I have a question I've been thinking about for quite a while,and I appreciate any answers I can get. Preamble: In any book on relativity you will find the following example. We have 2 twin brothers on earth. One of them goes on a trip in a spaceship that travels at 7/8 the speed af light, the other brother stays on earth. After 20 years the brother on earth is obviously.20 years older, but the one on the spaceship (because time slows down when you move close to the speed of light) has aged only one year. My question is this; Since everything is relative.(there is no fixed point in the universe from where we can measure everything else) who is to say that it is not the spaceship that is standing still and the earth moving away from it at 7/8 light speed. And so the age of the two brothers should be reversed? It's sort of like the Olbers paradox, but unlike Mr. Olbers who solved his own paradox, I can't. Regards apolo Qoute: So far as the laws of mathematics refer to reality, they are not certain. And so far as they are certain, they do not refer to reality. Albert Einstein.