# How can an infinite universe be dense at the big bang? [closed]

If the universe is infinite, it always had to be spatially infinite since at the big bang. And I'm assuming that cosmologists don't think that a Big Bang singularity actually occur in the real universe therefore the universe has to always be infinite from the beginning.

In the big bang theory says that the universe evolved from a denser early stage at the big bang. But there was already infinite space even at the big bang. So how can the infinite space be dense?

## closed as unclear what you're asking by JMLCarter, stafusa, sammy gerbil, CR Drost, Kyle KanosOct 26 '17 at 9:53

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• When in doubt about the Big Bang, refer to (mostly) John Rennie's excellent answer to the question Did the Universe happen at a a point /. At the end he specifically mentions the issue of the universe being infinite. There's also Luboš Motl's answer to How can something finite become infinite. – StephenG Oct 25 '17 at 21:34
• I cannot be technical enough to post an answer. Consider that a spatially infinite universe does not imply density ----> 0. Current understanding is that universe was denser before because space did expand and it keeps expanding. In simple words the infinite size of NOW is bigger than the infinite in the past. Thinking of density (m/V) should help you. 1 g in a cubic meter is less than 10g in a cubic meter. Nothing is said about the total volume. Indeed it seems to me that without referring to density there will be no cosmological models at all. – Alchimista Oct 25 '17 at 21:40
• Possible duplicate of Did the Big Bang happen at a point? – JMLCarter Oct 25 '17 at 22:52
• I don't quite understand this question. Is it claiming that a spatially infinite universe must have (1) constant density, (2) increasing density, (3) zero density, but not (4) decreasing density? – Alfred Centauri Oct 26 '17 at 0:53
• Could you explain why you claim that "If the universe is infinite, it had to be spatially infinite right after the big bang"? – Dr. Ikjyot Singh Kohli Oct 26 '17 at 3:47