I realise this question includes relativity, but I think it is more appropriate here than in that forum? [Tell me if I should cross-post it elsewhere; I'm new to this forum :)] I'm working on a paper based on reading material that doesn't address big bang cosmology directly, but rather focuses on relativity, with a lot of emphasis on special relativity and its influence on time and simultaneity. The question I'm working on is: "According to the currently accepted Big Bang Cosmology the universe is expanding uniformly. Hence there is no absolute rest but there is absolute simultaneity." Discuss. I don't want a direct answer of course, just a little help with my research... as far as I can make out special relativity alone doesn't allow for absolute rest or absolute simultaneity, but this is not in reference to the big bang. So does the Big Bang have a significant effect on relativity, or vice versa? I think I'm in danger of sidestepping the question, but I'm not sure how the two ideas are actually linked. As far as I can see, lack of absolute rest is confimed by BB theory, since the universe is expanding in every direction, and not away from any central point of reference, while I can address simultaneity by explaining a thought experiment along the lines of the train-and-platform scenario. However, am I missing something vital? Should I be looking at general relativity as well, or something else not in the reading? Thanks in advance.