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Everettian chance in no uncertain terms

Steeger, Jer, Read, James

Published Sep 16, 2025• 0 citations
OpenAlex

Abstract

The current landscape of views on chance in the Everett interpretation is rocky. Everettians (Wallace 2012, Sebens and Carroll 2018, McQueen and Vaidman 2019) agree that chance should be derived using principles governing uncertain or partial belief, but they cannot agree on how. Critics (Baker 2007, Dawid and Thébault 2015, Mandolesi 2019) maintain that any such approach is circular. We smooth the landscape by shifting focus from what Everettians take to be uncertain to what they should think is certain: namely, the conditions under which branches are isolated. Our approach to isolation resolves the main tensions among the different Everettian chance derivations while clarifying how they avoid circularity.

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The current landscape of views on chance in the Everett interpretation is rocky. Everettians (Wallace 2012, Sebens and Carroll 2018, McQueen and Vaidman 2019) agree that chance should be derived using principles governing uncertain or partial belief, but they cannot agree on how. Critics (Baker 2007, Dawid and Thébault 2015, Mandolesi 2019) maintain that any such approach is circular. We smooth the landscape by shifting focus from what Everettians take to be uncertain to what they should think is certain: namely, the conditions under which branches are isolated. Our approach to isolation resolves the main tensions among the different Everettian chance derivations while clarifying how they avoid circularity.
Abstract Those who criticize the Everett interpretation on the grounds that it makes no sense of probability apply a double-standard, for no other physical theory of probability does any better in explaining probability or in deriving its link with decision theory. In fact, others do worse, for in any one world theory it is a mystery as to why, given that only a single outcome of a chance process occurs, we should nevertheless act so as to maximize expected utilities, which involves all possible outcomes of a chance process. This difficulty does not apply to the Everett interpretation, in which all outcomes happen.
How does it come about then, that great scientists such as Einstein, Schrödinger and De Broglie are nevertheless dissatisfied with the situation? Of course, all these objections are levelled not against the correctness of the formulae, but against their interpretation. […] The lesson to be learned from what I have told of the origin of quantum mechanics is that probable refinements of mathematical methods will not suffice to produce a satisfactory theory, but that somewhere in our doctrine is hidden a concept, unjustified by experience, which we must eliminate to open up the road. (Born [1954], pp. 8, 11) It is truly surprising how little difference all this makes. Most physicists use quantum mechanics every day in their working lives without needing to worry about the fundamental problem of its interpretation. (Weinberg [1992], p. 66) I endorse the view that it may be of no relevance to the acceptability of the Everett interpretation of quantum mechanics as a physical theory whether or not an informed observer can be uncertain about the outcome of a quantum measurement prior to its having occurred. However, I suggest that the very possibility of post-measurement, pre-observation uncertainty has an essential role to play in both confirmation theory and decision theory in a branching universe. This is supported by arguments which do not appeal to van Fraassen’s Reflection Principle. 1. Dendritic Unitary Evolution 2. The Born–Vaidman Rule 3. Greaves on Uncertainty 4. Retroactive Counterfactual Uncertainty 5. Odds and Ends
I propose, in the context of Everett interpretations of quantum mechanics, a way of understanding how there can be genuine uncertainty about the future notwithstanding that the universe is governed by known, deterministic dynamical laws, and notwithstanding that there is no ignorance about initial conditions, nor anything in the universe whose evolution is not itself governed by the known dynamical laws. The proposal allows us to draw some lessons about the relationship between chance and determinism, and to dispel one source of the tendency among Everettians to introduce consciousness as a primitive element into physical description.
Abstract This chapter discusses what would need to be done to address the epistemic difficulties associated with the Everett interpretation, then considers a number of putative solutions to the Everettian probability problem and assesses whether these approaches succeed in solving the epistemic aspects of that problem. The discussion covers naïve branch counting and Saunders’ sophisticated branch counting; Vaidman’s ‘measure of existence’ approach; the Deutsch-Wallce decision-theoretic approach; and the Sebens-Carroll and Vaidman-McQueen self-locating uncertainty approaches.