He says that the theory is "super duper testable" and "there is no more falsiable theory than many-worlds". [14:15] But he also says that the multiple universes can have no effect on us, so there cannot be any way of knowing whether they are real or not. There are freaky copies of yourself in parallel universes, but you should not worry about them because they are not truly you.
From his podcast last year:
Every time we make an important decision, it’s hard not to wonder how things would have turned out had we chosen differently. The set of all those hypothetical lives is a kind of “multiverse” — not one predicted by quantum mechanics or cosmology, but a space of possibilities that is ripe for contemplation. In their new movie Everything Everywhere All At Once, Daniels (the collective moniker for writer/directors Daniel Kwan and Daniel Scheinert) use this idea to tell the story of Evelyn (Michelle Yeoh), who is the “worst” of all her avatars in the multiverse. We talk about philosophy, filmmaking, and how we should all strive to be kind amidst the chaos.In the movie, Evelyn is a Chinese lesbian trying to cope with her parallel selves and her family. Carroll says the movie makers were not inspired by many-worlds theory or cosmology, but simply by other fiction writers who like to imagine alternate possibilities.
A new paper promoting the theory is Many-Worlds: Why Is It Not the Consensus?.
It is hard to believe that these guys sincerely believe the nonsense they are reciting.
The paper says:
Quantum mechanics is known to be resistant to a realist understanding, as it is unclear what picture of reality it provides us. Nonetheless, a variety of realist quantum theories have been proposed, and among these, one finds the many-worlds theory, also known as Everettian quantum mechanics.No, there is nothing realist about many-worlds. It postulates zillions of non-real parallel universes.
There are various readings of this theory, but they all have in common that all there is in the theory is a quantum state, evolving accord- ing to the Schrödinger unitary evolution equation, which produces experimental results distributed according to the Born rule.No, many-worlds does not use the Born rule, and does not produce experimental results.
Moreover, it is maintained, it is consistent with how physicists use the theory as well as its relativistic extensions. Therefore, one question arises naturally: why is it not the consensus? Why are all people not Everettians?No. The Born rule is a rule for collapsing the wave function, and is contrary to many-worlds theory.
According to some (Wallace p.c.), Everettian quantum mechanics is the implicit con- sensus, at least among practicing physicists; when they perform calculations, they use the Born rule, ... and they never need to modify the unitary evolution. That is, they implicitly adopt the many-worlds theory.
When informally asked, many of them say that they use standard quantum mechanics, namely the unitary evolution and the collapse rule, rather than unitary evolution alone, and they do not believe that they and their labs are continuously ‘splitting’ into infinitely many worlds. Indeed, some of them will not even see the point of ‘adding’ these worlds on top of the empirical adequacy of the standard theory. If the many-worlds theory makes the same predictions of standard quantum mechanics, but also postulates an infinity of unobservable worlds on top of the one we experience, then why should one prefer this theory to standard quantum mechanics?That's right.
Many-worlds theory does not make the same predictions. The only prediction it makes is that all things happen in parallel universes. It cannot tell the probability of something happening in one particular universe.
Personally, I favor a constructive explanation of the phenomena, and I think that, if one has such inclinations, the pilot-wave theory should be the clear consensus.This sentence alone discredits the paper. Pilot-wave theory is a spooky nonlocal theory. It is used as a philosophical example of non-physical interpretation, and that's all. No one uses it. It has no constructive explanation of anything.
Update: This recent paper, for example, admits that the "received view" of many-worlds is that interpreting the Born rule or any other probability is a unsolved problem.
Update: The Chinese lesbian multiverse movie, Everything Everywhere All at Once, won the Best Picture Oscar, as well as a bunch of others.