What happened before the Big Bang?
The current Big Bang theory literally requires that something existed before the hot big bang for the physics and math to work out, due to the observed smoothness in temperatures and densities. The Big Bang theory timeline starts at time t=0 but the hot big bang doesn’t occur until t=10-32 seconds. What occurred at time t=0? We have no reason to think any special event occured at t=0. It is simply the farthest time we can extrapolate backwards to. The time between t=0 and the hot big bang represents the final fraction of a second of the previous phase of the universe which had an unknown length that could possibly have lasted billions of years and is generally believed to be “cosmic inflation”.
https://bigthink.com/starts-with-a-bang/universe-infinite/We can only see the observable Universe created by inflation’s end and our hot Big Bang. We know that inflation must have occurred for at least some ~10-32 seconds or so, but it likely went on for longer. But how much longer? For seconds? Years? Billions of years? Or even an arbitrary, infinite amount of time? Has the Universe always been inflating? Did inflation have a beginning? Did it arise from a previous state that was around eternally? Or, perhaps, did all of space and time emerge from nothingness a finite amount of time ago? These are all possibilities, and yet the answer is untestable and elusive at present.
- All the particles and matter that we see today were created after the big bang event (hot big bang), which occurs at t=~10-32 seconds in the big bang timeline.
- The big bang was preceded and set up by an earlier era of cosmic inflation. We don't know when cosmic inflation started or how long it lasted. But new space was created at a much faster rate in the earlier inflation than in the later expansion, so the big bang event involved a drastic slowdown in the rate of new space creation, allowing the formation of our present particles and matter.
- We have reason to think something else came before cosmic inflation.