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]

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.”