Dax discussions of Beyond SM theories/including newcomer questions

[marcus]

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 realized 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==
https://www.physicsforums.com/showthread.php?p=2980716#post2980716

 

[marcus]

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 allows 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]

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.

 

[marcus]

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.

 

[negru]

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.

 

[Lt_Dax]

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?

 

[Lt_Dax]

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]

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 black holes 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 that's going for us.

 

[JustinLevy]

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.

 

[Lt_Dax]

@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).

 

[Lt_Dax]

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!

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

 

[Kevin_Axion]

There is a reason it's called theoretical physics.

 

[JustinLevy]

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.

 

[Lt_Dax]

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?

 

[Lt_Dax]

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]

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.

 

[Lt_Dax]

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

 

[Kevin_Axion]

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: . 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.

 

[Lt_Dax]

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]

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]

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.)

 

[Lt_Dax]

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]

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.

 

[Lt_Dax]

@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?

 

[Lt_Dax]

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]

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]

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.

 

[Lt_Dax]

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]

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.

 

[Lt_Dax]

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.

 

[Lt_Dax]

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]

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]

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]

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.

 

[Lt_Dax]

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.