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A Conservation of Information: Neutron Formation and Decay

  1. Apr 14, 2016 #1
    Has anyone analyzed the process of Neutron formation and decay from the perspective of "information conservation"?

    Does anyone have any thoughts on what the results of such an analysis would be?

    What is the status of the observed evidence of reality in respect of whether one should conclude that the law of information conservation is or is not universally applicable to all physical processes?
     
  2. jcsd
  3. Apr 14, 2016 #2

    mfb

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    Quantum field theory is fully time-reversible (if you also change CP). Nothing that is described properly by QFT can lose information, and I am not aware of any neutron-related experiments that would be in conflict with QFT.
     
  4. Apr 14, 2016 #3
    I understand that various physical quantities are conserved for the system during the process, e.g. charge, mass, energy, spin, lepton number etc. so that if one takes all that went into the formation of the neutron, all that it decays into, these "physical quantities" must be conserved.

    Perhaps my question is ill formed due to a misunderstanding as regards to "information conservation". Is information a further quantity which is conserved like all the others but which is somehow over and above the physical quantities? Is it a separate (i.e. additional) physical quantity itself? What does it mean to "conserve" information?

    Back to the process of neutron formation and decay:
    If one observes the decay of a neutron in the lab, do all the particular properties (e.g. momenta direction and magnitude) of the resulting proton, electron, and neutrino "preserve" all of the information possessed by the same types of particles that came together to form the neutron?
     
  5. Apr 14, 2016 #4

    jtbell

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    How does one define "information" for this system?
     
  6. Apr 14, 2016 #5
    Indeed that is one of my questions!

    Perhaps someone with knowledge of the black hole information paradox could shed light on this.
     
  7. Apr 14, 2016 #6

    mfb

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    At every point in time, if you know the precise state of the universe, you can determine the state at every earlier and later time - this is a purely theoretical statement, in practice we cannot do that for more than a few particles in an isolated system.
     
  8. Apr 14, 2016 #7
    Can you do that for a few particles in an isolated system such as a neutron decaying into an electron, proton, and neutrino?

    I had thought there was some "indeterminacy" to both the time of decay, as well as the precise momenta (direction and magnitude) of the electron, proton, and neutrino. I was under the impression that the initial states of those particles prior to neutron formation were no longer able to deterministically influence the timing of or the nature of the spontaneous decay, which I have been taught are "probabilistic" or "random" (of course limited to processes which do not violate laws of conservation of physical quantities such as energy and momentum).
     
  9. Apr 14, 2016 #8

    mfb

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    Sure. As long as you stick to quantum mechanics, and don't involve voodoo like wave function collapses, there is no way to say "the neutron decayed" or give specific values for momenta - you can just assign probabilities or similar numbers to it. Note that this system doesn't include anything that would perform a measurement.

    Quantum mechanics is a deterministic theory. In some aspects it is the most deterministic theory possible. Some but not all interpretations are nondeterministic.
     
  10. Apr 14, 2016 #9
    If quantum mechanics is part of the science of predicting and understanding reality, is not the "voodoo" a necessary part of it? If you stick to reality and QM you must connect the two and you can't dispense with the "voodoo"... although I hope we can replace it one day with "knowledge".

    I look forward to when this can properly be understood and defined. For now I think of this as physical "interaction" of sufficient and/or specific character ... so as to cause the "potentialities" to condense to actualities... to the extent of its "sufficiency".

    Would you call a "quantum state" which at time t is neither a neutron (undecayed) nor a disparate set of different particles flying off in different directions, but some indeterminate probabilistic mixture of the two, the product of a "deterministic" theory?


    Interpretation of the theory aside, my question is about whether the physical process of neutron formation and decay preserves information. Not whether a calculation of the unresolved, never actualized probabilities of a shadow of reality is somehow in the abstract, conservative of information.

    In reality the voodoo must and does happen.
     
  11. Apr 14, 2016 #10

    mfb

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    There are interpretations without collapses.
    Check the work on decoherence. This rarely finds its way into textbooks, but there was a lot of progress during the last decades.
    Yes. It is not indeterminate probabilistic if you take a deterministic interpretation.
    Good luck defining "information" in an interpretation-independent way while keeping effects of interpretations in it. Before you do that, the question is not well-defined.
     
  12. Apr 14, 2016 #11
    Can you point me to them? I am quite interested.

    Completely correct. Part of the motivation for the question was to elicit some sort of plausible answer as to what (as they are now being popularly claimed) "information" and "information conservation" actually mean. e.g. Why are black holes claimed to raise a "paradox" regarding "information conservation" when other processes like neutron formation and decay (not to mention "measurement") are not claimed to raise such a paradox?
     
  13. Apr 14, 2016 #12

    mfb

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    As usual, Wikipedia has a list
    Precisely due to the reasons I wrote: Know the state at any time and you can know the state at every time. Black holes could violate this.
     
  14. Apr 14, 2016 #13

    ChrisVer

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    Well, loosely put I'd say that there is no "information" lost during neutron decay...
    Why would it? you clearly have the neutrino,proton and electron at the end; you can [theoretically] measure them at any time. So no information is lost...
     
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