Well string theory suggests that the deeper universe, not just the observable and unobservable universe that we occupy, is a bunch of branes. Two or more of those branes colided, and our universe is the four dimensional space where they intersect.

If its hard to wrap your brain around 11 dimensional super branes, well dont feel bad, cosmology is a only a little harder than rocket science.

I think the simplest explanation is, we don't know. When people are prideful and dont know, they either blame God or another dimenson. I am happy to know I dont know, and if I knew with certainty, where would the mystery be?

There are enough mysteries to keep me occupied, that have the potential to be solved, or understood. I think questions like, what was the first cause, are a little vain, because every where we look, the universe seems to be infinite, both out into space, and down to the most fundamental quantum particles. In other words, worry about what you can know, and let the rest slide.