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Could light explain dark energy? 
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#1
May814, 09:17 AM

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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?



#2
May814, 11:11 AM

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Please note that we don't allow wild speculations beyond actual physics here. 


#3
May814, 01:37 PM

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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
May814, 03:16 PM

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Could light explain dark energy?



#5
May814, 04:27 PM

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[itex][/itex]the energydensity today can be calculated. Here is one method of estimating the energydensity today, though the paper calculates the energy density of photons as well as radiation
http://astro.dur.ac.uk/~csf/level1/C..._78_notes.pdf this paper has roughly the same energydensity for photons. [tex]\Omega_\gamma\approx5*10^{5}[/tex] variations occur in rounding, method used etc. http://iopscience.iop.org/17426596/...4_1_012009.pdf I've read numerous textbooks, articles etc that all have variations in the energydensity, though they are all close the the value I posted 


#6
May814, 05:19 PM

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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
May1014, 11:09 AM

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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 nonCMB light in general Those numbers are relative to the critical density, where dark matter has ~.23 and dark energy ~.72. 


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