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B How can dark matter exist in a vacuum?

  1. Jun 29, 2016 #1
    So if space is a vacuum, how can we have dark matter? What does it contain that means that space still acts like a vacuum?
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  3. Jun 29, 2016 #2


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    The vacuum of space is never completely empty. There are always some particles in space.
    Dark matter is a different thing altogether.
  4. Jun 29, 2016 #3
    There is no such thing as a perfect vacuum. There isn't even in theory, quantum fluctuations don't allow it. Some packets of space are simply less dense than others, and what you consider dense it highly relative. To a neutrino, matter is just slightly polluted space.
  5. Jun 29, 2016 #4


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    This isn't entirely correct. The vacuum state in quantum mechanics is stable and zero-temperature as long as there is no cosmological constant. It's just that in practice matter permeates our universe, such that there's no such thing of a perfect vacuum in our observable universe. Plus it looks like we have a non-zero cosmological constant.
  6. Jun 29, 2016 #5
    If space is a vacuum, how can we have regular matter?

    There's no paradox. The (relative) vacuum of space in the vicinity of dark matter is analogous to the vacuum of space in the vicinity of matter-more-mundane.
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