Okay maybe it's not just the Ender's Game series, and maybe its actually a cornerstone [STRIKE]fact[/STRIKE] [STRIKE]belief[/STRIKE] [STRIKE]theorem[/STRIKE] [STRIKE]postulation[/STRIKE] thing of relativity, but still! In the story Ender travels in ships which go at relativistic speeds. By doing so, centuries go past but he hardly ages at all. I don't get this. As he approaches c, time for him slows down, and outside everything speeds up. So he would travel... a long way, in (for him) a short time. As v = s/t, he would still travel the same distance but the time to do so would decrease through relativity, to such a degree that he would (or could) go faster than light. Trying to reword this: Though to an observer at (for example) his destination, it actually takes him centuries to travel light years, to him its not nearly as long. So an observer can travel faster than light, but no-one else can? If Ender (E) travels towards his destination (D) at relativistic speeds, D will observe E's time to slow down because E's travelling so fast, conversely E will observe D's time to speed up. However, relative to E, D is in fact the one travelling very fast, and so E will observe D's time to slow down and conversely D will see E's time speeding up. What?! Also, 1st post! I know its bad form to post more than one topic at a time (especially a first time poster), but some other stuff's been bugging me for a while as well, so if I'm allowed to ask more than one question (if not, I'll ask again later, I just don't want to spam): Could you measure time in metres? What the **** is gravity? (link to something might be easier than an explanation) Is the centre of the universe the beginning of the universe? If mass is energy, is energy mass? In other words would something with more energy always have more mass? Building on that, what about gravitational potential energy: would something on the earth have potential energy based on the displacement between it and the supermassive black hole at the centre of the galaxy and hence if it was knocked towards it, that Ep would turn to Ek, thereby meaning it has that potential energy stored in its... mass?