Could light explain dark energy?

[FrodeM]

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?

 

[mfb]

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.

 

[Matterwave]

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.

 

[Bill_K]

the CMBR accounts for only a tiny fraction of the total energy density of the universe today.

Do you have a number for this?

 

[Mordred]

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.

\Omega_\gamma\approx5*10^{-5}
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

 

[Matterwave]

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 $\rho_\gamma\approx 5\times 10^{-14}J/m^3$

 

[mfb]

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.