- #71
Morbert
Gold Member
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But is this general framing (exact unitary evolution, restriction of attention, and approximate contractive evolution) necessary in algebraic QFT? Fröhlich implies the reverse in some of his writing. In his article on the time-evolution of states He says unitary evolution and nonlinear state collapse "can be understood as an approximation to the fundamental [stochastic] law of evolution of states". I.e. in his AQFT formalism, stochastic state evolution is not arrived at by first sketching some unitary evolution and then coarsening it. He instead seems to start with a principle like Huygen's principle and event algebras implied by it.A. Neumaier said:This is the general mechanism; nothing is special here. See any derivation of decoherence or Lindblad master equations:
Restricting attention to less than complete information (absolutely necessary for an observer since complete information is never available) always turns the exact unitary evolution into a contractive evolution.
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