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

Cmb questions

  1. Feb 1, 2009 #1
    I was looking at a map of the cosmic microwave background, and began wondering if the cmb would look the same from another vantage point, perhaps Pluto, or a nearby star. Or what about if it were seen from another galaxy? And, in a related question, does the cmb evolve with time?

    I suppose no one knows. But has anyone done any speculation along these lines?

  2. jcsd
  3. Feb 1, 2009 #2
    it looks different from different locations of the Universe, but it order to have a different view you need to fly far away... Pluto, any nearby star or even Andromeda Galaxy are too close. You need to cross a significant part of the viible universe to see the difference.

    From the same location, the picture becomes redder and redder and the picture slowly changes too.
  4. Feb 1, 2009 #3


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    The change in perspective would be too slight to make a detectable difference.
    Even if you could jump to a nearby galaxy say 1 million LY away, it would still look the same.

    Also there is time evolution but it is too slow for us to detect on a human-lifetime scale.

    I should give some explanation so that it won't just be a flat assertion on my part. I don't know how much explanation you want though. The basic thing about perspective is that when we look at CMB we are observing matter which is in a spherical shell around us with radius 46 billion LY.

    The detectable variations in temp, the blotches, are over scales of 10 million to a billion LY.
    My hunch is that we'd need to jump to a vantage point some 10 million LY from here in order to get a noticeably different CMB skymap. Someone else may perhaps be able to refine that rough estimate.

    As time goes on the spherical shell gets larger and it has a different slice of matter on it. The radius of the surface-of-last-scattering increases faster than just ordinary Hubblerate expansion. So it encompasses a fresh slice of matter, and maybe after 10 million years that matter would be sufficiently different to have detectable different blotches. So there would be time evolution, but on too slow a scale for us as we currently think.
  5. Feb 1, 2009 #4
    thanks, Marcus and Dmitry67.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook