Abstract

Quantum theory has been formulated in several different ways. The original version was ‘Copenhagen’ quantum theory, which was formulated as a practical set of rules for making predictions about what we human observers would observe under certain well-defined sets of conditions. However, the human observers themselves were excluded from the system, in much the same way that Descartes excluded human beings from the part of the world governed by the natural physical laws. This exclusion of human beings from the world governed by the physical laws is an awkward feature of Copenhagen quantum theory that is fixed by “Orthodox” quantum theory, which is the form devised by von Neumann and Wigner. This orthodox form treats the entire world as a quantum system, including the brains and bodies of human beings. Some more recent formulation of quantum theory seek to exclude from the theory all reference to the experiences of human observers, but I do not consider them, both because of their technical deficiencies, and because they are constitutionally unequipped to deal adequately with the causal efficacy of our conscious thoughts.1 The observer plays a central role in both Copenhagen and Orthodox quantum theory. In this connection, Bohr, describing the 1927 Solvay conference, noted that: “…an interesting discussion arose about how to speak of the appearance of phenomena for which only statistical predictions can be made. The question was whether, as to the occurrence of such individual events, we should adopt the..