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How do we know everything in the universe is matter? (versus antimatter)

  1. Aug 19, 2015 #1
    As opposed to antimatter, that is. The whole search for the asymmetry of matter vs antimatter seems to rest on the implicit assumption that what we observe is matter, not antimatter, no?
    Is there a way of distinguishing from afar between the two?
  2. jcsd
  3. Aug 19, 2015 #2


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    Sir, you missed the occurrence of dark energy and dark matter too....

    But symetry is natural and follows set axioms in fields of nature and science, doesnt it? :)
  4. Aug 19, 2015 #3
    Yes, but the symmetry is clearly broken, that is the point of all the investigations whether matter and antimatter behave exactly the same.
    My question is, could not whole parts of the universe consist of antimatter and we simply wouldn't know?
  5. Aug 19, 2015 #4


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    There's no signs of annihilation at matter/antimatter region boundaries. An issue that only gets exacerbated the further back in time you look, when matter was packed closer together.
  6. Aug 19, 2015 #5
    I guess that kinda depends on where you postulate those boundaries to be :smile:
    But yeah, I can see how you can probably model those scenarios and look at what the distribution should be these days. Then again, there's a lot to the universe that we just can't observe (and never will, since it's receding faster than light); there's maybe the chance that the boundary region lies outside of the observable universe.
  7. Aug 19, 2015 #6


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    Then you'd encounter the issue of 'how come enough matter to comprise the whole of the observable universe separated from the equal amount of antimatter'.
    Rather than saving symmetry this way, you're introducing some unknown mechanism that breaks the symmetry in favour of matter in some places, and in favour in antimatter in other places. All casually disconnected, so that'd be in contradiction of the cosmological principle (different laws of physics for different regions).
  8. Aug 19, 2015 #7
    Well, I think any reasonably convincing theory of that kind would probably rely on something having been different right at the Big Bang. I agree, saying that different parts of the universe behave differently opens a totally different can of worms, as you'd just be shifting the lack of explanation somewhere else.
  9. Aug 19, 2015 #8


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    I would think that a separation of matter and anti matter like the OP describes would violate the 2nd law of thermodynamics - like adding sugar and salt to water and having each substance form pure pockets rather than mixing.
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