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

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)

“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)

“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.

“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

“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.