Good news everyone!
Einstein as we know was a brilliant man (but as it turns out not a outstanding student), producing E=mc2, the general and special theory of relativity and much more. I will be discussing one of his concepts – space-time.
Imagine a big trampoline in front of you. You place two bowling balls – one big and one small – on the trampoline apart from each other, you notice that the bowling balls make an indentation on the elastic surface; the bigger of the two balls causing a bigger indentation than the smaller. Now suppose you roll a tennis ball along the trampolines elastic surface, you’ll see that the path of the tennis ball is deflected by the indentations made by the bowling balls. In basics the trampoline’s surface represents space-time, the bowling balls represents stars or planets and the tennis ball – light.
You are probably exclaiming, “This is preposterous! We were told that light only travels in straight lines!” well for daily life this is true as the bending of light due to a house or that annoying child on his scooter is so small that it is unnoticeable, however on the scale of stars and such, it is quite a noticeable deflection. This analogy has some flaws such as forces that are acting on the tennis ball which would not affect light (friction and so fourth) but mainly that the trampoline gives the impression of space-time being flat whereas it is actually all around us. We can’t say that matter directly affects the path of light just that it affects space-time, which in turn affects light. From this it is reasonable to assume that light would have to slow down from being curved around a sun, but light is travelling at a constant speed therefore we can conclude that gravity slows down time!
The bending of space-time due to a large mass
Sir Arthur Stanley Eddington first proved this light bending in 1919 when he observed a solar eclipse in Principe (near Africa) taking pictures that showed the deflection of light from star passing by the sun which in normal circumstances are obscured by the Sun’s brightness. He compared them to pictures of a star when not in the presence of the Sun and showed an obvious deflection that showed conclusive evidence that General Relativity trumped the Newtonian World.
There is a particular type of star that has such a great mass that it creates a ‘well’ in space-time, a Black Hole. As a lot of you will know a black hole is a star that has a sufficient mass that it collapses in on its self where no light can escape. This mass warps space-time so much that it can be thought of as to fall into space-time or create a ‘well’ in it (see picture). The rim of this ‘well’ is the event horizon where the bending of light is so great that it falls into the ‘well’. If we were to use the trampoline analogy then it would be like putting a bowling ball of incredibly high mass (assuming the elastic sheet was unbreakable and the trampoline was very high up). A black hole’s great mass means that we could use it for time travel. As I have already mentioned gravity can slow down time, therefore if we managed to maintain an orbit around a black hole without being sucked in we could theoretically age slower than somewhere else, lets say Earth. So when we returned to Earth we would be further in the future than if we had stayed on Earth.
A black hole creating a ‘well’ in space-time
This great mass and curving of space-time also opens up the possibilities of wormholes (a hole that links two points of space). It supposes that two black hole ‘wells’ could join together and make a tube in space-time linking these points in space. However the chance of this happening is miniscule and if it did happen there is the problem of maintain this link.
Wormholes can be used to cross great distances in space
I hope you have enjoyed my blog that has touched upon the brilliant concept of space-time!
Christian Tuckwell-Smith – Farnsworth
Sources:
Stephen Hawking – A Brief History of Time
http://en.wikipedia.org/wiki/Arthur_Eddington
Science - Joy - Life 
Very interesting! I always struggled with imagining and understanding concepts in astrophysics. Special relativity and the fact that light travels at the same speed even if it’s projected from a moving object still bothers me a little.