Abstract
Everettian quantum mechanics (EQM) results in “multiple, emergent, branching quasi-classical realities” (Wallace (2009)). The possible outcomes of measurement as per ‘orthodox’ quantum mechanics, are, in EQM, all instantiated. Given this metaphysics, Everettians face the ‘probability problem’ – how to make sense of probabilities and recover the Born Rule. To solve the probability problem, Everettians have derived a quantum representation theorem. There is a notable argument against the soundness of the representation theorem based on so-called ‘branch counting’. Everettians have sought to undercut this argument by claiming that there is no such thing as the number of branches. In what sense is it both true that there is no such thing as the number of branches and that there are multiple branches? Various answers to this question have been given. These can be categorised into two kinds: that there are ‘indeterminately-many’ branches or that there are ‘indeterminably-many’ branches. I argue that neither suffices to undercut the argument against the quantum representation theorem. I conclude that the quantum representation theorem is unsound and that the probability problem facing EQM remains unsolved.
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Notes
- 1.
I do not consider the older “Many-Worlds” or “Many-Minds” interpretations, as these are no longer pursued.
- 2.
This was first put forward by Deutsch (1999) and has been greatly developed by Simon Saunders and David Wallace (2008). However, it should be noted that not all Everettians consider there to be a probability problem.
- 3.
For details see Wallace (2009).
- 4.
I subscribe to the view that ontological parsimony is fixed, ceteris paribus, by the number of kinds of objects not by the number of objects.
- 5.
- 6.
One may be tempted to say that if BI is literally the only available strategy then it must be rational to pursue it – surely it is rational to pursue the only available strategy? But here push comes to shove: it is not the case that BI is literally the only strategy – one could set one’s degrees of belief, say, at whim. (And notice that whim might, de facto violate BI!) In any case, the salient point is that rationality does not come by default. With regards, say, whim, one would need positive reasons to think it rational to do so, and so too with BI.
- 7.
Furthermore, the decoherence models that underpin the Everettian interpretation are highly idealised.
References
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Acknowledgements
I am grateful to the following people for interesting and instructive discussions/comments pertaining to this paper: Jason McKenzie Alexander, Seamus Bradley, Nazim Bouatta, Erik Curiel, Roman Frigg, Conrad Heilmann, Eleanor Knox, John Norton, Matt Parker, Wolfgang Pietsch, Miklós Rédei, Marie Toseland, Alastair Wilson, and members of the audience at EPSA 2011, Athens. I am particular grateful to comments I received from an anonymous referee; I found the comments insightful and they prompted several important revisions.
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Dizadji-Bahmani, F. (2013). Why I Am Not an Everettian. In: Karakostas, V., Dieks, D. (eds) EPSA11 Perspectives and Foundational Problems in Philosophy of Science. The European Philosophy of Science Association Proceedings, vol 2. Springer, Cham. https://doi.org/10.1007/978-3-319-01306-0_18
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