What do major theorists speculate as to what happened before the Big Bang and also what caused The Big Bang?

Question

This is the 1000 Trillion Dollar question, I guess.

If we accept the Big Bang theory, which I think most do, then what was going on before The Big Bang and what caused it? What caused the moment where the Bang occurred?

Answer 1

A lot of physicists don't see a need for a "before the Big Bang."  The way all the numbers work out, it's not necessary to come up with a model of the pre-Big Bang universe.  Stephen Hawking, in particular, has expressed his belief that such a model wouldn't be required to explain how our universe works.  The way he explains it is like this:

The Earth, a globe, is a two-dimensional plane wrapped around along a third dimension - we can only walk north, south, east, or west, but none of these dimensions ever terminates, as they exist on a sphere.  The universe is the same way, except with a few extra non-spatial dimensions, including time: if you were to travel back through time, all the way up to the Big Bang, it would be analogous to traveling all the way up to the North Pole.  Hawking equates "What happened before the Big Bang?" with "What's north of the north pole?"  The beginning of time is defined as the point when the Big Bang happened, so to ascribe any timeliness to any point "before" that would be meaningless.  In theory, anyway - maybe we're all wrong and something DID happen to initiate the Big Bang, but if it did, there's certainly no evidence of it.

As a side note, the theory of the Big Bang doesn't concern itself with what happened "before," any more than theories of how lightning works concern themselves with the precipitation that forms clouds.  The theory does concern itself with that first moment - the Planck Epoch - and the expansion that followed.