Shoutbox

There are two theories of relativity: special and general. I doubt you want the general one explained because it is vastly complicated and reserved for PhD level research only. There are two parts to the special theory of relativity:
1. That, in a vacuum, the speed of light is constant no matter your frame of reference, the inertia of the observers or the velocity of the object emitting the light. (c)
2. Basically that the laws of physics do not depend on the state of inertial motion.

The theory is basically E = mc². That's the widely known usage, to be physically correct it is: (delta)E = c²(delta)m. The change in energy is equal to the speed of light squared multiplied by the change in mass.

That's the fundamental, underlying stuff about it. That was basically me reciting what I remembered from my uni textbook. Heh.

Of course the effects of this theory are more widely known, i.e. the faster you travel the slower time goes, so if you travel really fast you age slower.

A small expansion to tantalise everyone:
Theoretically, purely as a mathematical construct, one thing can travel faster than the speed of light.
Imagine you have a donkey equidistant from two bales of hay that are exactly the same, EXACTLY the same... which bale does the donkey choose?
That's the analogy, and it forms a perfect symmetry. When that symmetry is broken (where such a symmetry exists) a particle called a tachyon is created and emitted, which travels faster than light.