I haven’t yet seen a copy of Marcelo Gleiser’s new book, but this weekend the Wall Street Journal had a review by John Gribbin, author of the 2009 multiverse-promotional effort In Search of the Multiverse. I don’t know how Gleiser treats this, but Gribbin emphasizes the multiverse as new progress in science (for some reason he’s now calling it the “metaverse”):
Within the metaverse, the story goes, there are regions that form inflating bubbles. Our universe is one such region or bubble. As Mr. Gleiser explains, the implication is that there are other universes, other bubbles far away floating across an inflating sea.
This seemingly speculative idea counts as a genuine scientific hypothesis, because it makes testable predictions. If other “bubble universes” exist in the metaverse, it is possible that, long ago, one or more of them may have collided with our universe, like two soap bubbles touching and moving apart. One effect of such a collision, Mr. Gleiser points out, would be to make ripples in the space of both bubble universes; they would leave a distinctive if faint ring-shaped pattern, known as a “cosmic wake,” in the background radiation that fills the universe. Data from the Planck satellite is being used to test this prediction right now. Is the metaverse real? We may well know in the next year or so.
This seems to be a reference to work by Matthew Kleban and collaborators, which I saw Kleban talk about recently (see here). My impression from that talk is that the actual state of affairs with Planck is that it has already looked for and ruled out most hoped-for signals of “bubble collisions”. I don’t know anyone besides Gribbin who believes that the next round of Planck data is going to answer the question “Is the metaverse real?”.
The really odd thing about the review is that Gribbin uses the multiverse to argue that John Horgan’s claims about physics in The End of Science are wrong. This is just bizarre. Gribbin and his multiverse mania for untestable theories provides strong ammunition for Horgan, since it’s the sort of thing he was warning about. Actually, I don’t recall anything in Horgan’s book about the multiverse, and suspect the idea that physics would end up embracing such an obviously empty idea was something that even he didn’t see coming. As the multiverse mania gains strength, physicists are blowing past the “End of Science” to something that has left conventional science completely behind.
Update: I took a look again at a copy of The End of Science, and, as I remembered, the chapter on “The End of Physics” has no mention of the multiverse pseudo-explanation of why one can’t ever understand the parameters of the Standard Model. Horgan ends the chapter with a vision of physics descending into “ironic science”, endlessly studying untestable string theory models and interpretations of quantum mechanics. With the multiverse we may already have gone past that point.
In the next chapter though, “The End of Cosmology”, there’s a long section about Linde and his “self-reproducing universe theory”, so Horgan more than 20 years ago already was writing about the place we’re ending up. I was interested to see the comment he got at the time from Howard Georgi about this kind of model:
quite amusing. It’s like reading Genesis.
Georgi also is quoted as describing inflation as:
a wonderful sort of scientific myth, which is at least as good as any other creation myth I’ve ever heard.
Of course what is different now is that 20 years ago the theory establishment saw Linde’s multiverse as kind of a joke, not at all part of science. Things have changed…
Update: While my favorite local bookstore doesn’t have a copy of the Gleiser book The Island of Knowledge, you can see parts of it on Google Books. Searching on “multiverse” you can read chapters 15 and 16 of the book which deal with the issue of the testability of the string theory multiverse. Reading these shows that Gribbin seriously misrepresents what Gleiser has to say about the multiverse. The context of his discussion of “Cosmic Wakes” and the possibility of seeing them in the Planck data is to argue that even if this happened (which he describes as having an “extremely small” probability), all that would show is evidence for a neighboring universe, not a multiverse:
However, I stress again that even a positive detection of a neighboring universe would not prove the existence of a multiverse. Within the present formulation of physics the multiverse hypothesis is untestable, however compelling it may be. [Page 129]
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