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How do I decide that a particle is isolated?

  1. Aug 31, 2013 #1
    Every particle in the universe has been, at a given point of its history, interacting with other particles. So, how is it possible to decide whether a given particle can be treated as an isolated quantum system the states of which are vectors of a single Hilbert space? Altenatively, what conditions will force us to consider electron pairs emitted by radioactive decay or photon pairs resulting of radiative cascade, as a single sytem describe by a tensor product of two Hilbert spaces?
    What is the criteria to decide whether a system is bipartite?
  2. jcsd
  3. Aug 31, 2013 #2


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    Staff: Mentor

    For the evolution of a particle or a system of particles, you can ignore the rest of the world if there is no decoherence happening within the timescale of your experiment.
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