There's something about being human — perhaps our brains' tendency for pattern formation — that makes us want to know the beginning and the end of every story. That includes the story of the universe itself. But if the Big Bang was the start of the universe, how was it triggered, and what existed before it? Will the universe someday end, and what will happen after that? Inquiring minds want to know.
A multiverse could provide an explanation for all of those things. Some physicists have hypothesized that the infinite regions of the multiverse are something called braneworlds. These braneworlds exist in many different dimensions, but we can't detect them, because we can only perceive the three dimensions of space, plus the fourth dimension of time, in our own braneworld.
Some physicists believe that these braneworlds are slabs, bunched together like slices of bread inside a plastic bag. Most of the time, they stay separate and out of reach. But occasionally, the braneworlds bump into each other. Hypothetically, those collisions are cataclysmic enough to cause repeated Big Bangs — enabling the parallel universes to restart themselves, over and over [source: Moskowitz].