H. Dieter Zeh

Submitted to “Quantum Nonlocality and Reality – 50 Years of Bell’s theorem”.

For the first time I met John Bell at the Varenna conference of 1970 (d’Espagnat, 1971). I had been invited on suggestion by Eugene P. Wigner, who had already helped me to publish my first paper on the concept of what was later called decoherence – to appear in the first issue of the Foundations of Physics a few months after the conference (Zeh, 1970). This concept arose from my conviction, based on many applications of quantum mechanics to composite systems under various conditions, that Schrödinger’s wave function in configuration space, or more generally the superposition principle, is valid and applicable beyond microscopic systems – for example in the form of wave packets instead of classical properties, and thus not only in a statistical sense. Superpositions often define novel individual physical properties, such as “momentum” defined as a plane wave superposition of different positions, but they can easily be “dislocalized” (distributed over many degrees of freedom) by means of interactions described by the Schrö­dinger equation. This disappearance of local superpositions (“decoherence”) may explain the classical appearance of the quantum world as well as apparent quantum jumps or “events”. So I had never felt any motivation to think of “hidden variables” or any other physics behind the successful wave function – see Sect. 4, or (Zeh, 2013) for a historical overview.

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