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Additional Emperical Observations of the Sachs-Wolfe Effect?

  1. Aug 8, 2013 #1
    I learned about the Sachs-Wolfe Effect when I was discussing the CMB, since it is a major artifact of it.
    I do have one very basic question: Is the CMB the only place we observe the effect, or do we see it every day in other places?

    I suppose the way to look for it would be to try to place a massive, closer gravitational body (some galaxy) in between a distance source of starlight in question. This might be accomplished by measurements half a year apart, similar to triangulation for near stars, so that the nearer galaxy moves across the background with respect to the more distant starlight.

    I know research like this must have been done, but I don't have access (sadly) to a scientific journal yet, so I can only find references to the CMB when I do internet searches for the SWE.

    Thanks, I very much appreciate your help!
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  3. Aug 10, 2013 #2


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  4. Aug 11, 2013 #3
    Thanks for the links; I actually do understand why the effect exists, and its great that we've observed light blueshifted by Earth's gravitational potential well, but that wasn't the question.

    If you check this link out here http://cmbcorrelations.pbworks.com/w/page/4563978/The late-time integrated Sachs Wolfe effect

    which explains the effect on a large scale, you'll see that eventually light can be either red or blueshifted, depending. Generally I've seen the blue-shifting explained under terms of a changing (by comparison to an earlier time, weaker) gravitational field as "something dark" affects the gravitational well. A photon entering a well will have energy added to it and therefore blueshift. But since the well has been "weakened" (we're dealing with the expansion of the universe, dark matter, dark energy), it does not take as much energy to "fight against" the potential well on its way out, and therefore, ΔE = E_after - E_before > 0. So photons are blueshifted.
    Sometimes. Othertimes, they are redshifted. I've been taught that we observe both redshift and blueshift in the Cosmic Microwave Background Radiation. My original question was: do we observe this grand-scale red/blue shift anywhere else in the Universe, or just in the CMBR? Also, if you could explain the mechanism by which light is redshifted, specifically in the CMBR context, (do we assume the gravitational well grew stronger?) I would appreciate it.

    Again many thanks.
  5. Aug 12, 2013 #4


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    Er, like the redshift of all the galaxies in the Hubble deep field. What else do you need? You really need to read some modern papers instead of science mythology.
  6. Aug 13, 2013 #5
    HDF is redshifted because of the expansion of the Universe, right? Thats why we can use it to see what galaxies look like billions of years ago. Its not ISWE redshift...
  7. Aug 13, 2013 #6


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