Why Chance make no sense in Many-Worlds

I have argued here that many-world (Everettian) theory is incoherent because it fails to make any sense out of probability. To believe in the theory, you have to reject probability as widely understood, and then to reject all of science.

No one admits this, of course, but see how a new paper dances around the subject.

Everettian chance in no uncertain terms

The current landscape of views on chance in Everettian quantum mechanics is a curious one. On the one side, longstanding critics of many-worlds theories maintain that probability is needed to make sense of the machinery that Everettians use to derive chance values, resulting in circularity (Baker 2007, Dawid and Thébault 2015, Mandolesi 2019). On the other side, Everettians seem to agree that chance values should be derived in terms of agents’ uncertain or partial beliefs—but they cannot agree on how.1

Perhaps the most famous of these uncertainty-based approaches is the decision-theoretic program explored by Deutsch (1999) and Wallace (2012): they purport to prove that a rational Everettian agent must order their preferences over acts in a way that recovers the Born rule. Sebens and Carroll (2018) take issue with one of the principles of rationality in Wallace’s approach and instead aim to derive Everettian probabilities from principles governing self-locating uncertainty. McQueen and Vaidman (2019) offer yet another self- locating uncertainty approach, taking issue with Sebens and Carroll’s metaphysical view of branching. Notably, all three approaches claim that symmetries of quantum states are central to their arguments, but none attempt to characterize the symmetries at play.2

The most common defense of many-worlds here is to give up on probabilities directly, but to argue that it could be rational to believe in them anywy, as some sort of subjective way of trying to make sense out of nonsense.

Any sort of scientific outlook requires saying that some things happen, some do not happen, and some things are more likely than others. Many-worlds is unable to deal with any of this. Just look at the above nonsense. It essentially says that many-worlds researchers are trying to make sense out of chance, and not succeeding.