Over the past few decades, the idea that our universe could be one of many alternate universes within a giant multiverse has grown from a sci-fi fantasy into a legitimate theoretical possibility. Several theories of physics and astronomy have hypothesized the existence of a multiverse made of many parallel universes. One obvious question that arises, then, is exactly how many of these parallel universes might there be.

In a new study, Stanford physicists Andrei Linde and Vitaly Vanchurin have calculated the number of all possible universes, coming up with an answer of 10^10^16. If that number sounds large, the scientists explain that it would have been even more humongous, except that we observers are limited in our ability to distinguish more universes; otherwise, there could be as many as 10^10^10^7 universes.

To work these numbers out, Linde and Vanchurin looked back to the time shortly after the Big Bang, which they view as a quantum process that generated lots of quantum fluctuations. Then during the period of inflation, the universe grew rapidly and these quantum fluctuations were "frozen" into classical perturbations in distinct regions. Today, each of these regions could be a different universe, having its own distinct laws of low energy physics.