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Proton: stable or unstable?

  1. Mar 7, 2004 #1
    Hi

    I've been reading websites about particle physics recently, and in some places they say the proton is stable and others they say it is unstable, with a half life of 10 to the power of 32 years. I know it is the most stable baryon.
    The only possible decay I've read about is a proton decaying into a positron and a photon, which does not conserve baryon number, in which case, how can it have a half life at all? Are there any other possible decays?
    Also, would a proton with a half life of 10 to the power of 32 years be classified as unstable or stable, as my physics teacher argued that this was so long that it would be pretty stable (and also that this was longer than the universe, which I thought physicists hadnt calculated the length of definitively yet).
    This could be a stupid question so sorry if it is.
    Thankyou
    Ellie
     
  2. jcsd
  3. Mar 7, 2004 #2

    selfAdjoint

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    They did an experiment where they observed 10^33 protons for a year, and none of them decayed. Nobody has ever reported seeing a proton decay. Some theories require proton decay after a very long time, but those theories haven't yet made enough correct predictions to become highly plausible.
     
  4. Mar 7, 2004 #3
    The proton is considered stable on time scales much greater than the age of the universe. Experiments like the one mentioned above establish that proton decay (if it happens) is extremely rare. The experiment referred to was carried out at the Super-Kamiokande water detector in Japan (also used for neutrino research). The lower bound for the proton half-life was something like 10^35 years. When you consider that the agreed upon age of the universe is in the 10-15 billion year range, that corresponds to on the order of 10^9 years. That's why the proton is considered a stable particle, though some Grand Unified Theories predict the decay on very long time scales.
     
  5. Mar 8, 2004 #4

    LURCH

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    Doesn't the second law of thermodynamics also require it? A proton has mass and therefroe energy. It constitutes a localised density of energy sarounded by an environment of lesser enrgy density. This is a condition that cannot remain intact forever, according to entropy. The energy contained in a small space must radiate otu into its relatively cold saroundings untill the two achieve equal energy states, mustn't it?
     
  6. Mar 8, 2004 #5
    Well, I don’t know how much I would meddle thermodynamics in that topic, after all it’s statistical model, and it doesn’t consider quantum properties of mass/energy. But theoretically yes.
     
  7. Mar 9, 2004 #6
    Following the same argument, one could also proclaim the electron to be unstabile. Does that follow from any of the unified theories so far?
     
  8. Mar 16, 2004 #7

    chroot

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    Terry and Antonio,

    I split your last posts off into a new thread of the same title in the Theory Development subforum. That is where alternative or personal theories should be posted.

    - Warren
     
  9. Mar 16, 2004 #8
    Who is "Terry and Antonio"?
     
  10. Mar 16, 2004 #9
    There is no any unified theories predicting the decaying of electrons, I think. LURCH's viewpoint is very interesting. Can anyone explain this?
     
  11. Mar 16, 2004 #10

    Nereid

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    Terry Giblin and Antonio Lao. Their posts - one of each - can be found in Theory Development, in a thread called "Proton: stable or unstable"
     
  12. Mar 16, 2004 #11

    Haelfix

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    Assuming conservation of baryon number is a good quantum number in the universe and quarks are subject to confinement, the proton in this ground state can't decay or give off energy. It would be 'stable'.

    Statistical mechanics applies of course, but ask yourself, what else can it decay too? Theres no other mode. Its stuck in that configuration essentially forever.
     
  13. Mar 17, 2004 #12
    Thanks! found it sorta strange as I didn't see there names attached to, or in, any posts in here (this thread).....
     
  14. Mar 17, 2004 #13
    I also have never heard of it. I'd be most interested in hearing more from LURCH's argument.
     
  15. Mar 21, 2004 #14

    chroot

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    MRP:

    I have split off your questions and comments about electrons and generators to a new thread, entitled "Generators and Electrons" in the Theory Development subforum.

    - Warren
     
  16. Mar 25, 2004 #15

    selfAdjoint

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    Jackiw, in his Yang-Mills retrospective says

    ‘tHooft concluded that baryon number is not conserved in the standard
    model. By evaluating the Euclidean functional integral in a Gaussian approximation around
    the instanton solution of Belavin et al., he calculated the baryon lifetime. Fortunately it is
    exponentially small, but diamonds in principle are not forever
     
  17. Mar 26, 2004 #16
    The particle which causes proton decay may be antimatter that decayed in the early universe along with all the other antimatter that's missing.
     
    Last edited: Mar 26, 2004
  18. Mar 26, 2004 #17
    Proton decay is a prediction of the grand unified theories. These are theories that attempt to unify the electroweak force and the strong force of particles and fields in quantum field theories. These theories assert that since quarks are heavier than leptons, quarks should ultimately decay into leptons. The theories have nothing to say about the involvement of antimatter.

    The mystery of the asymmetry of matter-antimatter remains to be resolved. At the present time, no such a theory of resolution exist.
     
  19. Mar 26, 2004 #18
    The mystery of the asymmetry of matter-antimatter remains to be resolved. At the present time, no such a theory of resolution exist.

    What if matter and antimatter have slightly different masses which in the conditions of the big bang meant that antimatter was split into tiny fragments which fill all of space whereas matter survived.
     
  20. Mar 26, 2004 #19
    I think that would violate the CPT-theorem.... That would be bad news.
     
  21. Mar 26, 2004 #20
    In order not to violate the CPT Theorem, the antimatter must be found dominantly in a universe by themselves and this anti-universe is connected to ours at various time-zero points which we call the vacuum. The phenomena of vacuum fluctuation is a direct proof that this is what is actually happening.
     
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