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Why annihilation of matter/antimatter occurs in dual pairs?

  1. Jul 18, 2013 #1
    Just a question. A particle and a corresponding antiparticle (e.g. electron and positron) can annihilate by mutual interaction, producing energy (photons).

    If the process of mutual annihilation occurs necessarily between particles and antiparticles (matter and antimatter), we would expect that - for example - an electron and an antiproton could suffer this process. However, they don't. We know that the annihilation process occurs between particles/antiparticles of the same family - in some way, we could say 'between a dual pair' (particle and corresponding antiparticle).

    However, this restriction seems to me very weak; I don't glimpse a convincing law, neither a "strong physical support" for this. The mere division (classification) of the elementary particles by their strongly abstract properties (spin, isospin, strangeness, etc.) seems to be more properly a rule than a very "touchable" reality. Then, the above restriction seems to be incomplete: I feel a lack of supporting information.

    This is the question: what is the "strong reason" for particle-antiparticle annihilations occur only between dual?
     
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  3. Jul 19, 2013 #2

    Simon Bridge

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    Why?

    What would it take for the law to be "convincing" for you - it seems to convince everyone else? The classification is a "touchable reality" - it is empirically determined. You can touch it.

    Particle anti-particle pairs were predicted by the "Dirac equation" and is an expression of a fundamental symmetry in the Universe which turns out to be well described by the equation. Particles have antiparticles that look like them in the same way that objects have mirror images that look like them.
     
  4. Jul 19, 2013 #3
    Hello,

    The rules of annihilation are no different to any other possible interaction.

    These are things that we have observed. I.e. how the particles interact has developed our theory. Such things are, conservation of charge. Conservation of colour quantum number.conservation of energy-momentum etc.

    It is that nature chooses what happens. We try to describe it the best we can.

    Some of these laws seem to make sense from a symmetry point of view. But there are lots of others, such as the amount of misalignment of the flavour sector which to me 'just are'. Of course there are still many things not understood.

    However, creation and annihilation is well tested from collider experiments.
     
  5. Jul 19, 2013 #4

    jtbell

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    Physics is about rules that we can test experimentally, not about "reality." If we ever find the "true reality" of elementary particles, how would we know it?
     
  6. Jul 19, 2013 #5

    ZapperZ

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    You will notice here that in your post, your objection is not based on any empirical evidence, or logical inconsistencies. Rather, it was based on a MATTER OF TASTE. You statied it because you FEEL "a lack of supporting information", or that it is ".. a rule than a very touchable reality" (whatever that means).

    Luckily, physics isn't based on anyone's feelings of comfort and warm fuzziness, or your preference on your favorite color.

    Zz.
     
  7. Jul 19, 2013 #6

    Dale

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    Conservation is the strong reason.

    The specific reaction you suggest would not conserve charge. Both an electron and an antiproton have negative charge, and photons have no charge, so the charge after would be greater than the charge before.

    I am not certain, but I also think that it would probably could not conserve energy and momentum.
     
  8. Jul 19, 2013 #7
    Hello everybody and thank you for your comments!
    In fact, my argumentation was essentially subjective. The intention was to consider new possibilities -to consider what was not previously considered, only by speculation. I mean that a colleague interpreted incorrectly my intention.
    Regards to all
     
  9. Jul 19, 2013 #8

    Nugatory

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    Nor lepton number, nor quark/baryon number...
    (Weirdly, energy and momentum don't have to be a problem; electron-positron pair creation for example uses a nearby heavy nucleus to dump the "excess" momentum).

    However, I'm finding myself more comfortable with RGauld's formulation: "... Nature chooses what happens. We try to describe it the best we can." The universe isn't the way it is because of the conservation laws; the conservation laws are the way they are because they describe the way the universe is.
     
  10. Jul 19, 2013 #9

    Of course. Sorry, I cited a bad example - electric charge is not conserved for electron-antiproton.
    And if we look for a "truly convenient pair", we will find always restrictions based on charge conservation (any charge). Then, any particle-antiparticle annihilation is prohibited. Case closed.

    But... if we consider that the outcome of the annihilation has not only photons (zero charge) but other balancing particles?
     
  11. Jul 19, 2013 #10

    Dale

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    Certainly, those reactions can occur, but they are not called "annihilation" if something other than photons are produced.
     
  12. Jul 19, 2013 #11

    sophiecentaur

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    . . . . and other interactions are just called . . . . 'interactions'. (reasonably, imo.)
     
  13. Jul 19, 2013 #12

    Bill_K

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    From Wikipedia:
     
  14. Jul 19, 2013 #13

    ZapperZ

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    Before you continue with your "speculation", please re-read the PF Rules that you had agreed to. If you wish to work out your own speculation on this forum, then you've found the wrong forum.

    Since you have admitted that this is purely subjective and essentially, a matter of personal tastes, then this is no longer physics, but a fashion show. This topic is now closed.

    Zz.
     
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