My endless rants here about the hot field of multiverse studies are mainly motivated by concern about the effect this is having on particle theory. Multiverse scenarios all too often function as an excuse for not admitting that string theory/extra-dimensional ideas about unification have failed. Such an admission would encourage people to move on to more promising ideas, but instead hep-th is stuck in an endless doldrums with the high profile public face of the subject dominated by excited claims about what a wonderful discovery this region is.
Independently of the string theory problem, I’m personally a skeptic that multiverse studies have any promise, simply due to the fact that the subject lacks a viable theory, any experimental evidence, and any plausible prospects for getting either. Others feel differently though, and very recently two of my fellow string theory skeptics have written about the subject much more positively.
The first is Lee Smolin, who has written an essay for the Foundations of Physics “Forty Years of String Theory” volume with the title A perspective on the landscape problem. Smolin’s interest in multiverse models goes way back, to long before the current string-theory-based mania. He’s got a good argument that he was the originator of the term “landscape” itself, which he wrote about back in his 1997 book The Life of the Cosmos. If you’re interested in the multiverse at all, Smolin’s article is well-worth reading. I very much agree with his emphasis on the principle that one has to be careful to stick to ideas that can legitimately count as science, by conventional standards of testability. He is pursuing “cosmological natural selection” scenarios which he argues do have testable consequences. I’m not convinced there’s enough there to ever lead to solid evidence for such a scenario, although there may be enough structure there to sooner or later make it clear if the idea is simply falsified by one fact or other about the universe.
Today’s New York Times has an article by Dennis Overbye about Lawrence Krauss and his new book A Universe From Nothing. Much of the book is an excellent discussion of cosmology and the physics of the vacuum, but it also devotes a lot of effort to discussing the meaningless question of “Why is there something rather than nothing?” and arguing against the invocation of a deity in order to answer it. Krauss is no fan of string theory, which he regards as overhyped, but he seems to have developed an attraction to multiverse studies recently, perhaps motivated by their use in arguments with those who see the Big Bang as a place for God to hang out.
Personally I’ve no interest in arguments about the existence of God, which epitomize to me an empty waste of time. Given the real dangers of religious fundamentalism in the US though, I’m glad that others like Krauss make the effort to answer some of these arguments. I’m less happy to see him and others adopting the multiverse as their weapon of choice in this battle, since it’s a lousy one and not going to convince anyone. In the New York Times piece we’re told:
“Maybe in the true eternal multiverse there are truly no laws,” Dr. Krauss said in an e-mail. “Maybe indeed randomness is all there is and everything that can happen happens somewhere.”
Given the choice between this vision of fundamental science and “God did it” as explanations for the nature of the universe, one can’t be surprised if people go for the man in the white robes…