Pre-Big Bang Speculation

Question:  What theories might propose a casual reason for the Big Bang?

Evidence is strong that the mass in the modern universe was born approximately 14 billion years ago in a hyper-massive explosion that we call the Big Bang.  But little is speculated about what caused the Big Bang in the the first place.

In order for the Big Bang to be a casual event (an event resulting from, caused from other prior events), then some form of universe must have existed prior to the Big Bang that lead to the Big Bang.  Relativity theory teaches us that mass and energy are interchangeable.  We can perhaps speculate that mass or energy or both existed in some form before the Big Bang explosion, and that that mass and or energy collected for eons prior to ending in a Big Bang explosion.

If we assume that the vacuum (or ether) of the pre-Big Bang universe was filled with massive amounts of energy, then perhaps we can imagine that this energy coalesced prior to the big bang.  We know that when enough mass and energy exists in a small enough space, it results in a black hole.  If the energy of the pre-big bang universe coalesced into a hyper massive black hole, perhaps a threshold was exceeded that resulted in the explosion we know as the Big Bang.  Alternately we might also imagine the possibility that the Big Bang was caused by a collision to two nearly equally sized hyper massive black holes.  Both are highly speculative concepts. 
Conclusion:  It might be possible that energy (or mass and energy) existed prior to the Big Bang explosion, and that energy eventually exploded into what we know as the Big Bang. Perhaps one possibility is that the energy in a pre-Big Bang universe slowly coalesced into a hyper massive black hole which eventually exploded, creating our current universe.  This conjecture is highly speculative, and it is not known if a large enough black hole would explode, but this speculative concept may be worthy of further work.