Could light explain dark energy?

  • #1
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Main Question or Discussion Point

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?
 

Answers and Replies

  • #2
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Could the momentum of light explain the effect known as "dark energy"?
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.
 
  • #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.
 
  • #4
Bill_K
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the CMBR accounts for only a tiny fraction of the total energy density of the universe today.
Do you have a number for this?
 
  • #5
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[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
 
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  • #6
Matterwave
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Do you have a number for this?
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##
 
  • #7
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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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