Post #856544

2026-03-19 23:46 UTC

In his last AMA, Sean Carroll is asked if, as David Deutsch has claimed, the many worlds interpretation of QM is as sure as Darwinian evolution. Carroll says that no, that although his credence on the MWI is 90 - 95 %, his credence on evolution is much higher. He mentions two (for him) slightly weak points. On the one side, the problem of probability. I think he perhaps means how to derive the Born rule. He says he considers this solved but he&#39;s not 100% sure. And on the other side, the question of why if MWI is right then the world looks so classical. I didn&#39;t know this last point was a problem...

Replies (1)

@internic@mathstodon.xyz 2026-03-20 00:02

@davidsuculum@mathstodon.xyz Interesting. For the first point, it seems this could mean the quantitative problem from deriving the Born rule or the more philosophical problem of assigning probability in a world where every possible outcome of a measurement happens (in some branch of the wavefunction). Since I think Carroll proposes to solve the latter by invoking a Bayesian approach in terms of credence, I suspect you're right that he must mean the former. Personally, while I don't object to the Bayesian approach to statistics in general, I do find it vaguely dissatisfying to turn an empirical prediction (as in the usual frequentist formulation of the Copenhagen interpretation) into a statement about belief. For the second point, I agree with you; I don't understand why this should be a problem particular to MWI. Presumably in MWI, as in any other interpretation, classicality must arise from decoherence, and I would expect the problems there (proving that it's a generic phenomenon that will lead to the expected classical dynamics) to be the same. He has probably already expounded upon this at length, but I'm not sure where. It would be interesting to read.

Open ##3124415