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Slow days

  1. Jul 14, 2005 #1

    wolram

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    As things seem a bit slow of late i wonder if anyone would give an over view
    of the gravity debate, i know the Higgs is still elusive and the graviton remains
    un found, no axions as yet, etc, etc, but what does this mean to string and
    loop theories?
     
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  3. Jul 14, 2005 #2

    marcus

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    it isnt just string and loop anymore, wolram, it's triangles too
     
  4. Jul 14, 2005 #3

    wolram

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    You beggars are never content, i have read about triangles, if they fit in then fine, i have no clue as to what they mean, but how do they fit with, no
    higgs, graviton, axion?
     
  5. Jul 14, 2005 #4

    marcus

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    I keep this link handy in my sig
    http://arxiv.org/hep-th/0505154
    I think it's this year's landmark paper, the other paper is just a help in reading this one.

    The Triangle people have generated a quantum spacetime groundstate, but havent yet put matter on it. this is definitely a different spacetime continuum.
    on page 14 it says

    "Having generated a ground state of quantum geometry nonperturbatively, we would like to understand its geometric properties, in the sense of expectation values, which can be done in various ways. We will currently concentrate on the purely geometric observables, leaving the coupling to test particles and matter fields to a later investigation. We will proceed by first determining a number of “rough” properties of the quantum geometry such as its dimensionality and its global scaling properties. These properties of quantum spacetime play an important role, because for any viable candidate theory of quantum gravity, they must be shown to reproduce the correct classical limit at sufficiently large scales, namely, geometry as described by Einstein’s general theory of relativity."
     
    Last edited: Jul 14, 2005
  6. Jul 14, 2005 #5

    marcus

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    When you ask me how things fit in the overall picture, you are asking for my opinion, wolram, and I will tell you without reservation. It's not a matter for scientific demonstration. Others may wish to disagree.

    I think to a first approximation loop and string don't matter any more. They are of dwindling importance.

    In a nonperturbative development of spacetime, the continuum pulls itself into existence by its own bootstraps

    In a perturbative theory like STRING you give the theory a static already shaped (usually flat) continuum to start with, and make ripples on it. Perturbative QG is no longer good enough, as a fundamental theory. It can be a useful adjunct for certain kinds of calculations but if a nonperturbative theory is possible, nothing else is good enough.

    Loop has been thought of as nonperturbative because it starts with an unshaped, kind of limp, continuum---something with coordinate functions called a diff. manifold. But I would call that "semi-perturbative" because the thing it starts with already has a fixed uniform dimensionality because of the readymade coordinate functions. The Triangle people have raised the bar.

    Triangles is more THOROUGHLY nonperturbative than Loop is.
    There is very little you have to specify in advance, very little you have to give Triangles. And the continuum it makes, pulls into existence starting with almost no prior structure, seems to ACT RIGHT. There is considerable evidence building up that the continuum that emerges this way will have the right dimension, the right classical limit.

    So this sets a new standard for what QG has to achieve. this is the most important thing that has happened in QG (and probably theoretical physics) for the past year. This paper defines the front line.

    And the bad news is what I quoted from page 14. The Triangles people have not gotten up to the point of coupling their quantum spacetime dynamics to "test particles and matter fields".
     
    Last edited: Jul 14, 2005
  7. Jul 14, 2005 #6

    marcus

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    This paper "Reconstructing the Universe" defines what is now the front line and it also sets the standards for future QG

    Perturbative approaches (where you feed in an initial version of what you want to get out) are to resort to if you can't get the nonperturbative to work. Perturbative QG is mainly STRING and to a first approximation we can forget about it.

    Triangles is more non-perturbative, more independent of reliance on a prior specified background, than Loop. And it also even SUCCEEDS BETTER in some ways. It has hamiltonians and lagrangians and the consequent dynamics that Loop has had trouble with, and there's evidence that the full theory achieves a standard semiclassical quantum cosmology limit that Hawking gave credence to. By contrast, LQC has good semiclassical behavior but it is not the full LQG, it is a somewhat simplified version.
    So Triangles not only bootstraps the universe into existence without much to go on, but it is showing positive signs of good behavior.
     
  8. Jul 14, 2005 #7

    marcus

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    besides this main paper "Reconstructing", there is stuff happening in outlying Triangles areas like Black Holes (recent Loll Dittrich paper) and Wormholes (recent Loll Westra paper)

    I think the point to get from the other stuff, especially the Loll Westra "sum over topologies", is that the new model quantum spacetime continuum that is emerging from Triangles is going to have a foamy commotion of very tiny very brief wormholes.

    this microscopic structure could have something to do with dark energy and it could have something to do with inertial and gravitational mass.
    Imagine a particle moving through this foam and interacting with it. Perhaps there is a mechanism by which particles acquire inertia and momentum by this interaction. The only inertia-giving interaction we know of, or hear about so far, is with the HIGGS FIELD. But suppose that interacting with the supposed Higgs field really corresponds to interacting with this topological foamy mess, all these wormholes, that it seems Triangles bootstraps into existence along with all the rest.

    Triangles bootstraps into existence a continuum which we are not used to, which looks nice at large scale, as would please Newton and Einstein, but which looks messy and worm-eaten at very small scale. this is just what it does. The Triangles people did not ask for it to be that way. It is actually quite puzzling that it looks different at small scale than at large---maybe feathery and moth-eaten is a better image.

    You were asking about "axion" and "higgs" and "graviton" and I am saying that when people start transfering their matter fields over from the OLD continuum that standard field theory is written on, and re-writing those fields on the new Triangles continuum, then the fields may look quite a bit different, or they may find they even need different fields altogether.
    They might not even need a Higgs. Some other mechanism might turn out to work better, because of the different microscopic structure.

    that is speculation, might be or might not, but my point is DONT TAKE FOR GRANTED that you are going to see this or that "this-on" or "that-on" that you heard about before carry over to the new context.

    Well I think you wanted my individual take on it, and a sketch of the overall QG picture as I see it. that's subjective and speculative of course, and that's my view for now
     
    Last edited: Jul 14, 2005
  9. Jul 15, 2005 #8

    wolram

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    Thanks Marcus

    I have so many thoughts, but i will not put them into words, one thing is
    i wish BHs were not so important in these works.
     
  10. Jul 15, 2005 #9

    marcus

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    I'm not sure I get the point. Did you mean to say
    "one thing is i wish wormholes were not so important in these works."

    Myself I have been leery of the notion of wormholes and Wheeler's image going back to 1970s of "spacetime foam".
    For much of my life it has seemed suspicious and overly speculative to me to imagine that spacetime would be very rough and chaotic and non-classical at small scale.

    But Wheeler is one of the physics greats of the 20th, and was Feynman's advisor, so one pays attention to what Wheeler says even if it sounds goofy.

    And then lately I am seeing mounting evidence that geometry at very tiny scales may actually be chaotic. Wheeler may actually have been right back in 1970 even though it seemed at the time that he didnt have much reason to launch the idea.

    but as for BLACK HOLES, if you really mean to say
    "i wish BHs were not so important in these works"
    then I have to point out that BHs are pretty much a fact of life, the simplest explanation for a lot of things astronomers see.
    and furthermore in Triangles work they aren't even very important yet
    Hardly anything has been done yet with BHs, by the Triangles people.
    There is this recent Loll Dittrich paper but it is of a preliminary nature, they are really just tooling up to deal with BHs. this has had no effect on the core of the theory as yet. So I would say it has very little importance so far in CDT. On the other hand, BHs have been important in Loop and String, going back to mid 1990s. I dont know whether that is bad though
     
    Last edited: Jul 15, 2005
  11. Jul 15, 2005 #10

    marcus

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    BTW a random note about the spacetime foam idea. Just now i happened to see this at Jacques Distler blog. He is a high-status string theorist with very pronounced views.

    http://golem.ph.utexas.edu/~distler/blog/archives/000605.html

    He doesnt think that string theory gives any evidence for spacetime foam.
    So if you were a "Single Issue Voter" and only cared about having a theory that doesnt support planckscale froth, then you would like String for that reason, I guess.

    "I’ve long been of the opinion that string theory gives zero evidence for the popular idea of spacetime foam. Juan’s remark seems to confirm that."

    ================
    [EDIT to reply to following post] I agree with you that hunches are part of what we are given to think with. And good to distinguish them from reasoned views. It is interesting that you have this hunch about what astronomers assume are BHs not really being BHs.

    [EDIT reply to Richard's post #12] hello Richard you say "I won’t go into my current battles with the bears." Hope you and the bears are all right. If I remember you said they like cooking oil a whole lot. I realize that is probably good advice about Mandelbrot and I really should go read up some. But it is tempting to put my hindfeet up on the table and enjoy a nice bottle of cooking oil.
     
    Last edited: Jul 15, 2005
  12. Jul 15, 2005 #11

    wolram

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    I admit i have no scientific reason for doubting the existence of worm holes
    and black holes as described in the literature, But i have a feeling that
    what ever lurks in the center of galaxies wont have an event horizon or
    weired properties.
     
  13. Jul 15, 2005 #12
    "Imagine a particle moving through this foam and interacting with it."

    Hi Marcus and Wolram

    Marcus, your grasp and focus on these things is astonishing. I don't know how you keep all this in view. I have come to rely on you for your steady, balanced viewpoint. Thank you.

    I quote you above because this sentence seems to encapsulate the one area in which I feel I have something to contribute here… (That is, other than providing amusement and/or irritation for the elders with cute nature stories. I won’t go into my current battles with the bears.)

    For my purpose in this post, foam might as well be generalized to include strings, loops, triangles, feathers, and what the moths did to my wool shirt. I just mean that Wheeler’s foam is only an image, as far as I can tell, meant to evoke a quality sensed in the structure of spacetime, a quality in which spacetime structural members (bones or triangles or whatever) are interspersed with regions of non-structure (wormholes, bubbles, perturbations, what have you) which seemingly must be present to give the spacetime model enough flexibility (background independence) so that our macroscopic 3-space + 1-time observations may be recovered.

    So let me imagine a particle moving through (insert spacetime model of your choice) and interacting with it. Particle moves through and interacts with spacetime. (Maybe to simplify the case we should only consider point-like particles. Presumably large particles like protons and neutrons will be resolved into point-like constituents such as quarks eventually.)

    I parse: “Particle”…..”Moves through and interacts with”…..”spacetime.”

    Clearly the particle is the macroscopic effect which we observe. The spacetime is the microscopic structure which we must infer, since no instrumented direct observation is currently available. “Moves through and interacts with” takes the place of the verb, and we see that whatever the verb in this case may be, it works in both directions. That is, the subject and object of the sentence are interchangeable. What the particle does to spacetime and what spacetime does to the particle is the same thing, or at least, the two sides are dual to each other.

    Now that we see that the verb operates in both directions, I can point out the difficulty. Here it is: Causality. The sentence, seen this way, eats its own tail.

    It is only a short step to see that spacetime and particle is in fact the one thing, and so the verb, whatever it might be, is inconsequential. We may get the full idea merely by stating “spacetime particle” or “particle spacetime.” Or we may choose the more elegant idea of an event. We wave our hands frantically, croaking out the existential assertion, with the frogs, “I am.” How can all this mathematical and philosophical elaboration be of any use?

    Sunbear of the Rainbow Tribe said “I am not interested in your philosophy if it does not grow corn.” String theory is criticized for not having any results. Can any theory that starts with the idea of particles moving through and interacting with spacetime really do any better? I think not. “Causal Dynamical Triangulations” is very cool and I like it a lot, but I wonder about the assertion that causality is preserved. Which, then, does CDT say came first, the particle or the spacetime?

    I have not gone through all of this merely to frustrate and negate. I wish to offer a solution. Here it is: Being is not conserved in the fourth dimension. Without the category we call “being” there can be no causality. How can one thing cause another if there is no thing? The very idea of cause depends upon a fixed arrow of time, and a way to separate that which causes from that which is caused. If there is only one thing, as seems to be necessary to any four dimensional view, then there can be no motion, no cause, no effect, no arrow of time.

    Our human intelligence is found in three spatial dimensions and one time dimension. Any theory of spacetime must recover our macroscopic view of reality, including the standard models and GR. However it is not implied that our three space plus one time view is in some way preferred. I have tried to show that causality is part of our three space plus one time view, and is not possible to maintain as we transition to a form of intelligence that transcends our current dimensionally limited view.

    I am not advocating a deterministic view. It is true that there are no degrees of freedom in 3+1=4 spacetime. But it is possible to extend intelligence beyond the rigid, frozen, acausal, deterministic 3+1 view. There are more degrees of freedom available as we learn to incorporate higher dimensionalities into our view. The freeze thaws as we follow the spacetime equivalence principle into the higher dimensionalities of 3 space plus 3 time view, and that is not the end of the transition.

    Now I would like to return to CDT for a moment. Such a beautiful structure can hardly be left lying in the swamps, no more valued than the croak of frogs. Consider please that three points define a triangle, but they also define a circle. Add a fourth point and the tetrahedron defines also a sphere. All the machinations of triangles in CDT can be seen as the machinations of spheres. I suggest that the math would be a lot easier, much of the computation in CDT unnecessary, if we just took the basic structure (in 3 space one time) as a stack of dense packed spheres. The Monte Carlo randomizations of triangle sides results in a circle when carried to the limits anyway.

    Marcus, I have been reading Mandlebrot on fractals, and he has a very good description of how dimensionality changes with scale. I think it would be worth a trip to the library to look at a copy of his book, which dates back to the 1970’s.

    Thanks for being here,

    Richard
     
  14. Jul 15, 2005 #13
    Nightcleaner

    Your approach seems solidly based in common sense to me, although the details are over my head. But the question arises, if you are right, of whether theorising at this depth is physics or metaphysics, or whether it is possible to make a distinction. Am I right in thinking that you see these issues as beyond a solution within physics?
     
  15. Jul 15, 2005 #14
    Hi Canute

    Someone once observed that scientists are almost always right when they say something is possible, and almost always wrong when they say something is impossible. I would not say that a resolution to this issue is impossible for physics, but I would say that some physicists are currently working very hard to solve a paradox. The paradox is sharp in the three dimensional space plus one dimension of time view, but is easily resolved in higher dimensions, as I tried to argue above.

    I think our physicists and mathematicians could learn something about the paradox if they would ask philosophers and mystics, who have been working on this same problem for centuries. Why do we have to battle over this same ground again and again, with increasingly elaborate models and more time consuming and expensive calculations, when it is clear as day to anyone who has thought about it that there is and can be no motion in spacetime? I speak of motion in the usual sense of some difference in a spatial quantity compared to some difference in a time, as in miles per hour or Kilometers per second and so on.

    If there is no motion then there can be no perturbation, can there? The old Zen koan about two monks watching the movement of a flag in the wind. One says the flag moves, one says the wind moves. The master, overhearing them, says it is their minds that are moving. The master knows that they are arguing over an illusion. The wind, the flag, nada. The only motion occurs within the mind. The spacetime reality is as fixed as the magnetic bits on a CD. They only make the illusion of music or video when the disc is spun under a lasar light. The point of light, traveling across the surface of the disc, creates the illusion of movement, just as the mind of the monk, passing through spacetime, creates the illusion of a flag moving in the wind.

    The question of locality is very similar. How do we determine if a thing is close or far? We do not want spooky action at a distance, but how do we determine that there is or is not a distance? We get our common notion of space from swatting at danglies in the cradle. We see objects hidden by other objects, then we see them reappear as the intervening object moves aside. So we deduce that there is space, since the two objects can pass without bumping into each other. But math and physics introduces us to all kinds of spaces, vector space, phase space, configuration space, cyberspace. Some of these spaces obey different rules from the space we have from the cradle. Advocates of wormholes want us to believe that places which are not local in three dimensional space can be local in four dimensional space....see, you just fold the paper, and there it is. Never mind that three dimensional space cannot be folded like a two dimensional paper surface. And you and I, talking like this in cyberspace. Are we right next to each other or far apart in some dark uncrossable void? Questions about locality become meaningless.

    Since the physicists and mathematicians are reluctant to study mysticism, I, having studied mysticism, have decided to undertake the study physics and math. I can tell you this: The language of physics and math is a lot more obscure and self-referential than is the language of mysticism. Background independent. Perturbative. DeSitter space. Calabi-Yau manifold. And indicies! It goes on and on. Vectors and tensors and spinnors, oh my. Dorothy only had to deal with lions, in the end, and tigers and bears never even entered the story. Lucky girl. Here, we have the whole menagerie, and most of the players are anything but cowardly.

    oh well. I am trying, anyway.

    Richard
     
  16. Jul 16, 2005 #15

    wolram

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    Richard, i think you should write a book, what a refreshing breath of air, your
    reply is thought provoking, but watch out for the main stream paddy wagon.
     
  17. Jul 16, 2005 #16
    Yes, a breath of fresh air is what that is. Few people are prepared to take physics and mysticism seriously. Yet in the mystical view there is an answer to all these paradoxes of physics if physicists bothered to check. They used to do this, and most of the pioneers of quantum theory had a fair understanding of the mystical view, and some even held it, but those days are gone. Bohr even had the yin/yang symbol added to his family crest, and in the view represented by this symbol motion is an illusion. As you say " Why do we have to battle over this same ground again and again, with increasingly elaborate models and more time consuming and expensive calculations, when it is clear as day to anyone who has thought about it that there is and can be no motion in spacetime?" Why indeed. Temperamental prejudice and lack of research is the answer, I feel, continually reinforced by the misleading gobbledygook written about mysticism in the current scientific press, where it seems that no publisher ever thinks of employing a qualified referee to cut out the nonsense. I look forward to discussing some of these things with you.

    Cheers
    Canute
     
  18. Jul 16, 2005 #17

    wolram

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  19. Jul 17, 2005 #18
    I'm in it!
     
  20. Jul 17, 2005 #19

    arivero

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    Indeed we did. Almost all our technique is built upon Democritus and Archimedes, who in turn built (esp. Democritus) upon Zeno. And the description in Lucretius's poem is still adequate if you are not interested in the fine details, (and even you have fermions bosons and a finite speed).

    That is the key: You speak of..

    Which we have learn, already from Zeno paradoxes if you wish, is that we can not speak of motion, that any way of speaking about it drives to inconsistencies. Your Zen monk very accurately points to the mind. You can not mind about motion (actually, with the English most current meaning of mind, I would say people don't mind about any of this, but that is other point). And you can not mind motion because you can not speak about it, you can not aspire to a precise description of it.

    The physics usually spoken about in this forum is mostly a try to inquire how much can we endure the inconsistencies when speaking of movement. We have advanced a long way by absorbing some of them into the uncertainty principle, and by getting used to logic systems of a different kind that classical logic. It is possible that a TOE will be not at the end a theory of the movement "out there", but a theory of the best language possible to speak about movement.

    We do not reject misticism, we build upon it. In more of one sense, the part of mystics we reject is, er, inmovilism.
     
    Last edited: Jul 17, 2005
  21. Jul 17, 2005 #20

    selfAdjoint

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    An interesting post. So you take the Zeno paradoxes seriously and consider discussions of motion (and I suppose any change - Zeno's point*) to be incoherent? I don't think many physicsts would agree with you, nor would Lucretius and his source Democrites.

    * Zeno was a disciple of Parmenides, who taught that change is an illusion. It is possible to accept this in the spirit of Minkowsi spacetime; all apparent change is just a static worldline in spacetime. Like MWI, this raises the question of how our consciousnesses track along such a thing.
     
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