"The whole universe was in a hot, dense state, when nearly 14 billion years ago expansion started .." The big bang (BB) is often recapitulated by noting the times when the universe was the size of a proton, or the size of a grapefruit, or the size of our solar system. This is most easily understood as the times when our currently observable universe was the size of a proton, grapefruit, etc. What is more difficult to understand (or calculate) is the extent of the entire of the universe at those same times. Most discussions of BB suggest that the primordial universe (the whole thing, not just our observable seed) was a finite expanding sphere. Our observable universe was a small piece of that sphere. So how big was it? The question came up as part of the "What is beyond the observable universe?" thread. In that discussion it was suggested that current models, either for simplicity sake, or to match the data most closely, presume that what is beyond the current observable universe is just more of the same. Carried to its logical extension, that would imply the universe is now infinite. It seems that if it is now infinite, then it must have been infinite to start with. I don't think there's any way to get to a currently infinite universe if we started with a finite universe. So far the best answer is: we don't know for sure, but we do know that it (the whole universe) is much larger than our observable universe. So I have a few questions for this thread: 1) I would like to know if it is possible that the primordial universe (the whole thing) was infinite in extent. Does GR allow such a beginning? Could it have started out infinite, and very dense, and then started expanding, creating more space everywhere at once and continuing to do so? 2) On the other extreme, if the primordial universe was finite, how small could it have been before we would notice it now? How we would tell (1) from (2)? 3) If the primordial universe was finite, and we (our observable universe) were just a small part of it, does it matter where we were within that sphere? It seems that if we were near one edge of the sphere, the CMB would be highly lopsided now. Since it isn't, does that mean we were within at least X% of the center?