Robinson Everett: The Citizen Lawyer Ideal Lives On

In this tribute to Professor Robinson O. Everett, Dean David Levi questions the view that the citizen-lawyer or lawyer-statesmen models are in decline. Tracing Professor Everett’s varied career, accomplishments, and commitments to individuals and institutions; Levi contends that Everett combined the lawyer\u27s traditional focus on the individual with an overall dedication to the larger community. Everett was not just a model citizen; he was a lawyer-citizen. Levi contends that the survival of the lawyer-citizen and lawyer-statesmen models is a matter of choice and character. Nothing in the current structure of the legal economy places these models out of reach for those who would follow in Robinson Everett\u27s footsteps

Probability in the Everett World: Comments on Wallace and Greaves

It is often objected that the Everett interpretation of QM cannot make sense of quantum probabilities, in one or both of two ways: either it can't make sense of probability at all, or it can't explain why probability should be governed by the Born rule. David Deutsch has attempted to meet these objections. He argues not only that rational decision under uncertainty makes sense in the Everett interpretation, but also that under reasonable assumptions, the credences of a rational agent in an Everett world should be constrained by the Born rule. David Wallace has developed and defended Deutsch's proposal, and greatly clarified its conceptual basis. In particular, he has stressed its reliance on the distinguishing symmetry of the Everett view, viz., that all possible outcomes of a quantum measurement are treated as equally real. The argument thus tries to make a virtue of what has usually been seen as the main obstacle to making sense of probability in the Everett world. In this note I outline some objections to the Deutsch-Wallace argument, and to related proposals by Hilary Greaves about the epistemology of Everettian QM. (In the latter case, my arguments include an appeal to an Everettian analogue of the Sleeping Beauty problem.) The common thread to these objections is that the symmetry in question remains a very significant obstacle to making sense of probability in the Everett interpretation.Comment: 17 pages; no figures; LaTe

Discussion: Byrne and Hall on Everett and Chalmers

Byrne and Hall (1999) criticized the argument of Chalmers (1996) in favor of the Everett-style interpretation. They claimed to show ``the deep and underappreciated flaw in ANY Everett-style interpretation''. I will argue that it is possible to interpret Chalmers's writing in such a way that most of the criticism by Byrne and Hall does not apply. In any case their general criticism of the many-worlds interpretation is unfounded. The recent recognition that the Everett-style interpretations are good (if not the best) interpretations of quantum mechanics has, therefore, not been negated.Comment: 6 page

Everett and the Born Rule

During the last ten years or so, derivations of the Born rule based on decision theory have been proposed and developed, and it is claimed that these are valid in the context of the Everett interpretation. This claim is critically assessed and it is shown that one of its key assumptions, although natural in the context of the Copenhagen interpretation, is not consistent with that of Everett. It is further argued that any interpretation that relates outcome likelihood to the expansion coefficients connecting the wavefunction with the eigenfunctions of the measurement operator must be inconsistent with the Everett interpretation.Comment: 22 pages 1 figur

Decision-based Probabilities in the Everett Interpretation: Comments on Wallace and Greaves

It is often objected that the Everett interpretation of QM cannot make adequate sense of quantum probabilities, in one or both of two senses: either it cannot make sense of probability at all, or cannot explain why probability should be governed by the Born rule. David Deutsch has attempted to meet these objections. He argues not only that rational decision under uncertainty makes sense in the Everett interpretation, and that under reasonable assumptions, the credences of a rational agent in an Everett world should be constrained by the Born rule. David Wallace has recently developed and defended Deutsch's proposal, and greatly clarified its conceptual basis. In this note I outline some concerns about the Deutsch argument, as presented by Wallace, and about related proposals by Hilary Greaves. In particular, I argue that the argument is circular, at a crucial point

Measurement Outcomes and Probability in Everettian Quantum Mechanics

The decision-theoretic account of probability in the Everett or many-worlds interpretation, advanced by David Deutsch and David Wallace, is shown to be circular. Talk of probability in Everett presumes the existence of a preferred basis to identify measurement outcomes for the probabilities to range over. But the existence of a preferred basis can only be established by the process of decoherence, which is itself probabilistic

The Everett Interpretation

The Everett interpretation of quantum mechanics - better known as the Many-Worlds Theory - has had a rather uneven reception. Mainstream philosophers have scarcely heard of it, save as science fiction. In philosophy of physics it is well known but has historically been fairly widely rejected. Among physicists (at least, among those concerned with the interpretation of quantum mechanics in the first place), it is taken very seriously indeed, arguably tied for first place in popularity with more traditional operationalist views of quantum mechanics. In this article, I provide a fairly short (15,000 words) and self-contained introduction to the Everett interpretation as it is currently understood. I use little technical machinery, although I do assume the reader has encountered the measurement problem already (at about the level of the well-known discussions by Penrose or Albert)

There Is No Basis Ambiguity in Everett Quantum Mechanics

The Everett-interpretation description of isolated measurements, i.e., measurements involving interaction between a measuring apparatus and a measured system but not interaction with the environment, is shown to be unambiguous, claims in the literature to the contrary notwithstanding. The appearance of ambiguity in such measurements is engendered by the fact that, in the Schroedinger picture, information on splitting into Everett copies must be inferred from the history of the combined system. In the Heisenberg picture this information is contained in mathematical quantities associated with a single time.Comment: 17 pages, no figures. Minor typographical change

A formal proof of the Born rule from decision-theoretic assumptions

I develop the decision-theoretic approach to quantum probability, originally proposed by David Deutsch, into a mathematically rigorous proof of the Born rule in (Everett-interpreted) quantum mechanics. I sketch the argument informally, then prove it formally, and lastly consider a number of proposed ``counter-examples'' to show exactly which premises of the argument they violate.Comment: 36 pages. To appear (under the title "How to prove the Born rule") in Saunders, Barrett, Kent and Wallace, "Many Worlds? Everett, Quantum Theory, and Reality" (Oxford University Press