What is the connection between the accelerating expansion of the universe and the existence of other universes?
The observation of the accelerating universe has crystallized a crisis. It’s yet another parameter in our fundamental theory that appears to be finely tuned to just the right value. If it were a little bigger, the universe would be empty. But if the multiverse picture is correct, and there are all these different universes, then the value of the cosmological constant could just randomly vary from one universe to the next. We should not be surprised to find one universe with a cosmological constant that is not lethal to our existence. Why do you refer to this as a crisis? A: Because it’s not a way that the vast majority of physicists wanted to go. It makes the task of figuring out the fundamental physics much harder if our universe is not directly connected to one set of fixed parameters. My feeling is that the new direction—picturing our universe as just a part of a multiverse—may very well be right, and all the controversy right now is because we’re in the middle of a difficult birthi
