Motion *is* relative, hence the theory of Relativity. :P When an object accelerates (relative to others) towards the speed of light, it will experience time, length and Mass Dilation, relative to the objects that are "at rest". This means that the moving quickly Object B, will experience time that is dilated, or dragged out, compared to time experienced at Object A. If you draw two lines on a piece of paper, one twice as long as the other, starting from zero. Both these lines represent 1 second: The longer line, or the "Longer" second, has been Dilated, this is Object B. Now, if you move your finger along both lines at once, at a constant and equal rate, you will notice that for every 1 second experienced by people at Object B, two Object A seconds are experienced by the people "at rest" To summarise, Time Dilation means that as you speed up, time slows down (but you, the one speeding around, don't feel it that way. To you everyone else's time speeds up) It works the same For Mass Dilation, and Length Dilation: As you speed up, your mass and length increase. This is why it is supposedly impossible to accelerate to the speed of light: as you get towards lightspeed, your mass increases *increasingly*, and therefore it takes more and more energy to keep accelerating. At the speed of light, Mass = Infinity, which means that in order to accelerate something to the speed of light, you would have to use all the matter and energy in the universe to accelerate all the matter and energy in the universe. Its Confusing, and we think its impossible :P Anyways, hope that answers your Question!