There was a prior state of the universe before the big bang known as “cosmic inflation”. This prior state lasted an unknown length of time.

https://bigthink.com/starts-with-a-bang/evidence-universe-before-big-bang/

We also know the now observable universe contained a significant amount of space at the time of the big bang. It was a minimum of 2 meters in diameter, and probably much bigger. Of course, the full universe would have been far bigger.

https://www.forbes.com/sites/startswithabang/2021/08/25/how-small-was-the-universe-at-the-start-of-the-big-bang/?sh=7e6c19735f79

https://www.forbes.com/sites/startswithabang/2018/07/27/there-was-no-big-bang-singularity/