Not being a physisist I've often idly wondered how the universe, constrained to a single point, at the start of the big bang avoided being a black hole, now there's a theory that it started as a 4 dimensional black hole, making it even more mysterious to me.
The "Big Bang model tells us that the Universe exploded out of an infinitely dense point, or singularity. But nobody knows what would have triggered this outburst: the known laws of physics cannot tell us what happened at that moment."
"It is also difficult to explain how a violent Big Bang would have left behind a Universe that has an almost completely uniform temperature, because there does not seem to have been enough time since the birth of the cosmos for it to have reached temperature equilibrium."