# Theory of Relativity

Everyone has heard of Einstein’s theory of relativity. Everyone has also heard of his most famous equation E = mc^2 . But what about the other consequences of his theory? It turns out that there is a lot more to his theory than just that one famous equation. Three of these consequences, are mind bogglingly weird.

Length contraction

According to the theory of relativity, when an object travels fast, it gets shorter. In fact, the faster it travels, the shorter it gets. If a long object travels at almost the speed of light, it can become very short indeed. (Remember objects cannot travel at or above the speed of light. If they could, there length would be 0). As an example, let’s imagine someone has a bus which can travel very fast. Let’s say the bus was 30 metres long before it set off, and some crazy driver gets the bus going at 99% of the speed of light. The bus would therefore shrink to just 4.2 metres long! As crazy as it seems, this is all completely possible under Einstein’s theory of relativity. When the bus slows down however, its length will go back to its original length.

Mass increase

Similarly to the above, the faster an object travels, the heavier it gets. An object cannot travel at or above the speed of light, as if it could, its mass would be infinite. Let’s consider the same example as above. The bus still travels at 99% of the speed of light. The bus weighed 2000kg before it set off. At this speed, the bus weighs an amazing 100503kg! Again, this is completely possible under Einstein’s theory. The increase in mass is caused by the mass of the energy that is required for the object to travel at such a speed. Remember, the bus will fall back to its original mass when it slows down.

Time Dilation

The third and by far weirdest consequence of relativity is the dilation of time. If an object is travelling fast, it experiences less time than it would have it if were stationary! Let’s go back to my favourite example, the fast bus. Again, the bus travels at 99% of the speed of light. A person who is not on the bus times the bus as it passes two points on a long straight road. The bus takes 10 seconds to get between the points. Although the person on the ground experienced 10 seconds, the people on the bus only experienced 1.4 seconds! This means that at this speed, time is flowing at less than a fifth of it’s usually flow. Again, as the bus slows down, the time experienced by the people on the bus will return to its normal flow. This wacky consequence of relativity is the closest thing to time travel. It can cause all sorts weird situations. One common example is the twin paradox. Imagine two twins, exactly the same age. When they are 29, twin A goes into space on a rocket that can travel above 99.5% of the speed of light, and twin B stays on earth. If twin A returns after he has experienced almost one year, he will be just short of his 30th birthday, while twin B will be 40!

So the theory of relativity isn’t so boring after all! There is a lot more to it than the famous formula. These weird and wacky consequences make relativity the most interesting branch of physics. Time, mass, and length can all be changed by speed. The speeds required though, are too fast to be practically achieved. An object has to be travelling at least 108 million km per hour for these effects to become noticeable, and the example here of a bus used 1070 million km per hour. It seems then, that although these effects are entirely possible, replicating them in practice on anything more than a tiny particle still remains in the realms of science fiction.