what is the big bang and how do i understand it?

I love reading this thread, the math is just enough that I can handle it and the 'narrative' just about my level as well. One thing has always bugged me though. Many people say either there was no 'before' the big bang and/or there is no 'outside' of the universe (it isn't expanding 'into' anything). I much prefer to see (but hardly ever do) that we don't KNOW what it's expanding into, or there is currently no way for humans to interact with anything 'outside' the universe, so we don't know. Or that our current math and physics have no way to explain what was going on before the big bang, b/c there was no information, or the 'bang' randomized it.
If, by chance, our universe is a result of a white hole, then there most definitely was a before and the universe is probably expanding into something. Or other scenarios of where the matter might have 'come' from would allow for a before or a tipping point to begin expansion or something. It just doesn't seem like good science to flat-out say there is nothing out there. Perhaps the maths point out that there couldn't be, I don't know.
Or if we can imagine that there may be another universe somewhere (or somewhen or some-dimension), what if one day it interacts with our universe? They either overlap, collide, or begin to tug at each other or something. I understand we don't know, but I don't think we should say it therefore doesn't exist.
I'm open if anyone has good explanations of why my 'what ifs' are nonsense.