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Giulio Prisco

- 76

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http://www.physicsoverflow.org/36063/given-decoherence-still-random-quantum-jumps-interpretations?

Environmental decoherence explains how the wavefunction of a quantum system q, as a result of the inevitable interactions and entanglement with the environment, appears to collapse upon measurement (Von Neumann's Process 1).

As far as I understand, decoherence works without needing a "real" collapse. The wavefunction of the total system (q plus environment and measurement equipment) continues to evolve according to the deterministic equations of quantum mechanics (Von Neumann's Process 2) and the total information is conserved, but q alone appears to undergo a quantum jump and lose information. The evolution of q taken alone appears as effectively random, but "q taken alone" is an approximation, and the evolution of the total entangled system q+environment is not random.

Decoherence explains why the world seems classical instead of quantum (with the exception of very carefully prepared cases difficult to realize). Decoherence explains why Scroedinger's cat is always either alive or dead, never in a combination of alive and dead states, without requiring ad-hoc additions to the equations of quantum mechanics (such as Von Neumann's Process 1). There is no Process 1, only Process 2.

Questions: Given the success and popularity of decoherence theories, are there reasons to stick to Von Neumann's notion of random collapse? Do we still need an interpretation of quantum physics?

The authors of "Decoherence and the Appearance of a Classical World in Quantum Theory" (which I believe is the "standard" text) do not seem to entirely agree on these points. What do you guys think?