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. (shrink)

A reply to a comment by Paul Tappenden (BJPS 59 (2008) pp. 307-314) on S. Saunders and D. Wallace, "Branching and Uncertainty" (BJPS 59 (2008) pp. 298-306).

According to the Everett interpretation, branching structure and ratios of norms of branch amplitudes are the objective correlates of chance events and chances; that is, 'chance' and 'chancing', like 'red' and 'colour', pick out objective features of reality, albeit not what they seemed. Once properly identified, questions about how and in what sense chances can be observed can be treated as straightforward dynamical questions. On that basis, given the unitary dynamics of quantum theory, it follows that relative and never absolute (...) chances can be observed; that only on repetition of a large numbers of similar trials can relative probabilities be measured; and so on. The epistemology of objective chances can in this way be worked out from the dynamics. its curious features are thus explained. But one aspect of chance set-ups seems to resist this subsuming of chancing to branching: how is it that chance involves uncertainty? And if that is not possible, on Everettian lines, then the whole project is doomed. I argue that in fact there is no difficulty in making sense of uncertainty in the face of branching. Contrary to initial impressions, the unitary formalism is consistent with a well-defined notion of self-locating uncertainty. It is also consistent without: the mathematics under-determines the metaphysics in these respects. (shrink)

Following Lewis, it is widely held that branching worlds differ in important ways from diverging worlds. There is, however, a simple and natural semantics under which ordinary sentences uttered in branching worlds have much the same truth values as they conventionally have in diverging worlds. Under this semantics, whether branching or diverging, speakers cannot say in advance which branch or world is theirs. They are uncertain as to the outcome. This same semantics ensures the truth of utterances typically made about (...) quantum mechanical contingencies, including statements of uncertainty, if the Everett interpretation of quantum mechanics is true. The ‘incoherence problem’ of the Everett interpretation, that it can give no meaning to the notion of uncertainty, is thereby solved. IntroductionMetaphysicsPersonal fissionBranching worldsPhysicsObjections. (shrink)

This is a philosophical paper in favor of the many-worlds interpretation of quantum theory. The necessity of introducing many worlds is explained by analyzing a neutron interference experiment. The concept of the “measure of existence of a world” is introduced and some difficulties with the issue of probability in the framework of the MWI are resolved.

Simon Saunders and David Wallace attempt to use a modified form of David Lewis's analysis of personal fission to ground the claim that prior to undergoing Everett branching an informed subject can be uncertain about which outcome s/he will observe. I argue that a central assumption of this seductive idea is questionable despite appearing innocuous and that at the very least further argument is needed in support of it. CiteULike Connotea Del.icio.us What's this?