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How much mass does 'Dark Matter' and 'Nothing' (empty space) have?

  1. Jul 17, 2012 #1
    I know these are ambiguous questions and am probably opening up a complex can of worms. I figure if we know how much of the universe is composed of dark matter and it's effects, we should also have an idea about its mass from its gravitational pull. Also I figure since truelly empty space also has a nearly infinite presents of virtual particals and contains zero point energy, that it might have a definitive 'mass' we can associate with it.
  2. jcsd
  3. Jul 17, 2012 #2


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    Baryonic [neutrons, protons, etc.] and non-baryonic [dark matter] comprises about 1/4 of the total energy content of the universe under the LCDM model.
  4. Jul 18, 2012 #3
    Thanks but I'm not asking about ratios, I'm more interested in solid numbers.
  5. Jul 21, 2012 #4
    Anyone here have any insight into this?
  6. Jul 21, 2012 #5


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    Matter and radiation together are estimated to amount to about 0.23 joule per cubic kilometer (energy equivalent).

    About 5/6 of this is dark matter, and 1/6 is ordinary matter. The contribution from radiation is very slight.

    If you paste this into google :
    .23 joule/c^2
    it will tell you 2.56 x 10-18 kilogram
    That is how much mass per cubic kilometer.
    I find the mass figure hard to remember and how to make intuitive. So I remember the energy equivalent of it. You can always divide energy by c2 to get the mass equivalent.

    I don't think that empty space has any mass comparable to what I just told you comes from actual matter (dark, ordinary) and radiation.
    The cosmological constant is just that, a constant in the law of gravity. There is no convincing evidence that it corresponds to some weird "dark energy" although some people talk about it that way.

    Dark matter has turned out to be real, concentrations of it can be mapped and it has played an important role in the formation of galaxies etc. But "dark energy" has been something of a passing fad. Increasingly in scientific papers the authors simply refer to the cosmological constant as that, and don't use the term "dark energy."

    If the cosmological constant WERE a manifestation of some kind of "dark energy" then that energy would be 0.60 joules per cubic kilometer. So the total would be 0.83 joules per km3.
  7. Jul 21, 2012 #6


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    About twenty million atoms plus about five times the mass in dark matter. Typical small swimming pool is about 10m on a side and 1m-ish deep. You're talking 2-ish atoms in the whole thing plus about five times as much dark matter.

    Compare the normal contents of a swimming pool, around 1031 water molecules.
  8. Jul 21, 2012 #7


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    'Solid' numbers are absolutely meaningless without comparison. Ratios are as good as we can get from cosmology.
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