Scientists are working to bring the multiverse hypothesis, which to some sounds like a fanciful tale, firmly into the realm of testable science. Never mind the Big Bang; in the beginning was the vacuum. The vacuum simmered with energy (variously called dark energy, vacuum energy, the inflation field, or the Higgs field). Like water in a pot, this high energy began to evaporate -- bubbles formed.
Each bubble contained another vacuum, whose energy was lower, but still not nothing. This energy drove the bubbles to expand. Inevitably, some bubbles bumped into each other. It's possible some produced secondary bubbles. Maybe the bubbles were rare and far apart; maybe they were packed close as foam.
But here's the thing: each of these bubbles was a universe. In this picture, our universe is one bubble in a frothy sea of bubble universes.
That's the multiverse hypothesis in a bubbly nutshell.
To read more, click here.