The Guardian has a podcast up today featuring Robert Trotta and David Wallace called The Multiverse in a Nutshell. It’s largely more of the usual uncritical multiverse hype that has been flooding the public expositions of fundamental physics for years now. Trotta gives the usual promotion of the cosmological multiverse, with no indication there is any problem with it. He assures us that this is being tested (by looking for “bruises” in CMB collisions). As far as I can tell, the Planck results released today, like all CMB data, show no evidence for anything like this. It appears that the Planck people don’t even think this is worth mentioning. The public channels used for this hype will never report the fact that there’s nothing there, instead they will just endlessly talk about this as something “scientists are looking for.”
Wallace talks about something completely different, many-worlds, with nobody telling listeners that this has nothing at all to do with the cosmological material. Instead we’re told that it’s all related, because “most theories” “tell us there must be a multiverse”. When challenged about the splitting universe business in QM, Wallace admits that at the fundamental level there is no splitting, there’s just one theory and one universe, that “many worlds” is just a way of talking about the emergent behavior of the classical approximation. His book about this, The Emergent Multiverse, is quite good and makes clear what the “Multiverse” there really is. It’s a real shame that he chooses to involve himself in this kind of attempt to muddy the waters and promote pseudo-science to the public.
Thankfully at least the physics community has one physicist trying to do something about this nonsense: Paul Steinhardt. In an interview with John Horgan, here’s his “Multiverse in a Nutshell”:
Unfortunately, what has happened since is that all attempts to resolve the multiverse problem have failed and, in the process, it has become clear that the problem is much stickier than originally imagined. In fact, at this point, some proponents of inflation have suggested that there can be no solution. We should cease bothering to look for one. Instead, we should simply take inflation and the multiverse as fact and accept the notion that the features of the observable universe are accidental: consequences of living in this particular region of the multiverse rather than another.
To me, the accidental universe idea is scientifically meaningless because it explains nothing and predicts nothing. Also, it misses the most salient fact we have learned about large-scale structure of the universe: its extraordinary simplicity when averaged over large scales. In order to explain the one simple universe we can see, the inflationary multiverse and accidental universe hypotheses posit an infinite variety of universes with arbitrary amounts of complexity that we cannot see. Variations on the accidental universe, such as those employing the anthropic principle, do nothing to help the situation.
Scientific ideas should be simple, explanatory, predictive. The inflationary multiverse as currently understood appears to have none of those properties.
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