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B Was the Big Bang a quantum mechanical vacuum fluctuation?

  1. Jul 28, 2018 #41

    phinds

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  2. Jul 28, 2018 #42
    Yes I know that.

    My point is that our current theories are not complete.. what appears to us as violation to the law of conservation of energy, and what makes it appear to only work "localy", could be our lack of knowledge on the complete picture.

    Thats why we need a more complete theory such as a quatum gravity theory.
     
  3. Jul 29, 2018 #43

    haushofer

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    I think that these "pseudoproblems" are because we try to impose Newtonian concepts (e.g. energy conservation in fixed backgrounds) into general relativistic frameworks. It has nothing to do with a "lack of the complete picture". It's just a matter of oversymplifying, based on Newtonian intuition.
     
  4. Jul 29, 2018 #44

    PeroK

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    Why do you think energy must be conserved?
     
  5. Jul 29, 2018 #45
    Conservation of energy is not Newtonian concept!! It is a law of physics.
    In my view it is as fundamental as 2nd law of thermodynamics.
     
  6. Jul 29, 2018 #46

    PeroK

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    Why do you think it's a law of physics?
     
  7. Jul 29, 2018 #47
    Why you do not?
     
  8. Jul 29, 2018 #48

    fresh_42

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    I always thought it is Newtonian and the consequence of Noether's local theorem about invariant Lagrangians. I cannot see a system of differential equations for some particles be extended on the entire universe. That would result in serious problems with the atlas.
     
  9. Jul 29, 2018 #49

    PeroK

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    Because I've studied GR.
     
  10. Jul 29, 2018 #50
    "Laws of physics" are proposed by people, then tested against experiments. If experiments match, then the corresponding law might be true; if experiments contradict them, they are out. No law is secure against refuting by future developments.

    In this case, conservation of energy fell victim to the discovery of expansion of the Universe, especially accelerating one.

    Mathematically speaking, conservation of energy is consequence of time translation invariance ("the same experiment tomorrow has the same result as today"). Our local part of Universe on the scale of, say, our Galaxy, is very nearly time translation invariant. That causes conservation of energy to be not violated in our experiments.

    As it turns out, most global solutions of GR are not globally time translation invariant. Therefore, globally, no mathematical logic exists for conservation of energy.
     
  11. Jul 29, 2018 #51
    GR is not complete to describe universe on large scale.. GR is not reality it is a good approximation to reality!

    And no energy does not just evaporize into nothing, we are still far from completely understanding how the universe work on cosmological scale, to jump to a definitive conclusion that energy is not conserved.

    Btw "no energy conservation" is troublesome, imagine if we lived in a universe that is contracting instead of expanding? We will see as if energy is being created from nothing!
     
  12. Jul 29, 2018 #52
    Wrong. GR's problems lie elsewhere. Its description of large-scale Universe works just fine.
     
  13. Jul 29, 2018 #53
    I said "it is not complete" i didnt say "is wrong".
    The Standard Model is not complete too ..you know that.

    Not seeing the full puctures gives the illusion that energy is not conserved.
     
  14. Jul 29, 2018 #54

    PeroK

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    You didn't answer my question, so let me try to answer it for you.

    Someone told you once that energy conservation is a law of physics. And, for the physics you were learning at the time, this was true. But, it wasn't true in general and in particular for an expanding universe.

    And, because you learned conservation of energy before you heard about GR, you are inclined to reject the latter.
     
  15. Jul 29, 2018 #55

    PeroK

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    And the classical physics that suggested the conservation of energy in the first place is a complete theory?

    Conservation of energy arises from theories with less applicability than GR, not more. You may as well argue for Newtonian absolute time and space.
     
  16. Jul 29, 2018 #56
    I dont reject GR!! ofcourse not!!!

    GR does not state that energy should or should not be conserved. Our current expansion model suggess that it is not. GR is not even compatible with our expansion model in first place!!
     
  17. Jul 29, 2018 #57

    PeroK

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    You're the second person today to suggest that. It's an extraordinary idea. Modern cosmology is entirely based on GR!

    The Einstein field equations do not naturally admit a steady state solution but imply an expanding universe.
     
  18. Jul 29, 2018 #58
    Correction:
    "GR is not even compatible with our accelerating expansion model in first place!!"
     
  19. Jul 29, 2018 #59

    PeroK

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    Not true. Having a non-zero vacuum energy explains that.

    Where are you getting your misinformation?
     
  20. Jul 29, 2018 #60
    We need dark energy to make GR work for current expansion model, dark energy is theorized but never proven to actually exist. Thats why there are many alternative theories with and without dark energy.

    Dark matter is also needed to explain observed galaxies rotation speed that do not match what is predicted by GR, dark matter also has never been observed.

    That does not mean GR is wrong, it means that it is not the final ultimate theory.
     
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