The initial singularity of the big bag happened “everywhere” the whole universe was supposed to have infinite density.
If the density throughout all space was truly infinite, then the volume of space had to be ZERO. Otherwise the density would have been a very very large but finite number. And if it were infinite and non-zero volume, no amount of inflation would cause it to stop being infinite. Infinity divided by any positive number is infinity.
We know that there was a period of extreme density, but we don’t know what happened before that. When we extrapolate we EVENTUALLY come to a singularity. But that’s just a naive extrapolation, we don’t know there was a singularity. In fact, I think we can be certain there wasn’t, the way we can be certain that a coin flip never comes up head, tails and side all at the same time.
If the density throughout all space was truly infinite, then the volume of space had to be ZERO. Otherwise the density would have been a very very large but finite number. And if it were infinite and non-zero volume, no amount of inflation would cause it to stop being infinite. Infinity divided by any positive number is infinity.
We know that there was a period of extreme density, but we don’t know what happened before that. When we extrapolate we EVENTUALLY come to a singularity. But that’s just a naive extrapolation, we don’t know there was a singularity. In fact, I think we can be certain there wasn’t, the way we can be certain that a coin flip never comes up head, tails and side all at the same time.