The strongest limit on the number of possible universes is the human ability to distinguish between different universes. (PhysOrg.com) -- 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...