Newsweek: “What really interests me is whether God had any choice in creating the world.”

That’s how Albert Einstein, in his characteristically poetic way, asked whether our universe is the only possible universe.

The reference to God is easily misread, as Einstein’s question wasn’t theological. Instead, Einstein wanted to know whether the laws of physics necessarily yield a unique universe—ours—filled with galaxies, stars, and planets. Or instead, like each year’s assortment of new cars on the dealer’s lot, could the laws allow for universes with a wide range of different features? And if so, is the majestic reality we’ve come to know—through powerful telescopes and mammoth particle colliders—the product of some random process, a cosmic roll of the dice that selected our features from a menu of possibilities? Or is there a deeper explanation for why things are the way they are?

In Einstein’s day, the possibility that our universe could have turned out differently was a mind-bender that physicists might have bandied about long after the day’s more serious research was done. But recently, the question has shifted from the outskirts of physics to the mainstream. And rather than merely imagining that our universe might have had different properties, proponents of three independent developments now suggest that there are other universes, separate from ours, most made from different kinds of particles and governed by different forces, populating an astoundingly vast cosmos.

The multiverse, as this vast cosmos is called, is one of the most polarizing concepts to have emerged from physics in decades, inspiring heated arguments between those who propose that it is the next phase in our understanding of reality, and those who claim that it is utter nonsense, a travesty born of theoreticians letting their imaginations run wild.

So which is it? And why should we care? Grasping the answer requires that we first come to grips with the big bang. [Continue reading…]