How would you explain the theory of relativity?

Answer 1

Special theory of relativity:

1.The laws of physics are same for all observers in uniform motion relative to one another.

2. The speed of light is same ...

Later Einstein proposed General relativity.

Answer 2

There isn't any. At least none is known. If it were physicists would certainly like to use that one, because solving the equations of the theory of general relativity is not easy at all!

Certainly there are several analogues that have been manufactured of the years, such as the trampoline analogy (where a heavy ball on the trampoline is to represent the bent spacetime). But it is important to remember that these analogues are just that.. they are analogues, they are not the real thing; they all have shortcomings. The trampoline example for example fails because it does not correctly display the bending of time.

I guess one, more simpler explanation, might be the following. Gravity is the result of a local Lorentz invariance of the Universe. I.e. gravity is the result of the demand that the laws of physics be the same everywhere and at every moment for anyone.

Note that this is a mathematician's definition of simple, usually also known as elegant or beautiful. This concept is for example certainly not easier to work with! In fact there are many problems with local Lorentz invariance that haven't been solved yet (mostly having to do with something known as renormalizability, or actually the non-renormalizability of the theory).