system
Given the following post, respond as if you're commenting on Reddit:
human
Why do we think that space was created during the big bang and not just matter?

How do we know for instance that there isn't just an infinite field of ever expanding space, with occasionally disruptive quantum fluctuations that create a bunch of stuff?
gpt
We don't think that, nor do we know that.

In fact we know very little before the CMBR, previous to that we have models which predict what would happen and indirect evidence. As you approach the moment of the big bang things keep getting more and more fuzzy.

The only thing we can say is that we don't know. The reason that asking what happened before the big bang is a bad question because unless you know there was a before(Or that such a question was meaningful or could be answered) you are presupposing a before.

That said that's pretty much what a lot of physicists believe. As you rewind the clock all fundamental forces unify, and it's thought they'd all unify at the moment. Logic tells us something should be before it(Everything has a beginning right?) but often times "Obvious" and "Logical" have no weight on how the universe works. It doesn't have to make sense. It could be that there is absolutely no reason our universe exists, in fact it could be it's such an accident nothing actually does exist and this universe is just a one time event that will never happen again making it the first and last universe.

We don't know what caused it, or what is was, or generally what happened. All we can talk about is pretty much T = 1 and onward, trying to talk about T = 0 or T = -1 may not even make sense or exist.

That said most phyicists prescribe to a before, a fundamental force that splits due to quantum fluctuations most likely IS the right answer. The specifics are going to matter, and other models tell VERY different stories of before. Who knows? We probably never will.