tag:blogger.com,1999:blog-8666091.post110524199162657544..comments2021-05-03T21:54:48.969+02:00Comments on The Reference Frame: He believes it's true but he can't prove itLuboš Motlhttp://www.blogger.com/profile/17487263983247488359noreply@blogger.comBlogger56125tag:blogger.com,1999:blog-8666091.post-1106124360274057162005-01-19T09:46:00.000+01:002005-01-19T09:46:00.000+01:00More interesting beliefs, IMHO:
-Carlo Rovelli (a...More interesting beliefs, IMHO:<br /><br />-Carlo Rovelli (and see also Donald Hoffman) "Time does not exist"<br /><br />-Jesse Bering "I do never die" approach. A Linguist here, Agustin Garcia-Calvo, has a close one.<br /><br />-Maria Spiropulu use of no-thing, just because it remembers me of "my disciple" Democritus.<br /><br />-John McWorter about the language on Flores island<br /><br />-and Rudy Rucker multiverse "Reality is a novel"Leucipohttps://www.blogger.com/profile/14505549871207858030noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105748790939268942005-01-15T01:26:00.000+01:002005-01-15T01:26:00.000+01:00Incidentally, hidden variables and Bohmian theory ...Incidentally, hidden variables and Bohmian theory are "lost causes in physics number 1 and 11" of Streater. I endorse his text 1 and 11, which does not imply that I endorse all of this texts.<br /><br /><A HREF="http://www.blogger.com/r?http%3A%2F%2Fwww.mth.kcl.ac.uk%2F%7Estreater%2Flostcauses.html">http://www.mth.kcl.ac.uk/~streater/lostcauses.html</A>Luboš Motlhttps://www.blogger.com/profile/17487263983247488359noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105748137200577452005-01-15T01:15:00.000+01:002005-01-15T01:15:00.000+01:00You must have confused Bohm's theory with some com...You must have confused Bohm's theory with some completely different theory, or perhaps you misunderstood the very basic points of it.<br /><br />Bohm's theory is a key example of a theory of hidden variables. What do you think that the term "hidden variables" mean? It's the whole point of this problematic approach to quantum physics that it involves a lot of new variables - in the simplest case, it includes both the classical position and momentum of a particle, as well as a "physical" wave function whose "quantum potential" affects the motion of the particle. These new degrees of freedom can't be directly seen, and if they could be seen, the usual symmetries of Nature and causality would be violated.Luboš Motlhttps://www.blogger.com/profile/17487263983247488359noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105747646563493882005-01-15T01:07:00.000+01:002005-01-15T01:07:00.000+01:00Lubos,
That is not quite true. Mathematically, ...Lubos,<br /> That is not quite true. Mathematically, there are no additional variables. One has a phase, and an amplitude, the derivatives of which are called "momentum" and "position" in the Bohmian theory. One does not need to accept this assignation. However, by solving the quasi-newtonian equations for this "position" and "momentum" one is actually calculating the wavefunction of the system. So this is an interesting <br />calculational technique, which is still being worked on today. While you may consider this irrelevant because it applies only to non-relativistic situations, and does not have any use in QFT or any such thing, there are still several problems in physics which involve non-relativistic quantum mechanics, and <br />involve the calculation of wavefunctions and densities. The equations of motion due to Bohm's trick do have a limited use there. No one really believes that the pilot wave interpretation is correct, but the mathematics of the Bohmian theory is natural to the Schrodinger equation and can be thought of as a way of rewriting the same. <br /><br /> From a different point of view, any theory of hidden variables or otherwise which tries to supplant quantum mechanics is fundamentally pointless, unless it can predict all the set of things that QM does, and in addition make predictions that go beyond the QM framework. The Bohmian view fails this test, and so do all other substitutes for QM that I know of.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105740230792841332005-01-14T23:03:00.000+01:002005-01-14T23:03:00.000+01:00Of course that the Bohm interpretation adds extra ...Of course that the Bohm interpretation adds extra variables that don't exist normally; it has BOTH the wavefunction as well as CLASSICAL coordinates and velocities of particles.<br /><br />You don't have to use a correct interpretation of quantum mechanics unless you need to make correct predictions. In the simple models, one can construct an "awkward superstructure" (as Einstein called the theories of hidden variables) that is equivalent to the correct quantum mechanics, but it can't be generalized to other systems - such as relativistic systems - and even if it can, all the correct predictions of these bizarre theories are those copied from quantum mechanics, and all the new predictions are incorrect.<br /><br />The Bohm picture picks priviliged observables which is highly unacceptable especially in quantum field theory - which is the real picture we've been used to describe the real world already from the 1930s. In quantum field theory, one can talk about configurations with well-defined classical values of the fields, or about configurations with well-defined numbers of particles with well-defined positions. These bases are different, incompatible, and there is no physical sense in which one basis is better than another basis. There are also many other bases one can choose.<br /><br />However, in the Bohmian picture you HAVE to make a choice which variables will be treated as the extra classical degrees of freedom, and whatever choice you will make, you will eventually be in trouble. Also, the Bohmian picture will always violate Lorentz invariance and it will always have problems to incorporate spin etc. <br /><br />The de Broglie pilot wave theory could have been a serious research direction in the 1920s when people started to understand the framework behind quantum mechanics, but today the research of the Bohm theory is just an artifact of poor knowledge of physics - the Bohmian theories have nothing to do with the actual quantum physics of the last 60 years: spin, quantum field theory, gauge theory, renormalization, Higgs mechanism - but it's also un-helpful for entanglement, quantum computing, and understanding of quantum decoherence which is really the main piece of progress in the interpretation of QM in the last 25 years.Luboš Motlhttps://www.blogger.com/profile/17487263983247488359noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105738733397898862005-01-14T22:38:00.000+01:002005-01-14T22:38:00.000+01:00Lubos,
The De Broglie-Bohm interpretation does n...Lubos,<br /> The De Broglie-Bohm interpretation does not add extra variables to describe quantum mechanics, and neither does it place treat either momentum or position specially. All it does is mathematically reformulate Schrodinger's equation, and interpret<br />the phase of the quantum mechanical wavefunction as a classical action and the amplitude as a classical real space density, and then treat the corresponding momentum and position as the true classical variables underlying the quantum system. Since, the formulation is mathematically exact and equivalent to the schrodinger equation, one does not have to buy into its interpretation to use it to solve various, concrete problems, involving the treatment of some variables as quantum objects and others as classical ones.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105410827221062532005-01-11T03:33:00.000+01:002005-01-11T03:33:00.000+01:00Hi travis-
It's clearer now, except that I don't ...Hi travis-<br /><br />It's clearer now, except that I don't make head or tails of your concept of 'compressible'.<br /><br />Anyhow, to make this shorter and possibly correct I will use lumo's replies. Since I elsewhere saw a statement that 'Consistent histories' was an interpretation of QM I haven't looked into it before. lumo tells us that in fact you have QM+CH, consistent with QM, but with larger scope (histories).<br /><br />In lumos CH reference (http://en.wikipedia.org/wiki/Consistent_histories) there are two more postulates. Histories Hi are defined as a product of projection operators and they are consistent, ie Tr(HioHj') = 0 and Pr(Hi) = Tr(HioHi'). No branching, no MWI.torbjornhttps://www.blogger.com/profile/03072037567907266083noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105389170269766022005-01-10T21:32:00.000+01:002005-01-10T21:32:00.000+01:00hey lubos, thanks for your answer, I have still so...hey lubos, thanks for your answer, I have still some remarks....<br /><br />you said:<br /><br />"It is often difficult to say what a quantum theory, defined in terms of its classical limit, means - and gauge-fixing is often kind of necessary to make sense out of the theory.......Other gauge-fixings are more problematic, at least according to string theory - they don't allow us to solve the theory easily and they have also other problems."<br /><br />Is it true that gauge fixing is 'necessary'? Dirac's approach, if I'm correct, was to construct observables in term of gauge invariant objects. It is certainly true that we can talk of observables in any gauge and therefore, in principle, have the same answer. <br />Now you are telling me that some gauges are problematic in string theory, does this mean that there is not a consistent gauge invariant way of quantize string theory? If so, what does it mean that some gauges are 'better' than others in physical terms? (in other words, why QM picks certain gauges over others and what would that tell about the theory. This has a very simple example in standard QM with the choice of canonical pairs and factor ordering issues I never completely understood. That's a good one actually, how do you treat factor ordering in the path integral approach?)<br /><br />another thing, you said:<br /><br />"According to the Wheeler-deWitt equation, we *must* kind of gauge-fix - to choose the time as a function of some other, gauge-invariant degrees of freedom - if we want to make any contact with observable physics."<br /><br />Firstly, the choice 'x^0=s' doesn't look like a function of gauge invariant degrees of freedom, in fact in a totally covariant framework gauge invariant objects are frozen, they don't evolve at all. I agree that WdW is gauge fixed, my question was more related of how this equation, which represents 'the physics', will account for time-fluctuations if now time is an external parameter in it. I disagree though that to make contact with observable physics we have to gauge-fix, the basics of a relational construction lies in totally the opposite, namely, to construct gauge invariant objects that will represent 'evolution' in a relational way, like a gauge invariant answer to the question: what's the value of q_1 'given' q_2=t. This translate into QM as: "what's the probability of q_2=x 'given' q_1=t". I found this approach remarkably in that now q_1 plays the role of the clock but it is in the same footing that all the other variables contrary to the gauge fixing process where I can't see how can you treat time as a quantum object. That's why quantum mechanically the difference between to gauge or not to gauge become, I think, physically relevant. <br /><br />I like this:<br /><br />"But I believe that this is just the truth: if your correct physical theory tells you that some objects are relative - they depend on your conventions, reference frames and other choices - you must accept it. Also, if it tells you that some observables are inaccurate, they can't be defined exactly, you must accept it as well."<br /> <br />We all have some degree of belief in this business, 'the truth' is an strong statement I will hesitate to use. I agree that if the theory is correct, namely, explains nature, you have to learn to live with it whatever it tells you about 'her'. So far it is not clear what the final theory of gravity is, I will save here my words for the future. I disagree that observables depend on conventions, I do agree that observables are relational objects and therefore depend upon choices, our choices. If that's what you meant, you are close to relational ideas as well :)<br /><br />This is even more interesting:<br /><br />"Every nontrivial statement must have some evidence - either a direct experimental proof, or evidence that it follows from the consistency of any acceptable theory. I reject all statements about the physical world that are done purely on the philosophical grounds, especially if they seem to contradict our experiments and the knowledge that we've obtained from these experiments."<br /><br />It would take days to discuss this, but let me just make a few remarks. String theory so far doesnt have any direct experimental proof, and the consistency of an acceptable theory is a source of debate. I am curious about 'the knowledge that we've obtained from experiments' and the birth of string theory. As far as I know string theory was ruled out as a description of the strong interaction and suddenly promoted to a theory of everything without any ground but the belief that the spin-2 massless particle is the 'graviton'. Gravity has been always based on philosophical insights, look Newton's idea that it had to be universal, and Einstein construction of GR without any clue but it's equivalence principle. String theory claims to fulfill Einstein's dreams, I'm afraid that most of his dream were based on philosophical grounds and beliefs. <br />In addition, physicists, like for instance Glashow, claim we won't be ever able to rule out string theory. How do you handle a theory that can't be confronted with nature? <br />I am not against following philosophical beliefs but I agree with you that we should make contact with Nature ocasionally.<br /> <br />You also said:<br /><br />"General relativity as well as string theory show that the "indifferent podium" is never indifferent after all. All features of reality that influence other objects tend to be dynamical and "equally fundamental", so to say." <br /><br />I agree with that and so does the LQG people. The very heart of relationism is that: " All features of reality that influence other objects tend to be dynamical and "equally fundamental", so to say." The problem with this is how do you treat time and it 'equally fundamental' status. We can't treat it as an external classical parameter and that's why relational ideas are necessary. <br /><br />In addition you said:<br /><br />"It's just a wrong approach to imagine that a theory is defined in a two step process - one defining the background where things take place (or the relations that the objects can have), and then defining some objects assuming the first assumption. In reality, the objects influence each other in both ways."<br /><br />Totally agree, but historically, as pointed out by Witten to me, string theory was more a two step theory that a background independent one. What you just said here is again the core of relationism to which I totally agree.<br /><br /><br />I agree this is a very vague chat and I appreciate the time you take in answering my quesions. <br />I disagree that lqg ideas are totally rubbish as I also believe string theory is a beautiful mathematical construction as far as I know. However, there are a lot of beautiful constructions (subjective topic btw) which do not represent our world. <br />The type of argumentation between the two is not good for our physics society nor for young students. Saddly it doesn't look like is gonna be better. <br /><br />With respect to QCD, I was asking you for an equivalent landmark of asymptotic freedom not how does it come from string theory. Incidentally, talking about ADS/CFT, holography was originally proposed by thooft who is a nonlocal hiden variables advocate by now if I understood him clearly. <br />We can also discuss about leny's landscape and the anthropic principle, but I guess that there is too much information here so far, it might create a BH :)<br /><br />best regards,<br /><br />RAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105388125261987272005-01-10T21:15:00.000+01:002005-01-10T21:15:00.000+01:00"some continuous physics done properly" Yes, the k..."some continuous physics done properly" Yes, the kind of proper work that is reflected in the renormalisation groups methods, in Kadanoff or in Wilson-Kogut: that a proper work with the continuous limit is basically to keep track of the process. The need of a renormalisation point, movable but undisposable, in the deepest clue we have nowadays about the communion between the discrete and continuous.Leucipohttps://www.blogger.com/profile/14505549871207858030noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105387619182938562005-01-10T21:06:00.000+01:002005-01-10T21:06:00.000+01:00Hi Michael,
I agree that results such as Coleman-...Hi Michael,<br /><br />I agree that results such as Coleman-Mandula, or books as the one of Aspects of Symmetry, are clearly more illuminating for physics that the works of Smolin I know of. I reserved my oppinion because on one hand I have never worked (just read) over Smolin shoulders, and on the other hand I feel that some level of debate is needed in our overspecialised age.<br /><br />I found funny your remark because just yesterday I was drawing some genealogies and I found also this surprising heritage from Coleman to Smolin. By the way, it is probably the longest known pedigree in theoretical physics, going up to Otto Mencke, the cofounder of Acta eruditorum.Leucipohttps://www.blogger.com/profile/14505549871207858030noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105386947412429302005-01-10T20:55:00.000+01:002005-01-10T20:55:00.000+01:00Hi Torbjorn -
Yeah, I did write that at 3 a.m. -...Hi Torbjorn - <br /><br />Yeah, I did write that at 3 a.m. - let me try to be a little more clear. There are two general issues:<br /><br />#1 Say we want a deterministic theory of nature, and QM in particular. The original Copenhagen interpretation is obviously no good (it describes a very incompressible type of universe!), so that leaves us with the MWI (which is highly compressible - all you need are the initial states, and you can then evolve forward, producing lots of different histories in the classical limit) (*). But the existence of all these different decohered histories jars with some people's intuition of how the universe should be, so they conjecture about cellular automata rules at the Planck scale that would determine, for instance, precisely when a radioactive atom will decay. I am arguing their gut level rejection of the MWI was wrong however, and a many different histories universe can be perfectly intuitive.<br /><br />This requires a bit of a detour:<br />#2 I am going to make 2 natural assumptions about the universe to build the case that many worlds can be intuitive. First I assume that the universe actually is a mathematical structure, i.e. we can form a complete mathematical model of reality so that the model and reality are one to one. This claim is bolstered by every successful prediction in physics. It is fun to think about which result best supports this worldview - the spin-statistics theorem perhaps?<br /><br />2nd assumption: Now accepting that our universe is a mathematical structure (and we are particular permutations of atoms within it), it is then reasonable to assume that all mathematical structures exist - there is no distinction between possible and realized mathematical structures (**). That is, what basis could there be for only our universe existing when it is just another particular type of information? <br /><br />But then we and our histories are just permutations of basic mathematical building blocks, and so by the 2nd assumption all the other permutations would exist as well. Otherwise it would be as if you were saying that only 1,4,3,2 existed, and not 1,2,4,3 or 4,2,3,1 and so on ( - switching the large numbers of spherical harmonics and Laguerre polynomials for a couple integers...). More concretely, say the universe was of a classical Newtonian billiard ball type - so that all of the future history, including how we now find ourselves, was based on some particular initial conditions. The second assumption would then hold that all other sets of initial conditions would exist as well, giving rise to a huge family of completely disjoint histories. As it turns out we live in a quantum mechanical world which is even more interesting - from one set of initial conditions it effectively splits into many different almost completely disjoint histories in the classical limit. In general, if you accept both assumptions, then you shouldn't expect that only precisely one history and version of yourself exists. If you are nothing more than a permutation of mathematical objects, it is reasonable that all other permutations exist as well. Even in the dubious cellular automata universes, you could start with different initial conditions and get other histories, just like in the Newtonian case.<br /><br />Is that any clearer?<br /><br />*and perhaps this CH interpretation. I still need to look at it a lot closer, but I am betting that you will still have branching of worlds, such as when you measure the left-right spin of an electron that has already been determined to be spin up. So far I have read that the CH demands that you use commuting basis functions for describing your states, which is how it should be, and which is perfectly compatible with the MWI.<br /><br />** At first glance it would appear that there would be serious problems with this - how could one make any predictive theories when all information exists? I don't think it is quite that bad however. First you can rank the information by it's complexity - if you reduce everything to integer strings which can be thought of as programs, then there are many more complex programs than simple ones. It would also seem at first that the 'noise' programs which contain no patterns would dominate the counting, but I think you can eliminate them by only considering representation independent programs - i.e. a 'real' program on one computer would be linked unambiguously to another version on a different computer (representation independence), while on the other hand there would be no reason to link a particular 'noise' program on one computer to any other program on another computer. It's vaguely reminiscent of getting rid of the infinite contributions to path integrals by gauge invariance - you separate it out via Fadeev & Popov and only count over the important stuff - in this case you only count over the representation invariant programs, i.e. the real ones that actually describe something (hmm, I wonder if you could get ghosts... ;-). <br /><br />Even still, there are going to be many more complex programs than simple ones, which I think makes the 2nd assumption testable - that is you don't ever expect an end to physics. If perhaps string theory is verified at some point, you would still then expect to find new surprising phenomenon (like we found with dark energy and neutrino mass) that would necessitate reinterpreting string theory as a particular limit of some yet more complex theory (add more stuff to the lagrangian? Higher derivatives and larger solution spaces? ...) - simply because statistically there are many more complex theories possible than the simple one where just string theory would turn out to be eternally valid and complete. We'll see!Legacy Userhttps://www.blogger.com/profile/14533919714213634034noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105386531770639062005-01-10T20:48:00.000+01:002005-01-10T20:48:00.000+01:00lubos said:I could continue, but the lesson seems ...<B>lubos said:</B><I>I could continue, but the lesson seems clear to me. The discrete rules are either a qualitative motivation for something that must eventually be justified by some continuous physics done properly, or they're just small subtleties that are added to the continuous rules.</I>--------------------------<br /><br />I must thank you for the history lesson, with a slightly different view of the Lubos Framework:)<br /><br />Why discard the measure of the ole view of Q<->Q measure, and continue it, as a relevant move to a higher significance? You no longer fixate upon the metric view, but look to the fields around it:)<br /><br />That is part of that evolution I see you are talking about in this history lesson. Thanks from my laymen, heart of hearts.<br /><br />As well your <A HREF="http://www.blogger.com/r?http%3A%2F%2Feskesthai.blogspot.com%2F2005%2F01%2Femergence-of-time-what-lies-beneath.html">differences of opinions</A> on Peter's Woits might have been looked at, for consideration?<br /><br />I would like to be able to see better with the higher faculties, of my new brain attachment:)My third eye, is developing fine?:)Legacy Userhttps://www.blogger.com/profile/01554579710459395706noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105383806112271832005-01-10T20:03:00.000+01:002005-01-10T20:03:00.000+01:00Hi leucipo!
What exactly do you find funny about m...Hi leucipo!<br />What exactly do you find funny about my remarks defending Coleman and Deser? You did say that you are not willing or capable of having your own opinion, but if you know anything about physics, the importance of Coleman's and Deser's contributions can't have escaped you. And that's exactly where my criticism of Smolin begins: As a student of them, he should know, too, yet his work is a string of misinformed sub-standard speculations, more often than not in open conflict with the foundations laid by his former advisors.<br /><br />I know that those people who have felt the thrill and excitment of reading and understanding a quality physics-paper will understand where I'm coming from. The really important contributions are typically very transparent insightful explanations of things that were thought to be too difficult to solve. <br /><br />Let me name an example: Coleman and collaborators realized that the Schwinger model contained a new parameter that is clearly absent in the classical theory. This must have seemed mystifying to everyone involved, try to imagine how difficult a problem this must have seemed to be! Yet, a short time later, Coleman was able to provide (see his paper "More about the massive Schwinger model") an explanation so clear and obviously correct, even a layman could understand the essence of his argument. (The parameter is the theta-angle which, in 1+1 dim, corresponds to a constant electric background.)<br /><br />Or look at Deser's "Topologically massive gauge theory". Mass terms typically spoil gauge invariance -- Deser in no uncertain terms showed how to give the gauge fields a mass anyway. This is real understanding of important issues.<br /><br />Name one paper of Smolin's that lives up to these standards...!<br /><br />Work in areas like loop quantum gravity is almost always different. A complicated formalism usually hides purported insights, and the arguments given are hardly ever summarized in understandable terms -- or they are just wrong. Even worse, the justification for introducing the formalism in the first place is shaky at best. What *is* the justification for assuming that the phase space of 4d gravity is in 1:1 correspondence with its QM counterpart? There is none. In fact, any smart grad student in 2005 can show that it's wrong.<br /><br />I agree with one thing you said. There is a long tradition of smart people educating smart people. It's truly sad if such tradition is broken by a crackpot who didn't care to listen.<br /><br />To those who are not physicists (and there are plenty here it seems, certainly including this idiot quantoken), I would like to say: If you care about physics, you are right; there are few things as exciting and important. But don't try to have your own opinion too soon. It's like listening to an opera performed by professionals and starting to sing loud and wrong. No one is going to like it. And no one is going to mistake you for an artist. It makes you a heckler, nothing else. Listening, by contrast, is quite an enjoyable and reasonable thing to do.<br /><br />Best,<br />MichaelAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105383453731983692005-01-10T19:57:00.000+01:002005-01-10T19:57:00.000+01:00Hi guys,
I think that in actual physics, there is...Hi guys,<br /><br />I think that in actual physics, there is no tension between the discrete structures and the continuous structures. Both of them are clearly necessary, and there are lots of relations between them. For example, L^2(R) has both a continuous as well as discrete bases.<br /><br />Having said this, I think that most technical progress in physics has always been about finding a continous explanation of some qualitative observation - and qualitative observations are often discrete.<br /><br />Let me say a couple of examples:<br /><br />The ancient Greeks often thought that the world was continuous. Fortunately, they also discovered Euclidean geometry with its continuous rules, but they never directly thought that the continuous rules would govern Nature.<br /><br />The real physics started with Newton who could have only described motion of planets by simultaneously inventing the calculus, derivatives - highly continuous structures. This mechanism was then expanded to partial differential equations, field theory - which is in some sense even more continuous.<br /><br />Then there was a UV catastrophe, and attempts to discretely truncate the high energy frequencies. Planck was smarter and he truncated them continuously - and found a continuous formula for the black body and its continuous derivation.<br /><br />Bohr had the old theory of an atom that was discretizing the energies etc. - but only when Schrodinger and others constructed the continuous equations that implies the discreteness of the eigenvalues, things became convincing. Feynman reformulated quantum mechanics using path integrals - which involve continuous functionals on the space of continuous configurations - which is, in some sense an even more continuous concept.<br /><br />I could continue, but the lesson seems clear to me. The discrete rules are either a qualitative motivation for something that must eventually be justified by some continuous physics done properly, or they're just small subtleties that are added to the continuous rules.<br /><br />The dogma that the whole world should be discrete goes against most of the lessons that science has taught us in the last 500 years - it's just a naive, protoscientific viewpoint.<br /><br />All the best<br />LubosLuboš Motlhttps://www.blogger.com/profile/17487263983247488359noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105382858523468112005-01-10T19:47:00.000+01:002005-01-10T19:47:00.000+01:00Leucipo said:It is regrettable the quantity of dis...<B>Leucipo said:</B><I>It is regrettable the quantity of discussions around the net based in this false antagonism continuous<-->discrete.</I>There is no doubt that this is the root of all "<B>evil</B>?:)<br /><br />Discrete structures, are like my platonic solids, and nodal points flips sought in monte carlo methods, sound very nice.:<br /><br />But at high energy considerations, it asks you to think a little different and in topological forms. Here, there is no tearing which would to me imply dscrete structures? <br /><br />I might need help here as the evolving mind in the brain and the coverings, have vastly been changed from what it once was of my lizard brain:) That such fine structures might be viewed, in a more generalized visualization from such focused evolutions?:)<br /><br />Maybe the brains form is like the Doctor crossing the room, that it brings to it such abstractions, most appropriate for such visualizations. We'll see what next math is developed out of philosophical discussion.Legacy Userhttps://www.blogger.com/profile/01554579710459395706noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105380873412259902005-01-10T19:14:00.000+01:002005-01-10T19:14:00.000+01:00It is regrettable the quantity of discussions arou...It is regrettable the quantity of discussions around the net based in this false antagonism continuous<-->discrete. After two millennia and half, people does not learn, even with all the modern research on scaling and renormalisation group. Or perhaps, people is just lazy to do the homework (Lubos, here you have your insult for Quantoken and similar: lazy. Lazy as every man with a faith).<br /><br />As for Smolin, I will not hold a opinion, but I find funny the Anonymous remark about being a disciple of Coleman. Actually, Lee Smolin was a disciple of Sidney Coleman, who was a disciple of Murray Gell-Mann, who was a disciple of Victor Friedrich Weisskopf, who was a disciple of Max Born, who was a disciple of Carl Runge.Did you read DaVinci Code (Holy blood, holy graal)?Leucipohttps://www.blogger.com/profile/14505549871207858030noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105376525139517122005-01-10T18:02:00.000+01:002005-01-10T18:02:00.000+01:00My answer is that your comments are absolutely sil...My answer is that your comments are absolutely silly. What I solved was a limit of a differential equation that describes the quasinormal modes because they were claimed to be related to some weird, but ambitious discrete speculations about quantum gravity. The differential equations are the only well-defined things about this picture and everything else is just a speculation. The only hope for the speculation would have been that there would be some support for it coming from the continuous differential equations - there is no other support that these ideas are related to gravity. If you don't like the fact that important phenomena in this Universe are described by differential equations which are continuous structure, you should definitely try to move into another Universe and make all of us happier.Luboš Motlhttps://www.blogger.com/profile/17487263983247488359noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105374483223370382005-01-10T17:28:00.000+01:002005-01-10T17:28:00.000+01:00This comment has been removed by a blog administrator.Quantokenhttps://www.blogger.com/profile/08057876770160255308noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105373921986457172005-01-10T17:18:00.000+01:002005-01-10T17:18:00.000+01:00My impression is that they want something that I a...<I>My impression is that they want something that I also want - to find an equivalent way of looking at quantum mechanics that will also include the emergence of all other conceivable classical limits in different contexts.</I>-----------------------------<br /><br />You think anything, that might even hint of philosophy, should travel through the space of your ears?:)In planck time, this could not hold very much information for you:)The matter distinctions of your brain would require a finer apprehension of time?:)<br /><br />In respect of Smolin and Hooft and their requirements you are speaking about, are the realizations that they all have to recogized, is a viable means to measure what is illucive.<br /><br />This world that NIMa and others look at in dimensional parameters is limited as you know by high energy realizations. At supersymmetrical levels how would you measure time, seems a useless question when you do not have this measure to look at in terms of classical solutions in regards to gluon interactions?<br /><br />Smolin understood that quantum gravity would have these limitations, and you would be very happy to know that quantum gravity has a couple of roads that lead to it.:)<br /><br />I would not quickly dismiss the thoughts of the Penrose and Smolins, and others who also recognized the limitations and had to devise methods of determination.<br /><br /> It is very problematic that they would seek a deeper meaning and maybe "reject time" as a fundamental measure in gluon perception that they would have to approach it someway else?<br /><br />That we could have taken blackhole from the ideas of GR interpetation led too, in one parameter of thnking, and reduce to it to blackhole manufacturing at high energy considerations, would have sounded very nice by what you speak of from Steve Giddings.<br /><br />As a philosopher, the mathematical you encounter, is very much derive from some <B>basis of thinking</B> that you like to reject. Sometimes looking at there methods of apprehension of limiations drives many to create what is lacking in the question of what do we know. <br /><br />Even if I think Smolin has limited himself as well, I have been most appreciative of the roads he has lead many through.Legacy Userhttps://www.blogger.com/profile/01554579710459395706noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105372902049070912005-01-10T17:01:00.000+01:002005-01-10T17:01:00.000+01:00This comment has been removed by a blog administrator.Luboš Motlhttps://www.blogger.com/profile/17487263983247488359noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105372534679276942005-01-10T16:55:00.000+01:002005-01-10T16:55:00.000+01:00This comment has been removed by a blog administrator.Quantokenhttps://www.blogger.com/profile/08057876770160255308noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105370732914563312005-01-10T16:25:00.000+01:002005-01-10T16:25:00.000+01:00Dear R, happy new year to you, too!
I expect - mo...Dear R, happy new year to you, too!<br /><br />I expect - more precisely: we know - that gauge-fixing extends to a quantum theory if this theory is consistent. It is often difficult to say what a quantum theory, defined in terms of its classical limit, means - and gauge-fixing is often kind of necessary to make sense out of the theory. The Nambu-Goto action is really hard to quantize: it's not clear what it would mean. The Polyakov action is better, and the simplest way to get the spectrum is to gauge-fix.<br /><br />The light cone gauge is a good gauge choice for any theory on a background that admits it. Other gauge-fixings are more problematic, at least according to string theory - they don't allow us to solve the theory easily and they have also other problems.<br /><br />According to the Wheeler-deWitt equation, we *must* kind of gauge-fix - to choose the time as a function of some other, gauge-invariant degrees of freedom - if we want to make any contact with observable physics. These connections partly depend on conventions; they can't always be done exactly, and so forth. But I believe that this is just the truth: if your correct physical theory tells you that some objects are relative - they depend on your conventions, reference frames and other choices - you must accept it. Also, if it tells you that some observables are inaccurate, they can't be defined exactly, you must accept it as well.<br /><br />This is my viewpoint. If someone wants to claim that some things may be defined exactly and/or uniquely even though it does not look so, he or she must have some evidence unless he or she wants to leave the scientific approach. Every nontrivial statement must have some evidence - either a direct experimental proof, or evidence that it follows from the consistency of any acceptable theory. I reject all statements about the physical world that are done purely on the philosophical grounds, especially if they seem to contradict our experiments and the knowledge that we've obtained from these experiments.<br /><br />Philosophy is usually a wrong guide in physics and this philosophical approach is usually just a manifestation of people's prejudices and misconceptions.<br /><br />There are simply many people who have some strongly held prejudices or beliefs - that things must be certain, the uncertainty principle must be wrong after all, that it must be possible to derive uniquely what are the right questions one can ask, that there must be an "objective reference frame", that geometry must be an exact notion, and so forth. They have these prejudices, they don't allow anyone to question them, and they insist that the physical theories will be constructed in order to agree with their prejudices.<br /><br />One should not be surprised that the theories that are constructed to match these prejudices will usually be junk. The valuable theories in physics are constructed to agree with experiments and the natural mathematical beauty that the real Nature displays.<br /><br />I don't think that the Mach-principle-like relational approach is something up-to-date because it is an approach that might say that only the relative positions of objects and events are physical, but it still assumes that the relative positions form an absolute set of observables that are "more fundamental" than other observables (such as the values of various fields). It just goes against the 20th century physics. General relativity as well as string theory show that the "indifferent podium" is never indifferent after all. All features of reality that influence other objects tend to be dynamical and "equally fundamental", so to say. It's just a wrong approach to imagine that a theory is defined in a two step process - one defining the background where things take place (or the relations that the objects can have), and then defining some objects assuming the first assumption. In reality, the objects influence each other in both ways.<br /><br />This is a very vague chat, but once someone defines a particular theory that is meant to satisfy these medieval prejudices - such as loop quantum gravity - one can show why this theory is rubbish much more factually.<br /><br />You ask me "What is the string theory equivalent of asymptotic freedom". Well, if you really want an "equivalent", I can tell you an exact equivalent, of course. It's the dilaton going to zero at the boundary of anti de Sitter space. This is the string theory equivalent of the gauge theory statement about asymptotic freedom, according to the AdS/CFT correspondence. ;-)<br /><br />Sincerely<br />LubosLuboš Motlhttps://www.blogger.com/profile/17487263983247488359noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105364767236390772005-01-10T14:46:00.000+01:002005-01-10T14:46:00.000+01:00CIP - questions vs. answers. First, be sure that m...CIP - questions vs. answers. First, be sure that my private communication with Hartle show that he's not aware of any serious problem with CH either, as of 2004.<br /><br />Second. You and others seem to feel uneasy about the fact that one must first ask a question before the theory can calculate an answer for her. Yes, it's so. You can't uniquely calculate what are the questions, especially if you go away from the quasiclassical limit. If someone imagines that the theory must eventually give him a deterministic model that knows what the variables are and what their values were, then he's misled.<br /><br />The emergence of the "right" questions is not something that is statically encoded into the structure of the theory. The main point of CH is that it reveals dynamically which sets of questions may be asked. Dynamics decides what's a forbidden interference among the outcomes we want to decide between. Dynamics determines how fast decoherence is. If anyone wants to decide about the right questions without dynamics, then he's doing it wrong.<br /><br />All the discussed differences between the interpretation of the actual history are academic - and none of the critics ever derived a "wrong" conclusion from the CH. I use a very different thinking than constructing the literal decoherence functionals to decide whether the dinosaurs were around - because there would be just too many histories and too many projectors to take into account. And I am convinced that this this thinking is compatible with CH. It's simply because every step, every process that we know physics predicts - like reproduction of DNA - occurs with the same probability in CH.Luboš Motlhttps://www.blogger.com/profile/17487263983247488359noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105363343809128222005-01-10T14:22:00.000+01:002005-01-10T14:22:00.000+01:00CIP... First of all, what Smolin says about Dowker...CIP... First of all, what Smolin says about Dowker and Kent may be described by the same words as your comments about Dowker and Kent; well, it's probably not an accident because you just copied and pasted. It does not make much sense.<br /><br />Second of all, Dowker and Kent may have written a review, but they certainly did not start to think in the CH framework. On the pages 79-81, they propose a lot of conjectures that are in direct contradiction with the CH formalism. Of course that they can't find any evidence for their claims because their claims are wrong.<br /><br />For example, they say that one needs to construct a special theory of consciousness to make the picture complete. This is rubbish. CH was exactly designed to solve this biggest problem - CH decide what is a "good history" and what is a "bad history" purely in terms of the actual dynamics - roughly speaking, a history emerges as a legitimate description once the objects are large and interacting enough. It is kind of always OK to assume that the Moon's center of mass is sharpy in one of the regions defined plus minus a micrometer, and use it as an extra splitting to make the histories finer. One can prove it.<br /><br />Also, Gell-Mann and Hartle showed how can you show that quasiclassical physics emerges in the right limit, and the complaints of Dowker and Kent are too vague. Incidentally, such an isolation of a quasiclassical limit in a given theory is the closest replacement for a "unique" set selection mechanism, and whoever looks for an even more unique one, is misled.<br /><br />Next, Dowker and Kent seem to call for a unique set of fine histories, once again. But that's a basic misunderstanding of the structure. CH are not meant to provide one with a unique fine-graining. There is no unique fine-graining and only Bohm-like people who have not gotten what quantum mechanics is may continue to look for "unique fine-graining". In real quantum mechanics, one can possibly define different sets of histories, and as long as they're consistent or approximately consistent up to the errors one can tollerate, these histories are equally fine. One may formulate one set of questions about the future history, and if the set is consistent, QM+CH answers it. One can do it with other consistent set, too.<br /><br />This has nothing to do with personal consciousness or solipsism. Even objectively, taking all other people and computers into account, we are able to define various slightly differing sets of consistent histories.<br /><br />If this conclusions violates someone's religion, it's his or her problem, but definite not Gell-Mann, Hartle, or Omnes' problem.<br /><br />Also, there can't be any unique statements about the past. Many macrophenomena are "irreversible" - entropy increases. Consequently, there is no reliable way to reverse them "deterministically". This distinction between the past and the future is very important in a correct interpretation of QM, too - simply because decoherence is a phenomenon very analogous to friction and dissipation. And it's reality.<br /><br />If you ask the question whether dinosaurs were around, and you construct a set of consistent histories - some of them with dinosaurs, some of them without dinosaurs - be sure that QM+CH will unambiguously answer that the dinosaurs were most likely around. It's the very same reasoning that we would use otherwise. If Dowker believes that there will be another answer, then he probably believes that fossils and science can't be trusted. But it's his belief, not mine.<br /><br />On the other hand, we can possibly construct consistent histories that DON'T talk about dinosaurs et al. - very different sets of histories (I don't know exactly how to do it). And conceivably, they can be consistent. But the resulting probabilities can't be interpreted as "dinosaurs were not there" because this was not the question. Someone is confusing two situations: "answering a question by NO" and "not asking the question at all". These are two very different things.<br /><br />OK, I think that the main proposals of Dowker and Kent are misled - the proposed search for a "unique" set selection criterion; the proposed necessity to construct a theory of consciousness; and so forth. I don't want to read it anymore because it's no physics.Luboš Motlhttps://www.blogger.com/profile/17487263983247488359noreply@blogger.comtag:blogger.com,1999:blog-8666091.post-1105360587946727322005-01-10T13:36:00.000+01:002005-01-10T13:36:00.000+01:00Dowker and Kent again: If you check out p. 79-80 ...Dowker and Kent again: If you check out p. 79-80 Of the D&K paper (PDF version) I cited above, I think you will find concerns expressed about deduceability and predictability equivalent to those Smolin attributed to Dowker in her talk.CapitalistImperialistPighttps://www.blogger.com/profile/17523405806602731435noreply@blogger.com