BenTheMan

alien--- I would add that there's so much we still don't know that it's hard to say. In my reply to Athiest, I said that everything would be different if we knew how to pick a vacuum, or even one consistent vacuum. Once we figure out how to pick a vacuum, THEN we can try to find test. In the meantime, we can use a shot-gun approach---shoot in the general direction and see if we hit anything. This is (more or less) what I'm doing.

Hi Athiest--- First, a story. This was a (famous?) short story by someone, who I forget. Either way, the plot basically goes that a man set out to produce a single page of ``Don Quixote'' from scratch---i.e. he never read the book. He studied Miguel de Cervantes' life, and devoted his whole life to understanding ``Don Quixote'' without ever actually reading it. Then, before he dies, he sits down and reproduces exactly the first page of the novel. After he dies, most people think he has wasted his life, except for one critic, who makes the point that what this man has done is so much more beautiful than everyone gives him credit for---he has understood Miguel de Cervantes SO WELL, he has understood the novel SO WELL, that he was able to reproduce a page of it without ever having read it. String theory is like this, in some sense. It doesn't tell us that many NEW things, but it DOES explain things that we already know. For example, things like the number of generations and supersymmetry are properties of the specific compactification we use. Chiral fermions are a given! The number of dimensions is derived. Gauge symmetries are natural, and not put in by hand. All of these things we can put into our low energy theories, but when it comes to string theory, we get these things out. There are some unique features of string theory that aren't present in other constructions, too. But ``unique'' often means ``consequences of specific solutions'' and not ``generic predictions''. So, for example, there could be cosmic strings (not topological defects, but actual strings) in the WMAP data. These things (I think) would seed structure formation, and this is something that is being looked for very closely. You can also have things like large extra dimensions, which would show up as Kaluza Klein towers at the LHC. Also, quite typically, there is exotic matter which you get out of string theory. Of course, none of these things would be PROOF of string thoery, because what you are measuring (at least at LHC) are parameters in an effective lagrangian. And a priori it is impossible to know what fundamental theory your effective lagrangian comes from. If we COULD know these things, then physics would be solved when the higgs mass is known. So to sumarize, I would say that generally there are no new features (below the planck length) of string theory that can't be incorporated into other models in an ad hoc way. One can write down an SO(10) GUT that gives good fermion masses, one can pencil in four dimensions into the calculations, etc etc. But string theory offers a framework to understand why we have all of these ideas. Of course, once we understand vacuum selection (i.e. moduli stabilization) all of this is liable to change

Whatever. Back to strings. ============

Well, with all due respect, we don't answer to you String theory explains quite a bit, and gives a complete picture of Nature. This is why it is interesting. Any other approach to gravity is not as complete as string theory. This is not an objective statement, but a subjective one. It depends on what kinds of things you think are important in a quantum theory of gravity. Background independance (for example) is hard to come by in string theory, and if you're looking to quantize geometry, then you're barking up the wrong tree. (GR is an effective theory anyway, so I don't understand why one would want to do this...). I should point out, though, that this is a moot point because Martin Schnabl has solved string field theory in some simple cases. This essentially means (as far as i know) that there now exists a background independant formulation of string theory. So, one has to ask...are the tradeoffs worth it? We have a vacuum selection problem in string theory, this much is evident. But are you willing to sacrifice the huge successes of string theory because of this?

I don't know what exactly Smolin is talking about, but this doesn't sound like physics...it sounds much more like philosphy. The act of ``observing'' is usually just an interraction between a probe and a process. The probe carries information away from the process. In some sense, Smolin is trying to show a reductio ad infinitum---he's trying to show a paradox that you can always find a closer observer. There's no real paradox, as Smolin would agree, because there is a fundamental length scale in nature.

I don't know man---I was utterly im-(explitive)-pressed that some rocket scientists in NASA could fire a rocket at a commet 3 million miles away and hit it. All I do is fiddle with pens all day:)

OBVIOUSLY A implies B.

Sure. But to suggest that one only does the mathematical fomalism as an addendum to the experiment trivializes a lot of great physics.

...the right answer OR the right TO answer. You've just reduced a thousand years of physics to a post script on some experiment. I disagree heartily, needless to say. It has ALWAYS been the position of science to PREDICT and the MEASURE. If you don't believe me, read something by Francis Bacon. Or just look at Wikipedia. http://en.wikipedia.org/wiki/Scientific_method

I think we are EXACTLY on topic Oh I could mention names. I call people crackpots all the time. Let me be the first to be counted. /Fredrik--- There seems to be a general tolerance for bad physics. Not bad science, mind you, but bad physics. Here are two examples which aren't by people whose names begin with Far... http://thesecret.tv/ http://www.whatthebleep.com/ People PAY MONEY for this shit. I know because my mom bought the second movie and I watched it with her. Ugh. When it comes to things like Evolution, and Intelligent Design, though, we are much more willing to voice our opinions. So why is it that bad biology (ID) and bad physics (see links) are treated differently? Why should I tolerate bad physics?

Many would probably want to call string theory a framework (by your definition of the word) untill there is a plausible vacuum selection mechanism. However, there ARE predictions coming from string theory. The most generic ones are just too hard to test. There are also POST-dictions, like chirality and gauge symmetry. Also note that Faraggi PREDICTED the top quark mass (BEFORE it was measured), based on his heterotic string models, in this paper: http://arxiv.org/abs/hep-ph/9405357. And he was right. So a GENERIC string theory makes SPECIFIC predictions: chiral fermions, gauge symmetries, ten dimensions, etc. These are predictions, and if we don't find ten dimensions at the Planck scale, then string theory is wrong. As for my own opinion of it all---it keeps me in business You are asking sociology questions like Martin. String theory is interesting to many people, so they work on it. I can assure you that string theorists never talk about ``gambling'' or ``risk analysis''. When other things become interesting to people, they change fields. The standard model was built in exactly the same way, I'll remind you, allbeit with more guidance from experiment. The quantum gravity enterprise split into two factions---those who tried to start with GR and those that tried to start with quantum mechanics. String theory STARTS with QFT---in some sense string theory is quantum field theory applied to strings. If you don't believe me, try to read Green, Schwarz, and Witten without having had any experience with field theory. I tried---it doesn't work. The one base assumption (yes, only one) is that the fundamental object is a string, and (ok, two) that a consistent quantum theory of strings can be built. From these two inputs, one can derive all of low energy physics, including GR and the standard model. You procede in the same way as quantizing a point particle---path integrals, ghost cancellations, etc., etc. Except what you find is that you don't have any UV problems like you do with point particles (i.e. no renormalization), the IR limit is GR, and you have a spin two mode which naturally pops up and gives you gravitons. So you end up with a UV finite theory describing (among other things) a spin two degree of freedom, which is completely consistent quantum mechanically, and which gives gravity in the IR.

First of all, I want to make sure you know I am no expert in this field But, anytime you have symmetry breaking in the early universe, you end up with ``topological defects''. I'm not really sure what the mechanism is that generates these defects, but typically they can be two dimensional (domain walls), one dimensional (cosmic strings) or zero dimensional (monopoles). We can look for cosmic strings and domain walls using something like WMAP, and monopoles we look for with direct searches. The best that any experiment can do is put a limit on what it sees---this is why there is no direct experimental proof that the photon is massless, for example. A massless photon is CONSISTENT with the experiments. The current round of experimental bounds on cosmic strings rule out the old type of cosmic strings, the ones left over from symmetry breaking. But the types of cosmic strings which come from string theory evade these astronomical bounds.

The scale comes from dimensional analysis, just like in every approach to quantum gravity. In physics, we are often lazy about dealing with problems, or we like to be. So to figure out where things apply, we often use dimensionful analysis, which is a beautiful tool. Let's take an easy theory, like quantum electrodynamics. Quantum electrodynamics has only one parameter in it---the electron's mass. Now, even though this is a mass, we can relate it to an energy scale, and a time/distance scale by using simple relationships like E = mc^2 and L = ct. Usually we just set c = 1 (along with hbar) so that we have E=m and L=t. You can also use the compton wavelength, [math]\lambda = 2 \pi \frac{\hbar}{mc}\rightarrow\lambda \sim \frac{1}{m}[/math], to relate distance and mass. So just having one number sets all of the four dimensionful parameters in your theory. Back to QED. In QED, we are given the electron's mass, or we measure it, and put it in the theory. Once we have the elctron's mass, we can now work out all of the dimensionful parameters in the theory. On what length scale would you expect to find QED effects? The compton wavelength of the electron (which is a bit smaller than the bohr radius, which explains why non-releativistic quantum mechanics works so well for hydrogen). What time scale do you expect to find QED effects? 1/m. And so on. When it comes to gravity, the only dimensionful numbers are the Newton's constant, hbar, and c. We can form a length, a time, and energy, and a distance out of these units, see here. These are the scales where we expect quantum effects to become important. And this holds for ANY approach to gravity, be it loops or strings. Some people have had the notion to fool around with the Newton's constant, G_N. If some of the dimensions are larger than other in the compactified space, then the Newton's constant changes at those lengths. This allows you to change the Planck units, with the possibility of actually SEEING quantum gravity at a particle accelerator. This is the large extra dimensions that people like Dvali, Arkani-Hamed, and Dimopoulos work on. The idea is to leave two or more of the small dimensions ``large'', but not too large. If this is the case, they can evade experimental bounds, and we may see strings in the very near future. About cosmic strings I know much less. I do know that one CAN get cosmic string solutions out of string theory, but in such a way that the current astrophysical bounds can be evaded. The old (c. 1980 ish) cosmic strings are leftovers from some processes that occured in the early universe (topological defects, if you want to impress your friends), and have been ruled out by observation. All I know is that the cosmic strings that come from string theory can evade these bounds by two or three orders of magnitude. These strings aren't a generic prediction of string theory, so NOT seeing cosmic strings is not a way to rule out string theory.

There have been plenty of doormen, certianly. But for some reason, the attitude of many people (even some who post here) is that Einstein can do NO wrong. This is inherintly unscientific. Sorry:) If Einstein's the doorman, I'm the guy in the kitchen washing dishes.

Whatever. Back to strings.

This is an excellent point. Take Richard Feynmann, for example. I have heard that he regularly didn't do that well on IQ tests (mid 120's was the number I heard). Yet, he completely revolutionized the way that physics was done in the 20th century, and his theory of QED is tested EVEN MORE ACCURATELY than general relativity. Plus, he could pull more chicks than Einstein any day of the week.

Heh, yeah, Lubos thinks that all other non-stringy QG approaches are wrong or trivial. He's extremely intelligent---the rumor is that he was posting (good) stuff to the arxiv when he was in high school. He is probably the least diplomatic of all scientists to the Smolin crowd, but he makes points that are difficult to argue. Yeah, me too. Especially since Einstein was more or less not doing physics for the last thirty or so years of his life. He was looking for a way to interpret everything in terms of geometry, and never quite got there. It turned out that he was just wrong---for example, he never even addressed Fermi's theory, as far as I know. (Don't take my word at this, though.)

someguy---settle down. I was just pointing out that you are arguing things that people can't really test, and in doing so you are missing the point of the original argument. One can always find exceptional cases in humans where your arguments fail---you admitted as much when I first pointed this out to you four pages ago. But you continue to argue your case about ``perception''. I have already shown you that certain humans can no longer ``perceive'', and by your arguments, those people should not be granted rights. This is the question you should address: If ``perception'' is your criteria for granting rights, when should humans be allowed to have rights? Should babies (which you have admitted) be stripped of their rights? What about people in persistive vegetative states? If you can't handle criticism of your ideas, maybe you should argue with people who agree with you.

This is what you said: And this: If your position is that LQG is NOT a UV completion to the standard model, then I must say---string theory IS. Then we are talking about two different things, and we can safely end this conversation, per iNow's request: I was working under the assumption that moderators wouldn't flame the thread, but...

Here are two blog postings. One of them is good, one of them is rubbish. You can decide how I feel I will choose my words carefully in what follows... Either way, in talking with people who...think that...all of physics since Einstein is wrong, I have noticed a very disturbing trend. Specifically, these...people...seem to worship Einstein. This attitude is very...ridiculous---Einstein was a great scientist, but he was no smarter than any of the other scientists in the 20th century who revolutionized physics. The first article starts with this contention, that physics is desparately searching for a new Einstein, which is simply not true. http://grenouille-bouillie.blogspot.com/2007/09/shrug-of-resignation-in-physics.html The second article is a very well-written response to these ideas: http://motls.blogspot.com/2007/09/bad-physicists-and-populism.html Enjoy.

Certainly not! The entire argument is based on this book ``Animal Liberation'' or some such, whose MAIN POINT is that animals should be granted rights so that we have a consistent moral code---that is, their argument is that granting rights to some humans and no animals is arbitrary because some animals have the same capacity for pain as some humans. My point is that this same reasoning should be applied to fetuses in the third trimester, because they meet the same criteria as animals do. Again (like someguy) you are missing the point. We have plenty of cows, for example. We don't normally eat things into extinction. Where did you get dolphins?

I won't acknowledge anything until you or someone explains to me how in the hell a top quark and a tau neutrino can have the same Yukawa coupling This is pretty instrumental in their top quark mass prediction (or post-diction), because if the tau neutrino coupling is small (as it SHOULD be), then the top quark mass in the model is 198 GeV, which is clearly wrong. This is coupled with the fact that all of the precision electroweak data say that the higgs mass has to be less than 150 GeV, with a preferred value of somewhere around 120 GeV. Otherwise there are tremendous fine tuning issues. All of this aside, there is still no UV completion of the Connes model---only your hand waving that this is ``probably been done''.

Will give? Before you told me that these people already HAD gotten the SM out of quantum gravity? Now, I haven't been able to think about why someone would claim that the top quark and the tau neutrino Yukawa couplings should be the same. Secondly, what of generations? They seem to be put into Connes' model by hand (I missed this before). In strings they come from topology. Finally, in another paper (http://arxiv.org/PS_cache/hep-th/pdf/0608/0608226v2.pdf), he seems to get a top quark mass of somewhere around 200 GeV (=173 x 1.102 GeV), which is wrong. (See equation 39.) He also predicts a higgs mass of 170 GeV, which is pretty far out of line with what all of the electroweak data are telling us, which point to a fit of somewhere less than 150 GeV. And lastly, this scentence, in the conclusion: This seems to mean that he's working independant of any quantum gravity approach? I don't know. This is, of course, the caveat that you forgot to mention Oh, and if you don't believe me about the top mass, I could ask some OSU undergrads...

Don't include pictures of clocks, beans, or optical illusions. And be prepared to defend your arguments even more vigorously than you have here, and with more details. Most journal reviewers are post-docs, or young professors, who know their stuff VERY well.

Martin--- It certainly isn't my intent to attack your character, because I don't know who you are. (Conversely, you have quite a bit of information about me.) ``Hypocrite'' is kind of a strong word, I agree---perhaps I should have said that you were very John-Kerry-ish about it Either way, I just wanted to point out that you spent a long time crticizing the fact that string theory predicted ten dimensions (I could cut and paste if you REALLLY want me to), only to say that some quantum gravity approaches predict TWO dimensions, and FRACTIONAL dimensions, no less. Perhaps if we ever meet, we can have coffee and talk about baseball