The measurement problem revisited

Abstract

It has been realized that the measurement problem of quantum mechanics is essentially the determinate-experience problem, and in order to solve the problem, the physical state representing the measurement result is required to be also the physical state on which the mental state of an observer supervenes. This necessitates a systematic analysis of the forms of psychophysical connection in the solutions to the measurement problem. In this paper, I propose a new, mentalistic formulation of the measurement problem which lays more stress on psychophysical connection. By this new formulation, it can be seen more clearly that the three main solutions to the measurement problem, namely Everett’s theory, Bohm’s theory and collapse theories, correspond to three different forms of psychophysical connection. I then analyze these forms of psychophysical connection. It is argued that the forms of psychophysical connection required by Everett’s and Bohm’s theories have potential problems, while an analysis of how the mental state of an observer supervenes on her wave function may help solve the structured tails problem of collapse theories.

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Notes

  1. 1.

    It seems that Maudlin’s omission is deliberate as he has a defense for it (Maudlin 2007). According to Maudlin (2007), we had better avoid explaining how determinate conscious experiences supervene on the wave function, since this brings in the mind-body problem, the problem of explaining how consciousness could supervene on anything physical in the first place, a problem which many take to be unsolvable. I respond to Maudlin in what follows.

  2. 2.

    Note that in Wallace’s (2012) latest formulation of Everett’s theory the number of the emergent observers after the measurement is not definite due to the imperfectness of decoherence. My following analysis also applies to this case.

  3. 3.

    If this is not the case, then for other evolution or other post-measurement states such as those containing only one branch of the superposition, the predictions of the theory may be inconsistent with the predictions of quantum mechanics and experience.

  4. 4.

    By comparison, if for the post-measurement superposition (2) there is only one observer whose mental content is composed of seeing a spin up result and seeing a spin down result, then her mental state will not change after the above evolution, and the principle of psychophysical supervenience can be satisfied (see further discussion about collapse theories in Sect. 5).

  5. 5.

    I will consider only objective versions of collapse theories here.

  6. 6.

    Note that this issue is independent of whether the observer can correctly report her mental content, which is related to the bare theory (Albert 1992; Barrett 1999).

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Acknowledgements

I am very grateful to two anonymous referees of this journal for their insightful comments, constructive criticisms and helpful suggestions. The basic idea of this paper came to my mind when I taught the course The Philosophy of Quantum Mechanics to the postgraduates at the University of Chinese Academy of Sciences. I thank the International Conference Center of the University for providing comfortable accommodation. I am also grateful to Arthur Fine, Kelvin McQueen, Peter Lewis, Mark Stuckey, and Ken Wharton for helpful discussions at the 2016 International Workshop on Quantum Observers hosted by International Journal of Quantum Foundations. This work is partly supported by a research project grant from Chinese Academy of Sciences and the National Social Science Foundation of China (Grant No. 16BZX021).

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Gao, S. The measurement problem revisited. Synthese 196, 299–311 (2019). https://doi.org/10.1007/s11229-017-1476-y

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Keywords

  • Measurement problem
  • Psychophysical supervenience
  • Everett’s theory
  • Bohm’s theory
  • Collapse theories
  • Structured tails problem