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Dark matter

  1. Jan 24, 2006 #1
    Do dark matter bend light? Have they found dark matter?
  2. jcsd
  3. Jan 24, 2006 #2


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    Dark matter is assumed to exist because it explains why galaxies are held together. There is no evidence of any sort of clumping, which would be needed to bend light. It appears to be very diffusely spread in space.

    Other than the gravitational effect there has been no experiment which demonstrates the existence of dark matter.
  4. Jan 25, 2006 #3


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    Dark Matter is required cosmologically to make up the matter content of the universe to fit the WMAP data on the anisotropies of the CMB.

    It is needed to explain the flat rotation profiles of spiral galaxies and to hold clusters of galaxies together.

    Yes touqra - DM does bend light gravitationally, the gravitational lensing of distant quasars by nearer galaxies in the line of sight is consistent with those galaxies having a massive dark halo.

    But what is DM? As mathman said, it has not been discovered in any other observation, expecially in laboratory experiments. The standard LCDM model, L being Dark Energy (Lambda is the cosmological constant), CDM being Cold Dark Matter, determines the amount of matter, dark or otherwise to be 27% of the universe's density, of this the standard model can produce only 4% ordinary baryonic matter (hydrogen and helium) out of the Big Bang. And we can see only about 0.3% as stars and gaseous nebulae. Therefore the model, interpreting these observations, using the gravitational theory of General Relativity, requires 23% exotic (unknown non-baryonic DM). (Note it also requires 3.7% as Dark ordinary matter, 12X that which is visible!)

    I hope this helps.

    Last edited: Jan 25, 2006
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