In my article “Multiverse, a semantic gimmick? http://tienzen.blogspot.com/2012/05/multiverse-semantic-gimmick.html “, I have showed that the argument about the possibility (or the fact) that there could be multiple big-bangs simultaneously cannot be the reason for multiverse.
Yet, Greene also said in his article “… detailed analysis of the theory’s [string theories] equations revealed numerous solutions, each representing a different possible universe. And numerous means numerous. Today, the tally of possible universes stands at the almost incomprehensible 10500, a number so large it defies analogy.”
The possible universes are well-studied subject in philosophy. There are many ways to define the “current” universe. For me, the best way to define it is with my four kids. About some years ago, I had three choices for my kids’ mother. If I selected a choice different from the history, this “current” universe will be significantly different, and that difference can be clearly identified by my kids who would have carried different mother’s genes. Thus, the three “possible” universes some years ago have only one manifested. There are zillions possible universes at any given point, but there is still only one universe.
The argument that “… that the big bang would likely not be a unique event. Instead, … it would power countless other bangs, too, each yielding its own separate, expanding universe. Our universe would then be a single expanding bubble inhabiting a grand cosmic bubble bath of universes—a multiverse.” cannot be the base for multiverse.
In Greene’s article, he did said, “And rather than merely imagining that our universe might have had different properties, proponents … 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.” This description is not about possible universes. They are definitely different universes. Then, there are two vital questions.
1. Can those different physics laws be tested in “our” universe? If not, the Multiverse theory cannot be a viable science.
2. Can those different physics laws be “reasoned” with the intelligence of our universe?
Before these two questions are answered, the proposal of Multiverse is meaningless. The bottom line is that we must not confuse the multiverse with the possible universes.