Could the big bang be caused by a black hole getting so incredibly dense that it crosses the threshold between nothing to everything?
a black hole could consume everything in its galaxy and become so gravitationally powerful that it draws in and consumes surrounding galaxies to a "point" where it can not become any more dense. It literally consumes itself and crosses a threshold where nothing becomes everything. That is the so called big bang. It is happening on a routine basis throughout space (multiverse).