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Why isn't there Cosmic Visible Background Radiation from gamma rays?

  1. Jun 1, 2013 #1
    If what used to be visible light when the universe was smaller and younger has been stretched due to the Doppler effect so that it is now microwaves and detectable as the Cosmic Microwave Background Radiation that can be found everywhere, why hasn't the gamma or x-rays of the same period not been stretched into the visible light range and also found everywhere?

    This occurred to me watching about Olbers' paradox and I couldn't find any information on it.

    Thanks for any help.
     
    Last edited by a moderator: Sep 25, 2014
  2. jcsd
  3. Jun 1, 2013 #2
    I can't specifically answer your question [which is a good one] but I think it has to do with the characteristics of the 'recombination era'.....and photon decoupling.....how photons interact with ionized hydrogen gas.....
    I'm guessing the higher energy radiation was absorbed in the post big bang plasma....thermal radiation seems to have made it through after ionization was reduced....

    you can get some insights here:
    http://en.wikipedia.org/wiki/Recombination_(cosmology [Broken])

    Hopefully, someone will have more specifics...
     
    Last edited by a moderator: May 6, 2017
  4. Jun 1, 2013 #3

    Vanadium 50

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    They have. There's just not enough of them to see.
     
  5. Jun 1, 2013 #4
    Thank you both. Just read about recombination, very interesting. I have a question for Vanadium 50: Is this a theoretical answer or can sensitive instruments find visible cosmic background radiation?
     
  6. Jun 1, 2013 #5

    George Jones

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    CMB accounts for 1 % of

    http://zuserver2.star.ucl.ac.uk/~hiranya/Hiranya/Hiranya_Peiris.html [Broken]
     
    Last edited by a moderator: May 6, 2017
  7. Jun 2, 2013 #6
    I appreciate what you're saying, George, but the link is still talking about microwave radiation, which I am not talking about, so it's not really pertinent to the discussion.
     
  8. Jun 2, 2013 #7

    timmdeeg

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    When the cosmic background radiation was emitted, the matter was very close to thermal equilibrium.

    Gamma-rays are originating from high energy processes e.g. caused much later by neutron stars and black holes. As it happens to any radiation the wavelength of gamma rays increases due to the expansion of the universe.
     
  9. Jun 2, 2013 #8

    Chalnoth

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    Before the CMB was emitted, the universe was opaque, and such high-energy photons would have bounced around many, many times, distributing their high energy among many particles. This is basically the same reason why our Sun doesn't put out a lot of gamma rays, despite it having a monstrous nuclear fusion reaction going on in its core: it's made of the same form of matter as the early universe (a plasma).

    Most of the higher-energy radiation from the Sun is actually produced at the surface. There were no physics like that occurring as the CMB was emitted (the cooling of the CMB from a plasma to a gas was a relatively gentle affair).
     
  10. Jun 2, 2013 #9

    Vanadium 50

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    On earth this is hundreds of magnitudes darker than the night sky. In space, maybe you see a photon, but how do you know it's not from a galaxy too far away to resolve?

    No, it's just not bright enough.
     
  11. Jun 2, 2013 #10

    Vanadium 50

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    On earth this is hundreds of magnitudes darker than the night sky. In space, maybe you see a photon, but how do you know it's not from a galaxy too far away to resolve?

    No, it's just not bright enough.
     
  12. Jun 4, 2013 #11

    Chronos

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    The CMB has a nearly perfect blackbody spectrum that peaked at about 3000K when emitted. You need only look at the theoretical emission spectrum for a 3000K black body to realize there are hardly any photons at gamma ray intensity.
     
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