Reality
Role of "observation" in quantum mechanics

The quantum mind –body problem refers to the philosophical discussions of the mind–body problem in the context of quantum mechanics. Since quantum mechanics involves quantum superpositions, which are not perceived by observers, some interpretations of quantum mechanics place conscious observers in a special position.

The founders of quantum mechanics debated the role of the observer, and of them, Wolfgang Pauli and Werner Heisenberg believed that it was the observer that produced collapse. This point of view, which was never fully endorsed by Niels Bohr, was denounced as mystical and anti-scientific by Albert Einstein. Pauli accepted the term, and described quantum mechanics as lucid mysticism.

Heisenberg and Bohr always described quantum mechanics in logical positivist terms. Bohr also took an active interest in the philosophical implications of quantum theories such as his complementarity, for example. He believed quantum theory offers a complete description of nature, albeit one that is simply ill-suited for everyday experiences – which are better described by classical mechanics and probability. Bohr never specified a demarcation line above which objects cease to be quantum and become classical. He believed that it was not a question of physics, but one of philosophy.

Eugene Wigner reformulated the " Schrödinger's cat " thought experiment as " Wigner's friend " and proposed that the consciousness of an observer is the demarcation line which precipitates collapse of the wave function, independent of any realist interpretation. Commonly known as " consciousness causes collapse ", this controversial interpretation of quantum mechanics states that observation by a conscious observer is what makes the wave function collapse. However, this is a minority view among quantum philosophers, considering it a misunderstanding. There are other possible solutions to the " Wigner's friend " thought experiment, which do not require consciousness to be different from other physical processes. Moreover, Wigner shifted to those interpretations in his later years.
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