Is Decoherence essentially a measurement? Then what?

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Discussion Overview

The discussion revolves around the concept of decoherence in quantum mechanics, specifically questioning whether decoherence can be equated to measurement, its implications for quantum systems transitioning to classical states, and the interpretation of probability in the context of quantum particles, particularly in the double-slit experiment.

Discussion Character

  • Exploratory
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question whether decoherence is essentially a measurement and its implications for quantum systems becoming classical.
  • There is a suggestion that decoherence does not permanently set quantum particles into the classical world, raising the possibility of returning to a superimposed state.
  • One participant argues that decoherence is simply the entanglement of a quantum system with its environment, maintaining a pure superposition state according to the Schrödinger equation.
  • Another participant clarifies that it is misleading to say a particle is "everywhere" but rather that there is a non-vanishing probability of finding it in various locations.
  • A metaphor is used to illustrate the concept of probability, comparing it to not knowing a person's exact location but acknowledging they exist in one specific place at a time.

Areas of Agreement / Disagreement

Participants express differing views on whether decoherence can be equated to measurement and its permanence in setting quantum systems into classical states. The discussion remains unresolved regarding these interpretations.

Contextual Notes

There are limitations in the assumptions made about the nature of decoherence and measurement, as well as the interpretations of probability in quantum mechanics that remain unaddressed.

rasp
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2 basic questions from a non-physicist (sigh!). Is decoherence essentially a measurement? And if so is the system of quantum particles set into the classical world forever? Or is there a mechanism by which it will evolve again into a superimposed state? Secondly, if the particle (as in the 2 slit experiment) is essentially everywhere possible at a given time, then what sense can be given to assessing the probability that the particle can be found in a specific place?
 
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Clarification: 2 basic questions from a non-physicist (sigh!). Is decoherence essentially a measurement? And if so is the system of quantum particles that has experienced decoherence set into the classical world forever? Or is there a mechanism by which it will return into a superimposed state? Secondly, if the particle (as in the 2 slit experiment) is essentially everywhere possible at a given time, then what sense can be given to assessing the probability that the particle can be found in a specific place?
 
Decoherence is merely the entanglement of the quantum system with the quantum (assuming everything is quantum) environment. It remains in a pure, superposition, state, evolving according to the fundamental Schrödinger equation.
 
rasp said:
Is decoherence essentially a measurement?
Essentially, yes.

rasp said:
And if so is the system of quantum particles set into the classical world forever? Or is there a mechanism by which it will evolve again into a superimposed state?
The latter.

rasp said:
Secondly, if the particle (as in the 2 slit experiment) is essentially everywhere possible at a given time, then what sense can be given to assessing the probability that the particle can be found in a specific place?
It is not correct to say that the particle itself is everywhere. Instead, it is a non-vanishing probability of finding the particle which is everywhere.

For example, I don't know where do you live on Earth right now. Perhaps New York? Or London? Or a small village in India? I have no idea, so I can say that you can be "everywhere". But of course, I know that you are not at all those places at once. If I find you, I know I will find you at only one of those places.
 
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