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Could light explain dark energy?

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  1. May 8, 2014 #1
    Could the momentum of light explain the effect known as "dark energy"? I know the distances between galaxies are wast, but so are the surface areas of galaxies, as well as all the stars emitting the light. Would be interesting to see a calculation of the fate of the universe if this was true, perhaps gravity would pull everything together again after the stars burnt out, and we'd have a cycle of big bangs. Any thoughts?
     
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  3. May 8, 2014 #2

    mfb

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    No. Energy and momentum of light in the universe are well-known (because we can see it) and they are a small positive (=attractive) contribution to the total energy-density.

    Please note that we don't allow wild speculations beyond actual physics here.
     
  4. May 8, 2014 #3

    Matterwave

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    Most of the light energy in the universe is actually contained within the CMBR, and not from the light radiated by the stars! Even then, the CMBR accounts for only a tiny fraction of the total energy density of the universe today. Also, as mfb stated, this effect is well accounted for and would produce a deceleration in the expansion of the universe, not an acceleration.
     
  5. May 8, 2014 #4

    Bill_K

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    Do you have a number for this?
     
  6. May 8, 2014 #5
    [itex][/itex]the energy-density today can be calculated. Here is one method of estimating the energy-density today, though the paper calculates the energy density of photons as well as radiation

    http://astro.dur.ac.uk/~csf/level1/Cosmich/lecture_7-8_notes.pdf

    this paper has roughly the same energy-density for photons.

    [tex]\Omega_\gamma\approx5*10^{-5}[/tex]
    variations occur in rounding, method used etc.

    http://iopscience.iop.org/1742-6596/354/1/012009/pdf/1742-6596_354_1_012009.pdf

    I've read numerous textbooks, articles etc that all have variations in the energy-density, though they are all close the the value I posted
     
    Last edited: May 8, 2014
  7. May 8, 2014 #6

    Matterwave

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    Mordred provided them. :)

    His number is the one I'm familiar with. If you wanted actual numbers with actual units, using ##\rho_{crit}\approx\rho_0=9\times 10^{-10}J/m^3## we get ##\rho_\gamma\approx 5\times 10^{-14}J/m^3##
     
  8. May 10, 2014 #7

    mfb

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    From the cosmic energy inventory:
    10-4.3 or 5*10-5 for CMB
    10-5.8 or 1.5*10-6 for "optical" light, and just a bit more for non-CMB light in general
    Those numbers are relative to the critical density, where dark matter has ~.23 and dark energy ~.72.
     
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