Hi Jacek,

I have been curious about the role of LQG. I will confess that I am primarily oriented towards the string theory perspective. I do think LQG has some relevancy to physics, but it is uncertain what that is. LQG comes from the ADM approach to general relativity, which give constraint equations NH = 0 and N^iH_i = 0 with no explicit time dependency. The lack of time dependency means that energy is not defined. This is a manifestation of Gauss' law, where on a general manifold there is no boundary from which to integrate over to define mass-energy as the source of the field. So the Wheeler DeWitt equation, and spinor variations on that theme in LQG, are in effect constraint systems. The problem is that we do not know what this contrains exactly.

I have thought that LQG is some sort of "target" of a renormalization group flow in string/M-theory. However, string theory has at its IR limit a graviton in a weak coupling regime on a background. This theory is renormalizable as a perturbative field theory, even if we know it is a weak coupling approximation to quantum gravity. LQG is not renormalizable. So we are sort of left with an open question. Is LQG a strong coupling S-duality to the string weak coupling theory? There are some problems with an idea of this sort. In particular LQG is not easily embedded into a larger unification scheme with gauge fields or supersymmetry.

However, LQG is based upon basic general relativity in a way that is hard to ignore. I suspect it is not completely wrong, as is often thought in the string theory community. However, where it fits into things is unknown.

LQG is related to Regge calculus, which is run on a computer. It is one of the tools numerical general relativists use. However, this approach to general relativity is also a manifestation of the action principle. Underlying it all is an extremal principle. Extremization is a continuous process and from a set theory perspective it is a manifestation of a nondenumerable set of numbers, or the reals. This is one motivation to suggest that the universe is not entirely a computer, even if it has some computer or algorithmic-like structures to it.

Cheers LC

    Things become distinguishable with the breaking of symmmetry. This results in a scale dependency and/or a broken degeneracy which permits that. The world around us has lots of distinguishing features because it is in a low energy or low temperature state. In the case of snowflakes or water in the frozen state there has been a phase change which breaks a symmetry for the equiprobability for an H_2O molecule in each volume of space.

    It is rather clear that you are not that familiar with the nature of physics, or with what Feynman wrote in "Character of Physical Law." The problem is this discussion has reached an impass. I will simply say that your assessment of things is simply wrong. I doubt that anything I write here will convince you of that.

    LC

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    • Post #43

    Dear Lawrence,

    I have followed your past postings(your personal theories) and they were interesting. But this time you have gone a bit philosophical, so I want to understand what you are saying. Lets say what you are saying is true, so in what sense that affects physics in any meaningful practical way. I mean are you saying no ultimate laws can be formulated, or the constants of nature will never be found, or no ontology exists or can be known, or particles inherently have no trajectories, EXACTLY what?

      The metaphysics, or analytical mathematircal philosophy, baseically is that any scheme for causality is going to be incomplete. It will not be able to encode all possible physical states. As a result it means there exists a deeper foundation to the universe. In the second half of this paper I argue this involves the associative property of the vacuum with respect to quantized event horizons.

      Cheers LC

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      • Post #45

      Thanks for the reply.

      "baseically is that any scheme for causality is going to be incomplete. It will not be able to encode all possible physical states"

      In which physics problem this problem appears. Is it in scattering s-matrix or in describing proton wavefunction. I mean EXACTLY which physical problem you are having trouble solving because of this issue. Sorry for repeating my question, I hope I am more clearer this time.

      Hi Lawrence,

      I do not believe that LQG /CLQG is a serious candidate for quantum gravity and it is not my favorite. In LQG the space is granular (a network of finite loops) and this is contradictory to my view of continuous spacetime. However I like its evolutionary aspect in the sense of SOC and the scale-invariance that is crucial to fill the gap between GR and QM. I have mentioned LQG / CLQG only for reference to your determinism in a "clockwork" and evolution. After all the evolution notion is used very often by physicists but usually in the common meaning as a process of a change e.g. stellar evolution. But this has nothing to do with self-organized criticality. I would like to apply Darwinism beyond its original sphere of organic evolution on Earth using SOC.

      I like the extremal principle in a sense of non-equilibrium thermodynamics to look for the likely steady states. This is also a kind of evolution of a far-from-equilibrium system to a steady state.

      String theories do not generate predictions so they are non-falsifiable.

      And finally I am sorry but the language of modal logic is not my 'mother tongue'... just like English. Maybe I should start to learn...

      The situation pertains when there is an uncertainty fluctuation of event horizons. This is a possible window into quantum gravity. The physical states in the S-matrix channel are entangled states, with entanglements across the horizon. If the event horizon is classical then everything is nicely associative. A fluctuation in the horizon results in this uncertainty in associating states interior and exterior to the black hole/

      The graviton has quantum numbers equivalent to an entangled pair of QCD gluons, or a bi-gluon system, that is neutral with respect to color charge. In that sense this form of S-matrix does connect in formalism with the old S-matrix theory or the so called "bootstrap." In fact string theory is really that unitary bootstrap theory in another guise.

      I hope this answers your question.

      Cheers LC

      I think spacetime is continuous or granular depending upon which sort of measurement you make. The Planck scale is just the minimal length scale which can contain a qubit of information. Space or spacetime on a smaller scale can not contain a qubit with any certainty. An experiment that involves the transmission of information over a vast time distance has no uncertainty with respect to the existence of it information or qubit content due to quantum gravity. As a result spacetime appears perfectly smooth. An experiment on the other hand which attempts to localize a very small region of space, say at high energy, will then register a different perspective on spacetime. In that setting it may appear highly choatic and granular.

      The predictions of string theory involve cosmology and black holes. In a stringy universe there are some observable consequences, in particular with respect to multiple vacuum nucleations or bubbles that we call a "universe." Signatures of this may be imprinted in the fine grain detail in the CMB anisotropy. The graviton has quantum numbers equivalent to an entangled pair of QCD gluons, or a bi-gluon system, that is neutral with respect to color charge. This means that plasmas of gluons can be formally equivalent to a black hole. In a funny way it is a black hole. So holographic physics should in principle be testable in heavy ion collisions. These are admittedly rather indirect or oblique sorts of tests, and even if confirmations of string predictions are found the whole string-M/theory enterprise is likely to remain on rather unsteady ground.

      The real problem is that we appear to be reaching a sort of ceiling of technological possibilities. One of these is of course directly testing Planck scale physics. Other limits seem to be with high density energy sources such as fusion, that seems as remote as ever, the future of manned spacetravel appears in trouble, and there are slow downs with Moore's law with computers. We also need to consider the pile up of huge problems like global warming. We may be approaching the end of the foundations of physics because of our limitations.

      Cheers LC

      Dear Lawrence,

      I agree we are hitting the technological limits within contemporary experimental physics. However there is a hope - a new idea falsifiable with a simple experiment. I have proposed one that could be even an exercise for students. But to carry out the experiment we need someone who is ready to risk his authority like J.A.Wheeler.

      Best regards

      I am slowly making my way through the essays. I have not yet gotten to yours. Are you proposing this experiment in your essay? I will try to get to yours in the next few days. I can only read one of these papers in a day, so it is a bit slow going.

      Cheers LC

      Dear Lawrence,

      In my essay I have only mentioned the spin experiment but in references you can easily find a link.

      I just pulled up your essay and gave it a quick reading. It is not terribly long. It appears that you are asking whether certain properties are physical or geometrical. At this time I don't have an assessment of your work. I will need to read a bit more.

      Cheers LC

      4 days later

      Hello Lawrence Crowell,

      First off, I'd like to say I like your style, and the way that you seem to put issues in their proper perspective! It brings a calming sense of reason to an area of question that retains so much hype that it no doubt triggers numerous thoughts every time one hears Q.M. and locality are mentioned. Secondly, I don't think determinism should dictate the development of a new theory. It, as your historical view has made clearer to me, is an idea used to adapt old world views into current problems.

      About the idea that the computer, either a real one or the universe as one idea, being faulty because it doesn't model the entire set of events, could it be that this is not against saying that there is a separateness between real entities in space which unaccounted for doesn't describe all events in the universe? Or, does a clock here have to do with one spatially separated over there? Not being mathematically trained enough to see clearly the math in or around the black holes, I will leave this comment with one question only. As an aside, I'm glad to hear someone say "bottom-up" once in a while.

      Best,

      W. Amos Carine

        The relationship between events in the universe and causality was noted by David Hume to not have a strict logical relationship. As I indicate in a footnote Godel's second theorem according to modal operations is a form of Hume's argument about causality =/= logic.

        I sort of have to make this a bit brief due to other things I have to attend to now. I will say that the issue of clocks with a spatial separation and synchronization is a subject of considerable interest. This involves Cauchy data on spatial surfaces and how to integrate the Einstein field equations.

        Cheers LC

        Thank you Lawrence C. for giving me something else to look into!

        I agree with you that the universe computes itself and thus discovers itself. I've presented an argument that supports this view. According to this argument Plancks constant h is nothing else than the physical expression of something which is commonly known as "natural digit".

          The self computation of the universe probably leads to this Turing-Godel limit with Lambda calculus. There is clearly a computational aspect to the universe, which is a causal structure.

          I will take a look at your essay soon. The Planck constant is in naturalized units just "one," and does probably reflect a unit of of natural numbers that sum up to give the total action. I notice yours seems to be in the latest introduction of new essays.

          Cheers LC

          4 days later

          Lawrence,

          When reading; "A model of the physical universe encoded by algorithmic means will not compute reality" I suspected I may enjoy reading your essay. I was right.

          You present a very level and balanced view, and more readable by the target audience than previous years. I do suggest something rather radical regarding that above sentence myself!

          I also found other resonances with mine; "It is entirely possible this could be used to argue for a 'top-down' physics with the emergence of higher level properties." which I identify in terms of higher 'sample spaces' and subsets and test against the EPR paradox.

          I also agree your analysis; "GR is a geometric theory of spacetime, which means that quantum gravity is quantization of spacetime itself. It is not entirely clear what this means. A number of questions have to be answered, and currently there are obstacles in our current theories which do not permit us to address these issues well."

          But are the apparent 'obstacles' it not only 'assumptions'? so testing other assumptions may be fruitful (without the feared ether), i.e. that quantized atomic scattering to c maintains the SR postulates locally, (the LT then emerges naturally as a know optical effect).?? (You may recall from my last years effort how modal logic applies to that case).

          I hope you can read mine and look forward to your and comments. I'm sure you'll stay in a more elevated position this year.

          best of luck.

          Peter

            Hi Peter,

            I am true to my usual trend falling behind in reading papers on this list. I just did a scan of your paper. You do reference Godel's paper on prepositional logic. The main point of my work is that any Lambda-calculus or Turing machine approach to the structure of a causal system is bound to be incomplete. I do get a sense in reading the first couple of pages of your essay that you are leading into something similar.

            I probably will not get to reading papers much until this weekend. I'll post my observations when I do. As I said I am falling behind, and I notice another lot of papers showed up on the list today.

            Cheers LC

            Hi Lawrence,

            I've just had a complete read and I really enjoyed your essay. The quantum nature of information does seem to point towards us concluding that neither it nor bit are more fundamental. I reached a similar conclusion in my essay. I particularly like the idea that this may have applications in consciousness.

            Regards

            Antony