas Young started investigating shadows. Although the edge of a shadow looks like a sharp line between dark and light, if you look closely you can detect faint bright lines running alongside the main light-dark line in the areas that should be dark.

"You're really telling me that light spreads a very tiny amount around corners?"

As strange as that sounds it's true. Young wasn't the first person to see strange things in shadows but he was the first to be able to explain it. In 1803 Thomas Young looked at the shadows made by shining light through two narrow slits that were very close together. In the middle of the shadow cast by the solid bar between the two slits was a faint line of light. Some of the light must have been bent around the solid edge in the same way that waves in the sea can bend around the edges of boats or harbour walls. There were also fainter lines of light, fringes, each side of this central line. All this only makes sense if light are like waves.

“It doesn’t quite make sense to me I’m afraid Albert.”

It’s a bit complicated but here is how it works. Young worked out that these fringes depend on the light from one slit ‘interfering’ with light from the other.

"What does ‘interfering’ mean?"

Interference is science-speak for where two waves collide. It doesn't matter what type of wave you are thinking about; sound waves, light waves and even waves on the ocean can all produce interference. Thomas Young worked out that the lines of light appeared where the peak of the two light waves from the two slits combined and added together. Imagine the peak of a wave hitting the two slits at the same time. At the two slits only a small amount of the wave gets through, just enough to make two smaller waves which are in exact synchrony because they are starting off at the same time. If these little waves travel the same distance then they will remain in sync with each other. So at the centre of the bar's shadow they will have travelled exactly the same distance and all the peaks of the little waves will all line up. The peak of one wave will meet the peak of the other making a wave that is twice as big. This is called constructive interference and that’s how you can get a light of light in the middle of a shadow. At all the places where this interference happens you get a fringe of light. Here is a website that shows what happens (CLICK HERE).

“So light is a wave after all.”

Well it certainly can certainly act like a wave. Young also found that different coloured lights had fringes that were different distances apart, fringes from red light being further apart than fringes from blue light. From this he worked out the light of different colours had a different wavelength.

"What's a wavelength?"

It's how long a single wave is, from the peak of one wave to the peak of the wave following immediately behind it. In the sea there might be 10 metres between waves so a sea-wave has a wavelength of 10 metres. A sound wave will have a wavelength of a bit less than a metre depending on the pitch. Young worked out from the spacing of the fringes that light had a wavelength too but it was very very small. He calculated that red light must have a wavelength of 700 billionths of a metre and blue light 400 billionths of a metre.

"How big is my wavelength?"

Tiny, about 500 billionths of a metre. You also have a frequency; if you could stay at one point and let another light wave pass you by, then the number of peaks that pass you in a second is the frequency of the wave. It also means how many times a second you are vibrating. Frequency and wavelength are related. The smaller the wavelength, the more bunched together the waves and the more waves that will go past in a second and so the higher the frequency.

"So if our wavelength is so small then our frequency must be very large."

It certainly is, our frequency is 600 trillion. In other words in our beam of light we are vibrating 600 trillion times each second. Sound waves from a note somewhere in the middle of a piano keyboard will only vibrate a few hundred times a second. Light of different frequencies and wavelengths have different colours but the whole range of colours is squeezed into a surprisingly small range of wavelengths. If you think of a piano keyboard, which only covers a fraction of the range of possible pitches of musical notes, then you could fit the whole range of visible light into just one octave or a scale of eight notes.

“But I can see millions of different colours, not just eight.”

The high frequency or long wavelength light on this keyboard would look red and be like the low pitched notes in sound terms. The short wavelength light would be blue and be like the high pitched sounds with the whole of the rainbow in between. There appears to be so many colours because the eyes is much better at detecting fine variations in light than ears are at detecting differences in the pitch of a sound, unless you are a bat of course.

"So if I made my wavelength shorter and shorter, would I get bluer and bluer then disappear completely?"

No you'd still be a photon; it's just that humans couldn't see you.

"What would I be?"

An ultraviolet photon. If you were a really short wavelength you might be an X-ray like the ones that black holes make.

"And if I got stretched into a longer and longer wavelength, what would I be then?"

An infrared photon, that's the sort of photon that carries the heat and warmth across space. And if you kept on being stretched you would change into a microwave photon, then a radio wave.

"Could I be stretched or squeezed into a sound wave?"

Never. Sound waves are just vibrations in air. Light is a completely separate breed altogether. After all no matter how much you stretched or compressed a dog, it would never become a cat.

“And all this could be worked out from looking at shadows?”

Amazing isn't it. Most importantly none of this made sense if light was just like small billiard balls travelling in straight lines.

“So are we travelling on a beam of light particles or on a beam of light waves?”

For most of the rest of our journey scientists on earth will be arguing about that with each side convinced that they are correct and the others are wrong.

"Will they have made up their minds by the time we arrive?"

Well sort of, but it won't be a clear victory for either side of the particle-wave argument.

"Why not?"

By then both sides will have conclusive proof that they were right all along. So by saying that light must be a particle and a wave at the same time they reach some sort of agreement.

“That sounds a bit weird.”

Oh, there are weirder things than that ahead of us. I’m only just getting you prepared for the really strange stuff like quantum mechanics and my theory of relativity.

The end of the Dark Ages and Invention of the Frozen Chicken

2007-06-16T02:50:00.000-07:00

“I’ve told you a lot about science, now let me ask you a question.”

Okay, Albert fire away.

What is science?

“Science is the all the facts about how things work, space and all that kind of stuff.”

No it’s not.

“Yes it is.”

Science is not just about the facts it’s about the discovery of things. It’s a journey not a place.

“So how do you know when you’ve arrived?”

You never quite do, that’s the beauty of science. A lot of people think that all the important things have been discovered already.

“They haven’t?”

Not at all. A wise man knows how little he knows, only a fool thinks he knows everything. Science is like a travel across a vast ocean. You are happy for a while living on one island comfortable in how well you understand that island. Then someone comes along and decides to explore a little further and finds a bigger and better island just over the horizon. Facts and even reality are only what we currently think of as true.

“So you mean your theories are wrong too?”

Newton’s theories lasted over two hundred years and mine are only a little over a hundred years, so it’s too early to say. You can still fly a spaceship around the solar system using Newton’s theories or work out how the planets move pretty accurately. I really just extended his theories. If you start flying your space ship very fast or start circling a black hole then you’ll need to start thinking about my theories of gravity and general relativity but we’re getting ahead of ourselves Europe hasn’t even heard of me yet. They have barely started thinking about science properly at all.

“What date is it on Earth now then?”

We’re a little over 500 light years away so it’s the early 1500’s still on Earth. For a thousand years nothing much has happened in science in Europe. This is the end of the dark ages. Monks have been making beautiful copies of manuscripts from the ancient civilizations, keeping alive the knowledge that is over a thousand years old while most people couldn’t care less. As I told you last time, Arabic scholars were making advances in astronomy and mathematics but nothing much new was happening in Europe. The dark ages ended when Europe started thinking for itself.

“You mean no-one had any thoughts in Europe for a thousand years?”

Oh they were thinking about all sorts of things I’m sure, and fighting of course this was the age of the crusades, but not much science. Most of the ancient knowledge had been lost or forgotten in Europe. The first thing they had to do was find it all. The monasteries had some of the books from the ancient Greeks, but a lot were brought back with the Crusaders. Others were stolen back from the Arabic libraries in Spain when it was won back from the Moors.

“Why were there Arabic libraries in Spain?”

The Moors had taken over Spain for centuries and set up an Islamic culture and had brought thousands of ancient books with them. The library in Cordoba was the best in world back then, full of the best writings and ancient Greece and Arabic science.

“I thought you said the ancient Greeks got it all wrong?”

They didn’t get everything right and were certainly wrong about seeing but they had invented the art of thinking. Do you know what the word philosophy means?

“Thinking?”

It means the love of wisdom and that is what the ancient Greeks had and the Europeans had forgotten. Back then science was called natural philosophy, the love of wisdom about the natural world. When all these ancient books were recovered and read it opened their eyes to wisdom and the pursuit of knowledge. The advances made by Arabic scholars also showed them that new things could still be discovered. If you don’t believe that you’ll never discover anything new. So a few brave souls started to challenge the ancient ideas, people you’ve probably heard of like Leonardo da Vinci.

“He was just a painter. He did the Mona Lisa and the Last Supper.”

Oh he was more than that he was a brilliant architect, scientist and inventor, thinking of things that wouldn’t or couldn't be built for hundreds of years like helicopters and parachutes. This was the start of an explosion of thinking called the Renaissance or literally rebirth. Another of my heroes is Galileo, he came a little after Leonardo, and was the worlds first great scientist. He made huge discoveries in astronomy and physics. He was even the first person to talk about relativity in very simple terms.

“He invented relativity?”

No, but he introduced the concept to science. He compared the situation of someone standing on deck of a moving boat or inside a cabin on the same boat with no windows. On deck the person could tell they were moving forward, but inside the cabin apart from a little side to side sway they’d feel they weren’t moving forward at all. If you dropped a ball it would seem to fall straight down even though really it was also moving forward at the same speed as the ship as it falls. That is the simplest form of relativity, what you experience is only relative to what is around you. It just took a few hundred years more to work out the details.

“What took you so long?”

I had to be born first and that took hundreds of years. While I was waiting to be born Europeans were still busy working out what science was. Science was really given a kick start in the year 1605, when an Englishman called Francis Bacon published a book called The Proficience and Advancement of Learning. This gave birth to what would now think of science. Rather than just studying the writings of the great Greek philosophers, Bacon urged people to think for themselves and come up with new theories for how the universe worked. Bacon is now thought of as the father of modern science.

“What did Francis Bacon discover?”

Well he invented the scientific process, or at least a version of it. He thought that a theory would naturally come from examining the world. In his writings he didn’t talk much about experiments and sparks of creativity but in his last week alive he managed to invent the frozen chicken and die as a result.

“Francis Bacon died trying to create the first frozen chicken?”

In a snowy March in 1626 Bacon was visiting London with the King’s doctor when he had the spark of an idea that cold could stop meat from going off. They didn’t have refrigerators back then of course. So he got out of his warm carriage in Highgate to buy a chicken and have it stuffed with snow. Sadly the chicken probably stayed fresh as long as he did. He caught pneumonia and died a few days later.