A Blog for the Curious and the Scientifically Perplexed

This is the story of a great journey that started with a great thought. One day in 1895 a boy looked into a mirror and wondered what the universe would look like if he could travel on a beam of light. That sixteen year old boy was Albert Einstein and that one thought started him on the road to discover his Theory of Relativity. The great man has been reinvented as Albert 2.0 to come back and blog about a journey through space on a beam of light and explain the science behind everything from atoms, blackholes to global warming. If you've just joined and want to start at the beginning use the index on the left. If you're bored try these links below just for fun.


Saturday, July 28, 2007

Naming the planets, a story stranger than the Sopranos

“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.

Wednesday, July 25, 2007

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

“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?”


“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.”


“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.

Saturday, July 21, 2007

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

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.]

Wednesday, July 18, 2007

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

“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.”

Saturday, July 14, 2007

Space the final Frontier (and how many aliens know we are here)

“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.


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?

Tuesday, July 10, 2007

To Relativity and Beyond

“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.


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.


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.”


“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.

Saturday, July 7, 2007

Relatively Weird. How to get younger, thinner and fatter all at the same time.

“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.

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[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.]

Tuesday, July 3, 2007

Relatively simple. An easy guide to relativity

“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.

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