Question

Do scientists know what happened before the big bang?

Answer 1

Put simply, no.

Explanation:

All possible theories governed by our current laws of physics cannot even simulate the first few minutes after the Big Bang (extra information: the four fundamental forces were combined into one "super-unified force" and we do not know how it works).

The generally accepted explanation is that a singularity used to exist before it collided with something (itself or something else) and the Big Bang happened.