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I Ratio of abundance of sub-atomic particles in the universe?

  1. Mar 14, 2016 #1
    I was wondering if there is a current hypothesis about the quantities of which matter particles were created?
    I'm not completely au fait with the standard model, but I've seen the picture:
    https://upload.wikimedia.org/wikipe...tandard_Model_of_Elementary_Particles.svg.png

    And when I was at HS I always wondered if it was a property of the universe that matter was made like 'one electron for every proton'? (Sort of thing)

    So is there any theory regarding the ratios of abundance of those sub-atomic particles in the universe (including dark matter) ?

    Thanks
     
  2. jcsd
  3. Mar 14, 2016 #2

    mfb

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    The universe has a net charge of (approximately?) zero. As proton and electron are the only stable or long-living particles, there are about as many protons as there are electrons in the universe.
    To a good approximation, baryonic matter is 75% hydrogen-1 and 25% helium-4 by mass, which means we have a ratio of about 7 protons to 7 electrons to 1 neutron. And keeping that scale, we have to add about 15 billion photons, roughly 10 billion neutrinos and an unknown number of dark matter particles (their energy density is well-known, but their mass per particle is not). Everything else is negligible.

    The latter two numbers are from cosmological observations (and conversion of the energy density to particle densities).
     
  4. Mar 15, 2016 #3
    Thanks for that really good answer. Ok so a net charge of approximately zero.

    So does current theory permit dark matter to be comprised of some already sort of identified standard model particles? (just like exotic forms)

    What about photons, is there any limit to the 'number' of photons created? like conceivably was it just matter that was created "IN THE BEGINNING"? And photons are just generated from taking energy from the matter?

    Thanks again
     
  5. Mar 15, 2016 #4

    mfb

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    There are a few exotic models, but they all don't work well.
    There is no limit, but we know the density of photons.
    As far back as we can trust our theories, there were always photons and matter at the same time. And all the other elementary particles as well.
     
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