Related to the post last week on quantum mechanics, here is a talk that got mentioned in the discussion thread. Warning: Carroll is a passionate advocate for the Many Worlds Interpretation, so don’t expect a fair and balanced discussion. The video is about an hour long.
A couple of points. Carroll notes that we shouldn’t judge Everettian quantum mechanics by its implications. I think this is right. Judging it by those implications is a reductio ad absurdum argument. I honestly don’t know why people bother with reductio ad absurdum arguments anymore since reality has clearly demonstrated to us, time and time again, that it is definitely absurd.
But Carroll also notes that we shouldn’t criticize the MWI (Many Worlds Interpretation) for not being falsifiable. Here I think he’s wrong. (Carroll’s relationship with falsifiability is a bit rough. He questioned the value of the concept a few years ago.) The problem is that what currently is falsifiable applies to all interpretations of quantum mechanics. This makes all of them equally susceptible to this criticism (except for the instrumental/epistemic version of the Copenhagen Interpretation). To avoid this criticism, the MWI would need to be uniquely falsifiable.
Science fundamentally is about building theories that can make accurate predictions. An instrumental version of quantum mechanics meets this standard. But while all the interpretations that attempt to go further make their own predictions, none are testable, at least not yet. Until they are, they’re speculation, fascinating speculation to be sure, but speculation just the same.
Still, the MWI is arguably an elegant solution to the core issue. If it didn’t imply undetectable branches of the wavefunction (universes) everywhere, there’s a good chance we’d all be on board. And remember, reality is absurd.