Where are we heading?

Every summer the IAS in Princeton runs a program for graduate students and postdocs called “Prospects in Theoretical Physics”. It’s going on now, with this year’s topic LHC Physics. Much of the program is devoted to the important but complex technical issues of extracting physics from LHC data. Things began though with a talk on Where are we heading? from Nati Seiberg designed to explain to students how they should think about the significance of the LHC results and where they were taking the field.

Most of the talk was about the hierarchy problem and “naturalness”, with the forward-looking conclusion the same one that Seiberg’s colleague Arkani-Hamed has been aggressively pushing: the main significance of LHC results will be telling us that the world is either “natural” (likely by discovering SUSY) or “unnatural” (in which case there’s a multiverse and it’s hopeless to even try to predict SM parameters). Given the negative results about SUSY so far, this conclusion pretty much means that the students at the IAS are being told that the LHC results mean it’s the multiverse, and they shouldn’t even think about trying to figure out where the SM comes from since that’s a lost cause. The talk ends with the upbeat claim that this is a “win-win situation”: reaching the conclusion that the LHC has shown we can’t learn more about where the SM came from will be a great scientific advance and “The future will be very exciting!”. Seiberg does at one point make an interesting comment that indicates that he’s not completely on-board with this conclusion. He notes that there’s a “strange coincidence” that theorists are making this theoretical argument about the necessity of giving up at just exactly the same time in our history that we have run out of technological ability to explore shorter distances. A “strange coincidence” indeed…

For more conventional wisdom along these lines, see Naturally Unnatural from Philip Gibbs, which also argues that what we are learning from the LHC is that we must give up and embrace the multiverse.

Frank Wilczek has just made available on his web-site a new paper on Multiversality. It has the usual arguments for the multiverse, although unlikes Seiberg/Arkani-Hamed he doesn’t try to claim that this is an exciting positive development, closing with a “lamentation”:

I don’t see any realistic prospect that anthropic or statistical selection arguments – applied to a single sample! – will ever lead to anything comparable in intellectual depth or numerical precision to the greatest and most characteristic achievements of theoretical physics and astrophysics…

there will be fewer accessible features of the physical world for fundamental theory to target. One sees these trends, for example, in the almost total disconnect between the subject matter of hep-th and hep-ex.

and a “warning

There is a danger that selection effects will be invoked prematurely or inappropriately, and choke off the search for deeper more consequential explanations of observed phenomena. To put it crudely, theorists can be tempted to think along the lines “If people as clever as us haven’t explained it, that’s because it can’t be explained – it’s just an accident.”

He does see possibilities for understanding more about the SM in two places, the SUSY GUT unification of couplings and axions as an explanation of the smallness of the QCD theta parameter. The last part of the paper is about axion cosmology and anthropics. Wilczek has written about the stories of the 1981 origin of the SUSY GUT unification argument and the 1975 birth of the axion. It’s striking that we’re 32 and 38 years later without any idea whether these ideas explain anything. A depressing possible answer to “Where are we heading?” would be an endless future of multiverse mania, with a short canonical list of ancient, but accepted ideas about fundamental theory (SUSY Guts, string theory, axions) that can never be tested.

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52 Responses to Where are we heading?

  1. vmarko says:

    Given the negative results about SUSY so far, this conclusion pretty much means that the students at the IAS are being told that the LHC results mean it’s the multiverse, and they shouldn’t even think about trying to figure out where the SM comes from since that’s a lost cause.

    This is extremely bad from an educational point of view. This doctrine of giving up on attempts to explain the SM is horrible even for seasoned scientists, let alone students!

    I am just hoping someone outside string theory will get a flash of inspiration and propose a method to predict at least one coupling constant in terms of the others, for example. If this happens, and if that prediction turns out to be numerically correct, it will be a straight slap in the face to all multiverse/anthropic hype. That is, in addition to being a revolutionary theoretical discovery.

    Best, 🙂

  2. Zathras says:

    I am surprised the “Where are we heading” talk made such short work of dark matter. With the death of SUSY it would seem that the most likely place to see non-SM physics is with dark matter.

  3. weichi says:

    The Gibbs article is quite well written; seems like a very clear exposition of the pro-multiverse point-of view. And Lubos has a nice article in response discussing fine-tuning.

  4. Adam Treat says:

    Hi Peter,

    I watched the recent talk by Penrose about his Conformal Cyclic Cosmology theory in Warsaw. He ended the talk with new details about the prediction for concentric circles in CMB data. Apparently he now has another independent team saying they’ve found the circles in the Planck data and the previous claimants have also updated results.

    I bring this up here, because it seems that an affirmative finding of such rings would boost Penrose’s theory as a serious opponent of multiverse mania. From what I understand CCC would preclude the idea of a multiverse.

    So that is one more hope for stemming the tide of these multiverse propenents. If not Penrose’s theory, then perhaps other progress will continue and show the way forward.

  5. Adam Treat says:

    Also, I wanted to ask what you thought of this new talk. I know you have been highly skeptical of this theory as you should be, but at least it is science and making predictions.

  6. Peter Woit says:


    I’m still pretty skeptical about the Penrose CCC business, haven’t seen any reason for more optimism about it. But I’m no cosmologist…

    It also really says nothing at all as far as I know about the SM parameters, and from what I remember, one of the biggest problems is that he has to invoke some unknown mechanism to make masses go to zero and get conformal invariance. Even if there were evidence for his picture, I doubt it would be all that difficult to incorporate CCC in some tweaked form of multiverse mania.

  7. Eric says:

    It really troubles me that people seem to so easily accept the statement to the effect that “supersymmetry is dead”. This is not even remotely true. At the worst, one might be able to claim that a low-energy supersymmetric solution to the hierarchy problem requires a small amount of fine-tuning at the 1-3 percent level. It is quite possible that all squarks and sleptons have masses in the range 4-10 TeV, and the hierarchy problem can still be solved with fine-tuning at only the 3 percent level. In this case, there would likely not be an observable signal at the LHC. However, in such spectra the lighest neutralinos are Higgsino-like with fairly light masses which might be observed at the ILC. So, it will not be possible to claim that supersymmetry is dead for quite some time. It would be great if people would educate themselves on the actual situation rather than repeating misinformation.

  8. Brian says:

    Adam, the best argument for Penrose’s ideas are the low multipole data from Planck2013 – which somewhat disagree with LCDM. One could argue forever about circles.

  9. Chris W. says:

    We seem to be in a true fin de siècle period. The real seeds of what is to come will germinate largely in the dark.

  10. Peter Woit says:

    Chris W.,

    Funny, but I remember thinking we were in a fin de siècle period back in the 90s. Maybe these siècles are getting shorter…

  11. Igor Khavkine says:

    I’m sensing that Peter and other readers of this blog (as embodied in vmarko’s comment) consider the realization that the parameters of the Standard Model cannot be predicted as “giving up”, in a negative, unwarranted sense. Granted, the reasons given by the likes of Seiberg and Arkani-Hamed, namely the cosmological multiverse, are very dubious. However, I’d like to turn this question around. What reason was there to expect that any of the Standard Model parameters could be predicted at all?

    My question is not totally rhetorical, but I think the answer is None, at least not in the sense of vmarko (as it appears to me). My reason for saying so has nothing to do with the multiverse or anything similar. Simply, I don’t know that, historically, this ambition has ever succeeded and do know that it has notably failed.

    Just to clarify my argument, the situation we have with the Standard Model is that all its parameters are already known (with varying precisions) and no empirical reason to suspect that they are not fundamental (in the usual reductionist sense). There’s always room to discover a new pattern or symmetry in among the know parameter values, but that is no longer prediction, just observation.

  12. Peter Woit says:

    It’s not just continuous parameters of the SM, but also the general features one would like some explanation for. Maybe there is no answer to a question like “Why SU(3)xSU(2)xU(1)?” other than “just because”, or “the Multiverse did it”. I don’t see a solid argument explaining why this is something we can’t possibly know, so it seems like a good idea to keep thinking about it and seeing what one can learn. Claiming that the failure of one’s pet idea means that no one can ever find the answer to such questions, because the universe was constructed to as to make you fail, seems on the other hand like a bad idea. My problem isn’t so much with people raising the possibility that such questions can’t be answered, rather them doing so to evade having to admit that an idea they promoted heavily just didn’t work.

  13. hhoonneeyy says:

    To be honest, the general attitude towards naturalness vs multi-universe among the students is who cares……

  14. Yatima says:

    “What reason was there to expect that any of the Standard Model parameters could be predicted at all?”

    None whatsoever, or the same as the reason to expect that the Standard Model had anything to do with group theory.

    On the other hand, why aren’t there more free parameters? Is there any reason to expect that may be even less free parameters? Where is the dividing line between numerology and coincidences of some interest?

    How about one might start considering the multiverse idea when a complete description is found with only one free parameter left (under the constraint of not pushing these DOFs into epicycles), and not earlier? That may take some time though.

  15. Lafargue says:

    hhoonneeyy: Are you attending the program? As student or as lecturer? What do the students care about?

  16. amused says:

    Well that all sounds very bleak and depressing, but I’d just like to point out that some people in HEP have been, and continue to be, heading in what seems a much more promising direction: finding new physics beyond the SM in quark flavour physics (CKM matrix elements and that kind of stuff) by confronting increasingly high precision theory calculations (involving Lattice QCD) with experimental measurements. Discrepancy between SM theory and experiment at the 3sigma level has already been reported for a few years now – see e.g. here for a recent review. A detailed program for uncovering and studying new physics beyond the SM in the quark flavor sector over the next 10 years has been presented here.

    The lack of attention this seems to get from the rest of the HEP community is astonishing (to me at least). You would think people who lament the lack of prospects for finding new physics beyond the SM would at least be mildly interested in existing 3sigma discrepancies with the SM…
    On the other hand, it is amusing and not hard to understand sociologically. The university affiliations of the people doing this stuff are all non-elite – no one from Harvard, Princeton, Stanford etc. If such people were the ones to discover new physics beyond the SM it would be a terrible offense against the natural order of things. So the the elites of HEP can’t bear to acknowledge this work, and when they don’t talk about it then no one else will – such is the sociology.

    (Disclaimer: I don’t work on that stuff myself and have nothing personal at stake in it. But as someone who works on formal theory/maths aspects of lattice gauge theory I’m vaguely aware of it from following the lattice literature.)

  17. Krzysztof says:

    Gian Giudice has given in Stockholm a great talk on naturalness :

    Interestingly, though not supported by Templeton, he managed to evoke St. Thomas Aquinas…

  18. MathPhys says:

    This is no good. This is less than professional. No one should teach ideology camouflaged as physics. Definitely not to students.

  19. Krzysztof says:

    MathPhys: Ideology? I was just joking, as was GG I would guess… To ease the tension let me quote Wolfgang Pauli : “Well, our friend Dirac, too, has a religion, and its guiding principle is “God does not exist and Dirac is His prophet.”

  20. vmarko says:

    @ Igor Khavkine:

    I’d like to turn this question around. What reason was there to expect that any of the Standard Model parameters could be predicted at all?

    Let me comment on this just for completeness. The SM features some 20-30 (depending how you count) coupling constants, and cca. 100 elementary particles, with a lot of various structure (gauge groups, finite groups, generations, flavor, lepton/baryon groups, etc.). When you draw it all down on a piece of paper, it looks very similar to the Mendeleev periodic table of chemical elements — they both have periodic, similar structure, and even a comparable number of 100 or so “elementary atoms”.

    If history is allowed to teach us anything, the whole SM “smells” like having some simpler underlying structure all over the place. This simpler structure is “simpler” in the sense that it has fewer free parameters and fewer elementary particles, while the SM parameters are to be expressed as functions of these. Btw, this is an old idea, look up on preons for some historical attempts to address this.

    Granted, it might be that SM really does not have any underlying structure of that kind and that all parameters are really fundamental. But students should not be indoctrinated into thinking that way just because string theory has 10^500 vacua and no way to distinguish between them.

    Best, 🙂

  21. MathPhys says:


    I had N Seiberg’s talk to summer school students in mind. My point is that his is not straight, undiluted science. It’s too ideological.

  22. Krzysztof says:


    OK – but then, only half-joking, I would say that is rather pseudo-religious, in a direct relation to Pauli’s quote. Fortunately, Dirac did not mixed up his believes with physics, but it seems now we are facing this problem in fundamental research. In my view, it could be traced back to the idea of the ToE, which from very beginning sounded pretty non-scientific.

  23. Richard says:


    This may be a little off-topic, but have you heard “Popsiecles and Icesiecles” by the Murmaids*?
    It’s a really good song.

    — Rich

    P.S. I like SUSY and the Banshees, too.

    * Siecles are not the only ones with fins!

  24. weichi says:


    “Simply, I don’t know that, historically, this ambition has ever succeeded and do know that it has notably failed.”

    I’d love to hear you expand upon this. What episodes in science do you have in mind? As vmarko points out this ambition has succeeded enormously in regards to the periodic table. I suppose one could argue that the ambition failed in regards to explaining the orbital sizes and masses of the planets in our solar system – we now understand that these things are basically random facts.

    But the science of newtonian mechanics and astrophysics has explained so many other things, and has lead us to pose so many new and more interesting questions (questions that astrophysics has also been able to answer!) that I don’t think anyone really cares about the “random” answers.

  25. srp says:

    The most fascinating thing in this thread is the deafening silence in response to amused’s cogent point. I’ve tried to point out similar things a few times and Peter asked me to stop (so I have). The only non-sociological explanation I have is that the HEP folks have implicitly decided that the proton isn’t fundamental enough to be worth their time–it’s gotten classed with those messy composite topics like nuclear physics and chemistry.

  26. Peter Woit says:


    Actually I’m kind of in favor of deafening silence in response to comments that, while reasonable, could easily turn into an attempt to hijack discussion off-topic to something the commenter is more interested in…

    That said, the topic of better understanding QCD and flavor physics isn’t a completely neglected one, there are many people working on this. It’s likely to get more attention in the US in coming years since US experimental HEP has no short-medium term path to a new high energy machine, but is concentrating on a plan for exploiting a new high intensity machine.

    Yes, this kind of research isn’t popular at high status places like the IAS, but that’s only partly because of the domination by topics like SUSY, string theory, and ideas about extra dimensions. HEP theory has always been very faddish, but when healthy the fads were driven by experiment. The problem here is that the size of apparent violations of the SM that have been seen just aren’t convincingly large enough. If there were a solid 5 sigma SM violating phenomenon being observed, I think you’d have almost every prominent theorist at Princeton, etc. dropping everything they were doing and working on something related to that. Absent a convincing deviation from the SM, it’s not surprising people looking for something high profile and faddish to work on go for black holes instead.

    SUSY has been an endlessly popular fad because it’s complicated, but can be studied with quite conventional techniques, so there is lots for theorists and experimentalists to do. The failure so far to see anything I suspect will make this a less popular thing to work on, and no SUSY in the next LHC run will seriously damage interest in the subject. Unfortunately, as long as the faddish sociology continues, what this is likely to mean is just that people abandon one fad for an even worse one (e.g. the multiverse), and my fear about talks like Seiberg’s is that they are paving the way for that.

  27. amused says:

    I don’t want to be a hijacker and start off a discussion about the prospects for flavor physics 🙂 Will just mention that 3 sigma discrepancy with the SM already seems serious to me, and that the prospects for improving on this with higher precision calculations and measurements to reach the 5 sigma discovery level in the coming years look pretty good (although I’m far from an expert on it). Considering all the current doom and gloom about prospects for finding new physics beyond the SM, I just think people should be aware of this (which most people aren’t since it’s such an unfashionable topic). And it seems not completely off-topic to mention it here in a thread about “where are we heading”. The depressing multiverse isn’t the only direction.

    I guess what we all ultimately want is to discover the next layer of new physics beyond the SM. From a scientific viewpoint the avenue for reaching this shouldn’t matter as long as we reach it. But from a sociological viewpoint it matters enormously…

  28. emile says:

    Hi Amused,

    For a CMS or ATLAS physicist, a 3-sigma discrepancy is not that significant because the data are sliced and diced thousands of ways. Many distributions will have had strange features that will have disappeared when adding more data. I agree with Peter that when these discrepancies reach 5 sigma, they will get attention from the community. I also agree that, without a machine that goes beyond 13/14 TeV (or a linear collider anytime soon) and assuming no new physics at those energies, we’ll have to look in loops to find signs of anomalous contributions.

    Back on topic: I think Wilczek’s warning is spot on.

  29. amused says:

    Hi Emile,

    At the risk of getting my comment deleted for continuing in an off-topic direction (and I will understand if that happens):
    The flavor physics stuff is quite different from the stuff done at CMS/ATLAS: high intensity “precision physics” vs high energy “discovery physics”. The 3 sigma discrepancy is not occurring in some experimental signal but rather in a mismatch between various experimental and theoretical constraints on CKM matrix elements (and other flavor stuff). From what I understand (and I’m no expert on this!), the experimental measurements are already very precise, and it is on the theory side that precision is lacking. So the goal (as I understand it) is to increase the precision of the theory calculations, with more precise lattice QCD simulations playing an important role for this, so as to push the existing discrepancy from 3 to 5 sigma thus confirming new physics beyong the SM. Looks like this could happen already in the coming years.
    (And if I got some or all of that wrong then hopefully someone more knowledgeable will correct it…)

  30. Ravi says:

    It is interesting that Frank Wilczek’s article has the Warning “There is a danger that selection effects will be invoked prematurely or inappropriately, and choke off the search for deeper, more consequential explanations of observed phenomena…. I believe there are at least two important regularities among standard model parameters that do have deeper explanations, namely the unification of couplings and the smallness of the QCD θ parameter (for which, see below)….”

    While the only solution discussed by Prof. Wilczek for the smallness of QCD theta parameter is the axionic one that has been around for a long time, non-axionic solutions could well be what nature has picked. In recent papers 1009.5651 and 1203.2772   I showed that just discrete space-time symmetries parity (P or left-right symmetry) and CP (equivalent to time-reversal T) can solve the strong CP problem and predict neutron EDMs in experimentally interesting regions. Moreover 1209.3031 shows that spontaneously broken P itself can stabilize dark matter without need for R-parity etc. Leptonic CP phases can vanish in these models for the same reason that strong CP phase vanished at the tree-level.

    We may yet discover that nature was left-right symmetric and time-reversal in its fundamental laws.

    (There are also non-axionic solutions that include proposals by several researchers that usually involve either P or CP along with other symmetries such as SUSY, Z_2 and with different predictions).


  31. fuzzy says:

    hi igor,

    sm does not have to explain anything of course. it is up to each specific model, that aims to extend the sm and to be predictive, to tell us something useful. (btw, even theta is not a issue in sm; if it is small it stays small.)

    supersymmetric sm, with its sliding scale and its huge number of free parameters, does not satisfy the criterion of predictivity in my view. concocting naturalness, in order to camouflage this shortcoming, seems to me a rather mean position.

    i think high energy physics should care of measurements. there are not so many measurements we have to account for assuming something outside the sm, but these measurements should be considered with more care and less arrogance.

    alternatively, the mask should be thrown, admitting of having forgotten the mission of physicists and of preferring to play to the games of the philosophy.

  32. Igor Khavkine says:

    @vmarko, weichi:

    Since the example of the periodic table was brought up, consider its history. Mendeleev identified the periodic structure in the properties of elements. The observation of this pattern was extremely useful and its value stands on its own. However, I don’t think this observation is an “explanation” in the usual sense. There were multiple theoretical research programs to actually come up with explanations for the periodic structure and the additional spectral line data. These included vortex knots theories, as well as plum pudding models, and I’m sure others that have been forgotten by history. Successful explanation in terms of atomic structure theory came only after crucial experimental breakthroughs: Thompson’s discovery of the electron and Rutherford’s discovery of the nucleus. These experiments revealed that there actual subatomic constituents and set the challenge of explaining atomic properties in terms of their dynamics.

    That challenge was speedily and successfully met. But note the chronological order of the experimental and theoretical input. Those models that preceded the crucial experimental discoveries are now relegated to history, essentially without exception. The apparent pessimism expressed in my earlier post is an expression of my opinion that the existing theoretical research programs aimed at “explaining” the structure of the Standard Model are most likely analogous to the vortex knot and plum pudding models of the past, highly unlikely to succeed. Moreover, without any sharp empirical evidence of compositness (or something similar) of SM particles, the already observed structure and symmetries of the SM are already a great achievement (like that of Mendeleev), which does not necessarily cry out for any kind of “explanation”.

  33. Armin Nikkhah Shirazi says:

    You make a fairly compelling argument for your position, but I think there is a loophole.
    If the foundations and interpretation of QM and, by extension of QFT, were as settled as they seem to be for classical physics and even that additional ‘Understanding’ failed to provide any addititional clues, then the outlook might be as bleak as you think. But as it stands, the SM is a sophisticated mathematical pattern fitting scheme with little understanding of its deeper meaning. Feynman understood this, recall his analogy with the Mayan Astronomers, who were able to make accurate precision predictions of planetary cycles with essentially zero understanding of planetary dynamics.
    The fact that none of the mainstream interpretations of QM has been able to conclusively establish itself may just be another facet of this problem. I for one would not be surprised if we recognized the eventual ‘correct’ interpretation by noticing that its application to the SM would point to novel approaches for calculating its parameters. It is quite possible in my view that we have already gathered sufficient experimental data to be able to elucidate the deeper meaning if we were only more imaginative. Remember that the technology that led to Newton’s laws was essentially available also to the Mayans, since much of the underlying data leading from Kepler to Galileo came from Tycho Brahe who performed naked eye astronomical observations.
    So, to answer the question you posed in your first post, as long as we don’t understand the deeper meaning of the SM, we have every right to expect that several or perhaps even all of its parameters can eventually be predicted because, taking an even longer view of the history of science, so far it has been thus.
    Your perspective may be just too entrenched in the current zeitgeist.


  34. pitpstudent says:


    I do not know if you are basing your critique of Nati’s talk on just the slides which are online. Because I attended Nati’s and Nima’s talks at the summer school, and both of them made it very clear they do not like the multiverse at all. They would much rather prefer an alternate explanation, and encouraged students to think outside the box and outside current wisdom, for new ideas.
    Nima also mentioned that those people in the field who keep updating their “prediction” for masses of various particles as the LHC bounds improve, give the field a bad name. He said you could keep massaging the theory and making it more and more complicated to escape the LHC bounds, but he doesn’t believe in that. He gave some very clear numbers for masses, which seem to be already in some trouble after the first run of LHC, and he said that the 14 TeV run will settle the matter once and for all.

  35. Peter Woit says:


    Thanks for the report and comments.

    I was basing the comments on Nati’s talk just on the slides, and I haven’t heard him talk about this. The question isn’t really whether he “likes” the multiverse, but whether he’s following what is becoming the conventional wisdom of “we don’t like the multiverse and anthropics, but the LHC results are making it the leading explanation for fundamental physics.” As I noted, from one of the slides he seemed to at least be alluding to one argument against anthropics.

    I have seen several versions of Nima’s talks about this, in person and online. He’s been making the “unless the LHC sees new physics below 1 TeV, the multiverse is the leading explanation, even if we don’t like it” argument consistently for many years. I know that he’s still describing the situation as naturalness not quite yet ruled out, but the discussion is now about how close to death it is, with even David Gross, one of the great SUSY enthusiasts saying the theory may still be alive, but is not kicking. I don’t think Nima or anyone else would now bet a dime on the 13 TeV LHC seeing “natural” new physics, even if they’re saying it isn’t quite ruled out yet.

    In his talks for many years, Nima hasn’t been one to say that the LHC would definitely see natural SUSY. He is quite fond of his own “split SUSY” from 2004 which is an “unnatural” version of SUSY, with superpartners that can be at masses inaccessible to the LHC.

    I’m glad to hear that both Nati and Nima are encouraging others to challenge the current “we don’t like it, but the multiverse is the leading explanation” wisdom. I’d be happier though to hear them challenging the current wisdom themselves.

  36. weichi says:


    Thank you, that is very clear! I suspect you are correct that any deeper explanation for the SM will not be discovered without further experimental input. The more interesting argument is that without experimental evidence we have no good reason to expect a deeper explanation. I don’t think this is right, but I admit that this could certainly just be a pro-reductionist prejudice of mine.

  37. Shantanu says:

    Peter and others,
    FYI: See C. Rovelli’s comments about susy etc at LOOPS 13 meeting

  38. Noah Smith says:


    A depressing possible answer to “Where are we heading?” would be an endless future of multiverse mania, with a short canonical list of ancient, but accepted ideas about fundamental theory (SUSY Guts, string theory, axions) that can never be tested.

    I don’t understand why this is “depressing”. We have theories that are very accurate at predicting everything we can observe at the small scale, given our current level of technology. That sounds like an enormous victory to me.

    Unless you can derive all of physics from math – and there seems to be no reason to assume you can – you’re going to be left with some empirical facts that just seem to come from nowhere. Doesn’t seem too worrying to me.

    And it seems to me that “multiverse mania” and untestable theories are silly, but not necessarily harmful. If there are no unexplained phenomena at the small scale, why not let our theorists indulge in science fiction and metaphysics and math until technology improves and some new puzzles and anomalies pop up? It doesn’t seem likely to actually hurt the progress of science.

    Do you disagree?

  39. Yatima says:


    Unless you can derive all of physics from math – and there seems to be no reason to assume you can – you’re going to be left with some empirical facts that just seem to come from nowhere.

    If the history of physics since at least Copernicus “is no reason to assume that all of physics can be derived from math” and that random ad-hocery like the one found in badly written programs is inherent to the thing …

    … then I don’t know what you need.

    (‘derived from math’ should and must be ‘constrained by an appropriate mathematical description’, as ‘derived’ is rather meaningless, because it assumes that the description exists as prior – it doesn’t, it must be built first)

  40. emile says:

    Noah, you wrote “And it seems to me that “multiverse mania” and untestable theories are silly, but not necessarily harmful. If there are no unexplained phenomena at the small scale, why not let our theorists indulge in science fiction and metaphysics and math until technology improves and some new puzzles and anomalies pop up? It doesn’t seem likely to actually hurt the progress of science.”.

    I think it hurts science when what is really scientific speculation is not clearly labeled as such. The public can get confused about what are our standards in determining what is “true” about the world. It seems there is pressure from some corners to relax those standards.

  41. Peter Woit says:


    “why not let our theorists indulge in science fiction and metaphysics and math until technology improves and some new puzzles and anomalies pop up? It doesn’t seem likely to actually hurt the progress of science.”

    I’ve no problem with the idea of physicists “indulging” in math. Turning to mathematical physics and working on things like better understanding deep questions about the relation of mathematics and QFT might be a good idea absent hints from experiment. Unfortunately physics in recent years has moved in the opposite direction, with physics departments losing interest in mathematical physics. The conventional wisdom now is that the string theory debacle was due to “too much mathematics”, a failure to pay attention to experiment (rather than a failed physical idea).

    As for indulging in science fiction or metaphysics, the problem is that people are not going to do this honestly. If you announce that you’ve given up on real physics and you’re now doing science fiction/metaphysics, billionaires will stop giving you prizes, the NSF will not renew your grant, your colleagues will not hire your students, etc. So, unable to do this honestly and above-board, it gets done dishonestly, with people refusing to admit what they are doing. Having a whole academic field take up dishonesty as a major operational principle isn’t a good idea. The other problem with this is that you drive out of the field people who still think there is progress to me made, even if it is very difficult. Science fiction/metaphysics is easy, and many people find it entertaining. If it becomes a route to professional success, your field is going to be quickly dominated by it, with no motivation for people to keep thinking about hard problems.

  42. Anonyrat says:

    …..when these discrepancies reach 5 sigma, they will get attention from the community.

    Should the community be paying attention to supersymmetry before 5 sigma discrepancies are found with the Standard Model? Since the attention to SUSY exists, it is clear there are strong expectations of where the signal of new physics will come from (SUSY – more likely even without 3 sigma discrepancies, lattice QCD discrepancies – less likely, even with 3 sigma discrepancies). The nature of HEP research is that one has to place such career bets; what I’m curious about, and perhaps those in the know can tell us, how much have people in the community hedged their bets? That may help with understanding where we are headed.

  43. Bob Jones says:

    “Turning to mathematical physics and working on things like better understanding deep questions about the relation of mathematics and QFT might be a good idea absent hints from experiment.”

    The kind of work you describe is practically synonymous with string theory. I guess you’d like to see physics departments hire more string theorists.

  44. Peter Woit says:

    “The kind of work you describe is practically synonymous with string theory”

    If only…

  45. Bob Jones says:

    Do you want to elaborate on what’s wrong with my statement?

  46. Ravi says:

    I am surprised that Prof Seiberg’s talk “Where are we heading” has a basic mistake that should be corrected — Slide 23 says “Strong CP problem … the explanation must involve low-energy physics”. This is the case with axionic solutions — in the sense that axions have only a very small mass. It is not in general true for axionless solutions like the ones I mentioned before. All new particles in these models can be at a high scale so that standard model is the effective low energy theory — however they can predict some of the low energy parameters such as neutron edm (or \theta) and leptonic phases as in the papers I mentioned before.

    The naturalness of smallness of the Higgs mass (compared to Planck mass) probably needs low energy physics. But naturalness of smallness of the strong CP phase does not need low energy physics.


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  48. Another Igor says:

    This discussion reminded me that “the difference between theory and practice is much bigger in practice than in theory”.

  49. Peter Orland says:

    Bob Jones,

    Peter Woit hasn’t answered you yet, but I’ll offer my response, for what it is worth. Here is what is wrong with your statement:

    THE issue in quantum field theory is quark confinement in renormalized asymptotically-free non-Abelian gauge theories. Not supersymmetric N=4 or N=2 theories (though N=1 would help). There is inspiration from (mostly late sixties early seventies) string theory. AdS/QCD models are exactly that – models. They have the same problem that lattice strong-coupled models had in the mid-seventies.

    However the confinement problem will be solved, it’s clear that 15 years of AdS/QCD has done no better than the 3-4 years of lattice strong-coupling expansions (which the lattice people abandoned once Monte-Carlo methods started to work).

    By the way I’ve spoken many times with people who use AdS/QCD to make claims about entropy, glueball spectra or whatever, in New York, Santa Barbara and Copenhagen. None of them claim to do anything at small bare coupling, where the theory is renormalized.

    Maybe some parts of string theory will help. But none of the string theorists I know work on this problem. And they don’t plan to either.

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