the earth types see is that 2 hours but modified by this thing over here and it's called the lorentz fitzgerald contraction factor, all right? and then v is the speed, the relative speed. and c, of course, the speed of light. and we've done that, we find out that, wow, a 2-hour trip appears to be 2 1/2 hours. and that's what we saw in the film. now if you go at higher speeds, the time dilation-- dilation means stretched out. the stretch-out of time is even more. if you went 87% the speed of light, i'm not gonna take the time to do that now. but if i put the 0.87 in here, i would come out over here where the time is twice as much. twice as much time, see? so 2 hours will be 4 hour trip. and if i went 99.5% the speed of light, that fast, then it turns out the time would be 10 times as much. so a 2 hour-trip would look like 20 hours. let's take the extreme case. what if i went at the speed of light itself? okay. then this would be just c, not a fraction of c, but c. and c-squared, c-squared, what? is one. what's one take away one, gang? - zero. - zero. what's the square root of zero? - zero. - zer