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B Does antimatter fit into the standard model

  1. Nov 2, 2016 #1

    wolram

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    AFAIK antimatter was produced equality in the big bang, and in the matter antimatter fight the matter won .
    Does antimatter react to gravity the same as matter, surly if it does then the antimatter will be annihilated
    due to matter antimatter mixing
    IF matter repels antimatter how did the universe form, or does gravity repel antimatter, if it does then surly
    gravity is a force not just a distortion of space time.
     
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  3. Nov 2, 2016 #2

    Jonathan Scott

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    The process which apparently created the baryons as mostly matter is called baryogenesis, and there is no definite explanation for this, although there are ideas which could account for some imbalance. See the Wikipedia article: https://en.wikipedia.org/wiki/Baryogenesis

    If the initial generation processes created some mixture of both matter and antimatter, then much of it would annihilate into energy until only the excess was left.

    As far as we know, all forms of energy react to gravity in the same way, including not only matter and antimatter but also for example electromagnetic radiation.
     
  4. Nov 2, 2016 #3

    wolram

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    If matter and antimatter feel the same gravitational attraction how come all the antimatter has not been annihilated, or does antimatter exist in voids in the universe as one article i have read suggests.
     
  5. Nov 2, 2016 #4

    Jonathan Scott

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    As far as we know, essentially all antimatter has been annihilated, but small amounts are still being created (paired with normal matter) by extremely energetic radiation processes and similar, especially in the form of electron / positron pairs.
     
  6. Nov 2, 2016 #5
    Geoneutrinos are electron antineutrinos produced by beta decay of U, Th and K-40 in the earth.
     
  7. Nov 2, 2016 #6

    wolram

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    Is it not the opposite, matter antimatter mixing causes extremely energetic radiation, or is that the same thing?
     
  8. Nov 2, 2016 #7

    Jonathan Scott

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    That's the same process in the opposite direction. If matter and antimatter collide, that produces radiation. If electromagnetic radiation of sufficient energy arrives from different directions, the collision can create electron and positron pairs.

    Antiprotons (which are used in the LHC) can be created for example by processes involving firing high-energy protons into other materials, which will sometimes create an additional proton and antiproton pair from the excess energy, after which it is possible to filter out the antiprotons based on their opposite charge using electromagnetic fields.
     
  9. Nov 2, 2016 #8

    Chronos

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    It certainly is a part of the standard model. Anti matter was posited by Paul Dirac in 1928 in this famous paper 'The quantum theory of the electron' for which he received a nobel in 1933 - re: https://timeline.web.cern.ch/timelines/The-story-of-antimatter. Only about 1 ppb of anti matter survived annihilation in the early universe for reasons that are still debated. Few scientists believe, and even fewer observations suggest, large pockets of antimatter survived intact.
     
  10. Nov 2, 2016 #9
    There have been searches for antimatter dominated regions of the universe and we've come up with nothing. On the boundary of matter / antimatter regions, we would see very specific gamma rays and we don't.
     
  11. Nov 3, 2016 #10

    wolram

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    One thing i am not sure about, does antimatter fall down a gravity well or does it fall up, is antimatter confined to places in between galaxies?
     
  12. Nov 3, 2016 #11

    Bandersnatch

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    No, it behaves exactly the same gravitationally. It just has the opposite electric charge.
     
  13. Nov 3, 2016 #12

    Jonathan Scott

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    The scientific consensus is that it must fall the same way as ordinary matter, as in General Relativity everything in motion, including light, follows the shape of space-time. (Photons are their own antiparticles anyway, so they couldn't behave differently).

    There is no sign of any antimatter concentration in places between galaxies, as this would produce characteristic annihilation radiation from interaction with the thin distribution of normal matter in intergalactic space.
     
  14. Nov 3, 2016 #13

    wolram

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    So is antimatter a by product of high energy events.
     
  15. Nov 3, 2016 #14

    Jonathan Scott

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    Most antimatter existing in the universe now (especially positrons) was probably created by high-energy events. Antineutrinos can also be created by lower energy events including radioactive decay.

    On earth, antimatter can be created in tiny quantities by lightning and some forms of radioactive decay. Newly created positrons will normally annihilate soon afterwards with electrons to produce gamma rays.
     
  16. Nov 5, 2016 #15
  17. Nov 7, 2016 #16

    Garth

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  18. Nov 13, 2016 #17
    If a considerable amount of antimatter has been generated by the big bang, it has been annilihated to radiation long ago. Now we do not observe the according high energy radiation. Therefor a mechanism must exist, which has transformed this radiation to lower energies. (E.g. even down to the cosmological background radiation)
    Does the Standard Model include such a mechanism? Where is the according energy now?
    Is it possible, that this mechanism also affects radiation from far distant galaxies? If this is the case, cosmological inflation detected by doppler shift is an illusion.
     
  19. Nov 13, 2016 #18

    Jonathan Scott

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    I presume the annihilation of any excess antimatter would have occurred during and shortly after its creation during baryogenesis, so there would be no separate later annihilation process.

    There's plenty of high-energy radiation around in the universe anyway. The signature of antimatter annihilation between zones of matter and antimatter would be radiation around specific energies corresponding to annihilation reactions, but so far nothing matching the predicted signature has been seen. There are however plenty of cases where characteristic radiation from electron/positron annihilation is seen, especially in the vicinity of jets, but in those cases the positrons are created by high-energy electromagnetic interactions.
     
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