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Does GR remain in a universe without matter?

  1. Sep 1, 2011 #1
    Basically since we use QM for the very small, and GR for anything bigger than an Atom, can we assume GR has no place in the universe if there is no matter?
     
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  3. Sep 1, 2011 #2

    Nabeshin

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  4. Sep 1, 2011 #3

    Bill_K

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    Gravity couples to energy, not to "matter". Does your universe without matter also have no electromagnetism?
     
  5. Sep 1, 2011 #4
    I'm sure it would- I'm referring to our own in a decayed state where matter stopped existing.

    It appears the decay state would have to be when energy dies off before GR would quit being applicable.
     
  6. Sep 1, 2011 #5
    GR always holds it is a law. If it doesn't hold then you would ask the question why not. I know that sounds Zen but think about it...

    Ok now you have reached Nirvana. In what universe would GR not apply?
     
  7. Sep 1, 2011 #6
    Quite.
     
  8. Sep 1, 2011 #7
    A universe where none of what it governs exists :)
     
  9. Sep 1, 2011 #8
    :wink:
     
  10. Sep 1, 2011 #9
    So then the next question is, will the universe ever decay to this state?
     
  11. Sep 1, 2011 #10
    It seems to me that in an empty universe GR would still apply, and result in a Minkowski metric.

    But then, what is a metric without an observer? Unless we have a mass-energy free observer somewhere ... hovering over the face of a bland and lifeless void.
     
  12. Sep 1, 2011 #11

    Drakkith

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    Our models of how the universe works describe how matter, mass, and energy interact and behave. If the universe has NONE of the above, then it isn't that the rules simply stop working, it's that they don't have anything to follow them. Also, is there anything that QM applies to that GR doesn't? I'm not talking about the different effects, but about the matter, mass, or energy or whatever that the laws apply to.
     
    Last edited: Sep 1, 2011
  13. Sep 1, 2011 #12
    Could a vacuum act as an observer? It seems the fact that it can and does interact with particles and/or vacuum pressure fluctuation would be re-iterating information.
     
  14. Sep 1, 2011 #13

    Drakkith

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    That depends on what you mean by vacuum. In reality a vacuum is still occupied by various fields, as the electromagnetic force and gravitation have an infinite range. We usually mean vacuum to be the removal of nearly all matter within a volume. If you mean vacuum to be the absence of absolutely everything, all matter, energy, and mass, then I don't see how, as not only would there be nothing to observe, but I'm not sure you could even call this vacuum "something".
     
  15. Sep 1, 2011 #14
    Whats the minimum that would be required for there to be a negative vacuum pressure? Could there be a negative pressure simply due to the absence of matter once all else is removed?
     
  16. Sep 1, 2011 #15

    Drakkith

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    Matter or mass?
     
  17. Sep 1, 2011 #16
    Mass gone, matter's ability to take up 3 dimensions leaves a negative vacuum pressure in its absence.
     
  18. Sep 1, 2011 #17

    Drakkith

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    It is the mass that affects spacetime, not the matter itself. The ability for matter to form 3d structures has nothing to do with vacuum pressure. As to the absence of mass, I don't know. If having no mass affected the vacuum pressure, then I would expect the existence of mass in an area to slow down local expansion. However I have no idea if this is true or if it measureable on such short scales.
     
  19. Sep 1, 2011 #18
    Well if having no mass did effect the pressure, I'd have to say that masses information had been observed by the negative vacuum pressure. Which leads me of course to wonder if negative vacuum pressure can induce energy and mass again.

    I'm dead certain this universe is a cycle, I'm still working out the kinks on how, lol. You've helped alot though, thanks for all your replies.
     
  20. Sep 1, 2011 #19

    Drakkith

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    I wouldn't use my posts to develop a serious theory. You would need lots of math and observations to support anything. I can't give you those as I don't know myself.
     
  21. Sep 1, 2011 #20

    PeterDonis

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    What do you mean by "negative vacuum pressure?"
     
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