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Do elementary particles know how old they are?

  1. Jul 18, 2010 #1

    I am interested if there is yet a theory that states or has relationships that can be interpreted as stating the age of an elemetary particle. For example, if a neutron just sits around (unbounded) passing the time, does it know that it is not allowed to survive a certain age?

    This question is triggered by a line I read (in an elementary particles physics book or maybe quantum theory book and it seemed like a personal comment of the author, not a scientific trend) saying something like "neutrons do not know how old they are". I can't remember what book it was in. Does this seem familiar to anybody?

    Any kind of help is appreciated
  2. jcsd
  3. Jul 18, 2010 #2


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    Staff Emeritus
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    Elementary particles do not 'know' - as we define knowledge.

    Protons and electrons have ostensibly been around forever. A free neutron is much less likely to have been around for as long as a proton or electron, since free neutrons decay with a half-life of approximately 10.23 min. Half life though is a statistical concept based on a population of particles or radionuclides, which decay. Not all particles/nuclei decay during the same period - about half survive the first half-life, a quarter of the original the second half life, and so on.

    A free neutron could survive for 1, 2, . . . , 10, . . . 20, . . . , 30, . . . half-lives. However, the probability of survival decreases with time.

    Neutrons in a nucleus could have been around forever.
  4. Jul 18, 2010 #3
    I have a neutron in my left toe that has been around untainted since the BB. Honest!

    That aside: tleilax, particles don't have some mechanism or sense of apoptosis like animal cells, as Astronuc says, it's just a matter of odds.
  5. Jul 18, 2010 #4
    I know that the accepted view is what you guys said. And I am not saying that neutrons have souls, but "just odds" is not enough for me. I was just wondering if there was some underlying physics I missed.
  6. Jul 18, 2010 #5
    What would be a cause of decay other than odds?
  7. Jul 18, 2010 #6
    it's odds accordig to the beautiful mathematics of quantum mechanics and the fact that they actually do fit experimental data:)

    but there were people before that did not agree to dynamics based on dice throwing and I am wondering if some of the newer theories discuss concepts related to what might be called "rest frame knowledge of age"
  8. Jul 18, 2010 #7


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    The exponential decay law can be derived from the assumption that all particles of a particular type have a fixed probability of decaying during a unit of time, regardless of their age. For example, a free neutron has a probability of 0.113% of decaying during the next second, provided that it still exists at the start of that second.

    Therefore, when considering particle decays, it is not necessary for the particle to "know" how old it is. Maybe it really does, but as far as we know, it doesn't make any difference for anything we can observe.
  9. Jul 18, 2010 #8
    Would it be wrong to answer the title of this thread with, "A cesium clock."? :biggrin:
  10. Jul 19, 2010 #9
    Thank you jtbell, what you are saying makes sense at some level and it is important that you said that we cannot discriminate observationally in this issue. But, as Feynman said, we still do not know the rules of chess.

    Thank you all for taking the time to answer. I'll be in touch if I find something else:)
  11. Jul 19, 2010 #10
    I was going to say they don't know their ages, but they do know the dates of their next birthdays.
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