Here is Einstein’s theory of relativity explained in words that are four letters or less.

Old Al, he came out the blue and said, “Not only do rays move at c if what puts them out is held fast or not: they move at c even if you are held fast or not.” Now that may not look like such a big deal on the face of it, but hold on. What this says is that you can move as fast or as slow as you want, and rays will go by you at c all the time.

Read the rest of it here: http://www.muppetlabs.com/~breadbox/txt/al.html