View Full Version : Dax discussions of Beyond SM theories/including newcomer questions
Lieutenant Dax (at the moment newcomer, 5 posts) presented some thoughts/questions about BSM theorizing, string in particular, in hopes of getting some useful or enlightening response from us. I'm taking a chance by copying her initial post(s) here out of context so people can focus on them without it getting mixed up with a more technical discussion.
Please contribute your thoughts on the issues she is raising and let's try to answer any specific questions, if we can.
==first Dax post==
Here is my view. Feel free to squash it if there's reason to.
Isn't the main criticism of String Theory nothing at all to do with falsifiability, use of abstract mathematical trickery, or usefulness?
(It is clear that an unfalsifiable idea may become falsifiable at technology improves. Weird mathematics is not a sign of overstretching ourselves, as was pointed out with regards to hilbert spaces in QM, for example. And nobody doubts the usefulness of string theory and AdS/CFT in pure mathematics for example).
Isn't the primary criticism of string theory that it introduces features uncalled for? What do I mean, well we usually formulate a quantum field theory with 4 space time dimensions and point particles because that is exactly what we observe in nature. Forgive me for being "old-fashioned", but usually we develop a scientific theory by making observations first, then drawing conclusions. We chastise literalist creationists for doing things the opposite way around.
Of course, sometimes theory matures so fast that it gets a little ahead of experiment. String theorists often cite Dirac's theory and the prediction of the positron as proof that it's acceptable to jump the gun. I disagree. While it is clear that Dirac was inspired and a genius to bring special relativity together with quantum mechanics, he didn't introduce anything exotic. No strings, bells, whistles, extra dimensions or any other peculiar entities. His theory assumes point particles and four dimensions, since there was no experimental evidence that anything more than this exists (and there still isn't, as far as I know).
It's also tempting to claim that Planck introduced, seemingly as a random fudge, the quantum in order to explain the unexplainable. "See, there you have it, that's what string theorists do!" they claim. Except that Planck did what he did because there was no other way to explain the data. He knew it felt like a fudge and he felt bad doing it, but it worked well because there was no alternative, and experiment quickly supported the idea (in fact, the experimental proof for the existence of the photon already existed, it was just languishing without explanation).
Then there is the claim that Einstein developed special and general relativity "just by thinking about it", divorced from experiment. String theorists seem to use this idea (which is highly questionable anyway) to validate the claim that they're actually "discovering" new physics all the time. Ed Witten is particularly fond of making this claim, suggesting that by writing equations down we are actually discovering things. But you don't discover things with theory, you explain things with theory. You discover things with experiment. Surely experiment (observation) is the arbiter of truth.
In any case the comparison with Einstein's approach is flawed. Special relativity follows from the requirement that electromagnetism produces invariant results in different reference frames coupled with the constancy of the speed of light, an experimental observation. General relativity follows from these things but obviously not straightforwardly otherwise it wouldn't have taken him another ten years, but general relativity is as devoid of exotic concepts as it can be. Curved space time is a necessity, and was quickly confirmed experimentally, just as Planck's hypothesis was.
Another claim I've noticed that string theorists make is that it does in fact originate from experiment, because it was proposed to explain the strong force (another attempt to parallel the introduction of the quantum, for example). However, this hypothesis was rejected in favour of QCD which (unsurprisingly in my view) in based on point particles and four dimensions, nothing uncalled for and nothing unobserved. So what is the continuing motivation for studying string theory as a candidate for explaining nature (as opposed to just mathematical interest)?
It may finally be tempting to say that unification is the motivation, but although it looks compelling, there is not yet any proof that all the forces are unified. Making the coupling strengths match at the appropriate energy scale required altering the standard model so I remain unconvinced. Physics may or may not be unified. It is my firm belief that experiment will tell us whether or not all of the forces are unified together, and how they are (we don't even have a grand unified theory minus gravity yet!).
Isn't it also clear that Einstein, if we wish to follow his career with interest (which string theorists understandably like to), was far more successful in his early years. What distinguished his early career? In his younger years, he studied experimental results, unsolved problems and he reaped large results from listening to nature. In his later life, he tried to dictate to nature, and he made little progress. The rest of the physics community viewed him as an old timer who'd lost touch. And yet the string theorist community choose to imitate the later half of his career. The fact that Einstein tried to find a unified theory seems to provide some sort of validation for thousands of physicists to engage in a global effort to do so, when in my view his failure actually teaches the opposite lesson.
Isn't this the key, then: experiment is king. Theory is (or should be) subservient, in my view. The predictability of theory is surely meaningless unless the theory has its origins in observation in the first place; an experiment sandwich with theory in the middle. Why do I say that? Because without some form of experimental constraint both in the formulation and confirmation of a theory, there are literally an infinite number of ways to solve the same problem (isn't that the fundamental reason why there are so many string vacua?) There are probably an infinite number of (unconstrained) uses for a paper clip.
In my view, because I view the origin of a theory as just as crucial as its later validation, string theory doesn't even fit the usual definition of an empirical theory, which originates from experimental observations, by definition. The standard model fits this description well, and contains within its parts some of the most spectacularly verified predictions ever produced. Isn't it rather unfortunate that the Standard "Model" is a true theory, but String "Theory" is actually just a model? (Isn't that also a source of enormous confusion when discussing it?).
It's worth noting that although it's acceptable for a (real) theory to get ahead of experiment for a little while, this uncomfortable no-man's land does not typically last long. Never has it lasted for 30 years! Dirac's theory would have been discarded long before 30 years had passed. Before anyone claims that our technology has become so limited that we've reached an impasse, consider that there is currently an enormous list of unsolved problems in physics that are far more deserving of our attention. If our technology (ability to make experimental observations) is so limited/limiting, then how did it produce such an enormous list of unsolved observations?
Far fewer unsolved problems led to two huge revisions in our understanding of physics in the early 20th century, so we could probably learn a lot about the universe just by taking the approach of the young Einstein, to sit down and try to explain them by developing or revising a theory. We may even learn some things about high energy physics. If string theory is pure mathematics then put it in the mathematics department, surely. This is not a trivial issue; it actually takes up lots of PhDs and funding which the funding councils assume is used to advance physics, not mathematics.
Am I old-fashioned, behind the times and hopelessly naive? I'm not being belligerent, I genuinely want to know why I have the view I do. Did the entire physics community decide in the 1980s that we could change the way we discover new science, and I haven't realised the new "sophisticated" way of doing things? Or is the claim of sophistication and beauty just a cover to play in a sand box?
==endquote==
http://physicsforums.com/showthread.php?p=2980716#post2980716
Tom Stoer replied:
We had all these issues during our discussion; so I would say that everything has been discussed carefully, but I understand that some arguments are hidden in 400 posts so it is clear that you come up with some of them again.
I'll try to answer rather quickly and hope you will study the other posts, too.
The problem of falsifiability (in practice, not in principle - we discussed this difference) is not specific for string theory but applies to all theories including quantum gravity. Therefore either you accept this paradigm shift (that your guidelines are more mathematical then experimental) or you have to stop doing physics at all.
Yes, it's true that string theory introduces more new and abstract theoretical concepts then every other theory we had so far (but that was true even for quantum mechanics). The difference is again testability, not additional assumptions. Once proved experimentally nobody will care about.
A theory does not necessarily originate from experimental observations only. This was a famous discussion between Einstein and Heisenberg.I thin with QM it became clear that the basic entities are not necessarily directly accessible via experiment.
Regarding the 30 years: the Higgs mechanism has been discussed and used in the sixties to explain gauge invariant mass generation. Still the Higgs remains unobserved and is probably only a low energy effective degree of freedom, i.e. the GSW theory may fail to me UV complete.
Last sentence regarding what string theory "is". String theory seems to be more a framework than a single theory which allowes one to consider all theories including quantum gravity consistently; the main difference to gauge theories (which do the same for theories w/o gravity) is that in string theory the different theories are solutions (SU(N) + SUSY + ... theories emerge as solutions) instead of isolated theories.
I agree with most of your skepticism (this was the reason why I started this thread) but I have to admit that there are rather convincing arguments that string theory is a unique framework which has a lot of potential - I haven't seen any other approach which has the same richness.
That's definitely a thoughtful response appropriate to the original thread, where the main discussion going on was fairly technical. What I'm thinking is there may be some less technical material here that Dax and others could expand on. Let me know if you think this is not a good idea.
Kevin_Axion
Nov13-10, 02:09 PM
Every theory/model that is researched today or has been in the past possesses their own merits, the Standard Model does too. Instead of arguing the inconsistencies in both loop quantum gravity and superstring theory I believe we can all reach a single medium in which our viewpoints are agnostic and the unbiased by realizing the conflicts in the SM.
The Standard Model is the branching point of both SST and LQG, but this originating theory has problems that have been unsolved for over 30 years. Amongst these is the lack of explanation for the quantum nature of gravity (incohesive with General Relativity), dark energy, dark matter, neutrino oscillations, strong CP problem and the hierarchy problem. Both SST and LQG attempt to explain these ideas by extension of the Standard Model by remodeling how we define space-time, and the nature of particle physics and Cosmology both perturbatively and non-perturbatively. Now it is useless to argue that either of these ideas have had minimal effect on our understanding of the universe. LQG has given us a way to perceive the quantum of space-time and to effectively incorporate it into Cosmology and various other problems in physics. SST has similarly illustrated solutions to some of these problems but suffers from being unfalsifiable. SST is a theory that attempts to explain the "threads" (pun intended) of the universe, it is obvious to me that some of its ideas are unfalsifiable because the nature of anything is essentially defined by the non-intuitive constructs of it's substructure. Therefore the framework of the "entire" Universe, many use this term loosely but it's an idea that is unimaginable, must to some extent be unreachable in current technologies. In fact SST I believe will be left for some time but ultimately reemerge when some new form of mathematics is developed. LQG on the other hand will also not fully be defined like SST because the full content of the theory won't be understood due to mathematical/technological obstacles. The critical barrier is our mathematics at this time and people's immediacy for answers, understand the concept of what the Universe is, and a solution to everything becomes far more ambiguous. Therefore an idea that to some extent explores and explains various phenomena in the Universe like SST and LQG must continue to be researched. Clearly QFT brought these dilemmas to our attention and has seeded two great endeavours that will only help with our progression of knowledge, but then again it's great to be ignorant - it makes everything more interesting.
What I think is that Dax is raising an issue that does not exactly coincide with the tender topic of string theory but is nevertheless crucial
Is there an empiricist tradition in science? What is it? As fundamental physics has progressed in the past, how much was guided by phenomena (experiment, astronomical observation) and how much was guided by "pure mathematics". The role of Platonic or Pythagorean superstition (these sorts of equations have worked in the past, let's try the same type of equations, maybe they underlie the universe) aesthetics passionate mathematical conviction. The word "miracle" is sometimes used by theorists, when some unexpected equivalence or duality surprises them.
Dax mentions people like Dirac Einstein perhaps Newton one could also mention our dear slightly crazy Kepler who nested the Platonic solids in the Solar System and in the same book gave us P2 ~ R3. Who gave us mathematical wackiness and at the same time gave us enormously valuable mathematical truth. And was also tirelessly obsessively empirical---he crunched Brahe's data and found, at last, the ellipse.
Does the present situation facing Beyond Standard theories require us to revise our expectations about the mix of empiricism and mathematical guidance?
I think the string-nonstring division is orthogonal to this question. You can find string folks on either sides of that issue.
There are SOME string folks who sound as if they want to abandon the criterion of testability and postulate a multiverse of different versions of physics all ruled by the elusive M-theory and the siren call of supersymmetry. The actual universe we are dealing with then becomes accident and its physics mere happenstance.
But not ALL string folks are like that. Many want to use it as a math framework within which to arrive at testable physics.
So at some level the string-nonstring issue is irrelevant. The real question is how tightly do we want to hold on to the 400 year Baconian tradition of empirical science.
I get the feeling that the Lieutenant is asking about this.
The answer is easy I don't understand why we always have to revisit the issue.
1.we have experimental data: we use it
2.we don't have experimental data:
a. we do what we can
b. we do nothing
Choose between a and b.
1.we have experimental data: we use it
2.we don't have experimental data
I see your point, but in my view, we are not devoid of experimental data, we are simply devoid of experimental data which supports our notions of what we think a QFT should look like. I think that is a crucial difference.
We're certainly not short of a big long list of unsolved problems, and surely we shouldn't say that none of these would shed light on high energy physics? The old-fashioned approach of theoretical physicists tackling experimental problems was very fruitful (this is why I contrasted the two phases of Einstein's life).
Feynman once said something useful: the division of physics into theorists and experimentalists is artificial; it is necessary because of the increasing complexity of the subject, but it is artificial nonetheless. Physics is an experimental science by definition. The concept of labouring alone to try to advance physics theory is a new one.
You ask why we have to revisit old criticisms. Well I'm not a string theorist, and I'm rather inexperienced at physics theory, but if you try to claim that we occupy a no-mans land devoid of data, I don't believe you. I feel, rightly or wrongly, that misunderstandings about what string theory really is (model, theory, super-duper theory) have caused distortions in people's view of how terrible our current experimental situation is.
It seems a little odd to me that we hang on with great anticipation for new experimental data to confirm or deny our models, but all along there has been a vast number of unsolved mysteries which are probably rich pickings as far as learning new physics is concerned.
I don't doubt the incredible skill and genius of many string practitioners; I know some very smart ones myself - but what use is it being a great bus driver if you're going in the wrong direction? Ed Witten is a perfect example - he is clearly extremely intelligent, and he was a brilliant problem solver as a student (Zee mentions in his book that his solutions to TA problems were incredibly lucid). But clear thinking about technical problem solving is not the same thing as clear thinking about science itself and its philosophy. Ed Witten is also prone to statements about discovering new physics which in my view are uncalled for. Not even in the golden age of the Standard Model did we claim that theory development was discovery - not until we actually found results in the accelerators.
I'd also like to point out that there's nothing a priori wrong about a less-empirical approach to science, but this is where a study of the history of science is most useful. We follow the empirical approach because it works wonderfully, not because we have a dogmatic view of what is the right approach. History shows that physics advances from new experimental data. One of the most beautiful theories in all physics, Maxwell's electromagnetism, was developed because of decades of careful experimentation. I'm not convinced you'll find a genuine advance in physics which became established through pure thought alone; even Einstein's most inspired work rested solidly on observational physics.
If anyone has found evidence that the 400 year old tradition no longer works, or alternatively that we can do better by relaxing empiricism, then I am more than willing to listen to the reasons why - but I don't think it is helpful negru to sigh and huff and dismiss my views just because they've been voiced before. They may have been voiced before but have they been answered before? Have we found a new way of discovering things, which gives us a green light to ignore the long unsolved problems list, and work busily on our own notions of what we think the universe might be like?
Or am I still suffering from an incurable case of naivety?
By the way perhaps I should make clear that by "unsolved problems" I am not talking about difficulties with theories, with unification, etc. I am referring strictly to observations/experiments which are as yet unexplained.
It's also clear that an unexplained experimental issue is also, therefore, a theoretical problem (because it requires explanation), but the reverse is not necessarily true, i.e. some of what we think are theoretical problems just reflect out own biases.
This frustration of terminology seems to come from the fact that the physics community is split into theorists and experimentalists, as I've mentioned. In my humble opinion, we should eliminate all theoretical "problems" which are not experimental oddities - although obviously if you are a string theorist you won't view that as particularly humble. Of course the progress of physics is highly suggestive of unification, but is suggestive good enough? (I don't mean good enough to consider as a solution to a known problem, I mean good enough to invest lives, careers and decades).
Unless, of course... someone can find a clear example of a case where someone discovered that something was a "problem" before an experiment betrayed it to be so. I've tried to think of one by my brain fails me.
Haelfix
Nov13-10, 04:51 PM
Perhaps you could be specific and tell us what piece of experimental evidence you are talking about and why you think quantum gravity is necessary to explain it. The fact of the matter is that there are very, very slim empirical constraints on the nature of quantum gravity.
You have some constraints from big bang nucleosynthesis, as well as CMB probes, and possible upcoming gravitational wave detectors but the inverse problem is large there, and you have to drag your pure theory into quantum cosmology and extrapolate it through all sorts of violence in the early universe. In short, its extremely hard to get a clear signal out of it. In fact, arguably the only important number that has been tested at this time that really begs for a QG explanation, is the existence and nature of dark energy.
Contrast that with theory constraints. Even simple things like postulating exact lorentz invariance, the existence of blackholes and that quantum mechanics remains unmodified automatically rules out most ideas. Those assumptiona may or may not be valid, but at this point its pretty much the only thing thats going for us.
JustinLevy
Nov13-10, 05:19 PM
By the way perhaps I should make clear that by "unsolved problems" I am not talking about difficulties with theories, with unification, etc. I am referring strictly to observations/experiments which are as yet unexplained.
I think this, more than anything, is the issue at hand. You seem to feel there is clear distinction here, while it sounds to me like a false dichotomy.
I'm not trying to create a "strawman" here, but bear with me while I start with an absurd extreme.
Let's say I do experiment A many times and have found the result to be A0. Using empiricism, I deduce the "theory" that if anyone does experiment A, that they will get results consistent with A0. I could do many experiments and record these "theories". But these theories are nothing more than a table of experiments -> results. This overly strict empiricism approach make theory sound like nothing more than say the physical properties CRC reference books.
More reasonably, what we want is an over-arching view that allows us to understand phenomena in more complete way. In other words, "predict" new results for experiments not done yet but that are "close enough" to old experiments to fit in our theory. In other words, we create a mathematical theory and "interpolate" or "extrapolate" to get new predictions. We try to interpolate or extrapolate only within the "range of validity" of the theory.
You seem to want to say that if two theories disagree, that they are merely out of their "range of validity", and just leave it at that. Or alternatively that we should never extrapolate, only interpolate.
The reason I have trouble with that is I feel this violates a core idea of the scientific method: we assume nature can be described by rules, and experiment/observation can elucidate these rules. If we didn't assume nature could be described by rules, then doing an identical experiment N times had in principle no information to provide for the (N+1)th test of this experiment.
So if we have two conflicting theories, that both match experiment in their respective ranges, this alone is indeed experimental evidence that our theories are wrong.
You simultaneously are clinging to experimental evidence, yet denying it in other cases. You seem okay with Planck needing to introduce quanta to explain blackbody radiation, but weirdly seem also okay with the fact that this disagrees with classical physics. Do you think blackbody radiation was not experimental evidence that we needed to adjust classical physics? Or only that we should have restricted the range of experiments we should apply classical physics to? This is introducing a new theory, kind of like a piecewise function, of previous theories.
Does your complaint merely reduce to:
You like this "piecewise" theory, better than a "continuous" theory that could possibly explain all the data?
I think your complaint does reduce to this. If it does, then from a strict empiricist approach we have nothing left to say ... From a scientific method approach though, we can discuss which is more "natural" or applications of Occam's razor (ie. Lorentz LET vs Einstein's ideas), which at some level is debating aesthetics/opinions, so again not much left to say.
@Haelfix
I think we're in agreement, I can't think of any experimental evidence that absolutely demands an explanation in terms of quantum gravity. Even in cases where it is compelling, there may be a better explanation for said phenomenon.
I'm sympathetic to the idea that the universe can't have one set of rules for the small (action), and another set of rules for the large, so therefore there must be a quantum theory of gravity, but a "theory of everything" goes somewhat further than that.
I feel that we should probably develop theories based on what we know and observe until we have reason to believe otherwise, but I'm open to a clearly expressed view to the contrary. I remember seeing a funny cartoon once which was divided into two halves:
1) SCIENCE [People looking at broken bones] "Here is the evidence. What conclusions can we draw?
2) CREATIONISM [Person holding a bible] "Here is the conclusion. What evidence can we find to support it?"
I found this kind of stuff when I was investigating creationism and evolutionism a few years ago. The above criticism of literalist creationism is valid. It may be possible in principle to find 100% support for a pre-conceived idea, but it is kinda a backwards way of doing things as far as science is concerned.
Isn't this the reason why (historically) the strictly evidence-first approach has always worked best? (I'm not even sure any scientist has ever succeeded via a different way).
I often think of the way some new-agers or pseudoscientists try to tell us that there are "alternative ways" to discover new knowledge, such as by meditation or Eastern philosophy (alternative to science, that is), but of course we dismiss this as nonsense because new knowledge about the universe only ever comes from evidence (creative endeavours like creating Shakespeare or music are not really what I mean by new knowledge). Have some physicists, possibly, become guilty of the same self-deceit with regards to how we find out new things?
If I were to follow my current view mega-strictly (and the jury is still out, because I am still learning), I would never develop a theory based on anything other than things I already know about: point particles, four dimensions, Lorentz invariance, etc..
This is effectively Occam's Razor: yes the Standard Model is not perfect, yes ST is not perfect, and yes ST can in principle predict the SM, but we don't need the string object to describe physics at the energy scales we can see. Given this choice, I choose the one which made no a priori assumptions about what the basic physical objects are in the theory. If nature is made of strings, we'll view them one day in an accelerator with the appropriate resolution, or in a cosmological observation.
When the ancient greeks were guessing about the basic structure of matter, they guessed that it was it was discontinuous, but there were only two choices. In determining what the fundamental object in the universe is, is it really only a choice between string or point? There could be a thousand different possibilities and our imagination has failed us, in which case it really is premature to spend decades developing something which (just like the myriad of string vacua) may only be one choice among many. The only thing which can pin this down is experiment. The answers may even be right under our nose (another unwarranted assumption may be that the only way to advance high energy particle physics is with an accelerator).
You simultaneously are clinging to experimental evidence, yet denying it in other cases. You seem okay with Planck needing to introduce quanta to explain blackbody radiation, but weirdly seem also okay with the fact that this disagrees with classical physics. Do you think blackbody radiation was not experimental evidence that we needed to adjust classical physics? Or only that we should have restricted the range of experiments we should apply classical physics to? This is introducing a new theory, kind of like a piecewise function, of previous theories.
Can I be honest, I don't really understand much of what you're saying! :confused:
What I will say is that my view is simple (perhaps too simple?). Experimental evidence (assuming we perform our experiments with due care) never lies. I certainly don't cling to experimental evidence in some cases and deny it in others, I view experiment as king. If was a physicist in 1900 I most certainly wouldn't be ok with blackbody radiation disagreeing with classical physics, that's my whole point. Theory is (or should be) subservient - it's theory which needs to change if there's a conflict. As a 1900 physicist I'd be so busy working on a new theory that I wouldn't have the luxury of being able to question whether or not I cling to experiment or not.
Except of course to check that my instruments weren't broken :blushing:
Kevin_Axion
Nov13-10, 05:49 PM
There is a reason it's called theoretical physics.
JustinLevy
Nov13-10, 06:14 PM
What I will say is that my view is simple (perhaps too simple?). Experimental evidence (assuming we perform our experiments with due care) never lies. I certainly don't cling to experimental evidence in some cases and deny it in others, I view experiment as king.
I am confused.
You write: "I can't think of any experimental evidence that absolutely demands an explanation in terms of quantum gravity."
While we don't have experimental data where the quantum effects are on order of the gravitational effects, this is only a comment on how elucidating the experimental data is in probing the details of quantum gravity. However, we clearly have experimental evidence for gravity, and evidence for quanta (blackbody radiation, etc). Unless you are pushing for a new theory which is a piecewise in distance scale approach to physics (which I'd be interested in seeing the details of such a theory, as it would be quite contortionist), then if you consider "experiment as king" there is already plenty of experimental evidence for quantum gravity.
As I said before, if we have two conflicting theories, that both match experiment in their respective ranges, this alone is indeed experimental evidence that our theories are wrong.
I used blackbody radiation vs. classical mechanics as an example, which you then seemed to agree. So I am confused.
I can't figure out exactly what you are complaining about. If we try to construct theory using "minimal inputs" like you demand, well putting in experimental inputs (dimensions, symmetries, gravity, etc.) leads to an inconsistent theory under the framework that worked so well for the standard model. So we need to add something new to the mathematical tool box, or relax some of those extrapolated inputs from experiment that you are demanding to be true at all scales.
So is your complaint merely that the only possibilities they have found so far seem to add too much? You said before you were okay with Planck adding stuff because the experiments demanded it. Well, can you find a better way to get quantum gravity than string theory? Other people ARE looking. Experiment can't rule out string theory yet, but that doesn't mean experiment has proven string theory. Do you think people are claiming that?
I really don't understand what the root of the complaint is.
But I hope we can agree the experimental evidence already requires changing our current theories.
You said before you were okay with Planck adding stuff because the experiments demanded it. Well, can you find a better way to get quantum gravity than string theory?
There are probably many good ways to get quantum gravity, but my point is the comparison with Planck is flawed. He wasn't seeking to "get" any theory, he was trying to explain the experimental data with what physics he already knew. This is almost the first rule, "don't be so quick to create revolutions", albeit an unwritten rule. That's why he actually felt bad about doing it.
The comparison of string theory with Planck's quantum is not watertight, so be careful before accusing me of hypocrisy. String theorists don't seem to share Planck's discomfort; but most importantly, because he was so intimately involved with experimental data, his quantum idea was quickly confirmed. Not only this, but other direct experimental evidence for the quantum via the already existed even before this!
I really think that physicists should stop trying to "get" a theory of this, a theory of that, because that's where the comparison with great physicists of the past falls apart. Great physicists of the past, the productive ones, sought to explain experimental results and develop scientific theories from them, not in anticipation of them.
Imagine Schrodinger, Bohr, Heisenberg et. al. developing QM before there was even a shred of proof that energy was quantized. Not only would it have been rather silly (c.f. my creationism cartoon), but I doubt it would even have been possible. How much more so is this true for far more complex modern physics?
There is a reason it's called theoretical physics.
Hmmm. I'm really not sure what you mean by this, or which of my points you were responding to.
Since a "theory" in science is intimately tied to experiment by definition (both in its origin and verification), I don't see what point you could be making. The only reason theoretical physics appears to be a separate discipline is because of the division of labour.
Incidentally, the generally accepted definition of a real scientific theory is the reason that creationists are wrong when they claim that evolution is "only a theory". By this way of thinking, string theory (however useful or interesting it may be) is not a theory at all.
Kevin_Axion
Nov13-10, 06:45 PM
Because your saying experiment is king and that our theories should reflect the condition of experimental evidence, but when there is lack of experimental evidence we use logical deduction and thought. Hence this is theoretical physics not experimental physics. Yes, experiment is absolute, but the ideas we are discussing in physics are on eV scales that are far greater then we can currently probe. This is a useless argument, physics will remain the way it is, I'm sure the physicists see things in LQG and SST that we don't, if you don't like the way it does then go to "another universe", in the words of Richard Feynman.
Yes, experiment is absolute, but the ideas we are discussing in physics are on eV scales that are far greater then we can currently probe. This is a useless argument, physics will remain the way it is, I'm sure the physicists see things in LQG and SST that we don't, if you don't like the way it does then go to "another universe", in the words of Richard Feynman.
But why did we jump the gun so much that we vastly exceeded what we could measure? You make it sound like the Standard Model isn't being studied anymore, but I know that's not true. I genuinely want to know why physicists can study ST and talk about it as though it is a "discovery" or even a revolution.
I saw a talk by T'Hooft where he pointed out the vast energy scale between the LHC scale and unification, and he made the point that it is unlikely to be deserted. There is likely a continuum of rich and beautiful physics along the way. To claim that it will be otherwise is to ignore the lessons of history. And as I've mentioned, it's not as though there aren't any Standard Model issues to study at the LHC scale.
I'm not just making an assertion I'm asking a question - why is String Theory considered a form of physics discovery? I don't dislike ST, but even so I assume your last sentence about finding another universe was a polite way of telling me to get lost :frown:
Kevin_Axion
Nov13-10, 06:58 PM
No, I'm not telling you to get lost, I like it when people ask questions! I'm sorry if it sounded like that I just mean if you aren't willing to accept the the properties of the universe in a theoretical sense then you are essentially denying reality and as Richard Feynman stated: http://www.youtube.com/watch?v=iMDTcMD6pOw. The Standard Model is being researched, most of this research has to do with supersymmetric (SUSY) Yang-Mills theories, SUSY was discovered in the context of SST. SST is the only consistent model in which all of the fundamental forces, and particles are unified and various problems are resolved. Also it has provided various dualities in physics such as S-Duality, T-Duality, U-duality, Gauge-Gravity Duality (AdS/CFT and the like), and the holographic principle. It also resolved singularity problems and the information paradox. These are all ideas that have failed in QFT therefore SST appears to be a likely approach to understanding nature.
I just mean if you aren't willing to accept the the properties of the universe in a theoretical sense then you are essentially denying reality and as Richard Feynman stated
He was right - because once something has been accepted into a theory, it means it is already a proper description of reality. String theory may be all kinds of wonderful things, but it is not a theory (yet), and may never be. How can I deny reality if I don't know what it is? Why do we view ideas developed from ST as reality (question)?
And wasn't Feynman skeptical of ST when he was alive?
Kevin_Axion
Nov13-10, 07:06 PM
He was skeptical, that was before many of the major breakthroughs occurred, re-read my post, I edited it. I said denying reality in a theoretical sense.
JustinLevy
Nov13-10, 07:09 PM
Hmm...
we seem to be talking past each other.
My point with Planck wasn't about "how" to create a theory. My point is that it would not be acceptable to make a dichotomy:
1) here is a theory for blackbody radiation
2) and classical mechanics applies to everything else
You seem to agree this would be incorrect. But you seem to disagree that we do have some experimental evidence on quantum gravity. We have very stringent measurements on how gravity works (so far everything matches with GR if we include dark energy and matter), and have stringent tests on quantum mechanics. These experimental guides of course don't cover everything, but they do provide strict requirements ... which already can rule out some ideas of quantum gravity. Actually it rules out lots of ideas, which is why finding a plausible theory of quantum gravity is so difficult.
So that is my main point, and analogy to Planck, we already have experimental data to guide us in trying to come up with a theory.
...
Then, we can discuss what is the most appropriate way forward. I'd very much like to decouple these two points, since they keep getting mixed up in our discussions, so I'm having trouble understanding what the root of your complaint is.
So can we at least agree on the first point?
Then we can agree that we should continue looking for a way to explain all the experimental data. That this search for quantum-gravity is motivated by our experimental evidence, as the experimental evidence demands it.
This discussion is then what is the more appropriate way forward. As you suggest, following the scientific method the most appropriate way is indeed to apply tried and true techniques without makes tons of new postulates. You make it sound as if this hasn't happened. This has happened. People tried for decades to apply our usual tools of finding a quantum theory which gives us back the classical theory we expect in the appropriate limit ... these tools have failed to provide a quantum theory of gravity. So, can we then agree that we need to add something?
Hopefully now, the discussion is reduced further to: what needs to be added?
You wish as little as possible to be added. Well, so do all scientists. No one is arguing. If someone found a theory that fit all the data with less, it would be the preferred theory via Occum's razor as you argue.
This is why I don't understand what the root of your complaint is. People are looking for theories that describe all the experimental data -- experimental data is king. The experimental data is already good enough that this is extremely difficult. We can't just willie nilly make up a theory, as if we had no constraints. String theory (or better thought of as a mathematical "framework") is an approach that seems to allow a consistent explanation of all experimental data. This does NOT mean, nor is anyone claiming, this can be reversed to claim experiment proves the string theory approach is the minimal approach. (If this could be shown mathematically from the experimental constraints, then we'd have direct experimental evidence of strings ... we do not, which is why the search for quantum gravity continues.)
Yes but reality in a theoretical sense is the same thing as reality in the usual sense. A theory has a higher status than a model or an idea because it comes from experiment. Do you agree?
Kevin_Axion
Nov13-10, 07:17 PM
How can a reality in a theoretical sense be reality in the usual sense. That would presume you already know the nature of reality. I agree with your second point though.
@JustinLevy
So are you saying that decoupling from experiment is justified if we have no choice? I'm not convinced that you can learn anything about the universe without observing it. Even if our ideas are correct they have to be tested, and they have to be tested quickly before we wander off too far.
This is why (@ Kevin Axion) I think the idea of ST "breakthroughs" is flawed - how do you tell if something is a breakthrough unless you test it to see if it is?
How can a reality in a theoretical sense be reality in the usual sense. That would presume you already know the nature of reality. I agree with your second point though.
Ah I see - you're using the term theoretical too loosely. A scientific theory is something much more stringent. If something has been accepted into a theory, it has already been tested experimentally - it is reality.
This is why calling ST a theory has caused endless confusion. It is not a theory, even many string theorists acknowledge that! Feynman was saying that denying a real theory was denying reality, and he was absolutely correct, in my view.
Kevin_Axion
Nov13-10, 07:26 PM
I'm not sure how else to explain this, theoretical physics such as LQG and SST are the ONLY ideas we have that extend upon the Standard Model to provide a deeper understanding of the universe. There is also NO experimental evidence for anything BEYOND the Standard Model. Therefore these are ideas that are THEORETICALLY researched to provide a comprehensive understanding of everything. So do you suggest that we end theoretical physics? I seriously recommend that people who dislike ideas such as SST for problems such as falsifiability should at least read a paper on the subject or try to understand the richness within its framework, I'm sure surprised who himself is a string theorist would agree with me on this. Had SST not been developed I wonder where research would right now, no SUSY, no AdS/CFT, no dualities. These have become most active areas of research.
Kevin_Axion
Nov13-10, 07:34 PM
Actually the term theoretical physics doesn't imply the basis of a theory because if it did then all of physics would already be complete. You are right it is not a theory, it is a model, a brilliant one.
Getting angry isn't necessary.
I'm not suggesting ending theoretical physics, otherwise I wouldn't be training to be a theoretical physicist. You're using the word theoretical to mean several different things.
I view physics (which is theory and experiment tied together) as like walking. One leg is theory the other is experiment. We walk by putting one foot in front of the other, so sometimes it appears that we get a little ahead with theory, but we call it theory because we quickly submit to experiment even if we do get a little ahead.
ST is not like this. If the prediction of the quantum was putting the theory foot ahead, then ST is overreaching yourself and possibly falling over. I strongly believe that we can't get too far ahead of ourselves. Like the two legs, theory and experiment are inextricably linked, do you agree? So "theoretically" researching something has no meaning. It is done in concert with experiment, or else it isn't science. That is my view. If you disagree that's fine, but don't make out that I need to read more papers please.
Kevin_Axion
Nov13-10, 07:40 PM
I'm not getting angry, I'm just trying to emphasize certain points. And by reading more papers I mean it both literally and figuratively, you can't just say something isn't physical until you fully understand it. Using your analogy though, imagine your person has one leg, what do you do stand, or sit? I would suggest moving onwards.
By the way I won't participate in this thread any longer if it just becomes a means to sigh and groan and tell the student to wise up. The view of science I have may seem radical, but it was normal in the past.
Using your analogy though, imagine your person has one leg, what do you do stand, or sit? Or move onwards.
But this person (physics) still has two legs, but one is immobile. You try to get the stiff leg moving again, and stand still until you can move again, otherwise you fall over. The analogy works well because theory and experiment are never separated, by definition.
JustinLevy
Nov13-10, 07:49 PM
There is also NO experimental evidence for anything BEYOND the Standard Model.
Gravity, hence this whole discussion.
Also:
Dark matter.
Dark energy.
Whatever the heck the results of LSND mean for neutrinos.
Possibly the g-2 result for muons.
My point remains: these pursuits for theory beyond the standard model ARE motivated by experimental results. If we had more data, our efforts may be more successful, but that is a separate issue.
@JustinLevy
So are you saying that decoupling from experiment is justified if we have no choice?
My main point was, and continues to be, these efforts are due to experimental evidence. Experiment is forcing us to add something new to our usual tools or postulates. All that remains is what is this? Experiment is forcing this choice. So how is it decoupling from experiment?
If we had a theory that explained all the experimental data fine, then a theory with many extra dimensions and strings and so on would of course be only useful for mathematical investigations. We don't have a simple theory of quantum gravity though.
I'm not convinced that you can learn anything about the universe without observing it.
I'm not suggesting we don't observe it. But ignoring the experimental evidence that shows our current theories are wrong, so we need to work to come up with a replacement theory, would be removing the "predictions" part of the scientific method.
Even if our ideas are correct they have to be tested
Yes. Hence the conference on experimental quantum gravity. Hence people trying very hard to get M-Theory to the point where they can calculate predictions like the mass of the electron, etc.
In some sense experiment is way way ahead of theory. We don't have a theory that can calculate predictions which can consistently match all of the experimental data yet. All simple approaches have shown to be wrong and ruled out. People are trying. People are working to do exactly what you are hoping for: holding experimental data king, and find a self consistent model to describe all this data. They have yet to succeed.
So complaining about that these theories predict beyond what can be measured yet seems moot. Let them continue working to even get a theory that matches all experiment first. We still have a long way to go.
This is why (@ Kevin Axion) I think the idea of ST "breakthroughs" is flawed - how do you tell if something is a breakthrough unless you test it to see if it is?
It is a breakthrough because after decades of trying, it is the first approach that seems like it could possibly work. It isn't even a full fledged "theory" yet, more of a framework. So much still needs to be done on the theory side before we can fully compare to experiment.
Who knows, maybe this idea won't match with the effective electron and muon masses or whatnot. But to complain that people aren't trying to find a "minimal" quantum gravity ... when that is exactly what people ARE trying to do ... well, it severely confuses me.
JustinLevy
Nov13-10, 07:53 PM
By the way I won't participate in this thread any longer if it just becomes a means to sigh and groan and tell the student to wise up. The view of science I have may seem radical, but it was normal in the past.
I'm sorry to hear that.
I wish you wouldn't leave thinking that science isn't driven by the need to explain experimental results. Because it is. It is this drive that has lead to so many strange seeming suggestions for quantum gravity. No one can explain all the data quantitatively yet. People are trying very very hard.
Kevin_Axion
Nov13-10, 07:54 PM
Precisely my point, if one is immobile you can't hinder the other. If theorists hadn't invented SST or LQG then experiments would proceed. But experiments have reached a plateau, until the LHC finally starts deciphering information then we may see new physics. But theorists are original thinkers, they imagine, much progress has been made in this fashion and experiments made the conclusions. We have different perspectives and I respect yours, and I do sound harsh, but that is only because people come on this general sub-forum and completely deter String Theory and only focus on one idea falsifiability. Although, you do raise very critical points and am willing to listen.
But to complain that people aren't trying to find a "minimal" quantum gravity ... when that is exactly what people ARE trying to do ... well, it severely confuses me.
These efforts would arguably be minimal if we had proof that a string is the only possible fundamental object.
Kevin_Axion
Nov13-10, 07:57 PM
JustinLevy, I mean there is no experimental evidence for a theory Beyond the Standard Model, I do understand that there is remaining problems and physics beyond as I stated these ideas in my original post.
We have different perspectives and I respect yours, and I do sound harsh, but that is only because people come on this general sub-forum and completely deter String Theory and only focus on one idea falsifiability.
You may find it interesting that I view the falsifiability argument as a meaningless distraction - I care little about it, since an unfalsifiable theory may become falsifiable in the future; this is in my original post. My criticisms of ST are different, it's more to do with how we do science and how we discover real knowledge.
Kevin_Axion
Nov13-10, 08:03 PM
Yes, real knowledge precisely what we are lacking. I suppose you are right in that sense. We need real knowledge through experiments, but Theoretical knowledge is just as convincing. I suggest the idea of Bekenstein-Hawking Radiation, an unobserved phenomena but widely accepted. It is because it just seems right, as does SST, that doesn't mean it is though.
JustinLevy
Nov13-10, 08:07 PM
These efforts would arguably be minimal if we had proof that a string is the only possible fundamental object.
Come on, are you seriously suggesting people are not searching of a minimal description of quantum gravity?
People would LOVE to find a consistent 4-d field theory version of quantum gravity.
You ask why is string theory considered an advance, it is because this appears to be a possible explanation. This is a huge step forward.
Would you feel more comfortable if we worded it as:
For decades no consistent approach to quantum gravity could be found. People tried to add many different degrees of freedom, or use other mathematical tools, to cancel out divergences. Nothing seemed to work. String theory represents our first data point for finding an upper bound on the minimal amount that needs to be added to find a consistent theory of quantum gravity.
Theorists worked hard to get this data point. The information provided by this data-point should not be dismissed.
It's an awkward way to word it, but as already stated, there is no mathematical nor experimental claim that string theory IS the minimal explanation. I did not claim it was the minimum. I explicitly stated the opposite.
JustinLevy
Nov13-10, 08:10 PM
JustinLevy, I mean there is no experimental evidence for a theory Beyond the Standard Model, I do understand that there is remaining problems and physics beyond as I stated these ideas in my original post.
You seem to be making the same claim that Dax is making, which is confusing me.
How is experimental evidence of gravity, NOT experimental evidence beyond the standard model? Same with dark matter, which is not in the standard model either.
If you claim there isn't evidence beyond the standard model, then all efforts to get theories beyond the standard model DO appear to have no experimental motivation. Which falls right into Dax's complaint.
EDIT:
To make it more clear, I am trying to separate two things:
1) Experimental Evidence showing our current theories are wrong (or at least need adjusting/ something added)
2) Experimental data on gravity at a scale where the quantum corrections become clear over the classical effects
We already have #1. We have yet to get a theory to resolve this. In this sense, experiment has been ahead of theory for close to a century.
We do not have #2. This does not mean we don't have evidence for something "beyond the standard model", or need for figuring out how to get GR as a classical limit of a quantum theory.
Kevin_Axion
Nov13-10, 08:26 PM
I am saying that dark matter and dark energy aren't concepts that give us a framework but yes they do suggest something beyond the Standard Model.
bcrowell
Nov13-10, 09:01 PM
It seems to me that some of the responses to Lt_Dax have involved a lot more hand-wringing and ruffled feathers than was necessary. I think Lt_Dax's original post was spot on. If it hurts people's feelings, then the right response is to calm down, put those feelings aside, and try to write a response that answers intellectual points with intellectual points.
There is a reason it's called theoretical physics.
What is this supposed to mean? Does it mean that theoretical physics is not supposed to make contact with experiment?
The answer is easy I don't understand why we always have to revisit the issue.
1.we have experimental data: we use it
2.we don't have experimental data:
a. we do what we can
b. we do nothing
Choose between a and b.
Well, my opinion is that the answer should be 2b, in the sense that pursuits like LQG and string theory should get zero institutional support. (And this is not the same as saying that nobody will ever do any work on them. Once someone has tenure at a university, you can't stop him/her from working on something s/he finds compelling.)
Kevin_Axion
Nov13-10, 09:24 PM
Yes it is supposed to make contact with experiment but you don't need experiments to research theoretical physics, it's a purely logical subject based on reason and deduction. Others would differ as the OP has and I absolutely accept that viewpoint I was just expressing my own.
Well, my opinion is that the answer should be 2b, in the sense that pursuits like LQG and string theory should get zero institutional support. (And this is not the same as saying that nobody will ever do any work on them. Once someone has tenure at a university, you can't stop him/her from working on something s/he finds compelling.)
Well you see this is the issue. If the problem with "dubious" research is the funding, I'd have to agree with you. However, I also find "research" in literature, or humanities in general to be pretty worthless. Does that mean we should cut funding?
And why should tenured people be allowed to work on whatever they want? What's so special about them? Pretty much all universities receive federal funding whether they're private or not, so it's still tax money funding tenured profs.
Well you see this is the issue. If the problem with "dubious" research is the funding, I'd have to agree with you. However, I also find "research" in literature, or humanities in general to be pretty worthless. Does that mean we should cut funding?
Humanities can arguably be in touch with reality. But some areas of it, like paranormal research, still get funding from governments. I think QG and paranormal are in the same zone of priority according to bcrowell.
@Justin Levy
To make it more clear, I am trying to separate two things:
1) Experimental Evidence showing our current theories are wrong (or at least need adjusting/ something added)
2) Experimental data on gravity at a scale where the quantum corrections become clear over the classical effects
We already have #1. We have yet to get a theory to resolve this. In this sense, experiment has been ahead of theory for close to a century.
We do not have #2. This does not mean we don't have evidence for something "beyond the standard model", or need for figuring out how to get GR as a classical limit of a quantum theory.
This is the key. I think some have mistakenly thought that I don't believe there is evidence that our current theories need revising. On the contrary, one thing I have emphasized repeatedly is that not only do we have such evidence, but we probably have a lot more than we think (the "long list of unsolved problems" concept).
The main cause of confusion is that some people are saying that such evidence justifies developing entire 'frameworks' aside from experiment. This is bizarre because the actual point shows that we are not devoid of data or experimental oddities (I think this is a pernicious myth). The trend towards massive model building such as string theory is a separate issue, and seems motivated more by grandiose desires to build a theory of everything, not a lack of unsolved observational problems to work on.
My view, which could be overly simplistic, is that we should do theoretical physics by examining experimental problems. The g-2 may be a good example, and there are other examples (which people have mentioned) of where we need to extend or revise the standard model. The development of ST seems to be a separate exercise. I'm sorry to say, I find the concept of doing 'theoretical research' alone somewhat strange. The g-2 people, for example, do their research in concert with experimentalists. The other two main divisions of theoretical physics (Lattice Gauge Theory, Particle Phenomenology) fit the "old", proper definition of what theory is. The meaning of the word "theory" really does matter. If it didn't matter, then we can basically just do anything we want, no matter how wild. If "theoretical" physics is no longer a part of physics (an experimental science by definition), then that would probably result in a huge mountain of 'theory' papers which say a lot but explain very little.
So I don't question that there is physics beyond the standard model, I think there is evidence for that already, I want to make that clear. My main question is about why string theorists use such incredible language to describe what they are doing. Is it really justified to say we have had a "revolution" (or two, no less) even though it hasn't been confirmed experimentally? The two real revolutions of the early 20th century were tightly linked to experiment, front and back.* The Standard Model in the 60s and 70s is a brilliant example of a highly predictive theory which was developed and verified at famous particle accelerators in the USA and CERN in cooperation with theorists, but even with this level of success, they never ever made unwarranted claims about the importance of the theory. They knew that they could only be sure it was right up to a certain energy scale. Wilsonian renormalization taught us that beautifully.
Again regarding language, why do we describe the development of string theory as discovery? This is not a question regarding its usefulness in pure mathematics, or how interesting it is, it is a question about whether we can discover a real fact about the universe by writing down a new equation. In the Standard Model, didn't we write down equations to explain new observations (e.g. the QCD lagrangian wasn't written down before we had experimental knowledge of the features of the strong force). String theory doesn't just claim to explain what we already know, it is so unconstrained that it results in a unified theory (which may or may not be the case) and even branes and multiverses (which may or may not exist). Is this discovery? I'm still certain we've never done anything like this in the past, and surely it is false that we don't have any new data to work with?
* Not only that, but the judgment of whether something is a revolution is not made by the practitioners of the subject at that precise moment. It is typically made in the future, and it is typically made by others. So what makes Green, Witten et. al. so comfortable using these words?
By the way I'm still not purely making assertions - my questions are not all rhetorical. If any cool heads can explain why pure model building can be real discovery even without experiment, then I welcome it.
One thing I may anticipate is the "argument from beauty" - i.e. Dirac did it, so that's what we're doing. Well, I think there are essential differences (Dirac didn't develop the theory with exotic objects and dimensions, only new matrices), but apart from anything else, to use an old quark physics pun, truth comes before beauty. (This may be why Dirac was nervous about calculating g from his equation and left it til the next day, assuming he was nervous).
suprised
Nov14-10, 09:51 AM
What is routinely neglected in these discussions, is that there are, as a matter of fact, extremely non-trivial computational results! For example, state counting in black holes. This is a theoretical arena where the two pillars of modern physics, GR and QM, seem to clash and strings provide a way to reconcile these. It is very non-trivial that this, and many other things, do work at all! This is what has been "discovered" and the reason for excitement.
It is simply not so that string theory is an unmotivated "belief" and people just say: well let's postulate that we have those little strings and see what comes out. If it doesn't work, we "believe" instead in membranes, or yellow octopi, for that matter.
On the contrary, strings are a framework, or machine, that seems to "work" and make sense as a physical model, whenever one checks something, so many people view this as very meaningful and not as a random idea. This is a very important point and sets it apart from countless other attempts that have been tried in the past. Whether it directly or indirectly applies to nature is a different question. It is in principle testable, so qualifies as a scientific theory despite certain people want to deny this.
@suprised, you make some interesting points, but I'm not convinced that what makes a scientific theory is falsifiability - as I've said before, I think this is given greater importance than it deserves. An unfalsifiable idea may become falsifiable as technology advances, so it's irrelevant. All ideas are falsifiable in principle. Something only achieves theory status when it has been experimentally confirmed (and repeatedly!). We say this to creationists all the time when they claim that evolution is only a theory. Is it one rule for creationists, another for us?
It is very clear that string theory is not just a random idea. From what I know of it, it is a remarkable construction, but I think you can see that the implications of string theory go way beyond just state counting in black holes. It opens up a whole new can of worms, a vast array of new predictions. The demands upon String Model to make it String Theory are very big. (I might not be expressing this viewpoint very clearly so i apologize if that's the case.)
The real test of a 'theory of everything' is that it can explain everything, old experimental results and new experimental results. Isn't that a tall order?
suprised
Nov14-10, 12:01 PM
Well what one calls theory is semantics, there is eg in mathematics also the theory of modular forms and countless other "theories", so the string phyisicists just don't care how their field of research is called and go on. It is the self-declared critics who are obsessed with this kind of questions, in particular with falsifiability.
The string physicists are more interested in positive questions, like what can be learned from the results and how to make further progress. This is right now mainly conceptual, ie about understanding how things works. An example is holography in quantum gravity, which is a spin-off of string theory and seems to be a central point of quantum gravity. Many see this as one of the most important insight in theoretical physics in the last decades; if the naysayers would have had their will, this kind of research would have been stopped since long, and an enormous damage would have resulted. Fortunately, and for good reasons, the naysayers don't matter! Most of them are not even scientists.
Of course ultimatively the goal is to make contact with experiment, but this goal is far away (if it ever can be reached), so people content themselves with more modest goals for the time being. They are difficult enough.
Kevin_Axion
Nov14-10, 12:07 PM
That's exactly the points I was trying to address, surprised, you're a string theorist, correct?
Well what one calls theory is semantics, there is eg in mathematics also the theory of modular forms and countless other "theories", so the string phyisicists just don't care how their field of research is called and go on. It is the self-declared critics who are obsessed with this kind of questions, in particular with falsifiability.
Semantics (meaning) really does matter! It's unfair of you to call me a self-declared and obsessed critic because of that. The meaning of things really does matter, because if words can mean anything, then the discussion becomes meaningless. (And as I've said, I don't care about falsifiability because all ideas are "in principle" falsifiable).
Your comment about parts of mathematics which are called "theories" illustrates the point. I'm not talking about those parts of mathematics which can be called "formal theories" - where the word formal is used because we adhere to mathematical standards of proof. I am talking about "empirical theories" - which is what we mean when we call something a scientific theory. "Proof" in what scientists call a theory means something different.
Maybe the problem is that many string theorists trained as mathematicians, so they think that the only thing that matters is proof in mathematical sense?
The string physicists are more interested in positive questions, like what can be learned from the results and how to make further progress.
Again, your semantics are unclear to me. What do you mean by "results"? Part of the whole problem seems to be that people involved with speculative models feel comfortable with building upon results which haven't been rubber stamped by experiment yet. In the past, you could only build such a house of cards if you know that the foundations are correct.
In real science, contact with experiment is not a "goal", it is part of the enterprise. Right up until the 1980s it was always very close by.
Here's the problem: even for very high energy physics which might require something like a string theory, the cry of being devoid of experiments is false. Cosmological or even some condensed matter physics results may be capable of showing things which we can't do in a super accelerator (again some of these reports have been prominent lately). The point is that you develop a theory from these results, not in anticipation of them. This is what the creationism cartoon was mocking.
(And I believe there is a lot to be learned about how science works from the evolution/creation debate).
By the way, I'm beginning to wonder if string theorists often find no further recourse than a personal attack of some form. I realize that some of what I say is uncomfortable, but I'd prefer a crystal clear answer to some of my questions than accusations about personal character.
@suprised, you make some interesting points, but I'm not convinced that what makes a scientific theory is falsifiability - as I've said before, I think this is given greater importance than it deserves.
So who exactly gives it greater importance than it deserves? The people who work on it? It's their business what they're interested in. The people who fund it? See my post above.
So who exactly gives it greater importance than it deserves? The people who work on it?
No, the usual low-quality critics of string theory who haven't really thought about it. The problem is that string theorists then spend too much time trying to claim that string theory is in principle falsifiable, even though it is irrelevant either way.
And I have to say, if someone's career is publicly funded, then the public has a say in what they work on. It's our job to explain to people how we're advancing physics. If they're self funded, then that's different.
By the way, I'm beginning to wonder if string theorists often find no further recourse than a personal attack of some form. I realize that some of what I say is uncomfortable, but I'd prefer a crystal clear answer to some of my questions than accusations about personal character.
What you're saying is neither uncomfortable nor new, just usually uninformed, if you don't know what kind of results surprised is referring to. There have been a great deal of results coming out of string theory which apply to day-to-day physics, like scattering amplitudes in qcd. Today the easiest way to compute scattering amplitudes is via string theory.
Not to mention things like the klt relations. This has all been discussed hundreds of times on this forum. Just these applications to scattering amplitudes means that string theory will never go away, because it is directly intertwined with gauge theory and gravity. If there's any other qg theory out there, it will either be eaten by string theory, or eat it itself.
But of course, if string theory only says new things about old stuff, it wasn't actually needed in the first place, and if it says something completely new it's out of touch with reality.
No, the usual low-quality critics of string theory who haven't really thought about it. The problem is that string theorists then spend too much time trying to claim that string theory is in principle falsifiable, even though it is irrelevant either way.
And I have to say, if someone's career is publicly funded, then the public has a say in what they work on. It's our job to explain to people how we're advancing physics. If they're self funded, then that's different.
You have good intentions, but seriously, the public doesn't know the difference between quantum physics and teleportation. Most people who come to this forum don't know this, despite having a greater than average interest in physics.
This isn't to say that whoever gives the money shouldn't have the last say, but the say will always be uniformed. The public will want to continue research in QM because they want teleportation, and they will want research in string theory because they want wormholes.
There have been a great deal of results coming out of string theory which apply to day-to-day physics, like scattering amplitudes in qcd. Today the easiest way to compute scattering amplitudes is via string theory.
Why reinvent the wheel? I'm not uninformed about these "results", so please don't make uncalled for accusations, I just don't view them as necessary. If they are just a calculational device, then are you saying that you don't really believe strings exist? Is this just like using complex plane integration to simplify tricky integrals in the real plane?
Just these applications to scattering amplitudes means that string theory will never go away, because it is directly intertwined with gauge theory and gravity.
Has this "calculational device" approach ever explained things which the standard model could never explain? Has it made new predictions beyond the standard model which we can search for soon? If the answer to both is no, then was it a waste of time?
Maybe it would help to think in more general terms what a theory of everything would accomplish and what issues it would raise.
It might be with experiment we can discover smaller and smaller particles, and with time we can discover more interesting mathematical structures that describe them. But just because we can measure the properties of these smaller particles doesn't mean that we have an explanation for them. And just because we can predict their rate of occurance doesn't mean we understand why they exist.
We will always be asking why things are as they are until we can derive physics from the principles of reason alone. I think that's the ideal for a theory of everything, to be derived from logic alone. Such a theory would explain where the principles of QM and GR come from to begin with and why the SM has the constants it has. And I'm not so sure we're far off from that goal.
Then what becomes of the questions of falsifiability? Can you falsify a mathematical equation? Can you falsify a logical deduction? If the logic is impecible that give the physical prediction, then what are we to think if measurements are contrary? What are we to question, our sight or our reason? Perhaps that delemma is one reason many may be uncomfortable with supporting such efforts. Yet, isn't it the ultimate goal of science to "explain" everything - to prove that the universe is perfectly logical - to derive physics from logic?
This isn't to say that whoever gives the money shouldn't have the last say, but the say will always be uniformed. The public will want to continue research in QM because they want teleportation, and they will want research in string theory because they want wormholes.
Are you saying that we can just work on what we want, with a loose definition of how to build a scientific theory, because the unwashed plebians won't be able to tell the difference either way? I'm not comfortable with that view of the public.
Has multiplication explained anything that addition could never explain?
Has QFT ever explained anything SR and QM could never explain?
Are you saying that we can just work on what we want, with a loose definition of how to build a scientific theory, because the unwashed plebians won't be able to tell the difference either way? I'm not comfortable with that view of the public.
Well I'm not comfortable with publicly funded research in the first place. But if you're going to have it, it's not practical to ask the public what they want. I'm not comfortable with democracy either, but if you're going to have it, it's not going to be practical to ask the public to vote on every law itself. See what I mean?
Has multiplication explained anything that addition could never explain?
Has QFT ever explained anything SR and QM could never explain?
Answer to first question no, answer to second question yes.
suprised
Nov14-10, 01:10 PM
It's unfair of you to call me a self-declared and obsessed critic because of that.
Oh I didn't mean you, be assured - there were plenty of other threads here over the years which is what I was referring to. With obession I mean that the same claims are made over and over again, by the same people, despite explanations to the contrary. With self-declared I mean people who don't understand the issues but nevertheless behave in a way as if they would be experts.
Maybe the problem is that many string theorists trained as mathematicians, so they think that the only thing that matters is proof in mathematical sense?
I don't quite understand what you mean here; why would there be a problem.
Again, your semantics are unclear to me. What do you mean by "results"?
Results like the successful count of microscopic quantum states in blach holes, and the AdS/CFT correspondence. The latter relates gauge to string theories, which is obviously of great importance.
Part of the whole problem seems to be that people involved with speculative models feel comfortable with building upon results which haven't been rubber stamped by experiment yet.
In the past, you could only build such a house of cards if you know that the foundations are correct.
Yes...that's true also today. That's why people are working very hard to understand the foundations of quantum gravity etc. Do you want to criticise this?
"Speculative" is often used misleadingly. Many results (eg see the above) are not speculative but just plainly follow from, or are strongly suggested by computations. That's why we don't talk about religion here. What is speculative is to build models and claim these describe nature.
In real science, contact with experiment is not a "goal", it is part of the enterprise. Right up until the 1980s it was always very close by.
What do you mean by "real science". You you realize how biased already your language is?
The point is that you develop a theory from these results, not in anticipation of them. .
..
(And I believe there is a lot to be learned about how science works from the evolution/creation debate).
I doubt it, theoretical physics is different. Again an example: there IS an apparent clash between GR and QM. This is likely the deepest basic questions in physics. Do you view it as a "problem" if a few people sit down and try to resolve it? Is it "purely mathematical" or "non-scientific"?
By the way, I'm beginning to wonder if string theorists often find no further recourse than a personal attack of some form.
There wasn't any attack. And apart from that, string physicists have quite good arguments, so your "no further recourse" is not appropriate.
Kevin_Axion
Nov14-10, 01:14 PM
There is no need to be nihilistic towards a certain theory just because you may not understand the implications of String Theory or it doesn't conform to your idealization of what physics should be. If everyone had favoured your opinion in the 1970s theoretical physics, as suprised stated, would be absolutely bare of richness and beauty that has been discovered recently, particularly in the context of String Theory. Once again, I'll state that some people need to fully understand what something has done before ultimately stating that it's effects on physics have been minimal. Again, if everyone had said this about Superstring Theory SUSY wouldn't exist and SUSY appears to be a vital component to extending the Standard Model, Gauge/gravity duality wouldn't exist, String Dualities wouldn't exist, Holographic Principle wouldn't exist and unique approaches to understanding high-temperature superconductors wouldn't exist. String Theory has actually become unavoidable because its ability to explain certain aspects of reality is unprecedented.
Me: Maybe the problem is that many string theorists trained as mathematicians, so they think that the only thing that matters is proof in mathematical sense?
You: I don't quite understand what you mean here; why would there be a problem.
I'm tiring of this. If you actually believe that the criterion for accepting an idea in science is mathematical proof, whereas I believe it is experimental validation, then it is no wonder we are talking past each other.
Same goes for your conveniently loose definition of a "result". In my view the only kind of result that matters is an experimental one: either a result that calls for a new theory, or one which confirms a recent one. You talk about things such as AdS/CFT, which are new ways of thinking about QFT, as a result, but in a discussion like this, coffee break language doesn't cut it.
A conversation where we don't agree on the meanings of simple words can only descend into farce. Unfortunately, I assumed from the outset that these terms were so well established in science that we took them for granted.
I sought some clarification of why it is justified to claim that in BTSM theories we are discovering new physics rather than merely hypothesizing. People have made some interesting points but there has been no clear response to this question - I suspect that many string theorists actually disagree with it. Same goes for the theory issue - some of you guys have been claiming string theory is a theory, even though many string theorists accept that it isn't. With inconsistency like this within the same discipline, we can only ever descend into conversational farce.
So here it is: some people think I'm talking sense, others think I'm talking nonsense, and my initial criticisms have not been addressed, mainly because we are wasting time arguing about the meaning of words. Since I have to keep repeating points I made in my original post, I'm not particularly motivated to carry on with this discussion.
Dax, it puzzles me that although you stress the importance of physics being guided by phenomena (observation/experiment) you play down the value of nearterm falsifiability.
Falsifiability is one form of testability (a particularly strong form) which could include weaker forms such as constraint of parameters and other types of guidance as well. There is, I think you would agree, special value in near term testability.
The judgment as to whether something is legitimate empirical science, or abstract math, or crackpot, or pseudoscience must surely be a subjective consensus-type judgment by the scientific community involving some imprecision and perceived differences of degree. Can't ever be perfectly clear cut black-or-white. Science is an aristocratic community and a tradition, not a computer program.
I suppose that is why people find it necessary to get defensive, argue interminably, and engage in special pleading and occasional propaganda. These are community functions. :biggrin:
Anyway, I urge you not to deprecate the value of nearterm falsifiability. And note that it's important when the phenomenologists themselves (whose professional job is to identify and delineate testability) determine that a theory is falsifiable.
When they decide, that is, while the theoreticians have not asked for it and may even be a little reluctant to accept the idea. :yuck:
Well you keep arguing about the meaning of words, what is a real vs unreal theory, when string theorists couldn't care less about any of this and are busy finding interesting results, in whatever form they appear. You say people are focusing too much on reaching a particular conclusion, when in fact it's you doing that. String theorists don't care what they need to find. They just look for what's interesting. But we also had this discussion when we were arguing about the significance of the scattering amplitudes developments.
@marcus I agree that near-term falsifiability is practically important and you can't really make progress without it. I just think that it doesn't go into what makes something a theory or not. However on both counts, the case for pursuing string theory is weakened. Unfortunately, it's practically impossible to have a conversation about this with clever people who will play mental gymnastics with the meaning of words in order to accommodate their view.
It is a sad indictment on people's reasoning ability that I was accused of using biased language for claiming there is such a thing as real science. This is the reason I don't feel like carrying on with this discussion.
@marcus I agree that near-term falsifiability is practically important and you can't really make progress without it. I just think that it doesn't go into what makes something a theory or not. However on both counts, the case for pursuing string theory is weakened. Unfortunately, it's practically impossible to have a conversation about this with clever people who will play mental gymnastics with the meaning of words in order to accommodate their view.
It is a sad indictment on the current state of the physics community that I was accused of using biased language for claiming there is such a thing as real science. This is the reason I don't feel like carrying on with this discussion.
Please don't be offended or disheartened. This is your first thread here at PF and you have caused a very lively active one. We learn from observing what people get defensive about and become heated and impassioned over. The issues are not to be settled but we learn a lot by noting what arguments are employed. Bravo. (Now I am applying the masculine case as I think of you, perhaps it is the symbiont who is a he.)
I am not too concerned with stringery---I think that in practical terms like new jobs the interest in it is moderating in the physics community. People have to say a lot of things just to keep their morale up. Like trumpeting black hole entropy and taking credit for holographic principle.
We are not obliged to show reverence or devotion---we can ignore the hat-on-the-stick symbol if we choose.
Yes the symbiont has been a he on several occasions. :tongue2:
petergreat
Nov14-10, 02:25 PM
Imagine Schrodinger, Bohr, Heisenberg et. al. developing QM before there was even a shred of proof that energy was quantized. Not only would it have been rather silly (c.f. my creationism cartoon), but I doubt it would even have been possible. How much more so is this true for far more complex modern physics?
If these people were smart enough, they could have developed quantum mechanics in 1870, when Mendeleev had already published his periodic table but well before the discovery of electrons, atomic nuclei, photoelectric effect, Balmer series and so on. After all, the periodic table encodes many elements of quantum mechanics, i.e. quantized nuclear charge, gradual filling of electron energy levels, fermi statistics restricting 2 electron per orbit, and existence of neutrons to make up missing atomic weights etc. Certainly the periodic table was a better hint towards new physics than today's dark energy.
So Even if experimental physics halted in 1870, these people could have worked out a theory compatible with all the features of the periodic table. If they were as clever as string theorists, they might even come up with a beautiful theory explaining these elements as Kaluza-Klein multiplets, or obtain a whole landscape of periodic tables!
The periodic table is an experimental result, and indirect evidence of quantization, isn't it?
Kevin_Axion
Nov14-10, 02:33 PM
Ok, this will continue ad infinitum, let's just settle our differences and realize that they won't change by a mild debate amongst conflicting views.
... let's just settle our differences and realize that they won't change ...
I think we will choose not to, at this point, Kevin. Because the topic in Dax opener is the role of phenomena (observation, experiment, measurement, prediction...) in the development of physical theory. It is a general issue, more interesting than stringy specifics.
And some phenomenologists, possibly to the dismay of some Loop theorists, have recently determined LQG to be falsifiable by observation of the polarization in ancient light.
Some of these phenomenologists (whose past work has involved several other theories besides Loop) are Aurelien Barrau, Julien Grain, Wen Zhao. There are a half-dozen others who have co-authored with one or more of these in a series of papers.
http://physicsforums.com/showthread.php?p=2983268#post2983268
http://www.math.columbia.edu/~woit/wordpress/?p=3262&cpage=1#comment-67952
Zhao is at Cardiff, Barrau is at Grenoble (sometime CERN), Grain is at Paris.
What happened is kind of intriguing. The work of Ashtekar's Penn State group, and many others, has confirmed since 2006 that the bounce is a highly robust conclusion from Loop cosmology. Meanwhile a lot of bridges have been built between the full (spinfoam) LQG theory and the application to cosmology. One can even start with a simple spinfoam version of LQG and derive a bounce.
Possibly to some Loop theorists' surprise, Barrau and friends have determined that a Loop bounce must have a particular signature in the B-mode polarization of ancient light. It puts LQG at risk and is either interesting or exciting depending on one's moral character and point of view.
This may put several persons' noses out of joint and they may have nasty things to say about it :biggrin:---scorn denial etc. We can't predict but it will be instructive to see the reaction. Someone will probably mention Lee Smolin, but this whole thing has nothing to do with Smolin or any of his current research. It is basically on Ashtekar and Rovelli's plate and you need to know their recent work to comment intelligently.
To summarize: The conservative Baconian stance taken in Dax opening post is pragmatically correct. And quantum gravity theory is going to move ahead in concert with experiment/observation whether you like it or not.
I have to go out for a while but will continue later.
Loop QG space is tending to become the space we use to talk about the early universe. You can see that with a simple keyword search of the Stanford/SLAC database of physics research papers. Recent "quantum cosmology"
There's a simple reason for this. I'll try to explain when I get back. It won't always necessarily be the quantum geometric framework for early universe---could be replaced by an improved version or something different! But that's the current trend and there's a reason to point out.
Back later.
============
I'm back.
The reason has to do with what Dax said in the first post. But this may not be immediately obvious. It's not because of presumed "rightness or wrongness"----we only have superstitions about that, can't presume to know future.
The reason is that LQG gives a mathematical representation of the geometry of the whole universe, that you can calculate with.
It has a Hilbert space of quantum states of geometry and a pathintegral or spinfoam way for them to evolve---simple enough to calculate with. And this is what cosmologists need.
It is what General Relativity gives you, a dynamic geometry instead of a fixed pre-determined one. You have to have this to do cosmology. Cosmology is the key to observation here (because our image of the early universe is enormously magnified by expansion.) The only trouble with GR being that it fails at the bang---it does not allow time-evolution to proceed back before the start of expansion. The spacetime geometry of GR is the basis for cosmology, so to go back into the very early you need a quantum geometry to take its place.
LQG is experiencing rapid growth now precisely because it provides a simple tractable model of the geometry of the early universe. One you can try out your ideas with. To a first approximation for practical purposes it doesn't matter whether right or wrong. The competition currently offers dubious handwave, or fixed pre-determined geometries, or ones based on GR that blow up at the start. Whatever they offer it seems not to be what the cosmologists are used to or find convenient to work with.
=======================
A rival approach could get in on this action by offering an appropriate quantum dynamical model of the geometry of the whole universe, to compete for some of LQG cosmology business. But I didn't hear of any competition yet, in practical terms that you can get your hands on and play around with.
=======================
The reason this is a valuable stimulus for Loop progress goes back to what Dax said. Early universe is our window on extreme physics. Theory needs to progress in concert with observation/experiment. Quantum gravity MEANS QUANTUM GEOMETRY and to connect to quantum geometry phenomena you need to provide a spacetime geometric home for the early universe.
This may seem roundabout but contemporary experience bears it out and if you listen to the chain of reasoning you will hear Empiricism talking and giving you her advice.
If you do a search of Spires HEP archive with keyword "quantum cosmology" for consecutive years you will see this rapid growth I am talking about. Loop gives the observational people a quantum geometry they can use.
Or so I think. That's how I interpret the past 4 or 5 years changes. You may have different explanations and understanding.
http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=dk+quantum+cosmology+and+date+%3E2006&FORMAT=WWW&SEQUENCE=citecount%28d%29
(I've been troubleshooting intermittently failing RAM modules for the last days and now finally found the bad one)
I sought some clarification of why it is justified to claim that in BTSM theories we are discovering new physics rather than merely hypothesizing.
I missed out the whole discussion and I'm not sure what the key question really was, but I too certainly wouldn't label "discovering" dualities in ambigously created theory spaces as "new physics". That's not to say it won't lead anywhere, but I think theoretical speculation is a better word.
It's more like a exploration of a specific theory space, construction and transformations of theories, where we find mathematical patterns and relations. Wether this has any physical significance is still an open question IMO, beucase the logic of inference applied when doing this is NOT unique. It's perhaps almost unique given certain premises; but that's the same thing. The basic premises and abstractions of ST (for example; although I agree this discussion isn't specific to ST) aren't objectively justified.
I don't think it's not necessarily bad with speculations, mathematical or philosophical - they are needed - but one must still be fair and not confuse these things with the physics content.
/Fredrik
suprised
Nov15-10, 06:27 AM
I'm tiring of this. If you actually believe that the criterion for accepting an idea in science is mathematical proof, whereas I believe it is experimental validation, then it is no wonder we are talking past each other.
No I didnt mean that. What I meant is that the problem you allude to isn’t one. Only very few string theorists have were trained as mathematicians, and they think as physicists and not mathematicians. And they are smart enough to not confuse a mathematical proof with physical reality.
It is you who has a prejudice how poeple think and work, and this is sneaks in all the time. Like your “real science”…this expresses your doubts that string theory is real science. Or your “Same goes for your conveniently loose definition of a “result” below. Sorry, a result is a result! For example, that certain correlations functions in Yang-Mills theory and string theory coincide. This is a mathematical fact, and NOT a “conveniently loose definition”.
Same goes for your conveniently loose definition of a "result". In my view the only kind of result that matters is an experimental one:...
Well that’s your point of view. Fine. Many don’t share this point of view.
A conversation where we don't agree on the meanings of simple words can only descend into farce. Unfortunately, I assumed from the outset that these terms were so well established in science that we took them for granted.
Frankly I begin to doubt that you really know how science works.
I sought some clarification of why it is justified to claim that in BTSM theories we are discovering new physics rather than merely hypothesizing. People have made some interesting points but there has been no clear response to this question - I suspect that many string theorists actually disagree with it.
Again deriding: “merely hypothesizing”. Sorry, things are a bit more intricate than coffe table talk. Take for example, black holes. No one has yet seen one by naked eye (perhaps fortunately). Still they exist as solutions of Einsteins equations and people have been starting investigating them theoretically, even without initial experimantel evidence. You may call this “merely hypothesizing” but this is viewed by many as an important line of reasearch; and indeed, just because of the theoretical investigations which lead to understanding various properties of black holes, indirect evidence for their existence has been found, and I guess almost no serious astrophysicist would doubt their existence. If science would be done like you advocate it, namely starting from experimantal obervations, we wouldn’t be there where we are (as you need precise clues for what you look for, otherwise you may never notice it).
Same goes for the theory issue - some of you guys have been claiming string theory is a theory, even though many string theorists accept that it isn't. With inconsistency like this within the same discipline, we can only ever descend into conversational farce.
Because there is no absolute definition what a “theory” is. Every one may have a slightly different idea about this, that’s why you get different answers. And that’s also why this is an irrelevant point to discuss about. What matters are results, not names. It is you who brought up this irrelevant discussion, and now you complain.
You may call this “merely hypothesizing” but this is viewed by many as an important line of reasearch
I agree with that. Hypothesis generation - the precursor of any theory, is of course an important part of a scientific process. And the logic of hypothesis formation is extremely interesting. Something that is sometimes completely lost is simplistic analysis when one only focusys on the falsification/corroboration part, which is the easy part of the process.
I think one can simultaneously acknowledge the importance of thel logic of hypothesis generation (which relates to theory spaces) and still admitt that there is a difference between this and physics contents, although there may be some deeper ways in which they are related (but I don't think that's the main focus here).
/Fredrik
Frankly I begin to doubt that you really know how science works.
You smug and arrogant individual. People who resort to hubris usually do so when they feel threatened. (and it's not surprising that you didn't elaborate on the above point, because it was merely an ad hominem attack).
If I've learned one thing in this whole conversation, it's that it's other people who are apparently unclear about science works, not myself. You claim that the concept of a theory hasn't been well defined, which is ridiculous. If a "theory" can mean anything you like, or a "result" can mean anything you like, then you may as well be working on the perfect barm cake recipe.
This is why I will not choose to stay in academia: science is wonderful, but the people are ugly, petty and have muddled thinking, and there is too much of a tendency to "feather the nest". When people have decades-long careers to defend, they will change the meaning of words which have been well established through four centuries of history in order to squeeze in their pet project.
The google ads currently generated for my page about evolution being only a theory are somewhat amusing in the context. Hold that thought, I may come back to it in a few moments.
This is why I will not choose to stay in academia: science is wonderful, but the people are ugly, petty and have muddled thinking, and there is too much of a tendency to "feather the nest".
That is not a reason for you not to stay in academia. In fact, you can make yourself quite comfortable given that the vast majority is the very attached to science as you and me (I agree 100% with you) see it. Besides, it is a wonderful source of models to high energy physics.
I actually enjoy models, we can learn from them, they're just not oracles of physical reality. Hold that thought for now...
About the silly claim that the term "theory" is ill defined. It's not. Its meaning was not established through dogma (that is agreed) - it was established through centuries of experience. This generally agreed definition is accepted because it works (pragmatism).
Bear in mind that if this wasn't true, we wouldn't be able to respond to creationists who claim that evolution is "only a theory".
(Note that dictionaries also report colloquial definitions of theory, like hunch, and mathematical theories - I ignore those).
Webster's dictionary:
From the primary entry:
theory: ""a scientific hypothesis that survives experimental testing becomes a scientific theory".
Webster's dictionary (secondary entry):
theory (science): "An explanation for some phenomenon that is based on observation, experimentation, and reasoning."
theory (geology) "...but in science, something is not called a theory until it has been confirmed over the course of many independent experiments. Theories are more certain than hypotheses, but less certain than laws."
Webster's wiktionary:
theory (sciences) "A coherent statement or set of statements that attempts to explain observed phenomena. There is now a well-developed theory of electrical charge."
Wikipedia:
Scientific theory: "A scientific theory is constructed to conform to available empirical data about such observations, and is put forth as a principle or body of principles for explaining a class of phenomena."
Wikipedia:
Same entry, pedagogical definition, USNAS: "The formal scientific definition of theory is quite different from the everyday meaning of the word. It refers to a comprehensive explanation of some aspect of nature that is supported by a vast body of evidence." and "One of the most useful properties of scientific theories is that they can be used to make predictions about natural events or phenomena that have not yet been observed."
(Wikipedia distinguishes an empirical theory, which is a scientific theory, from a formal theory, which means mathematical proof not scientific proof).
Oxford dictionary:
theory, noun: "a supposition or a system of ideas intended to explain something, especially one based on general principles independent of the thing to be explained: Darwin's theory of evolution".
TheFreeDictionary.com:
theory:"A set of statements or principles devised to explain a group of facts or phenomena, especially one that has been repeatedly tested or is widely accepted and can be used to make predictions about natural phenomena."
Don't believe a string theorist who claims that there is no generally accepted view of the word theory. Evolutionary biologists, chemists, other physicists, geologists, etc., who are all professional scientists to be respected, and who all engaged in building scientific theories, all agree with the above definitions. You can't do careful work unless the basic principles of your subject are established.
suprised
Nov15-10, 10:33 AM
Look, this discussion is completely irrelevant. It should be about the scientific content and not the name. While the many hundreds of people working on the subject of strings happily call this string theory, you are welcome to call it different. I don't mind if you call it "string $#$*#$", it won't make any difference. But I doubt you can convince the people in the field to call it "string $#$*#$".
Let me rethink what I said about obsession.
I actually enjoy models, we can learn from them, they're just not oracles of physical reality. Hold that thought for now...
I was just giving you a reason not to give up academia.
Look, this discussion is completely irrelevant. It should be about the scientific content and not the name. While the many hundreds of people working on the subject of strings happily call this string theory, you are welcome to call it different. I don't mind if you call it "string $#$*#$", it won't make any difference. But I doubt you can convince the people in the field to call it "string $#$*#$".
Let me rethink what I said about obsession.
No, the discussion is not irrelevant, you just want it to be, because you find it uncomfortable.
You also make it sound like string theorists secretly know that it's just a model (or to use a cringeworthy term favoured by others, a "framework"), but I know this is not the case. If anything, the highest practitioners in the field (such as Green, Witten and others) talk in more grandiose terms than others. They not only think it is a theory, they think it is a theory of everything (!) and that the reason it is correct is because it is beautiful. Well beauty doesn't cut it. People who follow the Koran claim that its beauty is an indicator of truth , but obviously this argument is easily ignored.
I'll ignore the comment about obsession.
I was just giving you a reason not to give up academia.
I appreciate your support :smile:
It should be about the scientific content and not the name.
If any content is "scientific" then it can be, and should be, described in terms of meaningful words. Language, communication, really does matter. How can it not?
I've noticed that you are no longer challenging my point about what a theory is, now you've changed your argument to claiming that string theory is a theory, they just don't call it one by name - even though they actually do (huh? This is severely muddled up thinking). Both points are manifestly incorrect, and I have addressed both of these points in previous posts so there's no point in repeating what I've said before.
I think my original question about why we call progress in string theory discovery of new physics has been answered: string theorists don't even know. They contradict each other, and even an individual string theorist contradicts himself/herself!
Hypothesis generation - the precursor of any theory, is of course an important part of a scientific process. And the logic of hypothesis formation is extremely interesting. Something that is sometimes completely lost is simplistic analysis when one only focusys on the falsification/corroboration part, which is the easy part of the process.
I just want to pick up on this if I may. I never said that hypothesizing is not part of science. I said that engaging in hypothesizing alone, and claiming it is progress, or even discovery, as your hypothesis becomes more and more complex, is meaningless. Hypothesizing and testing the hypothesis to see if it can be accepted into a theory go hand in hand, like bangers and mash.
This is why it is absurd when people say that we don't understand string theory yet, using language as though we're actually slowly unveiling physical reality. You don't understand your own hypothesis which you seek to test? Ridiculous! The whole point of generating a hypothesis is that it is well understood so it can be tested. It certainly should not morph into some sort of pseudotheoretical collection of hypotheses (I'm sorry, a "framework" :rolleyes:). The claim made by Witten that string theory is 21st century physics discovered in the 20th century shows you the hubristic mentality of the people involved, in my opinion.
I'm surprised no one brought up the "but membranes aren't 1d why do people still call it string theory" discussion.
Dax, honestly, no one cares and will never care what exactly is a "theory" and if string theory qualifies as one. People only care about results. If you think the name of string theory should be changed...I don't know, try writing to your congressman.
And for the love of god (pun intended) do stop already with creationist vs evolutionist argument. It's childish, getting old, and you're misusing it.
Dax, honestly, no one cares and will never care what exactly is a "theory" and if string theory qualifies as one.
Correction, some string theorists don't care. Many thinking people do care. I'm not alone. You have a nerve accusing me of childishness, when you try to dismiss an entire thread with "nobody cares"!!!! That's school playground language!!
People only care about results.
And what makes something a "result"? Is something a result because it gets accepted for publication? This viewpoint stinks. Just because an idea is published, doesn't mean it represents physical reality. Maybe it's true that people only care about the number of publications and citations they get. Publish or perish?
And for the love of god (pun intended) do stop already with creationist vs evolutionist argument. It's childish, getting old, and you're misusing it.
In what way am I misusing it (care to explain)? It's highly relevant. There isn't one definition of science in evolutionary biology, and another in physics. The methods of science are universal. We only divide science into separate subjects to make it easier to understand. Nature doesn't have clean dividing lines.
You can't conveniently dismiss the discussion about evolution/creation just because it comes from a different subject. It illustrates the point perfectly about what a theory is. Need I repeat that it means something much more precise than just an idea? This really matters, whether you think it does or not.
I repeat that it's quite amusing of you to accuse me of being childish, when your concluding argument seems to be merely "it doesn't matter, nobody cares, stop whining". Is that the best you can do?
Haelfix
Nov15-10, 02:02 PM
I just want to pick up on this if I may. I never said that hypothesizing is not part of science. I said that engaging in hypothesizing alone, and claiming it is progress, or even discovery, as your hypothesis becomes more and more complex, is meaningless.
Suffice it to say, I think you'll find that most proffessionals will disagree with this statement. I certainly do, and I suspect most others will as well.
Sometimes progress can be made in pure theory, without the need for experiment. Its particularly true that you can falsify most ideas, long before you ever test them.
When a statement is inconsistent with logic, then thats all there is too it. I don't need experiment to tell me that the collision between two gravitons does not output pink elephants.
The reason so many people believe in string theory, is that there aren't many (arguably any) viable alternatives and you are very much bootstrapped into this way of thinking through a rather tight network of highly plausible inferences (for instance, the existence of blackholes as being 'real').
In some ways, it is the theory with the minimal set of assumptions necessary that also simultaneously explains the bewildering array of modern physics that is observed.
This is not supposed to be *obvious* to a layman! They see complicated mathematics, extra dimensions and a bunch of structure that looks many steps removed from the laboratory and immediately complain. Well, until one actually does the math and see's that the arguments for each step are actually pretty tame and natural, be sure that the person will stay hostile to the idea.
Suffice it to say, I think you'll find that most proffessionals will disagree with this statement. I certainly do, and I suspect most others will as well.
Hypothesizing is not discovery, no matter how sound or simple the step of logic used to achieve your hypothesis. It still needs to be tested to become a theory - a description of reality. A "professional" is not correct just because they have authority.
Sometimes progress can be made in pure theory, without the need for experiment.
The word progress could mean anything here. What do you mean? Lots of publications? By the way, the concept of "pure theory" is a contradiction in terms. A theory is linked to experiment by definition.
Its particularly true that you can falsify most ideas, long before you ever test them.
You can't falsify a hypothesis without testing it, by definition. However, if something is logically flawed, then it never gets called up for testing in the first place. It's not even a hypothesis, it's trash, surely.
The reason so many people believe in string theory, is that there aren't many (arguably any) viable alternatives
Alternatives in doing what? You're going to have to be more clear than this.
In some ways, it is the theory with the minimal set of assumptions necessary that also simultaneously explains the bewildering array of modern physics that is observed.
Most of observed modern physics is explained with the standard model, and the rest of the unsolved observations are not explained by string theory, otherwise we wouldn't even be having this conversation. So what are you talking about?
This is not supposed to be *obvious* to a layman! They see complicated mathematics, extra dimensions and a bunch of structure that looks many steps removed from the laboratory and immediately complain. Well, until one actually does the math and see's that the arguments for each step are actually pretty tame and natural, be sure that the person will stay hostile to the idea.
Well, I'm not a layman (although I'm not a string theorist), so I don't know how this applies in this case. I resent the implication that I'm too stupid to see how wonderful and beautiful string theory is. This sounds a lot like when religious people say that a person just doesn't have god's spirit and therefore couldn't possibly appreciate the beauty and truth of said belief. It's a bogus argument and a fallacy.
Haelfix
Nov15-10, 02:34 PM
When I say progress, I mean discovery about how the real world works (tm). When I say alternatives, I mean alternatives about the nature of the Planckian world.
"Most of observed modern physics is explained with the standard model, and the rest of the unsolved observations are not explained by string theory, otherwise we wouldn't even be having this conversation"
Umm, String theory contains the standard model as a low energy limit, and I don't know which 'unsolved observations' you are referring too? B/c in principle, it does contain the explanation! That's what it means to be a possible theory of everything! If you can find an observation about the real world that string theory does not contain, then by definition you have falsified the theory.
"You can't falsify a hypothesis without testing it, by definition. However, if something is logically flawed, then it never gets called up for testing in the first place. It's not even a hypothesis, it's trash, surely."
Now you are playing with semantics and besides, this is wrong! You *can* falsify theories without testing them. Most of the time a Gedanken is all that is required.
For instance, I don't need to test the nature and predictions of creationism. I know its wrong, b/c it is logically inconsistent and absurd and clashes with many known phenomenon that have been tested.
When I say progress, I mean discovery about how the real world works
To find out how the real world works you have to interrogate nature. There is simply no alternative - even if your ideas are wonderful, they have to be tested.
When I say alternatives, I mean alternatives about the nature of the Planckian world.
We bring up alternatives as and when they are needed. Special relativity was proposed because there were unexplainable experimental observations. We do currently have unexplainable experimental observations, but string theory doesn't explain them, it purports to do something different (I assure you that if string theory explained these things we don't understand, it would be all over the world's media).
Umm, String theory contains the standard model as a low energy limit, and I don't know which 'unsolved observations' you are referring too?
String theory contains the standard model, so what? Why reinvent the wheel? Some people have suggested that ST is merely a calculational device for amplitudes. In that case then, it doesn't even qualify as a hypothesis, it's just a tool. Some unsolved observations: Dark energy/matter, the arrow of time, the origin of mass, explaining confinement, neutrinos etc. etc. Has string theory had explained these things? If it had we'd have heard about it.
Now you are playing with semantics and besides, this is wrong! You *can* falsify theories without testing them. Most of the time a Gedanken is all that is required.
No, my semantics (meaning) are clear. I have been crystal clear about what I mean by "theory", "result", "hypothesis" - on the other hand, you contradict yourself within the same sentence even! You've already changed from "hypothesis" to "theory" in your response! So who's playing games with meaning? Not only that, but you merely made an assertion (that you can falsify a theory without experiment) without explanation. And I don't know what a Gedanken is...
For instance, I don't need to test the nature and predictions of creationism. I know its wrong, b/c it is logically inconsistent and absurd and clashes with many known phenomenon that have been tested.
Creationism does not qualify as a hypothesis because the existence of god, for example, can neither be proved or disproved and is therefore not a scientific question. This proves my point, not yours.
... String theory contains the standard model as a low energy limit, ...
Haelfix I don't think it is true that any version of SST contains the SM and its 20-some mass etc parameters (correct me if I'm wrong) but I would be interested if you would give me an arxiv reference to some paper which documents a version of SST which comes closest to that desirable goal. If you have a favorite amonst the many alternatives, I'd be delighted to read about it.
...String theory contains the standard model, so what? Why reinvent the wheel?...
But Lieutenant, where did you hear that SST contains the standard model of particle physics? I have always heard the contrary, from sources I consider reliable. They have made great efforts, trying various ways to roll up and stabilize the extra dimensions, in the attempt to get standard particle physics with its various particle masses, coupling constants and so forth. I think it would be great news if those efforts had succeeded!
Let's see what journal article preprint (online arxiv source) Haelfix offers us.
But Lieutenant, where did you hear that SST contains the standard model of particle physics? I have always heard the contrary, from sources I consider reliable.
I was just taking his word for it really - although since I've not seen any publication which shows this myself, I share your skepticism.
Kevin_Axion
Nov15-10, 03:41 PM
Lt_Dax do you think you can tell me what exactly everyone is arguing about, is it the merits and faults of String Theory? This has become very unclear to me.
Kevin_Axion, my primary point of contention has been about why it is justified to claim physics discovery and what it means to discover anything in science - my viewpoint has somewhat hardened from asking a question to making an assertion - mainly because it has become clear that many practicing string theorists have never sat down to think about what all these words we chuck around actually mean (I no longer feel like an inexperienced student asking a question - I overestimated the wisdom of the people I was asking.)
But as I've said in the distant past, this is not about questioning the interesting nature of string theory or its usefulness in model building - but I've never been able to have a decent conversation about this because some string theorists have been using words like theory, hypothesis, model, framework, result, progress interchangeably. Others are dismissive and say it doesn't even matter and that I should stop "complaining". So I agree with you that it is confusing, but this is not your fault or mine.
samalkhaiat
Nov15-10, 04:30 PM
If this was 1954, this thread would have been about Yang-Mill’s theory! Back then, some people (mostly non-professionals) called it “fancy mathematics”, others (including some professionals) said: “it is worthless” because it disagreed with the observed short-range nuclear force. But, a class of good physicists saw Yang-Mill’s as a “beautiful and logical next step in theoretical physics”.
It took those good physicists 20 years of hard work to realize that nature is indeed fundamentally Yang-Mill’s. They, deservedly, got Nobel prizes and we (thanks to them and to Yang and Mill) got the electro-weak and QCD.
So, people work on string theory because they see it as “the one and only logical next step in theoretical physics". Those who can't see this, well they just can't!!
Regards
sam
Well maybe this is the thing you're misunderstanding. String theory is both a framework and a model - it's just that awesome.
How to reconcile these things? Work in progress.
What are you arguing about? Results in any of these two categories?
-As a framework, it has already proven useful in a many areas, like scattering amplitudes. Anyone working on scattering amplitudes is just shooting himself in the foot by ignoring string theory.
-As a model, technically we're just missing a selection principle to choose from the landscape. Hardly an obvious dead-end or utter failure.
Progress in both of these areas is happening everyday. Sometimes small steps, sometimes larger ones. Why is everyone so anxious?
@samalkhaiat @negru
So it comes back to this argument - I'm just too dumb, too naive to see the awesome, wonderful, beautiful truth. Who knows, maybe it's true, and I just can't see what these towering genuises can see.
Of course, there's nothing more suspicous than a self-declared genius or a self-declared revolution. That is reason enough to remain skeptical.
Haelfix
Nov15-10, 04:49 PM
Again it depends what you mean by the 'standard model'. If you mean the group structure, generations and form of the particles and interactions then yes, string theory has had this for a long time. If however you want calculations of the exact mass of the Higgs down to 5 decimal places, sorry but the calculation is prohibitively difficult in many vacua. The best you can do is proof of concept.
http://arxiv.org/abs/hep-th/0512177 for an example of a paper with realistic vacua that also contains the SM. There are literally hundreds of other ones, that appear weekly on Hep-ph.
"I don't know what a Gedanken is..."
Oye! Look, i'm not going to continue this anymore. I don't feel like getting lectured about the scientific method... Seriously!
There's a difference between being skeptical and what you're doing in this thread. Personally, I'm also skeptical of the traditional path to unification, I'm more of a gauge/string duality fan. But I just leave everyone do their own thing, how's it any of my business what others work on? Including creationists. If you like evolution so much, why are you so stressed out? Natural selection will make sure wrong theories eventually die out, no?
I don't feel like getting lectured about the scientific method... Seriously!
Well then learn what it is. Nobody will lecture you about it then.
Isn't the question somehow, here we are in all our ignorance: What do we do to learn more in the most optimal way?
Some people apparently think the best we can do is to keep working on ST.
Some people, think otherwise, but then the question isn't ST or not. The question is: what else? No need to keep referencing to ST, lets get on with the discussions. ST is not a standard in my eyes, except in the sense that it has become the major BTSM field.
ST will have to prove itself eventually just like any other program.
/Fredrik
how's it any of my business what others work on? Including creationists.
Creationism isn't a part of science even in principle, even as a hypothesis, so your analogy is bogus.
Kevin_Axion
Nov15-10, 05:01 PM
You've been referencing creationists in a lot of your arguments, just pointing that out.
You've been referencing creationists in a lot of your arguments, just pointing that out.
Yes, why is that a problem? Are you a creationist? As I've explained, it illustrates the point well. In science we can't use multiple definitions of a theory across disciplines. Science is universal. The meaning of a theory in evolutionary biology is the same as in physics. You can't have it both ways.
Kevin_Axion
Nov15-10, 05:06 PM
No, I'm not, but you were refuting someone's point upon the basis of them using creationism yet sixty percent of the arguments you've made have referenced creationists. It just seems to be a loss of continuity. Anyways I don't want to argue, this thread has achieved absolutely nothing and it will remain this way.
arivero
Nov15-10, 05:06 PM
Natural selection will make sure wrong theories eventually die out, no?
Er, no. Natural selection permits the accumulation of "wrongs" if they are compatible with the ambiance in the sense that they do not handicapp the species survival compared to others. In this way, Natural selection can build complex structures, which is where a set of "wrongs" becomes, surpresively, because of accumulation or because of a change in ambient conditions, a "right"
sixty percent of the arguments you've made have referenced creationists.
Don't exaggerate.
this thread has achieved absolutely nothing and it will remain this way.
In your opinion. Stating something doesn't make it the case.
I tell you what, the quality of arguments from these so-called experts has been poor.
I tell you what, the quality of arguments from these so-called experts has been poor.
In your opinion. Stating something doesn't make it the case.
Kevin_Axion
Nov15-10, 05:19 PM
Exaggerating isn't the point, it's the principle in which states that you've made a hypocritical post.
No, I'm not, but you were refuting someone's point upon the basis of them using creationism yet sixty percent of the arguments you've made have referenced creationists. It just seems to be a loss of continuity.
Hey hang on - you were accusing me of hypocrisy here. The other person who raised creationism did so in a way that created a fallacy. He wasn't using it to create the same point I was making. I was using evolution to justify my point, not creationism. Read more carefully before you accuse someone of having double standards.
In your opinion. Stating something doesn't make it the case.
Oh aren't we the clever one. Actually, my statement just backs up something which is manifest. His statement was without support.
... If you like evolution so much, why are you so stressed out? Natural selection will make sure wrong theories eventually die out, no?
Good you mentioned that, Negru. Something analgous to natural selection happens with human theories, concepts, even mathematical ideas. As long as the community retains its critical standards.
I that is the root issue in this thread. The scientific community is a traditional aristo self-selecting community that decides who is and who isn't a scientist, and decides what is what isn't a scientific theory, what gains cred and is copied and replicated, and ultimately decides when a theory is no longer interesting---according to the subjective, sometimes adversarial application of some traditional standards.
You can't argue from definitions and axioms here--a lot of it is subjective, and even social. Somehow the scientific community continues to operate pretty well, however.
Historically there is a kind of put up or shut up rule, after a while if something produces no testable results it goes out of favor. The issue here, in this thread, I think is should the physics community relax its standards.
If standards were relaxed then natural selection would work differently. I suppose we could evolve in the direction of multiversalist fairytales---abandoning the effort to explain why this particular universe we live in is the way it is. Some overarching untestable theory provides for a landscape of 101000 possible versions of physics, and we just happen to live in one of them.
Or evolution could take many other courses---the explanatory fantasy of myth etc etc. If you change the selection criteria, natural selection goes on a different track. I don't want to speculate---just suggest that different futures are possible.
For me, in this thread, string is not the central issue. It is only people who see it as threatened and rush to its defense that make string an issue. The real issue is the perpetuation (or not) of Baconian scientific standards and expectations.
If we eliminate all references to string from our posts we would still have a discussion--maybe even a more interesting one.
Here's at least one reason this thread has not been pointless - I've learned something - that even practicing professionals can be arrogant, self-serving, nest-feathering and mentally manipulative, which further solidifies a view I had already acquired long ago that my mentors and colleagues at work only care about publications, travel, career kudos and what the next restaurant they want to eat in is. They don't seem to care about the methods of science, as long as they get the citations. My decision to not carry on in academia has been strengthened, not weakened.
Kevin_Axion
Nov15-10, 05:30 PM
How exactly did his post create a fallacy, he was merely stating that he believes it is not the customary observer's perspective to state what is and isn't right, people will do what they wish and care less about how one person believes high energy physics should be guided principally. I'm not arguing against you, I'm just stating what is.
His fallacy was that people's right to believe in creationism justified the right to study string theory. They cannot be equated. I pulled him up on that, and you bizarrely accused me of hypocrisy, like the wise old expert that you are (!)
Kevin_Axion
Nov15-10, 05:35 PM
And the fact that they can't be equated is an invention of your mind. In fact many people have stated that studying String Theory has become religious in essence, a most suitable relation it seems. Anyways I'll feel sufficed to your argument if you can present one fact that states in anyway how theoretical research in general or specifically String Theory has deterred our motivation or knowledge of physics.
arivero
Nov15-10, 05:35 PM
Marcus, the comparision with natural selection enerves me... by doing it, you seed the roots of Inteligent Design. It is not that you can not assume a ecosystem of theories, you could do it if the theories were varying randomly and they were surviving just on the grounds of consuming resources from other theories.
But if there is an Inteligent body, in this case the Humanity, selecting some theory in basis to an inteligent criteria, then it is not natural evolution.
Theories evolve not by natural selection, but by "Inteligent Pantheist Design" (opposed to Inteligent Monotheist Design").
Anyways I'll suffice to your argument if you can present one fact that states in anyway how theoretical research in general or specifically String Theory has deterred our motivation or knowledge of physics.
The fact that you probably view "theoretical research" as a valid stand alone pursuit shows why we can't make progress in this discussion. The fact that 30 years and countless PhDs, conferences and postdocs has produced few, or arguably no, testable predictions, in contrast to the productive times of earlier decades, is surely proof that real damage may have been done to progress? This would be true even if ST was a proper theory! And I mean real progress, which means do an experiment, build a theory, verify with another experiment, lather, rinse and repeat.
And the fact that they can't be equated is an invention of your mind. In fact many people have stated that studying String Theory has become religious in essence, a most suitable relation it seems.
And if they can be equated, then all the better for my argument, because it means they are both unscientific, and people lose their justification to thrust them upon society in publicly funded ways. If they can't be equated then my accusation of fallacy stands.
-As a model, technically we're just missing a selection principle to choose from the landscape. Hardly an obvious dead-end or utter failure.
... Why is everyone so anxious?
You tell me. Why are string theorists so anxious? The minute someone clears their throat and appears to have some reservations about the value of stringy research, a half-dozen defenders rush in and start talking about how great it is.
Speaking for myself I don't feel at all stressed or worried.
I see string jobs drying up. I see citations to string research have crashed. I see publication slacking off. Particularly by top level people.
I see that Nima Arkani-Hamed tells a small Princeton audience that we do not expect String Theory to tell us anything about particle physics. That was November 2009 as I recall.
The message was "give up on stringy unification".
"Landscape" papers were excluded from the Strings 2008 conference at Geneva, and almost completely absent from Strings 2009 in Rome.
For some 5 years after 2003 we were told the String Landscape was about 10500 different versions of physics, but I hear that the recent estimate is more like 101000. You are right to suggest the trouble is there is no selection principle.
I see the top former stars of string working all or part time on non-string topics. And many others working on applying string math to stuff that is extraneous to the unification program.
Basically the objective facts that I see denote a field in decline. This does not bother me, it is part of the natural cycles. They will find all sorts of extraneous applications for the math.
This is entirely unstressful and uncontentious AFAICS. The chorus of denialist defenders is not even mildly annoying. There are plenty of other things to think about.
And heck, the course of historical decline might reverse! We don't know the future! What I've mentioned is just how things are going for the moment. Don't hold your breath, but if I see any signs of that I will certainly let you know and let anybody else who will listen know.
Dax, if string theory were to move to the math department, pending experimental evidence, would that make you happy? How do you justify research in abstract mathematics? What's the difference and why is it relevant to anything?
Kevin_Axion
Nov15-10, 06:11 PM
No, it doesn't mean they are both unscientific, it means that they share the same strength of advocacy. String Theory uses rational argument and creationism doesn't. Anyways I do agree that String Theory is really lacking experimental inquiry and understanding but I don't believe it has devalued any other forms of research (LQG people would disagree). I'm sure you can agree that String Theory must hold some truth or else it wouldn't explain so much.
Dax, if string theory were to move to the math department, pending experimental evidence, would that make you happy? How do you justify research in abstract mathematics? What's the difference and why is it relevant to anything?
Yes, that's exactly the kind of thing I'm talking about. In my country (and earlier when you advised me to see a congressman, you assumed I was from the USA), physics and mathematics are mostly funded by different research councils.
The leaders of the councils aren't always aware that what's going on is abstract maths, they just assume they are funding the pursuit of genuine particle physics knowledge (the funding council which pays my QCD research also pays for LHC research, for example). These issues have a real impact.
Justifying research in abstract mathematics is surely an issue of mathematical proof, or whatever other things motivate the production of new mathematics. If funding claims to fund abstract mathematics, then that's fine. But the STFC in the UK, for example, does not fund abstract maths, they fund particle physics, in principle.
Marcus, people are anxious because none of this criticism id new. Everyone was well aware of the inherent troubles of string theory when they decided to start working on it. In fact, some of my profs said that's exactly what drew them to string theory: the fact that it's just testing human knowledge to the maximum, with little external hints to make things easier. So to them in particular it's mind boggling why or how these string wars appeared in recent years. Like woit or smolin had found some dark secret of string theory - when instead that dark secret was the feature some people liked most.
In any case I agree with what you said above regarding natural selection and science. Science has always been arbitrary. Science was never successful because scientists were some kind of pure, rational objective thinkers with no agenda. It was successful only because you could use science. And who used the better science prevailed (where "used" can mean experiment, check consistency, build technology, explain stuff, or anything like that). That's why I believe time will tell, and there's no reason to get all worked up about what everyone is doing (unless of course it's done on tax payers' money. but as long as global warming, math, literature, and other such fields get funded, I think everyone should be funded). I'm confident that good theories will stand the test of time. As for me, I'll just try to stay on the side which I believe to be true. And Dax will get angry here, but research is pretty much by definition the same as religion (in its initial stages). The only thing you can do is believe in it. If there were any objective evidence in favor of one path or the other, it wouldn't really be research.
I'm sure you can agree that String Theory must hold some truth or else it wouldn't explain so much.
I question how much it really explains. It (arguably) contains the SM, which I find boring. It is a quantum theory of gravity, but whether or not physics is a unified whole is a question for which there is no evidence, it is merely compelling. And even if it predicts new things (branes, colliding universes etc.), the validity of these predictions depends not only on their experimental validation, but on the premises of the theory being sound. We develop a theory with experiment front and back, not just at the front.
Dax, if string theory were to move to the math department, pending experimental evidence, would that make you happy? How do you justify research in abstract mathematics? What's the difference and why is it relevant to anything?
Excellent question! Mathematicians also have a traditional self-selected community with standards of what is good and interesting mathematics. If it moved over into a new setting, string would have to sink or swim.
Mathematics also undergoes something like "natural selection". Fruitful ideas are imitated. Ideas that get boring or don't lead anywhere (not "interesting" by the hard-to-define traditional judgment of the top mathematicians) are dropped, or left to low-status obscure folks.
Top mathematicians have a way of rating what is "hard" or "deep" or "nontrivial". It's part of what a mentor, like a PhD advisor, instills.
Mathematical ideas mutate spread and evolve in a kind of dialog with this critical scrutiny by the community. Eventually "deeper" ideas prevail. Community subjective judgment is involved.
You ask what would happen if String moved to the math department. That might be very interesting! Then it would be competing for jobs, for citations, for seminar attendance, for the hard to define "prestige" that math people confer on each other. It would be competing with different things from what it competes with in the physics department. That could be very interesting.
I remember in 2006 Witten came out here to Berkeley to give 3 lectures 90 minutes each on his current research interest. I attended all of them. One of the things that impressed me was that he did not mention string theory for the entire 270 minutes. At the end of the third lecture someone in the audience raised their hand and asked "and what about string theory?"
People say different things if it is a large widely-advertised public lecture versus a smaller unadvertised talk.
Nima Arkani-Hamed was very different at that small conference about the "Landscape" at Princeton from how he was, for example, at Cornell recently in a big format video-stream set of lectures.
Actually some string physicists have moved over into the Math Department and are now doing different stuff like more abstract category theory not so obviously related to string. Urs Schreiber used to be a string stalwart, boosting string all over the place. Now he is in the Hamburg University math dept and doing n-category theory and stuff. I think it was a very smart move. He is extremely smart. Making it as a mathematician---according to math department standards---is a really good way out, if you can do it.
And Dax will get angry here, but research is pretty much by definition the same as religion (in its initial stages). The only thing you can do is believe in it. If there were any objective evidence in favor of one path or the other, it wouldn't really be research.
There are many essential differences, come on you can't be serious??? :frown:
Everyone believes in things, belief is not the issue. Scientists believe in things, but they believe in things based on evidence (and they try to do this even in the fluffy early beginnings of a theory, otherwise there's no justification to call it a theory. Even hypotheses have experimental origin). Religious people believe in things based in faith.
I'm sure I don't need to list the myriad other ways in which science differs from religion: no personality cults, a competitive peer review system, institutions which foster learning rather than shut it down, etc. etc. ad infinitum). Of course adhering to the scientific method is not as clean as you would think from reading a textbook, but you can't argue that that makes it lack objectivity.
Kevin_Axion
Nov15-10, 06:33 PM
I'm not qualified to make a judgement anyways, I'm only 16. You probably thought I was slightly older unless my ignorance bled through the flaws in my arguments. It was a fine debate though.
Dax, if we had evidence for a theory, we wouldn't be talking about research. If you have evidence for it, it's established as fact.
How do people decide whether to go into string theory or LQG? Assuming we're at a stage were none had any evidence in its favor, how would you decide which one to follow? How would you decide which one was more likely to turn out being the correct one? There's no objective way to do that, you can only go with what you believe will happen.
Or just any simple problem. Why do people start working on a particular problem? Because they believe they can solve it. It's always a matter of faith.
Dax, if we had evidence for a theory, we wouldn't be talking about research. If you have evidence for it, it's established as fact.
But that phase where we lack evidence is transient, or it should be. If you can't test something, or the test fails, you discard it and move on. 30 years is not what I have in mind by transient.
I'm not qualified to make a judgement anyways, I'm only 16. You probably thought I was slightly older unless my ignorance bled through the flaws in my arguments. It was a fine debate though.
You're a superb thinker for your age. I'm in my mid 20s, in the thick of research, and you gave me a run for my money. Getting someone frustrated is usually a sign that you've made a good argument, and I think everyone has gotten frustrated at some point.
But that phase where we lack evidence is transient, or it should be. If you can't test something, or the test fails, you discard it and move on. 30 is not what I have mind my transient.
That transient phase represents the whole of research.
Kevin_Axion
Nov15-10, 06:56 PM
Thanks, I just love physics and enjoy reading about it and researching it. May I ask what you are researching? I believe you mentioned QCD. I will also add that I know of almost none of the technicalities of String Theory although I am lurking through The Road to Reality by Roger Penrose
I work on hadronic contributions to the muon g-2. Some people do things with nonperturbative QCD (e.g. on a lattice), but the work I do is better done using experimental data to estimate the specific contribution. It's very collaborative so no one person can work on g-2 theory alone.
Kevin_Axion
Nov15-10, 07:20 PM
Awesome! That's probably my dream job, something involving High Energy Physics.
Always follow your dreams, regardless of what other people tell you. And physics in 10 years will probably be fascinating, with less emphasis on this string argument. I remember a popular article a year back detailing some of the extremely smart new proposals for testable theories of quantum gravity, so string theory may reach the point where they stop making unwarranted claims about what it is, because its tools and methods will get sucked into the newer ideas (I think marcus made this point better than I could).
Kevin_Axion
Nov15-10, 07:41 PM
Yea, I actually live pretty close to PI so I'm planning on going to the University of Waterloo and they have awesome courses like introduction to QFT (Feynman Path Integrals) and Particle Physics in fourth year courses. I can't wait and thanks for the support despite my arrogant attitude before.
I skimmed a lot of this thread, could hardly read it all. I'm surprised I didn't see anyone noting the following positions which have been raised in other forum threads.
1) It is not clear that GR and QFT must be considered in conflict that must be resolved somehow. I've seen a growing number of papers arguing several related points:
a) The need for quantum gravity at all should be considered subject
experimental verification. Maybe some form of QFT in curved
space is a valid model.
b) Progress in quantizing GR as an effective field theory
least raises the question of whether the conflict is as deep or
needful of whole new frameworks.
2) Supersymmetry preceded string theory, if my recollection is right, and has been pursued independently of string theory.
3) Thus one could posit that a research program aiming to be more in touch with experiment would look for ways choose a preferred SUSY extension to SM that had appropriate dark matter candidates, and perhaps combined with effective quantized gravity explained dark energy.
In short, there are more minimalist approaches to make progress using current conundrums and unexplained results.
However, I have no problem with the idea that physicists should do what seems most promising to them. Dead ends will be be pruned eventually, no one knows them beforehand, outside officials certainly shouldn't be making these decisions.
And I see shifting emphasis happening naturally. 'Radical' approaches other than M theory and LQG are being done as well as a growing number of papers on more limited approaches, as above. Success will draw followers, stumbling blocks will push some people in new directions.
Haelfix
Nov15-10, 10:13 PM
Thank you Pallen, that's an excellent post that is succint, logical and has some nonzero probability for interesting physics discussions that others here might get something out off. It is also points of view that I happened to share not so long ago.
It is precisely questions like this (or should I say, the 'probable' answers) that lead people to believe in string theory.
On the other hand, this thread is so devoid of any meaningful content, that it would be best served in its own thread.
Hi PAllen,
Its possible some of the "other forum threads" relating to minimalist proposals were ones I started. Are you familiar with what could be called "no-frills" proposals of the following two sets of authors?
Hermann Nicolai and Kris Meissner
Shaposhnikov and friends
Nicolai presented his idea at the July 2009 XXV Max Born conference. It was LHC testable, predicted no new energy scales between EW and the Planck scale, required just one new field. No low energy SUSY. No extra dimensions etc. Gravity was not included in the talk, as I recall, but they have described a way to include it elsewhere. The slides are here:
http://www.ift.uni.wroc.pl/~planckscale/lectures/1-Monday/3-Nicolai.pdf
The 40 minute video of Nicolai's talk is here:
http://www.ift.uni.wroc.pl/~planckscale/movie/
The first 5 minutes provides an "executive summary" so you can get the gist without going the whole 40 minutes.
He refered to Shaposhnikov's work, and Shaposhnikov has also cited the Nicolai Meissner papers. Some points of similarity.
I've reported on these minimalist initiatives in other threads. So I am curious if these are some of what you were thinking. I haven't paid much attention to Effective Field Theory (EFT) à la John F Donoghue and several others, because I've been interested especially in Nicolai Meissner ideas. There is something more to it---the attempt is to extend the Standard Model, with very little extra, all the way to Planck scale and get something moreover that the LHC could falsify.
Their first paper was written in 2006 and has been followed up by a handful of others, indeed they just posted a new one in October 2010.
Here's the 2006 paper:
http://arXiv.org/abs/hep-th/0612165
A good way to dig up minimalist papers might be to look down the list of the 40 papers that cited it:
http://www.slac.stanford.edu/spires/find/hep?c=PHLTA,B648,312
I've highlighted some bits of your post that interested me especially.
I skimmed a lot of this thread, could hardly read it all. I'm surprised I didn't see anyone noting the following positions which have been raised in other forum threads.
...
In short, there are more minimalist approaches to make progress using current conundrums and unexplained results...
And I see shifting emphasis happening naturally. 'Radical' approaches other than M theory and LQG are being done as well as a growing number of papers on more limited approaches, as above...
There are some quite deep aspects of these things, but this can easily be misinterpreted as it's a thin line between acknowledging the subjective nature of expectations and arbitrariness in particular for anyone that doesn't understand the difference.
Scientists believe in things, but they believe in things based on evidence (and they try to do this even in the fluffy early beginnings of a theory, otherwise there's no justification to call it a theory. Even hypotheses have experimental origin). Religious people believe in things based in faith.
To believe in something due to evidence is basically a rational expectation; this is different from stating that all evidence is unique, or that there is an objective "TRUE" or "correct" expectation.
Two scientist making different observations, will form two possible contradictory but still RATIONAL expectations of nature. What further happens is that these scientist "interact" in the scientific community in order to negotiate an objective consensus. Still this consensus is only objective relative to the local community.
The idea of rational expectation is completely disjoint from the idea of objective truth, because evidence is not objective. I don't think we should confuse "science" which to me is all about rational and justifiable expectations and actions, with illusions absolute truth.
Science isn't necessarily about unravelling eternal absolute truth or timeless laws - it is IMHO about rationally learning and forming expectations of nature, for basis of further rational action.
An expectation can be fully rational, and yet "wrong", since the measure of wrong is also merely a rational expectation which is observer dependent.
This association with "intelligent design" everything one discusses this seems to be an american phenomenon, I personally don't have any problem distinguishing this discussion from religion.
/Fredrik
Hi PAllen,
Its possible some of the "other forum threads" relating to minimalist proposals were ones I started. Are you familiar with what could be called "no-frills" proposals of the following two sets of authors?
Hermann Nicolai and Kris Meissner
Shaposhnikov and friends
I've seen a couple of threads of yours here, not sure I've seen these specifically. I was using the work 'minimal' in a generic sense, interesting that it might have a more specific sense similar to what I was getting at.
Nicolai presented his idea at the July 2009 XXV Max Born conference. It was LHC testable, predicted no new energy scales between EW and the Planck scale, required just one new field. No low energy SUSY. No extra dimensions etc. Gravity was not included in the talk, as I recall, but they have described a way to include it elsewhere. The slides are here:
http://www.ift.uni.wroc.pl/~planckscale/lectures/1-Monday/3-Nicolai.pdf
The 40 minute video of Nicolai's talk is here:
http://www.ift.uni.wroc.pl/~planckscale/movie/
The first 5 minutes provides an "executive summary" so you can get the gist without going the whole 40 minutes.
He refered to Shaposhnikov's work, and Shaposhnikov has also cited the Nicolai Meissner papers. Some points of similarity.
That's really interesting, especially if they tackle gravity. Do they have dark matter candidate and any approach for dark energy? (I will look over these references, but can't right away; by look at, I mean understand what I can from the abstract and general logic; I can't follow details of such papers). I am particularly interested in the idea of explaining the major evidence beyond SM with a theory that may not be 'ultimate' but is less of a leap than M-theory. In effect, suppose something like M-theory is the ultimate theory at the Planck scale, yet given the enormous difficulties of completing its formulation let alone understanding how to use it, it could be really worthwhile to pursue more partial theories that make progress on currently known conundrums.
Besides dark matter, and dark energy, other things that might progress are reducing the number of free parameters in SM via some new explanations. I remember in highschool (60s) raising the plethora of particle masses as a signficant thing to explain, and being told that 'well, no one knows how to use such information'. Then, over next 10 years we get SM that now does derive things like proton/neutron mass (and was theoretically expected to explain such things evern before the calculations could be carried out).
Of course, I know the landscape hypothesis suggests most of these parameters may be accidents, and I can't say 'I know this is wrong', but I hope it is. I remember clearly the initial excitement with string theory, including the expectation (more than just a hope) that virtually all of these parameters would be derived quantities in string theory.
I've become somewhat enthusiastic about SUSY without string theory as a practical approach because of the synergy between something originating with unification (GUTs, QG separate from string theory as well as within string theory) that also predicts the seeming best candidate for dark matter so far. The big difficulty here (my opinion) being how to pick some preferred SUSY extension and work out the details.
I've reported on these minimalist initiatives in other threads. So I am curious if these are some of what you were thinking. I haven't paid much attention to Effective Field Theory (EFT) à la John F Donoghue and several others, because I've been interested especially in Nicolai Meissner ideas. There is something more to it---the attempt is to extend the Standard Model, with very little extra, all the way to Planck scale and get something moreover that the LHC could falsify.
Their first paper was written in 2006 and has been followed up by a handful of others, indeed they just posted a new one in October 2010.
Here's the 2006 paper:
http://arXiv.org/abs/hep-th/0612165
A good way to dig up minimalist papers might be to look down the list of the 40 papers that cited it:
http://www.slac.stanford.edu/spires/find/hep?c=PHLTA,B648,312
I've highlighted some bits of your post that interested me especially.
Atyy has posted several papers on effective field theory approach to quantum gravity over on the relativity forum. From these I perceive recent progress. Yes, one of them was by John F. Donoghue. What I like here is the ability to actually do quantum gravity calculations right now. Unfortunately, they seem to suggest that deviations from GR may not be testable for a long time.
A separate line of thought is the 'is quantum gravity' necessary at all. I am thinking here about recent papers arguing that you can 'almost prove' that the graviton will never be detected, even if it exists. Given the key role of the photon's particle like properties in the development of QM, this makes me ask the question of necessity for the whole enterprise. For example:
http://arxiv.org/abs/gr-qc/0601043
Closely related are papers like the following, proposing that the need for unification itself should be subject to experiment and is not strictly required:
http://arxiv.org/abs/0803.3456
http://arxiv.org/abs/0802.1978
http://arxiv.org/abs/0809.4218
Hope this reply isn't too 'all over the place'. My main thrust is there is a lot that can be done while 'waiting for TOE', if we need it at all. However, I don't perceive any 'problem' in theoretical physics. I have seen your (Marcus) threads noting changes in emphasis in research, and that is the natural way such things sort themselves out.
@Pallen
a) The need for quantum gravity at all should be considered subject
experimental verification. Maybe some form of QFT in curved
space is a valid model.
This is the kind of thing I've been trying to say all along. When your premise is also your conclusion, it's circular reasoning.
@Haelfix
On the other hand, this thread is so devoid of any meaningful content, that it would be best served in its own thread.
You can't just keep repeating that the thread is meaningless to keep yourself satisfied. If it it so meaningless, why participate in it? The fact that you started the sentence with "on the other hand" shows that it was preceded by some point you made, so clearly you are lying that there is nothing to engage with.
I still find it hard to believe that a seasoned veteran of physics (a science advisor no less) can resort to a cheap dismissal of an important discussion. There is a teenager here who shames you in terms of maturity. Many different things have been discussed for such a meaningless thread. The fact that you're irritated is sign enough that something substantial has been said which bothers you.
Pallen,
I think what I share with you is an interest in approaches which are seen as conservative, minimalist, with prospects for testing with the means at hand.
I'm not convinced that TOE is a logical next step.
Both the conventional SM and classical GR have problems, it gets my attention when I see people address the problems without necessarily reaching for complete unification.
Nicolai Meissner's proposal is intriguing and LHC testable, but not primarily TOE. They have discussed some nebulous ideas of how to link up with gravity and have tried teaming their model up with a version of supergravity. In Nicolai's talk at the Planck scale conference he said he was going to try to be "agnostic" about what version of QG could go with their proposal. My paraphrase doesn't do justice, I fear.
=========================
Where our thoughts differ is also interesting. It may simply reflect where we are coming from--prior concerns. In my case the needs of observational cosmology seem central---it's a personal perspective that influences how I see things. I'm sympathetic to your point that a graviton may never be observed. Indeed the concept itself may be more at home on a flat, or at least fixed, geometric background than in what I would call a more realistic setting.
Einstein thought that a TOE was the logical next step, but he was missing many important pieces of the puzzle (including two forces!). I've always believed it to be extremely strange that we act as though the current situation is different. A person pursuing a TOE is effectively claiming that the essential features of nature are known, and we just need to develop the correct mathematical apparatus. Extremely suspicious, and unlikely.
A person pursuing a TOE is effectively claiming that the essential features of nature are known, and we just need to develop the correct mathematical apparatus
I don't agree with that conclusion, there are other ways to think about that.
The inference perspective to physics, suggest a natural unifying framework based not on what nature is or must be, but rather on what inferences any observer can make on nature, and that from such a perspective all inferences should be unified in a general inference framework, because to suggest that there exits information that isn't the result of inference is to resort to non-scientific notions.
So unificiation is not expected because nature has to be this or that way, but rather because whatever nature is, all information about it must be the result of a scientific process. So the learning process "unifies" all knowledge.
Anyone that like me, thinks that physical processes in nature, can be thought of as inter-system inferences, may choose to seek a TOE (=GUT +gravity) in terms of trying to understand generic communication between two systems, and that unification corresponds to the limit where the complexity of the communicating parties approach zero. Then try to understand how to pull the 4 forces out of that abstraction, to the extent possible.
So I think the feature that no observer CAN know everything, is even the key to unification. Unification by undecidability. Whenever diversity isn't distinguishable, there is unification, not by enlightment but by ignorance.
/Fredrik
So unificiation is not expected because nature has to be this or that way, but rather because whatever nature is, all information about it must be the result of a scientific process. So the learning process "unifies" all knowledge.
... So I think the feature that no observer CAN know everything, is even the key to unification. Unification by undecidability. Whenever diversity isn't distinguishable, there is unification, not by enlightment but by ignorance.
I think we agree more than you might think. You could argue that unification (the way you describe) is the operation of physics as a subject, but it is and always has been a piecewise process, not a one shot approach, and above all, an evidence based approach. That's why we don't even have a proper union of QCD and Electroweak yet in the Standard Model. The SM, Higgs notwithstanding, represents what we actually know about nature, and nothing more.
If the 'let's try to develop a complete TOE' approach was a worthy method, it would have worked for Einstein. He failed because he had incomplete knowledge. Who are we to claim that things are different now? I would unhesitatingly bet money that future historians of science will view current attempts at a TOE in the same light as we currently view Einstein's attempt. This is the precise reason why the piecewise, experimental approach is the time tested way of discovering new information about how the universe works.
I want to see how Pallen would separate some issues out. He suggests that QG might not be needed because gravitons might in effect have no universal or fundamental existence---might just be an artificial construct that is perhaps useful for some purposes.
I agree with downplaying the graviton's significance---it doesn't come up much in nonperturbative QG. But that does not remove the need for QG, as I see it. One still wants a quantum spacetime geometry--a concrete mathematical representation of dynamic geometry--in order to do early-universe cosmology.
I guess my bias is kind of gradualist/incrementalist. The spacetime geometry of classical GR fails in the early universe. I want to see some improvements on GR tested. A TOE seems like a red herring, an impractical distracting goal.
I'm afraid of boring you with my list of phenomenologists. I find it exciting that they have taken the bit in their teeth. I just saw that Tsujikawa is on board. He has a paper in prep that says Loop cosmology is falsifiable* by available means: as I understand it, by the next CMB mission after Planck. Planck is now taking data.
We are talking about a bunch of phenomenologists who are not Loop people, and CMB polarization missions with provisional names like "B-pol" and "CMBpol".
Having Shinji Tsujikawa's participation is important, as I see it. In case someone is unfamiliar with him here is his home page at U Tokyo:
http://www.rs.kagu.tus.ac.jp/shinji/Tsujikawae.html
Key people, in my view, are Aurelien Barrau, Julien Grain, Wen Zhao, and Shinji Tsujikawa---together with the people who have co-authored with them on this topic.
*Broadly, not just one particular model or version.
You may decide I am responding to the current situation in a naive way. It requires going out on a limb. I hope to convince you that working cosmologists will not be satisfied with a perturbative treatment of geometry.
They are used to a geometry which can expand quickly by over 20 orders of magnitude.
The typical benchmark factor given is e60 or 1026 but the precise number hardly matters.
And if you change something may expand much less, or not at all, or may even collapse again. That kind of geometry is not a perturbation around some fixed pre-destined one.
A nonperturbative treatment of geometry should also be quantum--a QG in other words. Given that matter is quantum and influences geometry anything else seems unrealistic and even logically impossible.
What we are looking for is a conservative, minimalist, modification of GR. It must retain the most basic features of GR, to be conservative: no fixed geometric background, not perturbative, and so forth. It has to have, to a relativist/cosmologist, the "look and feel" of GR. And be quantum.
The idea is to do only what is absolutely necessary to achieve the incremental goal of a nonperturbative backgroundless quantum geometry. In other words don't go haring off after a TOE :biggrin:
And be testable.
The idea is to do only what is absolutely necessary to achieve the incremental goal of a nonperturbative backgroundless quantum geometry. In other words don't go haring off after a TOE :biggrin:
I would have to disagree with you here. Geometry is very basic and fundamental. And you seem to be talking about finding fundamental reasons for the geometery we observe, even reasons why this geometry changes and even comes about in the first place in the big bang. I suspect you will not find those answers without explaining everything else in the process. I think it will take a TOE to explain QG. For if you explain where spacetime comes from to begin with, then you'll probably discover where particles come from that move in that spacetime.
I have more to say about a TOE in post 58 of this thread.
What if it takes 5,000 years to develop this TOE? It still wouldn't prevent us from discovering things, but it renders the concept of a TOE somewhat meaningless. Why do people have the feeling that to discover fundamental things about the geometry of space time we need to explain "everything"? How can you explain everything until you know what everything is? As I've said, Einstein thought "everything" was GR + EM. I don't feel this theory of everything language has ever been justified. Letting go of it will not cripple our ability to make genuine progress. Some people have said, well, surely the language used in unimportant, but I think it is - because the belief that you can create an all-explaining, all-knowing "framework" is probably highly misleading and is not a meaningful goal for a physicist to work towards, in my view.
... I suspect you will not find those answers without explaining everything else in the process. I think it will take a TOE to explain QG. For if you explain where spacetime comes from to begin with, then you'll probably discover where particles come from that move in that spacetime.
...
Friend! You sound as if the game, for you, is to find ultimate answers to the most basic questions!
Ultimately you might well be right that to finally understand the intimate dialogue between matter and geometry one will have to express them as both rooted in a common mathematical ground. As different aspects of the same thing.
But we don't always aim directly at what we think we want. In the current situation cosmologists have the opportunity to make a little incremental progress in studying the early universe. There are massive amounts of data coming in. This data has to be organized and compared with mathematical models, even if they are not exactly the right ones. :biggrin:
Our models never are exactly the right ones. :rofl:
Take a more pragmatic view and agree with me that cosmologists are allowed to use LQG (as many now seem to want to) as conservative modification of GR (retaining essential GR features) applicable to the early universe.
Indeed in the process they may falsify the existing Loop cosmology framework, depending on what ripples the next spacecraft see in the CMB.
Friend! You sound as if the game, for you, is to find ultimate answers to the most basic questions!
Ultimately you might well be right that to finally understand the intimate dialogue between matter and geometry one will have to express them as both rooted in a common mathematical ground. As different aspects of the same thing.
Ever since issues of incompatibility arose between GR and QFT, there has been talk about having to make corrections to one or the other or both. This is because we don't have any logical justification for the absolute necessity of either. All we've accomplished is to find curves and equations that fit the data. Some are even asking what observations require us to apply the principles of QM to GR. So it seems we need to answer the questions of what make QM so logically necessay, and why should it be applied to GR? Something as funamental as why QM applied to something as fundamental as spacetime seems like a TOE to me. For I don't think you're going to find out why QM/QFT is necessary by finding higher energy particles. Those are just another reason to use it, not where it came from to begin with.
I suppose we can continue to grope in the dark and fit pieces together by chance. But I'm beginning to see light at the end of the tunnel.
I want to see how Pallen would separate some issues out. He suggests that QG might not be needed because gravitons might in effect have no universal or fundamental existence---might just be an artificial construct that is perhaps useful for some purposes.
I agree with downplaying the graviton's significance---it doesn't come up much in nonperturbative QG. But that does not remove the need for QG, as I see it. One still wants a quantum spacetime geometry--a concrete mathematical representation of dynamic geometry--in order to do early-universe cosmology.
I guess my bias is kind of gradualist/incrementalist. The spacetime geometry of classical GR fails in the early universe. I want to see some improvements on GR tested. A TOE seems like a red herring, an impractical distracting goal.
I'm afraid of boring you with my list of phenomenologists. I find it exciting that they have taken the bit in their teeth. I just saw that Tsujikawa is on board. He has a paper in prep that says Loop cosmology is falsifiable* by available means: as I understand it, by the next CMB mission after Planck. Planck is now taking data.
We are talking about a bunch of phenomenologists who are not Loop people, and CMB polarization missions with provisional names like "B-pol" and "CMBpol".
Having Shinji Tsujikawa's participation is important, as I see it. In case someone is unfamiliar with him here is his home page at U Tokyo:
http://www.rs.kagu.tus.ac.jp/shinji/Tsujikawae.html
Key people, in my view, are Aurelien Barrau, Julien Grain, Wen Zhao, and Shinji Tsujikawa---together with the people who have co-authored with them on this topic.
*Broadly, not just one particular model or version.
This will have to be my last post in a while due to outside constraints. I may check back real quickly.
I think Marcus has hit the nail on the head that we both are excited by theoretical progress that attempts to solve known issues by expeditious and testable means. (It would be different if there were no major loose ends to explain, just dissatisfaction with existing theories. I believe that is not the case, and has never really been the case).
However, it is really interesting how perception of what are big problems skews your preferences. For me, dark matter and dark energy are the elephants in the room (also, extending SM to work consistently higher energies, explaining at least some relationships of the fundamental parameters, are major things to focus on), while drawing strong conclusions about the first microseconds of the universe is risky business that is hard to firmly interpret. Marcus' information about testability of LQG is very interesting. Perhaps I should take early universe modeling as a theory testbed more seriously.
Be that as it may, my current thinking has been more along the following lines (it changes twice a year anyway):
First, I see the key ingredient of QG most likely will never be observed, distinguishing it from all other quantum theories. That is unfortunate, but not decisive by itself. Then, I see that it is not so clear QG is needed at all, instead you should try to test whether it is needed (see the 3 papers on this I posted in my other thread). Then, the effective field theory papers attempt to answer the testability question, and they come out mostly in the negative: no effects at accesible energies; look inside event horizons (and die happy) or the first moments of the universe. So, I wonder whether there is anything worth doing on this.
This underscores my bias toward dark matter and dark energy as the big things to focus on. For these, SUSY extensions to SM look very promising to me, as well as just directly trying to improve SM to extend to higher energies (thus Marcus' references are *very* exciting to me on this score). Look into new vaccuum theories to address dark energy.
Now I guess if you must to address those early universe issues, you need something more than this. So for this I guess I would have similar leanings as Marcus, for creative yet conservative approaches are worthwhile. Is a near singular modification of GR itself possible? Can the efffective field theory approach be extended to provide something useful here? Some other direct attack on the problem besides LQG? Maybe QFT in very curved space leads to exotic stress energy tensors that violate the assumptions of the Hawking-Ellis-Penrose singularity theorems?
(On the other hand, I definitely think string theory is still worth pursuing in the mix. Getting 4 forces without assuming them is not boring to me, it remains one of the high points of my following physics. Then there is the toolbox string theory has and presumably will continue to develop)
That's all I have for now, just the opinions of a long time avid follower of physics, not a practitioner (once upon a time, long ago, seriously studied physics).
@PAllen
On the other hand, I definitely think string theory is still worth pursuing in the mix. Getting 4 forces without assuming them is not boring to me, it remains one of the high points of my following physics.
I know you don't have the time to respond, just wanted to say I found your post very interesting. I'd like to pick up on the above point if I may. It's a plausible sounding view and I totally agree that models are worth studying because we can learn useful mathematical things from them (AdS/CFT is particularly interesting), but to me the inherent problem is, again, the assumption that we know what the new TOE "needs to do". There could be 7 forces, not 4. Where does that leave us then?
Such a drastic alteration would probably call for an equally drastic revision of what the fundamentals of the model are in order to "predict" the new reality. I find it to be totally suspicious, because that process of revising our view of what we need to predict from first principles could go on forever. There is a better way (and in my view the only real way) to find out new physics; i.e. experiment. Cosmological observations are the way to go, I would think, in the near term future, unless someone figures out how to build an accelerator the size of the universe.
@PAllen
I know you don't have the time to respond, just wanted to say I found your post very interesting. I'd like to pick up on the above point if I may. It's a plausible sounding view and I totally agree that models are worth studying because we can learn useful mathematical things from them (AdS/CFT is particularly interesting), but to me the inherent problem is, again, the assumption that we know what the new TOE "needs to do". There could be 7 forces, not 4. Where does that leave us then?
Such a drastic alteration would probably call for an equally drastic revision of what the fundamentals of the model are in order to "predict" the new reality. I find it to be totally suspicious, because that process of revising our view of what we need to predict from first principles could go on forever. There is a better way (and in my view the only real way) to find out new physics; i.e. experiment. Cosmological observations are the way to go, I would think, in the near term future, unless someone figures out how to build an accelerator the size of the universe.
Just a quick reply to this. Maybe we should eliminate the abbreviation TOE altogether. TOE is a very arrogant claim, that though no scientific theory has ever survive 500 years, ours will.
However, isn't a TOESF (theory of everything so far) of great interest? Maxwell's theory was a TOESF that was one of the great milestones of physics. If QM got delayed a bit, GR+EM (even without Einstein's attempt at 'further unification' ) would have been a coherent TOESF (I don't think unification per se, must be a feature of a TOESF). So why do I still find getting the 4 known forces without assuming them still exciting? Not so much for the unification per se, but the promise that the framework that does this can allow coherent computation of all of them together. If string theory had already achieved this, we wouldn't be having this discussion. So what if string theory is the right approach but it is like the Riemann Hypothesis in math? I like that analogy. It is a good candidate for being the most important open problem in math, but its great difficulty has led, over time to a balance - some people are always working on it, but not at the expense of other work.
I think we agree more than you might think.
Maybe.
but it is and always has been a piecewise process, not a one shot approach, and above all, an evidence based approach.
I fully agree - inference is evolving (~piecewise) - but if people have taken this seriously, then why doesn't our current theories reflect this inference structure? To me this is significative of lack of some deep insight. (that's not to say that people should have understood 100 years ago what we understand now, I'm just saying that MAYBE time is soon ripe for such insight, although it's still absent)
We do have some of this in history, for example statistical mechanics/thermodynamics, and to a limited extent quantum mechanics, but this is just scratching the surface as I see it.
If the 'let's try to develop a complete TOE' approach was a worthy method, it would have worked for Einstein. He failed because he had incomplete knowledge. Who are we to claim that things are different now?
Maybe we mean different things by TOE. I'm not talking about "a theory that answers every question" in the sci-fi sense, I'm talking about the nice but still more modest ambition to find a coherent understanding that includes the four konwn forces. Such a TOE would NOT mean we have absolute knowledge of anything, beucase such a "TOE" should SCALE with the observer, and with it the level of undecidability. What most realist would think of as TOE is the large compelxity limt of that scaling, which corresponds to a birds view - which I think is non-physical. So that limit is not interesting. What's more interesting is the scaling itself (not the limits), and how that encodes the forces.
All respect to Einstein but I find it unfair to compare Einstein with any new ideas. The inference perspective, and the idea of rational action and evolving law are IMO a complete new way of thinking that doesn't even compare to Einsteins old style, strongly realist type thinking, of TOEs Einsteins was looking for.
Edit: I don't mean it's complete new in absolute sense, there are some people in the past who has been into this direction (shannon, ET Jaynes, as well as current people), I just mean that relative to the dominating dogmas in physics so far, its' new.
/Fredrik
Dax, since new you may not know about the private message PM feature. Upper righthand corner of screen.
My question is along the lines of what's the best thing to do. Rest, assimiliate, have time for other things (like your research :biggrin:) or put some more thought into this thread---clarify issues, try for conclusions, take a new direction, risk another spate of vehement controversy,...
At the moment I feel like quietly mulling, but I'm up for other people's suggestions and initiatives.
I was amused by the debating use of the term barm cake. It impressed me as a flat-out body slam after which you really have to let your opponent get up and dust himself off.
Yes I've "ruffled a few feathers" here and there as one fellow put it, which on most occasions is probably a good thing! Nevertheless not all opponents resorted to weak arguments, so I've learned some things too.
And yes! Since the thread died down I've made much more progress at work! Such is life, doesn't mean it wasn't worth it... :smile:
Just to be clear Donoghue's exposition of gravity as an effective theory is not UV c omplete. It is a good theory of quantum gravity at low energies, and agnostic about whether the UV completion should be Asymptotic Safety or something like string theory.
Nicolai and Meissner are assume a the UV completion of their theory will be something like string theory.
Something someone said in this thread reminded me of Urs Schreiber, one of the string theorists who has moved out of physics into the math department. By coincidence he recently commented on Woit's blog, just this afternoon (22 November). I mentiond Urs earlier in this thread:
...
You ask what would happen if String moved to the math department. That might be very interesting! Then it would be competing for jobs, for citations, for seminar attendance, for the hard to define "prestige" that math people confer on each other...
...Actually some string physicists have moved over into the Math Department ... Urs Schreiber ... Now he is in the Hamburg University math dept...
That was my offhand remark, not especially considered, it would be better to let Urs speak for himself. I respect his ability despite differing viewpoint.
What he means by "spectral geometry" is what Alain Connes calls Noncommutative Geometry (NCG).
==quote Urs at Peter's blog 22 November==
...I suppose you have followed Alain Connes’ construction (here is a survey and links) of the standard model by a Kaluza-Klein compactification in spectral geometry. It unifies all standard model gauge fields, gravity as well as the Higgs as components of a single spin connection. Connes finds a remarkably simple characterizaiton of the vector bundle over the compactification space such that its sections poduce precisely the standard model particle spectrum, three chiral generations and all.
Alain Connes had computed the Higgs mass in this model under the big-desert hypothesis to a value that was in a rather remarkable chain of events experimentall ruled out shortly afterwards by the Tevatron. But the big desert is a big assumption and people got over the shock and are making better assumptions now. We’ll see.
Apart from being a nice geometrical unification of gravity and the other forces (credits ought to go all the way back to Kaluza and Klein, but in spectral geometry their orginal idea works out better) Connes’ model has some other striking features:
the total dimension of the compactified spacetime in the model as seen by K-theory is and has to be, as they showed, to produce exactly the standard model spectrum plus gravity: D= 4+6.
...
...
I think there is some impressive progress here. It is not coming out of the physics departments, though, but out of the math departments. For some reason.
==endquote==
http://www.math.columbia.edu/~woit/wordpress/?p=3292&cpage=2#comment-69896
Urs recent papers have been posted under the main headings Algebraic Topology, Quantum Algebra, Category Theory---math.AT, math.QA, and math.CT. Collaborated quite a bit with John Baez (similar mix.)
It's an interesting point, I don't how many people would agree. Another person that comes to mind is Matilde Marcolli (in NCG). She is in the Math department at Caltech. She organized that recent workshop at Oberwolfach on Spin Foam and NCG.
Another person is John Barrett at Nottingham. He does both NCG and spin foam LQG. I think he is in Mathematical Physics, I'll check. Yes, my impression of him is that he's a mathematician but maybe the fact is he is amphibious, foot in both communities, connections-collaborations-workshops in both.
I must admit distinctions blur for me. I'm not sure what to think. But what Urs said about more progress being made in math departments rang a bell.
Later the same day Urs posted again, saying in part:
==quote Urs 22 November==
because the most impressive progress in fundamental physics these days does not quite percolate through the physics community.
==endquote==
I don't know if what he says is right but it gets my attention when a ex-string physicist (of first-rate ability) says that Alain Connes' realization of the Standard Model is "the most impressive progress" in fundamental physics. And that this is not getting through to the physicists.
Connes, I guess you would say, is 100% mathematician. Never been in a physics department in his life. Like his collaborators Matilde Marcoli and Ali Chamseddine.
It sounds like he's critical of the community, would say the community got on the wrong track, and some mathematicians are on the right track. Do we take what Urs says seriously? I'm a bit puzzled. Maybe someone else can give a clear picture.
http://en.wikipedia.org/wiki/Lucasian_Professor_of_Mathematics
http://en.wikipedia.org/wiki/Lucasian_Professor_of_Mathematics
Physicists in the centuries past have often needed to be mathematicians too - Newton didn't have the luxury of being able to select the mathematical tools required to explain the motion of physical objects (observations), so he had to invent calculus. So the Lucasian chair has real meaning to these fellows as a mathematical accolade, but it doesn't mean that physics and mathematics are the same subject. I think we all agree that the standard of "proof" in mathematics (formal theory) and physics (empirical/scientific theory) are different (the few who disagreed were using such poetic license with the meaning of meaningful words such as to render the discussion meaningless, if you'll pardon my poetry).
Physicists can even make proper contributions to mathematics (e.g. Witten with topological field theory). Sometimes a person's activity can be properly described as mathematics, sometimes as physical science. It matters in terms of assigning public funding to advance our knowledge of the universe, but it doesn't matter with regards to assigning public chairs and the like.
I also noticed an earlier point someone made (mostly unrelated to this) about a parallel between the Yang-Mills controversy and the String controversy. I believe this analogy is deeply flawed and misleading. Yang-Mills theory was well suited to explain the remaining features of the SM because it only introduced a minimum of exotic concepts. Yang-Mills is an example of brilliant abstract mathematical machinery, and there is plenty of historical evidence that this is perfectly ok (abstract maths often precedes its actual use in explaining experimental oddities). Not only does ST go far beyond both minimalism and mere abstraction, but the analogy with explaining the unexplained in highly unclear - the most fantastic explanatory power of ST proposed so far is to explain that which we already have a theory for (and a real scientific one at that), the SM, and even this claim is questionable, which is something new I learned in this thread - strengthening my view further, rather than weakening it.
Does pure mathematics exist?
Does pure mathematics exist?
Do propositions "exist"? Any part of reality can be described with a proposition, no matter how small. And we can say that propositions that do describe reality have the truth-value of being true. Does this mean that the purely mathematical concept of a proposition can actually exist?
...the Lucasian chair has real meaning to these fellows as a mathematical accolade, but it doesn't mean that physics and mathematics are the same subject...
Dax, I think we may agree that they are different because they are practiced by different communities, in different departments, with different standards (as you point out.)
Ultimately there are these self-selecting (somewhat structured) communities that maintain and pass along traditions---of what is interesting, what you talk about, how you resolve disagreements, what you have to take seriously and what you don't, which journals are good to publish in...etc.
History is what historians do. No verbal formula exactly defines the discipline/activity.
Mathematics is what mathematicians do. It is separate from physics precisely to the extent that the communities are separate---which means the border is fuzzy, with shifting and irregular bits of overlap, but you can distinguish two communities.
A cluster analysis of journal citations and conference attendance would probably work for someone unable to see the difference.
And if long ago or far in future you didn't/don't see two different communities, then math and physics were/will be the same.
I think dictionary prescriptions don't work because a scholarly community is semi-autonomous--as long as it can get funding it will do what it wants. There is a lot of built-in inertia---tradition, mentorship, committees, seniority, institutional inertia--so it looks stable, but still no hard and fast dictionary definition.
So it could be a useless distraction to start trying to say in abstract terms what physics "is" and what separates it from mathematics.
==========================
What I had in mind was a more pragmatic and real-world community based issue that Urs raised.
He seems to criticize the realworld physics community for being impervious, for not letting significant progress in NCG particle model percolate through it.
His criticism may be wrong. It is not about an abstraction in any case but about behavior. He points to the behavior that, as he sees it, more progress in fundamental particle theory is being made in certain math departments than is occurring in physics departments.
When you think about it, that is a pretty radical statement. Sounds almost preposterous.
Back in 2004, when I became aware of Urs, he was one of the most promising young German string theorists. Much respected, exceedingly bright. An organizer too: one of the founders of the group blog "String Theory Cafe" and the USENET board called "sci.physics.string".
His criticism is basically directed at the theoretical physics community leaders---how they have managed their resources, directed research, assigned conference time, distributed theory grants, theory postdocs, promotions. He says "how did this happen?" Connes approach to Standard Model goes back 10 years or more (the big success being 2006). So why are there not already a lot of physics postdocs and junior faculty working on it? Why does this not "percolate" in the physics departments? What is wrong with the management?
Or is it the worldview?
And Urs could be wrong. Maybe someone here will want to dismiss him, or his criticsim, or say that is not really what he meant.
Atiyah constantly makes the point that mathematics must be in contact with physics, for the health of mathematics.
And does Penrose do maths or physics?
Yes, it is funny that Penrose accused Witten of being a mathematician :smile:
Go twistors!
I looked some more at what Urs is saying and he seems to have a good point. I or someone else here may want to start a separate thread about his ideas, so it doesn't get in the way of this one.
In the meanwhile, I'll collect some links and some more quotes.
http://ncatlab.org/nlab/show/FQFT
Functorial qft is a generalization of topological qft (TQFT). Atiyah's axioms.
http://www.math.columbia.edu/~woit/wordpress/?p=3292&cpage=2#comment-70046
The following is a reply to Prof. Thomas Schaefer (NC State Raleigh)
==quote Urs at Woit's blog 23 November==
The lack of response to Connes’ theory is indeed interesting. I think the problem is that nobody has been able to explain in a language that particle theorists can understand whether this is indeed a new idea (and if so, what the new idea is) or whether this is just a complicated way to formulate an old idea (GUT’s or maybe Gravi-GUT’s).
Yes. Generally my impression is that the number of theoretical physicists actively aware of or at least interested in the issues of what it means to find a conceptual or even axiomatic framework for fundamental physics is currently much lower than it used to be. It seems to me that in the early 90s or so the situation has been very different. In fact from that time date a few articles by string theorists who had read Connes, had understood what he is after and had tried to connect it to string theory.
Because the curious thing is: what Connes suggests is precisely the 1-dimensional version of the very idea of perturbative string theory (which is the 2d version of an even more general idea)...
==endquote==
You can see him striving to explain Connes NCG "in a language that particle theorists can understand"--which Thomas Schaefer says nobody yet has been able to do.
Maybe Urs will be the one to do that. And the community will become more permeable. And NCG or as he calls it "spectral geometry" will be able to percolate through it better.
In case anyone wants: the homepage of Prof. Schaefer.
http://wonka.physics.ncsu.edu/~tmschaef/
Yes, I would really like to know what Barrett means in this talk about NCG and spin foams (state sum models) when he queries "Other levels: strings, membranes??" http://hep.itp.tuwien.ac.at/~miw/bzell2010/Barrett-2010.pdf (slide 13)
I also want to know what the subtext of Baez and Huerta's http://arxiv.org/abs/1003.4485 is.
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