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Proportion of dark energy and dark matter

  1. Jan 19, 2010 #1
    Dark energy is observed to constitute about 72% of the mass density of the universe, dark matter about 23%, and regular matter about 5%. Is this proportion always like this or does it change over time? If it does change, how does one reconcile it with the requirement that the cosmological constant requires dark energy to have a constant energy density?
  2. jcsd
  3. Jan 19, 2010 #2
    As I understand, when Universe expands, density of DM and ordinary matter decreases
    DE density is the same or even increases (the Big Rip scenario)
  4. Jan 19, 2010 #3
    Hello Ranku

    This document gives an idea of the past and future distributions of regular matter, dark matter & dark energy (page 5)-

    http://preposterousuniverse.com/writings/skytel-mar05.pdf [Broken]

    Copy attached.

    Attached Files:

    Last edited by a moderator: May 4, 2017
  5. Jan 19, 2010 #4


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    I agree with Dmitry. Only I don't think very much about the big rip scenarios.
    So far I believe the observational data has been consistent with the dark energy density being constant.
    Roughly something around 0.65 nanojoule per cubic meter.
    The same everywhere and constant through time.

    This would be consistent with having a positive cosmological constant Lambda. That assumption gives rise to the standard mainstream cosmological model: LCDM. The L stands for Lambda.

    But one cannot be 100% sure! Maybe the dark energy is not exactly constant. Maybe it is very slowly changing and we just have not yet seen this in the data. I personally don't spend much time thinking about this but the possibility is studied in the NASA reports on the 5th year WMAP data. It has not yet been ruled out.

    Because dark matter thins out, on average, along with ordinary matter, the standard LCDM model predicts that in the far far distant future the makeup of the universe will be nearly 0% matter and over 99% dark energy. This will not be big rip. We will still have our galaxy and our solar system pretty much as usual. But there won't be much in the way of other galaxies around, and the stars will not be so good and it may get cold.

    There is an article about what can be expected, by cosmologist Lawrence Krauss. He describes what will happen according to the LCDM model. You might like it. He is reputable and a good writer.
  6. Jan 20, 2010 #5
    The link doesn't work. Is the article by Sean Carroll? Could you check the link and repaste it please?
    Last edited by a moderator: May 4, 2017
  7. Jan 20, 2010 #6


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    The link works for me. The reference is
    • Sean Carroll (2005) http://preposterousuniverse.com/writings/skytel-mar05.pdf [Broken], in Sky & Telescope, Mar 2005, pp 32-39.

    Cheers -- sylas
    Last edited by a moderator: May 4, 2017
  8. Jan 20, 2010 #7


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    I tire of hearing about DE and DM in the same sentence. Dark matter and dark energy have nothing in common save for the word 'dark'.
  9. Jan 20, 2010 #8


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    Yes, the relative proportions of the various components of the universe change dramatically with respect to time, depending upon the physics of the various components. From what we know now, going into the distant future, essentially all of the energy density will probably be in dark energy. A few billion years ago, nearly all of the density was in normal matter. In the very early universe, nearly all of it was in radiation.
  10. Jan 20, 2010 #9
    Thanks for the link. Very good review article.
    Last edited by a moderator: May 4, 2017
  11. Jan 20, 2010 #10
    Thank you for the file attached. Very helpful article.
    Last edited by a moderator: May 4, 2017
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