Well Michael, all this discussion seems to to be a waste of our precious time.
The human race will be extinct very soon, and we will be no nearer answering your question.    I suppose the most possible and least destructive theory is "God".

Any other theory is bullshit as the human brain is simply not equipped to understand something so immense...and who is to say that "our" universe is the only one.....what if there is no beginning?......What if the universe is never ending?

I'm going for "God"......EW!!