What happened before the Planck time?
As far as we know, nothing… the whole concept of “before the Big Bang” may not be meaningful, and asking what was before the Big Bang could be like asking “what’s more south than the south pole?” That being said, there are exotic ideas about what happened before, particularly in the context of “multiverses” in which other universes exist in dimensions inaccessible to us. Basically the answer is that nobody really knows, or knows if it even makes sense to ask.
