Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Universe with only e+ , e- , photons, and gravitation?

  1. Dec 7, 2011 #1
    Universe with only "e+", "e-", photons, and gravitation?

    In theory could we have a universe with only electrically charged spin 1/2 particles and antiparticles of mass m and electrical charge e and that interacted only gravitationally and electromagnetically?

    If so could we fine tune things so that such a universe was long lived and closed?

    In the early phase of such a universe would there be roughly twice the energy density in the fields of the charged particles as in the electromagnetic field?

    Thanks for any help!
     
  2. jcsd
  3. Dec 7, 2011 #2

    qsa

    User Avatar

    Re: Universe with only "e+", "e-", photons, and gravitation?

    maybe this is a bit linked to my thread "what is strong gravity". but what is your idea.
     
  4. Dec 7, 2011 #3
    Re: Universe with only "e+", "e-", photons, and gravitation?

    I'm thinking (I hope %^) that the answer to my first question is yes. If we get some deeper "Theory of Everything" then I'm guessing the answer to my first question might go either way.
     
  5. Dec 7, 2011 #4
    Re: Universe with only "e+", "e-", photons, and gravitation?

    Odd questions... Certainly you could write down a Lagrangian for quantum electrodynamics (with just one species of particle, as you describe) coupled to gravity, and you could calculate what this Lagrangian predicts in certain limits. You could also figure out the cosmology for such a universe, by imitating all the calculations performed in conventional cosmology, e.g. thermodynamics of the early universe. But your fictitious universe will be a lot simpler than the real one, e.g. it contains no atoms.
     
  6. Dec 7, 2011 #5
    Re: Universe with only "e+", "e-", photons, and gravitation?

    We would still have positronium %^)

    And if we made the mass m greater and e smaller then positronium might last long enough for more complicated temporary "atoms"? Under the right conditions two positively charged particles might be temporarily bound to two negatively charged anti-particles?

    Thanks for your replies!
     
  7. Dec 7, 2011 #6

    qsa

    User Avatar

    Re: Universe with only "e+", "e-", photons, and gravitation?

    Even standerd physics says only electrons exist. Protons are composites. But no agreed on confinment theory exists as far as i know. Almost all others have short life and are produced as part of interaction.
     
  8. Dec 8, 2011 #7
    Re: Universe with only "e+", "e-", photons, and gravitation?

    So I will take that as a yes, thank you %^)

    The follow up question relates to String Theory. Is String Theory "flexible" enough so that it could also include such a simple universe? If so wouldn't such a toy model be easier to solve then trying include all fields?

    Thanks for any help!
     
  9. Dec 8, 2011 #8
    Re: Universe with only "e+", "e-", photons, and gravitation?

    http://arxiv.org/abs/hep-th/0403247 contains a string theory model for quantum electrodynamics in four dimensions. It's Type IIB string theory with a space-filling D9-brane and another space-filling anti-D9-brane, and then you have a "probe" D3-brane interacting with that background. See table 2 and the bottom of page 5 for where the photon and electron come from.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook