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

Static CMBR ?

  1. May 13, 2004 #1
    To what extent does the CMBR vary over time ? If I have understood it correctly the intensity variations in http://lambda.gsfc.nasa.gov/product/cobe/cobe_images/cmb_fluctuations_big.gif, are due to the fact that some of this energy turned into matter in the early universe. So in a sense, the CMBR displays what the early universe looked like, correct ? .. roughly anyway ... :smile:

    If this is true, then this intensity distribution should be pretty static, right ? So if this sort of map is produced again in a couple of years, it should look basically the same, am I right ? Has this comparison already been made perhaps ?
    Last edited by a moderator: Apr 20, 2017
  2. jcsd
  3. May 13, 2004 #2


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    I believe you are right. The pattern of hot and cold spots should not change even over thousands of years.

    the overall average temperature (around 2.7 kelvin) is gradually cooling as the universe expands

    since the radiation was released it has cooled by an estimated factor of 1100 from around 3000 kelvin to the present 2.7 kelvin
    so, in this limited sense, the CMB is changing-----if we could wait a very very long time we would see it cool slightly
    but the pattern of variation from the average (the hot and cold spots) would not be expected to change even as the average declines

    BTW these maps showing variations of a few millikelvin around the average
    already have the effects of the observer's motion factored out.
    secular changes in the observer's motion would affect the CMB which is actually seen, over time (e.g. as the direction the sun is traveling in the galaxy changes) but that's been compensated for so it doesnt really count
  4. May 13, 2004 #3
    Thanx marcus..

    So if this comparison hasn't been done yet, when are we likely to see one ?
  5. May 13, 2004 #4


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    A comparison over time has been implicitly in progress since COBE in the 1990s and now with WMAP

    every year we get more data
    there is never any sign of a change
    the map just gets more and more refined

    the face of the CMB, in that map,
    is eternal

    it is like the Sistine Chapel ceiling that Michelangelo painted
    except even more permanent---well you think of a better image.
    it is more permanent than any other image I can think of

    It is not really correct to say "a comparison has not been done yet"
    since there has been continuous observation over quite a few years
    and any change would have been noticed

    only there is this very slow cooling, which is much too slow for any
    instrument to detect, coming from the very slow expansion of the universe
    Last edited: May 13, 2004
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook