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I Quantum Vacuum

  1. Apr 19, 2018 #1
    May I know objects are allowed and prohibited to exist in the quantum vacuum as sanctioned by Witten, Hawking and others of the authority?

    If all the quantum fields were gone.. and we have only branes left.. do you consider branes as existing in the quantum vacuum or outside of it? Or what official objects can exist in the quantum vacuum and is there an outside to the quantum vacuum?

    This is general question and not personal theory because I don't have any theory.
     
  2. jcsd
  3. Apr 19, 2018 #2

    Vanadium 50

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    The vacuum is empty.
     
  4. Apr 19, 2018 #3
    ha? I read electron field, photon field, higgs field, and all matter fields exist in the quantum vacuum..

    and I was wondering if only quantum fields were in the quantum vacuum.. how about branes.. where are branes located.. inside or outside the quantum vacuum?
     
  5. Apr 20, 2018 #4
    This is not as simple question as one thinks. At the end of an introductory paper about quantum gravity https://arxiv.org/pdf/gr-qc/0004005.pdf is this quote:

    "We have made great progress, but the fact that general relativity and the quantum are not yet united means that we have no single
    picture of what the world is that we can believe in. When a child asks, What is the world, we literally have nothing to tell her."

    Anyway. When a child asks.. What is the world.. we can perhaps tell him it's either quantum fields or general relativistic spacetime? This means there are things in this world not described by quantum fields. So perhaps quantum vacuum is just one of the things that can exist?

    What other objects in theoretical BSM physics that doesn't belong to the quantum vacuum?
     
  6. Apr 20, 2018 #5

    PeterDonis

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    Science doesn't work by authority. It works by making predictions that are confirmed by experiments. What predictions or experiments are you asking about?

    We have no evidence for the existence of branes. Nor do we have a theory that predicts any state where all the quantum fields are gone and we have only branes left. So I don't understand what you're asking about.

    "The quantum vacuum" is not a "place" where things can be located. So again I don't understand what you're asking.

    Although the paper itself is a peer-reviewed paper, this quote is from a popular book and represents the personal opinion of that author (Smolin). As such, it's off topic for discussion here.

    Our best current answer would be quantum fields contained in general relativistic spacetime.
     
  7. Apr 20, 2018 #6

    PeterDonis

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    I'm not sure where you read this (giving a reference would help), but it's not correct. The quantum vacuum is a particular state of quantum fields; it's not a "place" where quantum fields "exist in".
     
  8. Apr 20, 2018 #7
    Thanks. I'll always remember this.. that ultimately nature has no place where things exist in. Quantum vacuum is a particular state.. and spacetime should have no prior geometry. Our universe is not a place but a state.

    We are at dawn of physics beyond the substandard model. I'm just concerned if new forces of nature would be like gravity where it has difficulty merging with QFT.

    Our present 3 fundamental forces like weak, strong and electromagnetic field are dumb simple forces. Does it mean only dumb simple forces can be described by QFT? Up to what complexity a fundamental force can be when it can still be described by QFT?

    What other things is there being discussed at say the Perimeter Institute that is akin to spacetime and gravity where there is incompatibility with QFT? (this question is for others in case Peterdonis doesn't know the answer)
     
  9. Apr 20, 2018 #8

    PeterDonis

    Staff: Mentor

    That's not what I said. All I said was that "quantum vacuum" does not name such a place.

    According to classical (non-quantum) relativity, 4-dimensional spacetime is "the place where things exist in". According to quantum field theory, the same is true; the difference is that the "things" that exist in spacetime are quantum fields, not classical objects. Also, quantum field theory can be done in a spacetime of any number of dimensions; for example, string theory is a quantum field theory done in a spacetime of 10 or 11 dimensions (at least those are the numbers that come out of what appear to be the best current candidates for a string theory that can actually describe our universe).

    I don't know what you mean by "dumb simple forces".

    I don't know what you mean by this either. What do you think a "force" is?

    I think at this point it would be helpful for you to give some references for where you are getting your understanding from. You seem to have some fundamental misconceptions about our current theories of physics.
     
  10. Apr 20, 2018 #9
    That's just an effective field theory.. it's like saying a lizard can walk on the ceiling but we don't know how its feet touch the ceiling surface. For completeness, we must describe the microscopic mechanism (or the planck scale behavior of gravity or how quantum fields are really coupled to the spacetime manifold or high energy behavior).

    dumb simple forces mean they are just mechanical-like compared to intelligent fundamental forces where you can instruct them to do your bidding.


    Gauge bosons are the properties of our "fundamental force".. General Relativity is described by gauge symmetry too? I wonder if non gauge forces should be considered as part of the fundamental "forces" of nature too.. maybe it's time to drop the "there is 4 fundamental forces of nature" line?

    ok, i'll look for the reference. Thanks.
     
  11. Apr 20, 2018 #10

    PeterDonis

    Staff: Mentor

    According to the physicists who are working on quantum gravity, yes, that's true. But that doesn't mean you get to treat it as an established fact. It isn't. One day, if a quantum gravity theory is discovered and confirmed by experiment, then you'll be able to. But that hasn't happened yet.

    I have no idea what you're talking about. You either need to give a specific reference for where you're getting this from, or drop these claims.

    Ok, so by "fundamental force" you mean "something that can be described using gauge bosons the way the Standard Model interactions are described".

    Yes. In the case of GR, the gauge symmetry corresponds to the invariance of the equations of GR under changes of coordinates.

    Since there are no known non-gauge forces, this is a moot point.

    No, it's time for you to either drop these speculative claims, or give a specific reference for where you're getting them from. And please review the PF rules on personal speculations.
     
  12. Apr 20, 2018 #11
    What? You are saying there is possibility there will never be a quantum gravity and the effective field theory will be the final form? Then how do you describe planck scale interaction where gravity is strong and quantum mechanics is valid? unless perhaps you meant it is possible there was never a planck scale at all because gravity brane as described by Randall Warped Passages would occurred not far from the weak scale.. is this what you meant quantum gravity doesn't have to exist (what you were implying above)?

     
  13. Apr 20, 2018 #12

    PeterDonis

    Staff: Mentor

    Yes. It's one thing to express an opinion, as many physicists have done, about how you think future discoveries will go. It's quite another to treat such speculations the same as established facts. They're not.

    We have no evidence for any such thing, so I don't know what you're talking about. I think you are mistaking various speculations for actual proven theories. They're not the same thing.

    Which is a book describing a speculation. Not something that's actually been observed. (And it's a pop science book as well, which means you shouldn't be trying to learn actual science from it anyway.)

    At this point I am closing this thread since your original question has been answered and you keep talking about speculations as if they were facts.
     
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