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Are there currently any proposals for a complete physics?

  1. Dec 26, 2015 #1
    Has any model of physics yet been proposed that meets the following criteria?
    1. The model is believed to, in principle, yield a full description of behavior at all energy levels. (Nonnegative probabilities summing to 1, no singularities without full mathematical treatment, no infinite values to be artificially renormalized, etc.)
    2. The model can be expressed concisely. (A set of equations to print on a T-shirt.)
    Note that I am not demanding experimental falsifiability, nor that the calculations of behavior have been carried out- or are even feasible. I am also allowing any (finite) number of fine-tuned parameters, as long as they are constants everywhere. I want to know whether there is even a possibility that the fundamental laws of nature have yet been described (on this planet :-) ).
     
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  3. Dec 26, 2015 #2

    marcus

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    Not as far as I know.
    BTW would a "complete physics" include gravity? That is, how geometry and matter interact? Would a complete physics include superconductivity, black hole thermodynamics? Would it explain why the laws governing subatomic particles are the laws they are, and not some other laws? It's a curious idea, a complete physics. Could it be self-contradictory, like the idea of a complete map that includes itself?
     
    Last edited: Dec 26, 2015
  4. Dec 26, 2015 #3
    Thank you, Marcus!
    I'd appreciate if you (or someone else) would spell out where strings, LQG, and maybe one or two other lines of research are holding with regard to the criteria I mentioned.
     
  5. Dec 27, 2015 #4
    Last edited: Dec 27, 2015
  6. Dec 27, 2015 #5
    Yes, of course! How could there be "a full description of behavior" without that? Anyhow gravity is presumably relevant for all small-scale/high-energy behavior.

    Things like that should be derivable- in principle- from the laws. If the model posits a multiverse with varying force couplings etc. , you'd also need to specify the parameter values that apply in our region. BTW, isn't superconductivity already well-understood in terms of QED?

    That would be really cool but I personally don't think of it as a necessary criterion for a "complete model". It gets included in "allowing fine-tuned parameters"...

    Well, the fundamental laws presumably provide for the existence of physicists who can describe those laws- at least we hope so! What is the contradiction you have in mind?
     
  7. Dec 27, 2015 #6

    marcus

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    Maline, here Mitchell has offered an answer to your question. My advice: don't waste time philosophizing : ^), take him up on it. Follow the links and see if for example the Shaposhnikov nu-MSM is the kind of thing you are asking about.
     
  8. Dec 27, 2015 #7

    ohwilleke

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    "Nonnegative probabilities summing to 1"

    Don't knock negative probabilities. While you want probabilities to sum to 1 or 0 and want finite probabilities of observable events, negative probabilities, like imaginary numbers, can actually be quite useful tools in a physical theory that can describe reality.
     
  9. Dec 28, 2015 #8
    No, both of these are explicitly limited by the Planck scale, because they ignore expected QG effects. Unless it's possible to deny such effects and get a consistent model?

    Nonnegative probabilities for physically meaningful observables, with some appropriate definition.
    For instance, could a workable model be constructed in String Theory by assuming, ad hoc, some particularly friendly Calabi-Yau manifold?
    What would LQG need in order to yield predictions, per my criteria?
     
    Last edited: Dec 28, 2015
  10. Dec 28, 2015 #9
    Provided the combination of probabilities lead to real (i.e. non imaginary), AND POSITIVE outcomes, then they're all good.

    In our everyday lives, we should encounter, NEGATIVE distances due to the dual nature square of our office area, yet we simply ignore these results because they are not intuitive to our experience, and negative time because mathematically, GR works with future time in a negative direction!
     
  11. Dec 28, 2015 #10

    marcus

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    http://arxiv.org/abs/1509.05693
    Detailed analysis of the predictions of loop quantum cosmology for the primordial power spectra
    Ivan Agullo, Noah A. Morris
    (Submitted on 18 Sep 2015)
    We provide an exhaustive numerical exploration of the predictions of loop quantum cosmology (LQC) with a post-bounce phase of inflation for the primordial power spectrum of scalar and tensor perturbations. We extend previous analysis by characterizing the phenomenologically relevant parameter space and by constraining it using observations. Furthermore, we characterize the shape of LQC-corrections to observable quantities across this parameter space. Our analysis provides a framework to contrast more accurately the theory with forthcoming polarization data, and it also paves the road for the computation of other observables beyond the power spectra, such as non-Gaussianity.
    24 pages, 5 figures

    Maline, I'm not sure that LQG "needs" anything in order to yield predictions. But then, you understand your "criteria" and I don't.

    There are several different formulations/theoretical models within the LQG family, some have reached the level of maturity where they can make testable predictions and are thus falsifiable. this is rather down to earth and straightforward. A theory does or it doesn't. I don't know what "per your criteria" has to do with it. So only you can read Agullo's article here and decide if the predictions are "per your criteria".
     
  12. Dec 28, 2015 #11

    marcus

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    ==quote Maline post#5==
    ==quote marcus==BTW would a "complete physics" include gravity? That is, how geometry and matter interact?==endquote==​

    Yes, of course! How could there be "a full description of behavior" without that? Anyhow gravity is presumably relevant for all small-scale/high-energy behavior.
    ==endquote==

    It seems to me that what you are asking for is a "Theory of Everything", but referring to it with different words--"complete physics", "full description of behavior".
    That may be a pipe dream, a logical impossibility, a mirage. My suggestion would be to look at the answers people have given you---e.g. Mitchell. They are all partial descriptions of behavior---descriptions of SOME limited domain of behavior. There may be a lesson in this. You might need to adjust or clarify your criteria to adapt to the kind of answers you are getting. The old "no completely accurate map can include itself", among other considerations.
     
    Last edited: Dec 28, 2015
  13. Dec 28, 2015 #12
    Oh, sorry I wasn't clear. I didn't mean to ask about testable predictions. I just want to know whether LQG is yet able to reproduce ordinary physics, and if not, what would it take to bring these models to that point.
     
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