Greg Ross in American Scientist:
It’s often noted that the universe seems strangely tailored to support human existence. The cosmological constant, for example, is tiny but not quite zero, producing a delicate cosmic balance without which life could not exist. This unlikely hospitality has given rise to the “anthropic principle,” a controversial concept that invokes the requirement for human existence in seeking to determine the rules of our universe.
The principle is unpopular among physicists, who would prefer to reach a single elegant solution that prescribes values for all the constants of nature without appealing to our own existence. The difficulty is that string theory currently gives rise to an unmanageable number of possible solutions.
In The Cosmic Landscape (Little, Brown, 2005), Leonard Susskind offers a different conception. The Stanford physicist champions the idea of a “megaverse,” a sea of pocket universes whose local environments correspond to the myriad solutions offered by string theory. Rather than seek a unique theory that somehow allows for our existence, he argues, physicists should consider a landscape of parallel universes in which the “local weather” is, here and there, hospitable to life.
Read the interview here.