Sean Carroll has posted a passionate defense of the Many-world interpretation to quantum mechanics.
I have often talked about the Many-Worlds or Everett approach to quantum mechanics — here’s an explanatory video, an excerpt from From Eternity to Here, and slides from a talk. But I don’t think I’ve ever explained as persuasively as possible why I think it’s the right approach. So that’s what I’m going to try to do here. Although to be honest right off the bat, I’m actually going to tackle a slightly easier problem: explaining why the many-worlds approach is not completely insane, and indeed quite natural. The harder part is explaining why it actually works, which I’ll get to in another post.
Carroll’s description is well done, and I recommend reading the full post. My only concern is his characterization of the Many-worlds interpretation as inevitable. As I’ve written here before, I personally view Many-worlds interpretation as a candidate for reality, but I remain unconvinced that we’ve reached the point where we can move it from candidate to settled.
The conclusion, therefore, is that multiple worlds automatically occur in quantum mechanics. They are an inevitable part of the formalism. The only remaining question is: what are you going to do about it? There are three popular strategies on the market: anger, denial, and acceptance.
Or we can simply admit that we don’t yet have unique evidence for any of the interpretations. No anger or denial necessary, yet.
There are other silly objections to EQM, of course. The most popular is probably the complaint that it’s not falsifiable. That truly makes no sense. It’s trivial to falsify EQM — just do an experiment that violates the Schrödinger equation or the principle of superposition, which are the only things the theory assumes.
I think spreading superposition that we can’t observe, is an assumption. True, if we falsify the Schrodinger equation or superposition, we’ve falsified the Many-worlds interpretation, but haven’t we also falsified every other interpretation? To consider Many-worlds falsifiable, don’t we need to be able to, at least in principle, uniquely falsify it?
Occam’s razor often surfaces in these discussions. But Occam’s razor seems like a tough call on these interpretations. Is mathematical parsimony the same thing as ontological parsimony? I’m not sure of the answer, but dismissing the concern as silly seems unjustified.
A part of me wonders if there’s any real harm in people concluding that the Many-world interpretation is true, since its truth or falsity seems to have no bearing on the rest of the world. But this comes back to what should count as settled science, and I can’t see how a concept that is not testable in any foreseeable manner should count. And, as other physicists have said, there is a danger of accepting this interpretation and prematurely ceasing to look for what might be the real explanation, one that might turn out to open new doors.