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For the sake of understanding mass and radiation interaction, I hope somebody could explain how this hypothetical situation would look. I want to exaggerate the amount of photons, assuming that there is some correlation between amount of photons in the void and how large objects interact.

Hypothetical sitation: A spiral galaxy is subjected to such high levels of cosmic background radiation, that the gravity from radiation throughout the volume of the galaxy was equal to gravity originating from the mass of that galaxy. I.e. here is a somewhat isotropic, dense distribution of photons in the galaxy.

How would that galaxy behave, when seen from earth? Would it spin faster, or slower? Would gravitation between planets and their star appear weaker/stronger?

Would it be stretched, compressed, redshifted, blueshifted if we were observing it from a region of space where background radiation were much lower?

PS: This is question is not about the time immediately after the big bang, although one can of course agree that this is the only time in history that cbr was near the levels I am talking about.

Qmechanic
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frodeborli
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  • I see where I am being misunderstood. The second paragraph describes my hypothetical situation. I just want to understand how photons affect galaxy movement, by exaggerating he amount of photons. I will try to rephrase. – frodeborli Feb 13 '16 at 14:01
  • Related to the aspect of forming radiation affecting galaxies: http://physics.stackexchange.com/q/149976/ (in this case, a black hole jet appears to be inducing star formation in a galaxy near the BH, rather than the CMB affecting rotations). – Kyle Kanos Feb 13 '16 at 14:19
  • Also, at 13.2 Gly from earth, the amount of photons probably is significant with a much higher density than 1:689. – frodeborli Feb 13 '16 at 14:31
  • @KyleKanos then you for that link, it seems very related to what I am asking. I'd like to know how trajectories of objects in such a galaxy are a affected. If that happened to the milky way, would it affect the orbits of planets surrounding the sun? How? – frodeborli Feb 13 '16 at 14:54
  • That is a question to which I don't really have an answer for. Off the cuff, I'd suspect that given the density of the jet, density of the target galaxy & small size of particles, it really wouldn't affect the target galaxy's dynamics. – Kyle Kanos Feb 13 '16 at 14:57
  • @KyleKanos It would not affect the dynamics of the target galaxy, regardless of the density of the jet? – frodeborli Feb 14 '16 at 23:59
  • Well the densities we're talking about range $\in(10^2,,10^6),{\rm cm}^{-3}$ with velocities of $v\sim c$, so the energy of the particles is kinda small with respect to the energy of the orbiting stars of the target galaxy. – Kyle Kanos Feb 15 '16 at 14:00
  • @KyleKanos I understand. So even though the volume of empty space is enormous compared to orbiting stars, the energy of photons in this space is negligible - even when a black hole jet is energizing/filling this empty space with photons/plasma. I would not have guessed that. – frodeborli Feb 15 '16 at 16:13

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Have a look at this history of the universe, according to the current model:

big bang

The Cosmic Microwave Background radiation decoupled 380,000 years from the Big Bang, before galaxies formed. It starts at temperatures of 3000 K to be compared with the sun which has a black body temperature of ~5000K. So already, even before the evolution into galaxies, during the time neutral hydrogen forms, the temperatures are not equal to stellar temperatures.

The energy of the CMB falls as time progresses to the right. By the time galaxies form the CMB has degraded a lot and the scenario you envisage is not possible. At present the black body temperature of the CMB is the cold 2.725 K.

To see it differently, when the photon energies are equal to the energies of nucleons, electrons etc before 380,000 years, the energy of the photons is large enough to contribute to gravitational effects, but there are no galaxies. By the time galaxies form the photon energy has deteriorated by the expansion and its gravitational contribution is very small.

Glorfindel
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anna v
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  • Yes, but I am asking about a hypothetical situation, and not about the big bang. – frodeborli Feb 13 '16 at 14:11
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    In the hypothetical situation the physics would be the physics of the time neutral hydrogen forms, and before, in the picture above , and no galaxies would exist at those energy densities. You are talking about CMB after all. The energy that becomes galaxies is diffuse when the EM radiation energy is of the order of magnitude of the mass energies, is what I am saying. Not stars or galaxies. – anna v Feb 13 '16 at 14:13
  • Assume somebody turns on billions of giant flashlights surrounding the Andromeda galaxy, capable of flooding it with photons - so many photons that energy/gravity of the photons became significant but mostly isotropic. How would objects in the Andromeda galaxy move, as seen from earth. – frodeborli Feb 13 '16 at 14:27