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If y've read Wilczek's book (comment on ideas of chapter 8)

  1. Oct 3, 2008 #1

    marcus

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    If you've read Lightness of Being, which just came out, then you may see that the core ideas of the book are presented in Chapter 8. I'd be interested to read comment on the main ideas from other people who have read the book.

    The book aims to communicate a new intuitive idea of what the world is made of---what the entity we call empty space consists of. A key notion is condensate.

    For general reference see Physicsworld
    http://physicsworld.com/cws/article/print/22275
    The revolution that has not stopped

    also see wikipedia on various condensates, chiral symmetry-breaking cond. or more simply chiral cond.

    Wilczek explains the idea of what he calls QQ condensate, quark-antiquark (I write underline Q for Q-bar which I can't write easily)

    He imagines a composite of condensates, thinking of the vacuum as figuratively consisting of layers and he lists various layers each one a condensate, the QQ one, ..the Higgs one,.. a possible gravity one.

    He says what he wants to get from the LHC (which many are not as definite about) and where there is a range of possibilities he indicates the range. He says how what he expects to come out of LHC fits into his paradigm of what the world is made of. What the vacuum is made of (matter fields are just excitations of the vacuum, or as he calls it the Grid.)

    So far I havent told you anything about what he actually says or how he describes these things. I'd like to get your reactions to the book, from people who have read it, and especially enlightening comment on Chapter 8
     
    Last edited: Oct 3, 2008
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  3. Oct 3, 2008 #2

    marcus

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    I'll tell you an impression I have about what Wilczek is doing in Chapter 8, which I think is the heart of the book and has the core message that many of the other chapters, appendices, glossary etc connect in to and expand out from.

    If you've read the book then you can say whether or not you think I am right about this, and give a different interpretation if you want.

    He works hard on a description of the QQ condensate, which comes out of what he knows very well namely Quantum Chromodynamics:
    how quarks and gluons which have no mass or very little mass bind together in an energetically favorable way and the energy of their interaction is what actually what give the proton 95 percent of its mass.
    He uses this picture from Quantum Chromodynamics very hard, and he gets you to imagine a seething bunch of virtual particles and antiparticles in some detail and consider why some combinations are more favorable.
    the two ideas he works hard at developing are condensate and superconductor, and he works hard developing analogies between them, both are going to function as metaphors and they are going to be metaphors for the same situation.

    Now the guy is both a great theoretical physicist and a great science writer, so look at what he is doing. What is his strategy as a writer?

    Remember that a metaphor never takes the place of the mathematics. The metaphor is a way to exercise your imagination so as to make the mathematical model more intuitive. Don't ever treat a metaphor as the real thing. the math model is the real thing (or the closest you ever get) and the metaphor is a way to teach your mind to have intuition.

    Like in cosmology a very good metaphor is the expanding balloon. You can learn a lot about how to picture expansion of space from imagining the balloon, with painted dots for galaxies. But don't confuse the balloon with the universe. Space is not made of rubber. It's really about distances, not about material stretching.

    OK, Wilczek has a job of communicating what the world is made of and he tells you about QuarkAntiquark condensate, which he knows a lot about and is sure about and can describe very well. QQ condensate is, for him, like the rubber balloon. Likewise the superconductor as he describes it. These are the metaphors of an active dynamical Vacuum (almost like a material.)
    And these are his guides to what he expects to be able to put together when the LHC tells him how many and what kinds of Higgses there are. That will be another layer or facet of empty space, a condensate that attributes inertia to things.

    That's just my overview of what's going on in Chapter 8. It isn't necessarily right. You may see it in a totally different light. If so, please let us know what you think.
     
  4. Oct 4, 2008 #3

    marcus

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    If y've read Wilczek's book (Daney can help understand chapter 8)

    If you've read LoB and, as I do, see chapter 8 as the heart of the book presenting the main ideas, you may want some supplementary material on the Higgs mechanism to help in understanding what Wilczek is saying. I'd recommend browsing a bit in Charles Daney's website "open questions". He is a gifted and hardworking science writer with a lot of stuff online. Just go to openquestions.com and look at the site map--some of what is there may be useful to you.

    As a sample excerpt, here is a portion from his page on the Higgs mechanism:
    http://www.openquestions.com/oq-ph008.htm
    ==excerpt from Open Questions Higgs page==
    The Higgs mechanism
    Let's review where we stand so far.

    * We have a nice, well-behaved (i. e., mathematically consistent, renormalizable) Yang-Mills gauge theory of the electromagnetic force, based on U(1) gauge symmetry.
    * We would like to have an equally nice Yang-Mills gauge theory of the weak force, and it should be based on a SU(2) symmetry.
    * Experimentally, it is known that the particles which mediate the weak force are massive, instead of massless as required in a Yang-Mills theory.
    * The electromagnetic and weak forces are intertwined, because the weak SU(2) symmetry exchanges particles that have different amounts of electric charge.
    * Yet any potential symmetry between electromagnetic and weak forces can't be exact, since the forces have different strengths.

    A series of profound insights by Sheldon Glashow, Steven Weinberg, and Abdus Salam, mostly as independent contributions, led to the unified theory of the electroweak force. This was accomplished by taking the above givens, making a few inspired assumptions, and synthesizing everything in a new -- and quite effective -- way.

    The insights were as follows:

    1. Most of the theoretical difficulties result from the existence of nonzero rest masses of the various particles. The masses break the symmetry between electrons and neutrinos (and other particle pairs), they are incompatible with a straightforward Yang-Mills gauge theory, and they are the root of the problems with renormalizability.
    2. At very high energies, the energy contributed by a particle's rest mass becomes insignificant compared to the total energy. So at sufficiently high energy, assuming a particle rest mass of zero is a very good approximation.
    3. A consistent, unified Yang-Mills theory of electromagnetism and the weak force can be formulated for the very high energy situation where particle rest masses are effectively zero.
    4. At "low" energies (including almost all levels of energy which are actually accessible to experiment), the symmetries of the high energy theory are broken, and at the same time most particles acquire a nonzero rest mass. These two "problems" appear simultaneously when symmetry is lost at low energy, much as symmetry is lost when matter changes state from a gas to a liquid to a solid at low temperature.

    The "Higgs mechanism" is basically nothing more than a means of making all of this mathematically precise.

    The key ingredient not yet specified is to assume there is a new quantum field -- the Higgs field -- and a corresponding quantum of the field -- the Higgs particle. (Actually, there could be more than one field/particle combination, but for the purposes of exposition, one will suffice.) The Higgs particle must have spin 0, so that its interaction with other particles does not depend on direction. (If the Higgs particle had a non-zero spin, its field would be a vector field which has a particular direction at each point. Since the Higgs particle generates the mass of all other particles that couple to it, their mass would depend on their orientation with respect to the Higgs field.) Hence the Higgs particle is a boson, a "scalar" boson, since having spin 0 means that it behaves like a scalar under Lorentz transformations.

    The Higgs field must have a rather unusual (but not impossible) property. Namely, the lowest energy state of the field does not occur when the field itself has a value of zero, but when the field has some nonzero value. Think of the graph of energy vs. field strength has having the shape of a "W". There is an energy peak when the strength is 0, while the actual minimum energy (the y-coordinate) occurs at some nonzero point on the x-axis. The value of the field at which the minimum occurs is said to be its "vacuum" value, because the physical vacuum is defined as the state of lowest energy.

    This trick wasn't created out of thin air just for particle theory. It was actually suggested by similar circumstances in the theory of superconductivity. In that case, spinless particles that form a "Bose condensate" also figure prominently.

    The next step is to add the Higgs field to the equations describing the electromagnetic and weak fields. At this point, all particles involved are assumed to have zero rest mass, so a proper Yang-Mills theory can be developed for the symmetry group U(1)xSU(2) that incorporates both the electromagnetic and weak symmetries. The equations are invariant under the symmetry group, so all is well.

    Right at this point, you redefine the Higgs field so that it does attain its vacuum value (i. e., its minimum energy) when the (redefined) field is 0. This redefinition, at one fell swoop, has the following results: the gauge symmetry is broken, the Higgs particle acquires a nonzero mass, and most of the other particles covered by the theory do too. And all this is precisely what is required for consistency with what is actually observed.

    In fact, the tricky part is to ensure that the photon, the quantum of the electromagnetic force, remains massless, since that is what is in fact observed. It turns out that this can be arranged. In fact, the photon turns out to be a mixture of a weak force boson and a massive electromagnetic boson that falls out of the theory. The exact proportion of these two bosons that have to be mixed to yield a photon is given by a mysterious parameter called the "electroweak mixing angle". It's mysterious, since the theory doesn't specify what it needs to be, but it can be measured experimentally.

    So, the Higgs mechanism is a clever mathematical trick applied to a theory which starts by assuming all particles have zero rest mass. This is especially an issue for the bosons which mediate the electroweak force, since a Yang-Mills theory wants such bosons to be massless. While the photon is massless, the W and Z particles definitely aren't. Where, then does their mass come from? Recall that we observed that spin-1 bosons have 3 "degrees of freedom" if they are massive, while only 2 otherwise. It turns out that this extra degree of freedom comes from combining the massless boson with a massive spin-0 Higgs boson. That Higgs boson provides both the mass for the W and Z, as well as the extra degree of freedom.

    In fact, the mechanism furnishes mass to all particles which have a nonzero rest mass. This occurs because all the fermions -- quarks as well as leptons -- feel the weak force and are permuted by the SU(2) symmetry. And since quarks acquire mass this way, so too do hadrons composed of quarks, such as protons and neutrons, which compose ordinary matter as we know it.

    But this mechanism is more than just a trick. If the whole theory is valid, then the Higgs boson (or possibly more than one), must be a real, observable particle with a nonzero mass of its own. This is why the search for the Higgs boson has become the top priority in experimental particle physics.

    What about renormalizability? Has this been achieved in spite of all the machinations? It seemed plausible that the answer was "yes", which was of course the intention, since the high-energy form of the theory has the proper gauge symmetry. But it took several years until a proper proof could be supplied, in 1971, by Gerard 't Hooft.

    Supersymmetry

    It should be pretty clear by now that Higgs physics is very much tied in to the standard model. Indeed, it's necessary in some form to make sense of many features of the standard model -- such as electroweak symmetry breaking and particle masses. In fact, it -- or something very like it -- seems to be necessary just to make the theory consistent.

    And yet it's not quite a part of the standard model either. It has a bit of an ad hoc feel to it. If, in fact, the Higgs mechanism exists in more or less the form outlined here, then the standard model certainly has no explanation for why it's there, for what makes it happen. We shall want more than that. We want to know the source of the Higgs physics itself.

    There may be a number of ways to do that (which might be related among themselves). But there is one body of theory which can provide exactly the explanation of Higgs physics we're looking for, and which has been in gestation since the early 1970s (i. e., since the time the standard model assumed its present form). It's called supersymmetry. ...
    ==endquote==
    and at that point he moves on to talk some about SUSY. Go to the Daney site to read more. Thanks to Wolram for alerting us to Open Questions as a resource.
     
    Last edited: Oct 4, 2008
  5. Oct 4, 2008 #4

    marcus

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    As I see it, Daney's explanation dovetails with what Wilczek says and could make it easier to grasp.
     
  6. Oct 17, 2008 #5

    marcus

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    See if you agree with this:

    One of the best ways to understand Wilczek's message is to see how it gets translated into more technical language by another particle physicist!

    In particular, I think the Robert Percacci has nearly the same perspective on the new physics he hopes will come out of LHC and his vision of unification over the next 10 or so years.

    Percacci outlined his point of view in a talk he gave at Sussex in September:
    Here is the conference programme.
    http://www.ippp.dur.ac.uk/Workshops/08/CLAQG/Programme/

    Here are slides for Percacci's talk "A particle physicist's view of gravity"
    http://www.pact.cpes.sussex.ac.uk/~dl79/CLAQG/Percacci.pdf

    Sometimes it is good to hear the same message in both an intuitive non-mathematical style and a concise technical style. One gives metaphors and intuition and the other some additional clarity.

    Do you think they are saying essentially the same thing? Enough the same so that Percacci gives a useful angle on Wilczek?
     
  7. Oct 17, 2008 #6

    MTd2

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    Hmm, amazon sent me an email yesterday that my copy of this was shipped... Now, let's see how fast it can travel 12,000km.
     
  8. Oct 18, 2008 #7

    Fra

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    I am also waiting for this book, but mine hasn't even shipped yet :) I order my books from a local company that has the same selection as amazon and great prices and free shipping.

    /Fredrik
     
  9. Nov 4, 2008 #8

    Fra

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    "distinction without difference"

    At least I got the book some time ago but only read a few chapters so far. In general I like the book so far.

    One think that seems to be of his signature of his reasoning is his take one symmetry as a guiding principle.

    The phrase "distinction without difference" is interesting. I think this is the old paradox of symmetry. Is symmetry real? I mean, if we turn it around, how do you arrived at a distiction without a difference in the first place? And if a distinction makes no difference, what is the nature of this apparent redundancy?

    So far in the book he doesn't seem to address those questions. And I think this problem is fully analogous to the "problem/paradox" of background indepdendence in the most general sense. IE. can "symmetry" be absolute AND relatable to a real observer? If not, what are the consquences to the guiding symmetry principles for theory building?

    Those who advocate background independence in one way or the other, argue from a symmetry argument that any chose of background is completely arbitrary and can not be motivated. Thus a fundamental theory must be independent of such a thing.

    Other notes that the notion of background indepedence is kind of bunk since it does not make sense to talk about anything without a reference. Any statement, or measurement must related to a "background reference". Therfore to do away with this background is to suggest a statement living in thin thin air - and that seems to make no sense.

    IMO this is just the same argument behind the symmetry paradox.

    So which is it? IMO both views are partially valid points. I always liked slightly
    along smolins suggestive weird evolutionary law think, that the evolutionary concept
    is the solution to the paradox that can please both sides of this paradox.

    I was hoping to find Wilczek's point on this, how he put this grid idea in this context. I am roughly in liking of this idea to consider mass as confined energy, but is this entire construction absolute? I am looking for the inside observer perspective in his reasoning. I didn't see it so far.

    This was just the first things that popped up in my head when I read this. I'll probably get more enlightened as I keep reading the rest of the book.

    If MTD2 has started reading I'm curious to hear this idea as well.

    /Fredrik
     
  10. Nov 4, 2008 #9

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    Re: "distinction without difference"

    The book was shipped 2 weeks ago! But it's a looong path to arrive down here! :D
     
  11. Nov 4, 2008 #10

    Fra

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    Re: "distinction without difference"

    So where are you located?

    /Fredrik
     
  12. Nov 4, 2008 #11

    MTd2

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    Brazil, Rio de Janeiro...
     
  13. Nov 4, 2008 #12

    Fra

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    Ah that's cool. I've never been there but it would be an interesting place to visit someday.

    I think Ariel Caticha (now in US) is originally from Brazil and his brother is I think a professor in Sao Paulo. I am somehow curiously awaiting his book that I think Ariel is working on on "information physics" to pop up at some bookstore near me :) Some user on here knowing Ariels brother wrote on that here some year ago I think. He was kind to supply my some drafts of the early chapters, which is more or less the material from his published papers. I'm curious to see if he takes anything to another level in the book.

    /Fredrik
     
  14. Nov 4, 2008 #13

    MTd2

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    Well, Caticha looks like a hispanic name, not a portuguese name... Although ther is a lot of superposition between surnames between these languages, "ticha" of caticha sounds like hispanic... But it seems that he worked at UNICAMP, indeed.
     
  15. Nov 5, 2008 #14

    Fra

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    More reflections....

    I finished chapter 8 last night. His opinion of the analogy between all forces are clear. I think the key issue, to which he presents no clear suggestive solution as I can see, comes in the end of the chapter, is what gives his grid the very small but non-zero mass (as observations suggest), or basically the cosmological constant problem. This is made more interesting by noting that the vacuum field fluctuations predicted by the various quantum fields are way off chart in scale.

    I can't help associate this apparent "overcounting" of the degrees of freedom with the lack of the inside perspective regarding the concept of symmetry. Because I again insist that there is a common issues here emergent or absolute symmetry, emergent or absolute background, and various ergodic hypothesis. I think the "right observatioanl perspective" is supposedly what renormalization is set out to "cure", but the question is if the current way of doing it is the best way?

    This was a nice chapter. I'll get on to the next chapters!

    /Fredrik
     
    Last edited: Nov 5, 2008
  16. Nov 7, 2008 #15

    Fra

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    I like Wilczek's thinking of "profound simplicity". Mmm perhaps it's a bit like the devil reading the bible but at least the parts of his expressions of simplicity can be interpreted as IMO truly relative - to my liking.

    When you make the comparasion to datacompression, like Wilzcek does. Then clearly the notion of optimum compression, relates to stuff like memory size and computations times regarding both compressiond and decompression. An ultimate compression, compressed beyond practical DEcompression is clearly totally useless. Therefore, I think one angle of what he says, is that the notion of simplicity, is basically relating to a memory and a computing device for compression/decompression. And what is this device? As I see it the only sensible connection is the observer! Thus simplicity is observer dependent. So it seems each observer makes his own optimations, and the feedback lies at the population dynamics of observers.

    /Fredrik
     
  17. Nov 8, 2008 #16

    Fra

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    Wilczek's view on Popper

    In chapter 19 he makes this note that I found to be quite amusing and made me smile while reading it, but also quite deep statement that I think is a hint that he has some deeper visions that really trace down to the scientific method. This is also in line with his datacompression analogy of "profound symmetry".

    "We succeeded in producing a theory that was not just falsifiable but outright false. Very scientific, says Karl Popper. But somehow, we are not left feeling gratified"
    -- F. Wilczek, p183, The lightness of beeing

    I feel a connection here to his vague idea of thruthification, as a kind of more "contructive" version of falsification. It seems closely related to what I have called the "logic of revision or correction". He seems to suggest, to which I totally agree, that some more focus should be not only on "falsifiable hypothesis generation" but on the deeper mechanics for evolving a falsified hypothesis into a new hypothesis. I think this is what Wilczek calls truthification. But the not is short, so perhaps is emphasis is not too strong.

    /Fredrik
     
  18. Nov 8, 2008 #17

    marcus

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    Fra, your recent comments are helpful in more ways than one. For me, because I have been lending my copy of the book to friends and don't have it handy, your comments remind me of Wilczek's intriguing reflections and so keep me thinking about its thought-provoking ideas even when the book itself is not immediately at hand.
     
  19. Nov 8, 2008 #18

    Fra

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    Fundamental symmetry - the new form of "realism"?

    Now I've finished reading the book, and here is another thing that hit me in the face as a reader...

    Wilczek relies heavily of various kind of symmetry principles, and the search for larger symmetries seems to be almost like a methodology of howto make progress.

    I can not help asking, what exactly is the physical basis of this symmetry. In some parts of the book I think Wilczek reasons in a way that suggests that perhaps there is a deeper (not yet spelled out) logic around the concept of "simplicity" and "symmetry". In other parts of the paper, he argues in a way that gives the impression that he thinks of the existence and uniqueness of the fundamental symmetries almost in the old spirit of realism. IE. that the SYMMETRIES are the ontological elements that exists, in a realist sense.

    To me there is a slight tension between these views and even though the concept of symmetry, invariance etc is a very simple concept, that we have also in classical physics, there is something about this that I think isn't understood in depth. In particular when it's brought together with the problem of what elements in theory is really to be though of as "observable". It's a bit fishy, almost like the ergodic hypothesis is somewhat fishy in classical physics. Neither can one help associating this "issue" to SMolins ponderings of the problem of distinguishing initial conditions vs law. IE. we sometimes use "symmetry principles" as a rule of reasoning, or "law". But what about the origin of the laws?

    Does people really find it satisfactory to consider "physical law" as realism elements? I personally can do that.

    /Fredrik
     
  20. Nov 8, 2008 #19
    Re: Fundamental symmetry - the new form of "realism"?

    This doesn't seem like so much a mystery to me. If we were to have a mathematical formulation of physics, then what is observable is that which does not vary, at least while you are observing it. This means observables must comply with some sort of symmetry principles associated with invariances of this mathematical formulation.
     
  21. Nov 9, 2008 #20

    Fra

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    Re: Fundamental symmetry - the new form of "realism"?

    Friend, thanks for expressing your view!

    To explain on my previous post - I am not suggesting that the concept of symmetry is useless. On the contrary do i think it's important, but I think there is a difference in how you think of it, and then ultimately treat it, when builing models. It's the latter part here, our guidance in model building that I think is what may distinguish this discussion from fruitless philosophical or interpretational issues. In particular do I think these things get important when discussing, emergence of symmetry, and breaking of symmetry.

    I sort of understand your construction here, but you construction contains two variables. It's "we", and it's "vary with what". We would hopefully refer to an observer, right? And then the first issues comes into play, there are more than one observers. There is in fact a large class of observers. Often we assume a symmetry class, that generates all possible observers. Observer-frame transformations for examaple. But usually when we think of this, it's the scientific community of earth whose collective knowledge maintains these "transformations", and the "observers" really refer to say particles, small subsytems like measurement devices we have constructed. This IMO is a typical emergent symmetry. One might argue that human science are not observers on the same footing, but I think we are. I think that perhaps this emergence of symmetries, when applied also to particle particle interactions, MAY possibly be a key to unification.

    And then varying what what? time? what is time? who's clock? I think the story is the same, that an observer does not have real a priori knwledge of the global transformations that connects his view to another party. I think again that it should be emergent.

    This IMO is at least partly well in line with Wilczek's datacompression analogy, because as he points out there is not simple solution to that problem, and obviously part of the problem is that simplicity is relative! Relative to memory available, relative to computation power available. Therefore if we are to be really pragmatical, we must note that simplicity when it comes to physical laws, must ensure that they are computable. If predictions requires a computer the size of the unverse then clearly that is a completely usless theory.

    But this is just my view, I suspect that your not the only one to not see what bugs me here. Indeed these realist type of symmetries has and is still a heavy guide in model building and I think many simply doesn't see the benefit in asking these questions.

    I don't think the symmetry guide is wrong, but I think we will benefit from a reflection of the nature and origin of these symmetries, and this may suggest that these guides are not as solid as it may seem. The question, is how can an instance of a symmetry class, encode the meaning of the full symmetry class? i don't think it can. This encoding I think lies elsewhere.

    /Fredrik
     
    Last edited: Nov 9, 2008
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