“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.
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.
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]
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.
UNSCRAMBLE EINSTEIN'S BRAIN
PRACTISE SAVING THE WORLD FROM ASTEROIDS
ALIEN CONTACT CALCULATOR
HEAR THE REAL EINSTEIN TALK ABOUT E=Mc2.