BenTheMan

Because Woit's book is selling THAT poorly. Just do the average and you'll see.

Martin! How odd! When I suggest ten space-time dimensions at the planck scale, you go on long rants about how unphysical this is, because you only SEE four dimensions. Yet, in your response to criticisms about this, you point to research that claims LESS space-time dimesnions at the Planck scale, AND fractional dimensions, no less! Excuse me for thinking you a bit hypocritical in all of this! Aside from this glaringly obvious hypocricy, I will again point you to your own statements, that say that Smolin's aproach is ``on the fringes'', and he doesn't realy work on things that the rest of the community does. ====================== I think that some people have this opinion, yes. Certainly it was hoped that we could find a vacuum selection mechanism, and that the solution would be unique. Right now, however, we can't even find ONE vacuum that works (although we CAN get close). Why? In this sense many things are ``ad hoc''. People try something, and see if it works. This is how all theoretical physics works---space-time is ad hoc, particles are ad hoc, ... There are ALWAYS problems when you try to analyze the UV while sitting in the IR, which is why Martin and I are always arguing The point is, it is easy to integrate a theory DOWN in energy scales, but to go the other way is quite tricky, and, in fact, it is not unique. Proof of this is found in the fact that there are about a dozen ways to make the higgs mechanism work---scalars, technicolor, little higgs, ... And this is only over an energy scale of a few GeV! No imagine the same problem, extrapolated out 17 orders of magnitude! There are so many things about physics in the low energy, and we are trying to do physics at the Planck scale! Some (M)aster Theory, you say? I guess it depends on what you consider interesting questions. But this is just as ``ad hoc'' as assuming a string, with quantized energy You're talking about looking at M-Theory, which is what most people believe unites all of the string theories. I can't talk much about this research, unfortunately. I will say that there is still hope for a vacuum selection mechanism, as far as I can tell. The stock answer that you will get is that the problem is very hard, and it needs a lot of smart people working on it. I'm interested in getting the standard model out of strings, which is, in some sense, like looking the answer up in the back of the book. Once you know which vacuum you're looking for exactly, it should be easier to find out how to get there. I think that should happen in the next ten years or so---someone will find a compactification which gives the standard model. Once this happens, it should be easier to find out how to fit things together. You'll forgive me, of course, for stopping here, as there are others who are more qualified to finish this response than I

Lockheed---this is an interesting quesion. I think I have seen some research into relic gravitational waves. If you think about it, if the big bang is really a ``big pinch'', then the only things that can propogate across would be gravitational waves, so I'm not sure how much we could learn about a previous universe.

I don't follow that either. I think that that's the point---no one can tell what state a specific electron will be in before an experiment is done. To say that the many worlds interpretaiton is deterministic is akin to saying that you know WHICH universe (of the many) that you are living in. I think that I agree. Where did you read that it was deterministic?

Well, ask yourself... how big is the parameter space in quantum field theory? How many different quantum field theories can we build? Well, there are AT LEAST as many quantum field theories as there are string vacua, because every string vacua (to my knowledge, at least) is a consistent quantum field theory. In fact, I would wager a guess that there are MUCH fewer string theories that quantum field theories. (In fact, I think there is a paper about it, by Cumrun Vafa and Lubos Motl, called something about the ``Swampland''.) And no one doubts quantum field theory's ability to describe nature. So it may turn out that string theory is just a framework for quantizing gravity, and it's predictions are all vrey general. This is what I have gathered about non-stringy QG---they don't explain things like the standard model, and are completely fine with that. But this is exactly the approach that one SHOULD take. You have to know what you're picking before you know how to pick it. You look at the ways to write the action down in ten dimensions, and think of the ways you can get consistent solutions in four dimensions. This means compactifying on a Calabi-Yau three-fold (six dimensional space), of which there are many. Generally there are many ways to put conditions on internal degrees of freedom, and some moduli that you have to deal with. This is how I understand the vacuum problem---there is only a few ways to write down a ten dimensional theory, but many ways to get four dimensional physics. Again, this is simply not the way things are done. There is now way for a low energy effective field theory to know very many things about dynamics in the UV---I can give you two or three examples, if you like. The higgs boson is probably the most expected discovery at the LHC, and there are about a million ways to break the electroweak theory. Everyone expects the higgs is a scalar, but we cannot rule out the possibility, for example, that one of the competing theories is right. Supersymmetry and SUSY breaking is another example, as are grand unified theories. You have to understand the parameter space of your theory very well before you can understand how Nature behaves. So it doesn't address YOUR fundamental questions! I'm not of the opinion that physics should answer to anybody:) The point is that string theory (speaking in general) explains a huge number of things that we have just taken for granted. For example, gauge symmetries. String theory explains why we have gauge symmetries in our universe. Other things, like number of generations and number of supersymmetries are topological. This is what the quantum gravity people like Martin are doing. (I assume he's a scientist.) But they all have their problems. For example, string theory is the only way to quantize gravity that constrains the number of dimensions. In other QG approaches, this number is put in by hand. Scroll up to see the heated discussion ==================== This is why martin's index about ``String Research Quality'' is pretty useless. Everybody is citing Maldacena's AdS/CFT paper, which was written ten years ago, and so falls outside of Martin's arbitrary five year window. As an asside, I met some students from Michigan State and Minnesota this summer at Princeton (phenomenologists who work with Tony Gherghetta, and these people), and they all did higgsless models a la AdS/CFT. If higgs scalars aren't found at LHC, and we see something like technicolor, we could learn a lot about how AdS/CFT works in nature.

Well, then---I would say that string theory STILL has no competition, because one theory quantizes gravity AND explains some strange properties of the standard model, and another just quantizes gravity. Why? Strings and loops aside, this is not at all obvious to me. GR is a classical theory, which means it is an effective theory. We have seen several places in physics where quantum corrections GREATLY alter the classical behavior of a physical system. So to say that ``Any quantum theory SHOULD quantize geometry'' is not an obvious statement. Any quantum theory of gravity should look like geometry in the low energy limit, of course, but quantizing geometry is not something that everyone thinks is a good idea. Martin this statement is empty. You say that you get it without the extra dimensions, but YOU HAVE SPECIFIED THE NUMBER OF DIMENSIONS. GR is consistent in any number of space and time dimensions. I can get the standard model from SO(10), by adding arbitrary matter and higgs representations, but I've done it all by hand, so it is not a surprise that you get the standard model and no extra dimensions. Likewise I don't understand your objections to ten dimensions Why should you suppose that there exist four dimensions? The only statement that you can make is that we have checked directly to roughly 10 microns, and haven't found any. Any statements more than that are speculative. String theory makes no excuses about this---ten dimensions is a prediction of the theory. If you claim your theory explains space-time, don't you think you should explain its most fundamental property? And if his predictions are wrong? Won't he go back and tinker with his models until he fits the experimental data? This is a trick question, of course, because it's what every theorist does. The problem in string theory is that parameter spaces are just too big right now. If you're counting the indeces that you make up, then of course this is what you see... It is what you WANT to see. We must know different string theorists, is all I have to say.

Martin---first of all apologies for taking so long to respond. I wanted to think about a coherent response, and I have been busy trying to finish a project I am working on, before taking a few days off to drink beer, catch fish, and get sunburnt back home in Texas. I think that the problem is that we may be on different wavelengths. If I read correctly, when you say phenomenology, you are thinking primarily of cosmology. I have been using the word in a more limited context, referring specifically to the particle physics side. String theory DOES have problems getting inflation right, which leads to things like KKLT. You can take all of my comments about ``phenomelology'' as pertaining solely to the particle physics side of things---this is the only side that I really know about, anyway. I will not. But perhaps I am expecting too much from the program. To get good particle physics you still have to do the same things that people do in traditional GUTS---you put fields and couplings into the theory, instead of getting them FROM the theory. Surely you can see the difference? The comment that I made is that it is quite odd that someone would say that top quark and tau neutrino yukawa couplings had to be of the same size, when this naively means they should have the same mass. You have made no real attempt to explain this to me---your argument seems to be that we should rely on the fact that Connes is Connes--- ``Well, Connes is famous and you're just a grad student.'' All of the things that I've found online say that yukawa couplings to a driac neutrino are constrianed to be less than 10^-10, by experiment. Now it is your job to explain to me why this bound (aparently) doesn't apply here. If you don't know, then you don't know. And Josh doesn't do physics anymore, he works in finance and watches Packers games. When things slow down (I have three projects right now!), I will try to learn some of Reuter's stuff. My GR is pretty weak, because I've never really needed it for anything, so maybe I can learn something there, too. But, what guarantee is there that Connes' work has any relation whatsoever to Reuter's work? When I tried to ask general questions concerning ``LQG'' in another thread, you became quite elusive with your answers, like ``Well, Smolin is wokring on something else'', or ``There are many different approaches to the problem''. So which is it? As far as I know, you don't have dualities hanging around, so there is no hope to connect Connes work to Reuter's work by taking a large coupling limit, or something. This is, of course, the canonical response. Martin---I thought you were more creative I've heard BIOLOGY professors come up with better You will get a stock response from me as well. The thing is, suppose we DO find 6 dimension physics at LHC, at a TeV. Or suppose the gravity experiments in Univ. of Washington get positive results. This is pretty unlikely, but still possible. Will you say ``Well, non-string QG doesn't predict extra dimensions, so it is wrong'', or will you go around to all of your papers and erase ``SO(3,1)'' and write in ``SO(5,1)''? My guess is the latter, of course. Then you will still use the same argument that the world is six dimensional, and string theory predicts all of these extra dimensions that we don't see. The irony of it all is that, even if we did stuble on six extra dimensions, you theory STILL wouldn't be ruled out because you would just erase SO(4,1) and write in SO(9,1), and complain about background independance. And besides, can you see electrons? I can't. But I know what the experimental consequences are. We observe electron transitions in hydrogen spectra, for example, so we know there are electrons jumping around in there somewhere. Likewise, we have things like generations (and, hopefully) N=1 SUSY in our QFT. String theory says these things are all topological quantities. So we can see the consequences of extra dimensions even though we don't see the extra dimensions directly. One could argue that untill we find a vacuum selection mechanism, we are really tickling the theory by choosing the appropriate Calabi-Yau. This is still a significant improvement, because we have a finite choice of Calabi-Yaus, and (in principle at least) you can choose ANY number of dimensions and still make your theories work. We choose a compactification consistent with the low energy data, which is pretty restrictive, actually. I still think that predicting a number of dimensions is MUCH better than putting the space-time symmetry in by hand. The moduli stabilization is a huge problem, no doubt---mainly because so things depend on getting moduli to take specific values. More complicated in what sense? Are there more fields? Yes, of course---any LEEFT you get from string theory will be ``more complicated'' because E8xE8 is so big. But the low energy spectrum is exactly the same---good hypercharge directions, exotics decouple, realistic higgs sector, and (hopefully) good predictions about unification. We put in some constraints on the internal symmetries (boundary conditions and wilson lines), and we choose an orbifold. Everything else is specified from there. For example, in the specific compactification we are working in (T6/Z6-II), there are only 61 consistent ways to give boundary conditions to the internal degrees of freedom. Sometimes, late at night, when I have been coding for seven or eight hours, I ask the same question:) As you are no doubt aware, there is no one compactification of ANY string theory that gives good phenomenology. The closest, I think, is in a paper by Burt Ovrut and Volker Braun, followed by Kobayashi, Raby, and Zhang, and other models by Wingerter, Nilles and the people in Bonn, and Buchmueller, Leudling and Schmidt. Also, check papers by Cleaver (my master's thesis advisor at Baylor), Nanopoulous and Faraggi. Less succesful approaches are by Verlinde, and Cvetic, Blumenhagen et al. Without a doubt, though, the heterotic string is the way to go for good phenomenology. The idea is kind of like sighting in your rifle---you shoot, and check the target. You're a bit off, so you adjust and shoot again, each time getting a little closer to the bullseye. So, for example, Kobayashi, Raby, and Zhang don't get good unification. Others don't get good Yukawa couplings. The Type IIA people (Cvetic, Blumenhagen, Shiu, ... ) end up with chiral exotics. Anyway, once we have something that looks like the MSSM, with good Yukawa couplings and such, then we can start making predictions about experiments, which is what people like Smolin and Woit are bitching about. Presumably, there is not just one good model, but an ensemble of many models which give good physics. We can check the dualities and see what the model looks like in the other string theories. We can see how gauge coupling unification works. We can see how to get good cosmology. ... So really it's like a Jackson problem. Part a is derive the MSSM from string theory, which takes you 30 years to finish. THEN you have to start part b.

Martin---it seems pretty difficult to use your index. It seems like it fluctuates pretty rapidly, which is bound to be the case when the book sales are small (as all physics book sales are, comparitively).

They CAN look for brain activity in coma patients, but should brain activity be a factor? Further, babies don't seem to have controll over their bodies.

What is your prediction for the anomalous magnetic moment?

ummm a question about strings? Specifically, do you have any questions about string theory?

Ok, I guess I should give a eulogy for this thread, too, seeing as it was me who started it. Farsight has consistently failed to answer questions pertianing to the consequences of his ideas. Either he doesn't understand them, or hasn't thought about them. In any case, it is quite clear to the people who have sudied fundamental physics that there are major problems with his proposals. I pointed to the fact that pions decay into different numbers of photons, and that neutrinos don't couple to photons. I probably made some more good points that he ignored, and I don't feel like digging through 13 pages of posts to cut and paste them. Severian made the observation that if Farsight gets rid of the higgs, then the standard model violates unitarity at 1 TeV. Unless Farsight can introduce some new mechanism to stabilize WW scattering, his idea is dead. Farsight has spent his time in this thread talking about electron positron anihilation, and stuffing his fingers in his ears. He labels everything that kills his theory a ``red herring'', and uses the word ``kafkaesque'' more than a person should be allowed to. On a side note, I emailed John Baez a few days ago about applying his crackpot index to Farsight in this thread. I stopped counting when Farsight got up to 443, and John says ``Well, if you're computing the index correctly, I think that means he's really a crackpot.'' So at least John Baez agrees with me.

I think this idea was called the luminiferous aether, and was shown to be wrong in the nineteenth century.

Well, sorry to break it to you, but you're no Einstein, and you're certainly no Newton. And you didn't actually refute the point. If you'd like, I can spend thirty minutes or so looking for people who say the electron is pointlike. You've proven nothing! The argument that I used SHOWED that taking an electron to have any structure leads to a contradiction, namely that the speed at the equator of such an object would be faster than the speed of light. Again, you haven't refuted this point. You just got confused and told me I was wrong. elas---The standard model is based on a classical theory---classical FIELD theory. The lowest order results, the tree level results, are the classical approximation. But, doing tree-level calculations only gets you to within 15% of the correct answer, if you compare to experiment. This is why you must include quantum effects (i.e. loop diagrams in the perturbation expansion) to compare to experiment. The best example is QED, which has been calculated to something like 9 or 12 loops, and compares with experiment to 13 decimal places. QED is, without a doubt, the most accurately tested theory that man has EVER conceived, which includes GR. So to suggest it needs to be changed is pretty crazy.

Martin---I haven't forgotten about you. I will respond to you eventually.

Exactly! SOME humans are self-aware and some are not. And because it is impossible to tell the difference, we must assume that ALL comatose humans are ``self-aware''. Because this is the case, then we must grant all comatose humans the same rights. Now extend this argument to animals. It is possible that SOME animals, which we raise for food, are ``self-aware'', so we should grant ALL of those animals the same rights, inasmuch as we want to apply the same standard across the board, in the name of fairness. Paralith---In general I agree very much with you. Two responses to this, however. One, being born is a necessary part of having life, so in some sense this pain is unavoidable. The second question I would ask is, when does one become self-aware? Is it exactly at birth? If not, at what point do we grant babies the same rights as animals? These are the problems I have with the animal rights activists who argue their case with these points. They take a very liberal interpretation of what ``to feel pain'' means, and using this very general interpretation, they argue that we shouldn't willingly impose that suffering on any being, whether they be animal or human. I certainly do not wish to cause any animals harm, but I do enjoy hunting, and I do feel sorry for the animal when I don't kill it with the first shot. While this is abhorrent to most animal rights activists, late-term abortion is abhorrent to most people in America. This is, in essence, the point that I wanted to make.

What about a comatose human?

What does ``self aware'' mean? Actually you've missed thepoint of the argument. Generally people who argue for animal right make it a point to base that argument on the fact that animals can feel pain. This is based on an argument outlined by a man named Peter Singer in his book (1975) ``Animal Liberation''. The point of the book was that, in order to have a consistent moral code, one should grant rights to anything which suffers. My counter-argument is that, if this is the case, fetuses should have rights (at least equivalent to those that we would grant animals) starting in the third trimester, where most researchers AGREE that a fetus can feel pain.

vincent--- Thanks for the clarification. As I say---I haven't done these calculations, so I will differ to your expertise

Hi vincent---- I can't speak about M2 branes. As far as getting GR from string theory, first you have to believe in gravitons Then I think you just have to look at the IR limit of the four graviton scattering amplitude. The non-linear behavior of GR pops out of this, I think, or can be understood in terms of it. It can't reproduce EXACTLY GR, but that's not what we'd want anyway---GR has singularities which we're trying to get rid of by quantizing the theory. There will probably be alpha' corrections that GR doesn't know about, but this (again) is exactly what I'd expect. I should say I've never done this calculation myself, but there's probably a section on it in one of the textbooks you linked to.

Good question! The particles don't INTERRACT the way that you're thinking---they never all meet at a point an then go their merry way. The picture to have is a RANGE. When the particles get close enough, they interract. Usually ``close enough'' means something like within a compton wavelength, or something.

Hi foodchain--- Yes. I don't know if I can give a more detailed response. In what sense? Specifically, electrons are excitations of strings, and we can isolate them. String theory can explain dark matter pretty easily. The easy answer is that string theory can give the MSSM, which generally contains a dark matter candidate. Dark energy is a bit more troubling. If we lived in a universe with a negative cosmological constant (it is small and positive), then string theory would have no problem. But a small and positive cosmological constant is tricky in general. Generally, people say ``Ok, somewhere in the 10^500 solutions there's MOST LIKELY a few solutions with a small positic cc. So don't worry about it.'' If this sounds unsatisfying it is. Many people are trying to fix this, but little progress is being made.

Martin--- Are we talking about particle physics or not? And of course he gets the proper number of dimensions because he puts them in by hand. I don't know if you were ever a graduate student, but advisors don't appreciate when students come running to them with questions. I asked you if you knew the work---obviously you are familiar with it, or did you just do a google search? Either way, I will reiterate what I am confused about in the specific paper by Connes, et al. They claim that the top quark and tau neutrino have comparable Yukawa couplings. Yukawa coupling means fermion coupling to a scalar. So the paper implies that the coupling of the top to a scalar (i.e. higgs) is of the same order as the coupling of the tau neutrino, which doesn't make sense to me. At some point in the future I am sure that I will figure things out for myslef, as you are proving most unhelpful in all of this. I am probably wrong in all ofthis, and you are probably right---either that or I am misreading the paper. Maybe he has some more scalars in the theory (i.e. SUSY), in which case the neutrinos can generically couple to them. The paper is mathematically dense, and I can't understand it for the most part. This is exactly the point---dimensions and gauge groups are added by hand, just as in traditional approaches. This is tickling. Of course not, becuase you've written down 3+1 on your paper and called it a day. This really isn't that constructive, and I'd really rather hoped to avoid such conversations in this thread. ============================ Nono. It only has a length, no depth or height. Well, there are no stable orbits in higher dimensions, I think, so we wouldn't have our solar system... I think. ============================ Martin---these are things I know nothing about. Apologies. =========================== More on Yukawa couplings. http://www.physics.upenn.edu/neutrino/jhu/node2.html If the neutrino is a Dirac particle, then it can get a mass by coupling to the higgs. The limit on the Yukawa coupling for the neutrino is 10^-10. The top quark Yukawa coupling is 1. So either I am confusing what Connes is talking about (most likely) or he is off by ten orders of magnitude. Note, Martin---the abstract of the paper only claims to get the structure of the standard model correct, which was the situation in string theory for a long time. It took many smart people many years to understand how to get reasonable couplings out of the theory. Finally, if Connes is talking about a Majorana neutrino, he can get a dimension five operator (the smalles dimension which is gauge invarian). If this is the case, then he is supressing the operator by the cutoff, which is presumably the Planck scale. If this is the case, then perhaps a large coupling is allowed, given the fact that the effective operator has such a large suppresion.

Martin---I have never read or heard of a quantum gravity phenomenology paper that didn't include the word ``string'' in the title. Either the QG people assume that gravity matches smoothly onto a QFT in the IR, or they naturally get the correct structures out of the theory. If the former, then this is not an improvement over the well-known approach. One still adds a gauge symmetry with no motivation other than an ex post facto justification, probably as a cleverly choses stress energy tensor. String theory offers a significant improvement in this regard. The link you posted the other day seems to be an example of the latter, although they had tau neutrinos coupling to the higgs with a yukawa comprable to the top quark, which is not physical, inasmuch as I understood the scentence. Specifically, this means that one should expect the tau neutrino to be of comparable mass to the top quark. This is already ruled out by experiment. If you'd like, I can give you a page number from the particle data book. I have no problem admitting that I didn't understand most of the words in that paper. I scrolled down untill I saw something that looked familiar, then read about their neutrino sector. Unless you can set the record straight by explaining to me what exactly the authors of the aforementioned paper meant, then I will continue to say that people don't get good phenomenology out of other approaches. I will stand humbly corrected if you can show me where I am mistaken. Otherwise I will continue to tell people who ask me that string theory has a much richer and more successful phenomenology than other QG approaches. This cannot be disputed.

No. The string is TRULY one dimensional. I'm not sure I understand this. If you are asking if all the small dimensions have to be the same size, then no. The experimental limit is somthing like 10^-6 meters or something---that is, if the dimensions were BIGGER than 10^-6 m, we would have seen them in an experiment already. Well, there is no mechanism which chooses how the extra dimensions should look. Choosing how they look is done by looking at the answer, and tinkering until we get things right. As the reference you saw said, there are 10^500 ways to do this. This is a huge problem for the theory, because untill we get the mechanism down, we are just using string theory to describe low energy physics, and not actually predicting anything. Yes, he is a professor at KITP, in Santa Barbara. He's also written a very difficult textbook on string theory.