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Thread: Antimatter collisions

  1. #1
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    Antimatter collisions

    This may not be a really simple question to answer, but I wonder if anyone can explain why it is that protons and electrons generally don't collide, despite their charges (and I think it's because of the Heisenberg principle, though I'm not exactly sure how it works), whereas electrons and positrons will collide. Is it just a function of their masses, or is there some fundamental difference, like spin or something like that?
    As above, so below

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    As a very layman's guess, I'd expect they do, but since they need a neutrino in order to make a neutron, they won't actually interact much when it happens, whereas an electron and positron don't need anything else to interact so will do so happily end energetically.
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  3. #3
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    This is not a guess, but a handwavy, intuition-based
    layman's description, using backward logic:

    Combining a proton and an electron together would result
    in a neutron.

    Neutrons are unstable, with a half-life of about 15 minutes.
    They naturally and spontaneously fall apart into a proton,
    an electon, and an electron antineutrino.

    So you are asking why two things which normally fall apart
    spontaneously when they start out stuck together don't
    spontaneously stick together when they start out apart.

    They do stick together -- they just don't stick together all
    that well. They tend to fall apart fairly quickly.

    (It has something to do with the Weak Force. What, I
    don't know.)

    ETA:

    I just noticed that I replied about sticking together, while
    you asked about collisions. Nothing stops protons and
    electrons from colliding. It does take a relatively large
    amount of energy to get them to collide. That energy is
    the source of the antineutrino. The antineutrino from a
    decaying neutron carries off extra energy that the neutron
    has that a separate proton and electron don't have.

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    If by collide you mean annihilate then it is simple - only antiparticles can annihilate a particle to avoid non-conservation of quantum numbers. For example an electron and proton annihilating would mess up lepton number conservation (before you have a lepton afterwards you don't), as well as a host of others. An electron and a position annihilating doesn't have that problem since before you have 0 total lepton number (1 + -1) and after you have 0 total lepton number (just some photons which are bosons).

    Protons and electrons do collide - they just don't annihilate.

    Edit: Look up positronium - that is an electron and positron orbiting each other. They can do it but because there is a lower energy state (kablooie) then they naturally decay to it. And electron/proton system has no such allowable lower energy state to decay into

  5. #5
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    One lepton cant take out three quarks.

    Technically, this is what Shaula just said.

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    Quote Originally Posted by Jens View Post
    This may not be a really simple question to answer, but I wonder if anyone can explain why it is that protons and electrons generally don't collide, despite their charges (and I think it's because of the Heisenberg principle, though I'm not exactly sure how it works), whereas electrons and positrons will collide. Is it just a function of their masses, or is there some fundamental difference, like spin or something like that?
    Jens. Particle confinement is indeed in HUP,look at the bottom of the scroll down. The energy to confine an electron in the nucleus far exceeds the energy required to blow it apart ~ 10-20 Mev per nucleon.SEE http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

    as far as the electron adding to the proton, the electron-type antineutrino must be added at the same time, to make a neutron and conserve all the laws involved,and this process is endothermic not exothermic. It can happen in supernovae core collapses, as the gravitational binding energy supplies the punch.

  7. #7
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    Quote Originally Posted by Jens View Post
    This may not be a really simple question to answer, but I wonder if anyone can explain why it is that protons and electrons generally don't collide, despite their charges (and I think it's because of the Heisenberg principle, though I'm not exactly sure how it works), whereas electrons and positrons will collide. Is it just a function of their masses, or is there some fundamental difference, like spin or something like that?
    Three answers to the first part of your question here:
    Why don't the proton and the electron in a hydrogen atom collapse?

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