Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The source of cosmic background radiation

  1. Jan 10, 2012 #1
    All stars and Galaxies appear to give off the whole spectrum of electromagnetic radiation.
    If one views images of the distribution of background radiation in detail it appears to be filimetary in nature. Also if one views the distribution of visible matter in the universe it also appears filimetary in nature, it looks as though one could super impose one on top of the other.
    Why do we think that background radiation is radiation left over from the big bang and not just the radiation from all of the visible matter in the universe.
     
  2. jcsd
  3. Jan 10, 2012 #2

    BillSaltLake

    User Avatar
    Gold Member

    The number of photons created by light matter (which by the way were generated after the CMB was aleady in existence) is several orders of magnitude less than the number of CMB photons. Thus, these light matter photons cannot account for the observed number of CMB photons.
     
  4. Jan 10, 2012 #3

    Nabeshin

    User Avatar
    Science Advisor

  5. Jan 11, 2012 #4

    Chalnoth

    User Avatar
    Science Advisor

    No, it's not filimentary at all. And it's even worse for this view than a naive glance at the picture Nabeshin posted would imply: that image is not the temperature, but the difference in temperature from the average. The average temperature is 2.7K. Those little differences are 100,000 times smaller than the average. The CMB isn't filimentary: it's extremely uniform.
     
  6. Jan 11, 2012 #5

    Chronos

    User Avatar
    Science Advisor
    Gold Member

    It would not be a perfect black body spectrum.
     
  7. Jan 11, 2012 #6

    BillSaltLake

    User Avatar
    Gold Member

    That's another point: the average energy per photon from light matter (locally) is several tens of eV (about 1000x that of the CMB, and CMB photons are in fact local), yet the number density of light photons is lower than the CMB number density.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook