[spoiler]another phantom bump. I will appease these spirits with a reply[/spoiler]
There's two big reasons imo why things happen, two different sorts of causes: weak but constant forces, and strong yet sudden ones. Different people have different opinions on which is more shaping. The idea that history is more shaped by the unforeseeable catastrophes is called the Black Swan hypothesis.
Depending on which kind of force is more shaping, I see two possibilities: the universe has always existed and always will, or it was created in a black swan event. The Big Bang theory cheeses these together by saying that time is expanding and accelerating alongside space, so if you were to go back in time to the big bang time would get denser and denser and you'd never reach a single instant of genesis. It's a sort of four-dimensional fractal.
If there is a black swan event responsible for the creation of this fractal, however, I think it would have to be higher-dimensional collisions. Think about the surface of a lake as a two-dimensional abstract plane. It ripples as forces move around it, but never tears. If something lived entirely within the two dimensions of the surface it would never have any idea the laws of its universe were determined by swimming fish or gusts of wind. That's us. Something is swimming around or blowing around, ruffling up a surface, and the result is our universe.
You know what, fuck it, believing in a supreme creator requires fewer assumptions.