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B Was the Big Bang a quantum mechanical vacuum fluctuation?

  1. Jul 29, 2018 #61
    No. THESE particular issues do not disqualify GR from being completely correct and consistent. Dark energy is not a "bolted-on" crutch in GR, it is mathematically consistent with GR (and actually rather simple). Same with dark matter.

    There are issues which disqualify GR, but they are completely different (classical theories are fundamentally not compatible with quantum physics, so we need some sort of quantum gravity theory).
     
  2. Jul 29, 2018 #62
    What
    Again I never said something about disqualifying GR nor I mentioned anything about math inconsistency!

    My point one more time: GR is not the full picture
     
  3. Jul 29, 2018 #63
    Lets go back to conservation of energy:

    No conservation of energy not only means energy can be destroyed, but also means energy can be created from nothing.
     
  4. Jul 29, 2018 #64

    PeroK

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    What is?
     
  5. Jul 29, 2018 #65
    I believe a Quantum theory of gravity will give us a more complete picture.
     
  6. Jul 29, 2018 #66

    PeroK

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    In order to believe that fundamentally conservation of energy is an absolute law of physics, you need a full understanding of energy and a watertight physical model that shows why it is conserved.

    For example, pre Einstein you could have said the same about mass. Remember that? Mass can be neither created or destroyed. How can mass be created out of nothing?

    But, that turned out not to be a law of physics. As a result of SR, which certainly wasn't the full picture.

    Then GR came along and conservation of energy was modified as a law of physics.

    QM also shook previously accepted laws.

    Interestingly, you seem to be willing advances in physics not to further modify what we know but to return a pre-GR status quo.

    Who knows what golden rule Quantum Gravity might revise! Personally, I think it's a forlorn hope that it will restore a universal conservation of energy.
     
  7. Jul 29, 2018 #67
    Well, probably quantum gravity will not change that our Universe is not symmetric under time translations... @Deepblu you are familiar with the definition of energy and its connection with Noether theorem, aren't you?
     
    Last edited: Jul 29, 2018
  8. Jul 30, 2018 #68
    Btw no conservation of energy in GR is a subject that is open to debate. See this paper:
    [vixra link removed by moderator]
     
    Last edited by a moderator: Jul 30, 2018
  9. Jul 30, 2018 #69
    vixra.org is NOT a reliable source. Instead of arguing with specialists and physicists you should rather think why they say what they say.
     
  10. Jul 30, 2018 #70
  11. Jul 30, 2018 #71
    I have question:

    Is information conserved on universal scale?
     
  12. Jul 30, 2018 #72
    I'm starting to think that discussion with you is ... unproductive. Last try. If you continue acting up, I'll stop replying. I have better things to do with my time.

    You did say that GR has problems with dark energy and dark matter. Here, your words verbatim:

    """
    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.
    """

    The word "that" in last sentence refers to dark energy and dark matter "problems" allegedly plaguing GR. They aren't, so my reply was stating they are not. Now you are denying you said they are. What the actual F is going on?
     
  13. Jul 30, 2018 #73

    bhobba

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    See:
    https://arstechnica.com/science/201...-the-course-of-physics-but-couldnt-get-a-job/

    Why it is usually conserved and the situations when its not was worked out by the great Emmy Noether.

    There are various ways of having it conserved in those unusual situations by a suitable choice of the definition of energy - but we do not have agreement on those. We had a recent post from a research scientist on a slight generalization of Noether he thinks resolves it - but the whole thing is still a bit controversial and debatable:
    http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html

    Thanks
    Bill
     
  14. Jul 30, 2018 #74
    Frst, I am sorry for the confusion I caused in my replies.. maybe I was not able to deliver what I mean.
    Second, have patience with me, I am trying to understand.. arguing is not my purpose.

    What I meant in my last reply is that I know that dark energy and dark matter are mathematically consistent with GR, but GR will give wrong results without them.

    So my final question to you is: lets say that scientists suddenly announced that Dark matter does not exist, how we can explain galaxies rotation speed with GR after that?
     
  15. Jul 30, 2018 #75
    Rigorously proving negative is impossible. For example, sterile neutrinos, if they exist, are expected to interact with matter many orders of magnitude weaker than ordinary ones.

    Therefore there will be no "sudden announcement" that DM does not exist.

    The experiments will put more and more stringent limits on DM interaction cross-section (and other things, such as annihilation gamma-rays, if DM annihilates), while theorists, as always, will seek ways to explain observations by various new theories. Then either DM will be detected, or a new theory will explain observations without needing DM, and DM detection experiments will eventually fall out of favor.
     
  16. Jul 30, 2018 #76

    bhobba

    Staff: Mentor

    I don't think that no conservation of energy in under debate. In GR we do not have the defining condition on what Energy is ie the conserved quantity associated with time translation invariance - since GR is space-time curvature the definition breaks down. But that does not mean anyone wants to abandon conservation of energy - simply modify the definition in such a way it exists and is conserved in GR. There are a number of ways of doing it - the debate is which one to choose. Logically you could take the view its simply not conserved or even defined in GR but I haven't come across anyone that really wants to do that - for obvious reasons - it has proven a very useful law.

    Thanks
    Bill
     
  17. Jul 30, 2018 #77
    There are some voices saying that Dark matter does not exits, like in Emergent Gravity Theory by Erik Verlinde:
    https://arxiv.org/abs/1611.02269

    In this lecture he states that there is no Dark matter but only dark energy:


    So Dark Matter is still a subject of research.
     
  18. Jul 30, 2018 #78
    My problem of not digesting the concept that "energy is not conserved", is the idea that energy can be created from nothing. For example if we live in a contracting universe rather than expanding, then we will see an opposite effect and it will appear than energy is created from nothing.

    My second problem is that this will lead to no conservation of information (I may have misconception here).
     
  19. Jul 30, 2018 #79

    bhobba

    Staff: Mentor

    Well first you have to understand what the issue with gravity is. We have a perfectly good quantum theory of gravity valid to about the Plank scale:
    https://arxiv.org/abs/1209.3511

    These days since the work of the great Ken Wilson, who even other well respected physicists like Sidney Coleman stood in awe of - he was that good - we now think of all our theories as effective to some some scale beyond which other theories take over. We already know one famous case - at higher energy scales QED becomes the electroweak theory. I don't think any physicist believes the standard model is valid at the Plank scale. So really the issue isn't quantum gravity - its the laws at that damnable Plank scale. It was thought string theory may resolve it - but it has morphed a bit:
    https://www.ias.edu/news/cole-stringtheory-quanta

    Getting back to the title of the thread - yes it is possible - but nobody knows. There are all sorts of ideas about eg eternal inflation and a Google search will bring back all sorts of other weird ideas.

    Thanks
    Bill
     
  20. Jul 30, 2018 #80

    bhobba

    Staff: Mentor

    The modern definition of energy is as I stated - its from Noether so is automatically conserved. But in GR the defining conditions of that definition break down. So all bets are off. For example as the link about Noether explained in GR you can have 'that an object could speed up as it lost energy by emitting gravity waves, whereas clearly it should slow down.'. We can define energy in a way its still conserved in GR but not in an intuitive way. In other words it may seem like its coming from nothing - but really it isnt - it's just we are getting into regimes where energy is not what we usually think it is. BTW as far as energy goes the universe from nothing idea includes the concept of the universe having 0 energy:
    https://en.wikipedia.org/wiki/Zero-energy_universe

    Thanks
    Bill
     
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