Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Loschmidt's paradox-II: Quantum Decoherence

  1. Oct 9, 2009 #1
    So if you remember, Loschmidt's paradox is about "Loschmidt's paradox, also known as the reversibility paradox, is the objection that it should not be possible to deduce an irreversible process from time-symmetric dynamics" ( http://en.wikipedia.org/wiki/Loschmidt's_paradox )

    My question is, how time-assymetric Quantum Decoherence emerges from time-symmetric Quantum Mechanics?

    P.S. I dont think weak CP violation (which leads to T-symettry violation) plays any role in it.
  2. jcsd
  3. Oct 9, 2009 #2
    Isn't it simply that the wave-function of the universe/multiverse as a whole is time reversible, even though we can inspect it from a basis in which each part is not reversible? In other words, there's nothing preventing the SE from back-evolving a superposition of "observed dead cat" plus "observed live cat" into "haven't yet opened the box"; apparent asymmetry arises from our (self-centred) choices to ignore/drop part of the final superposition.

    (And classicaly, there is no paradox in time-symmetric laws predicting that if the universe had low entropy at its lower bound of time then it will have entropy increasing with time.)
  4. Oct 12, 2009 #3


    User Avatar
    Science Advisor

    Essentially, the same way how time-asymmetric second law of thermodynamics emerges from classical time-symmetric equations of motion:
    Special initial conditions + coarse graining -> time-asymmetry
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Loschmidt's paradox Quantum Date
I Two coherent sources Yesterday at 10:20 PM
I QFT paradox? Feb 3, 2018
A A question about the information loss paradox Oct 27, 2017
B Black hole information paradox and determinism Oct 4, 2017
I (Apparent?) paradoxes - Classical/Quantum theory predictions Sep 24, 2017