Hi In trying to get to grips with SR/GR (I'm still unsure about what differentiates them!) one of the things that springs to mind is what it means for the nature of time. I've always thought (not too hard, just as a natural consequence of everyday experiance) that time is some fundamental property of the universe. But, recently I've come to think of it as this: Since c is an upper limit for speed (not the right term I think) and space is assumed to be a fundamental quality of the universe, time becomes a direct consequence of these two things rather than a thing in itself. Ie time 'passes' because it is not possible for a particle to change its position instantaneousely. Is this a wrong way to think about time or just stating the obvious?