String Phenomenology and the Landscape

Science magazine this week has an article about the anthropic string theory landscape controversy, entitled A ‘Landscape” Too Far, by Tom Siegfried. The only theorist quoted as opposing anthropic landscape arguments as not science is David Gross, although experimentalist Burton Richter’s talk at SUSY 2006, and letter to the Times (“I can’t understand why they don’t take up something else — macrame, for example”) are also quoted. Gross says that anthropic explanations are not science but “fun parlor games”, that “they’re not science in the usual sense of making predictions that can be tested to better and better precision over the years.”

Quoted as strongly in favor of the anthropic landscape are Susskind, Linde and Polchinski (there’s an extensive side article about Polchinski’s conversion experience to the anthropic ideology). Sean Carroll and Frank Wilczek promote the idea of the multiverse as a new Copernican revolution, and Clifford Johnson defends anthropic landscape studies with:

It would be nice if we could explore some of those unpalatable ideas just in case that’s the way nature chooses to go.

Clifford has a posting about this on his blog, where he has more to say about this. He seems to have decided to deal with the very uncomfortable position that the evidence and rules of logic put string theorists in by advocating ignoring logic, quoting Moshe Roszali approvingly about the desirability of being able to hold contradictory viewpoints simultaneously.

The Science article does get a very little bit into the crucial question that determines whether landscape studies are science or not: is there experimental evidence that can test the hypothesis? Andrei Linde objects to people who say this subject is not science with:

It’s not an easy job to do, so if you don’t want to do it, then don’t do it. But don’t say it’s not science.

It’s true that the anthropic landscape is incredibly complicated and difficult to do anything with, but I don’t see how that fact is any kind of argument in favor of it being a science. Linde does claim that gravitational waves can be use to “verify anthropic predictions about the nature of spacetime curvature.” I don’t know exactly what that’s about, presumably something to do with possible effects in the CMB due to our universe being born out of a bubble nucleation. If anyone knows of any precise “anthropic prediction” of this kind, I’d be interested to hear it. But, in any case, whether or not you can by observation see whether the universe arose in this way, I don’t think Linde answers at all the objection that the string theory anthropic landscape is inherently unpredictive and thus not legitimate science.

The Science article also includes a heavily overhyped statement about the experimental support for inflation, describing the WMAP results as having “provided strong support for inflation’s predictions.”

For a much more serious discussion of whether the string theory landscape, anthropic or not, is inherently unpredictive, you can watch the video of a talk given yesterday at the KITP by Wati Taylor on String Vacua and the Quest for Predictions. This was the inaugural talk for the semester-long program on string theory phenomenology that will be taking place in Santa Barbara. The blurb for the program is a masterpiece of hype, telling us that string theory has “the potential to predict properties of superpartners that might be found at the Tevatron or LHC and provide new experimental tests and probes of the theory”, something that I don’t think any serious person actually believes these days.

Taylor’s talk was quite remarkable, very explicitly going over exactly how bad the current situation is for efforts to get any prediction at all out of string theory. There was a lot of discussion with the audience, and much nervous laughter. Unfortunately I found some of Gross’s comments hard to hear. Taylor explained that after spending ten years himself working on trying to better understand what string theory is (he worked in string field theory), he doesn’t see any realistic prospects for significant progress on this problem during the next ten years. He listed the basic problems as the lack of a non-perturbative definition in anything but special, non-physical backgrounds, the inability to do even perturbative calculations in the kind of Ramond-Ramond backgrounds that people are using to stabilize moduli, and the lack of any definition of string theory when supersymmetry is broken by a positive CC, and thus the background is deSitter.

Discussing the landscape, he said that there was no evidence for a dynamical principle that would select the vacuum, with no hint at all of how such a thing would work, and that there is no known mechanism that would destabilize the known conjectured constructions of vacua. He goes on to ask “what can we do even if we don’t know what we’re talking about?”

He introduced his own current philosophy, which is that unless some dramatic new breakthrough comes along in string theory (which he didn’t seem optimistic about), the only idea for getting a prediction out of string theory that is still conceivable is to look for strong correlations among standard model parameters in the landscape. He didn’t even bother to mention the fashionable idea of a couple years ago that one could make predictions using statistics of vacua, that idea seems to be completely dead. He noted that as time goes on, people keep finding more and more constructions of vacua, and it now seems clear that there are so many of these that one can’t use their hoped-for discrete nature to make predictions.

According to Taylor, the only possible hope for getting a prediction out of string theory is if one can show that, for all string vacua, there is some strong correlation between values of the low energy field theory parameters. If it turns out that (for example), for all string vacua the number of generations is always 3 when there is an SU(3) factor in the gauge group, then knowing about SU(3) predicts the number of generations. There’s no known reason why anything like this should be true, and it sounds like pure wishful thinking to me, but I guess Taylor’s point of view is that string theorists should be working harder on understanding the details of the landscape in the hope of finding such a thing, because it is the only hope for getting a prediction out of the theory, and thus justifying it as a science.

Taylor acknowledges that the state of affairs is that one can’t do at all realistic calculations along these lines, but he has been doing some unrealistic ones with Michael Douglas. They’ve been looking for correlations between the size of the gauge group and the number of chiral generations in intersecting brane models. These are quite unrealistic, with no supersymmetry breaking and unstabilized moduli. In any case, their result is negative: even in this simplified, unrealistic context, they find no sizable correlations.

Given this start, it will be interesting to see how the participants manage to get through the semester without getting so depressed about prospects for string theory that they abandon it and go on to something else. One new feature of the program is that a wiki has been set up to allow for communication and discussion between the participants.

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43 Responses to String Phenomenology and the Landscape

  1. anon says:

    Peter, you are a moron with the intellect of an amoeba. The Anthropic Principle does make some sharp predictions.

    Okay, I admit, the most general statement is a tad of an exaggeration:
    “Why should we believe the universe is anthropic? Because if it weren’t anthropic, we would not exist”.

    But consider a slightly less general version:
    “Why do String Theorist believe the universe is anthropic? Because if it weren’t anthropic, they would not exist.”

  2. Kea says:

    …and the lack of any definition of string theory when supersymmetry is broken by a positive CC, and thus the background is deSitter…

    de Sitter…which is, er, cough, in agreement with Riofrio’s analysis of, for instance, the type IA supernovae data, and also with a simple interpretation of certain interesting background independent QG models for which we understand the derivation of classical gravity.

  3. Kea says:

    How many nails need to go into this freaking coffin?

  4. MathPhys says:

    Look on the bright side, Peter. Statistical analysis of the Landscape prepares PhD students for a career on Wall St.

  5. Bob McNees says:

    de Sitter…which is, er, cough, in agreement with Riofrio’s analysis of, for instance, the type IA supernovae data, and also with a simple interpretation of certain interesting background independent QG models for which we understand the derivation of classical gravity.

    Can you please provide a reference to a “background independent QG model” for which

    A) we understand the derivation of classical gravity, by which I assume you mean the existence of a semiclassical limit

    and

    B) which leads to the appearance of de Sitter space?

    I honestly don’t know what’s being referred to here, which is why I’m asking.

  6. Kea says:

    This paper is a good gateway into the literature on BF theory and its variants, in the context of de Sitter gravity.

  7. Anon says:

    I think Kea is talking about the Kodama State.

    You can read all about why that’s nonsense in http://arxiv.org/abs/gr-qc/0306083 .

    But perhaps she is talking about something else. Kea?

  8. Rickkkkkkk says:

    Man oh man, I’m so lucky to have spent almost no time at all to be this ignorant, if I had gone to school for 10 years or spent my career just to know the same amount of nothing at all, I’d be in even worse shape

  9. Lee Smolin says:

    Unfortunately it appers there is still misinformation circulating about the Kodama state in the Ashtekar formulation, which, not for the first time, has to be answered here. This is a subtle issue, still unresolved, which people who have not studied the actual literature often get wrong because their reasoning is based on incorrect analogies with Yang-Mills theory. There are also interesting recent developments.

    -First, there can be no objection to its use as a semiclassical state as it IS the WKB state for (A)dS, as described in hep-th/0209079 and papers referenced there. This is the first way in which the situation in Yang-Mills and gravity are not analogous.

    -There is an open issue of whether the Kodama state in the Ashtekar representation is normalizable as an exact wavefunction in the physical inner product. (One reason is that it is only an exacxt solution in one ordering of the Hamiltonian constraint, whicih may not be the physically correct ordering. If so, there are corrections which have not been so far computed to the exact wavefunctional. Witten’s paper is related to this, but does not resolve it, as it concerns a different theory-Yang-Mills. Witten’s objection does not apply directly to the Ashtekar formulation for reasons discussed in hep-th/030114 and it also does not apply to its use in expansions around BF theory I mention below developed in hep-th/0501191.

    -The issue is resolved in cosmological reductions in which the vacuum energy is related to a physical degree of freedom so one can make a wavepacket in the cosmological constant. This resolves the problem in that context, as shown with Alexander and Malecki in hep-th/0309045.

    -The question can be investigated in the linearized case and we did so with Freidel in hep-th/0310224. The Euclidean linearized Kodama state is delta functional normalizable. The Lorentzian one has unstable modes. These may be unphysical or they may just reflect an instability of deSitter spacetime.

    -The Kodama state also appears in a different, recently introduced approach, in which GR is constructed by an expanding around an SO(5) BF theory, in hep-th/0501191 .That BF theory has a single bulk solution classically, which is (A)dS and a single bulk quantum state, which is related to Kodama. This may resolve the old issues about the Kodama state because it is a sensible state of BF (Indeed it’s the only bulk state of BF theory, work on this is in progress.

    -There is also a recent proposal by Randono that extends the Kodama state to a space of physical states, which he argues are normalizable. See gr-qc/0504010 and papers in preparation by him about this.

    Thanks,

    Lee

  10. Kea says:

    I am not talking about the Kodama state. Note the emphasis.

  11. Kea says:

    Sorry, Lee, I just saw your post.

  12. Sean Carroll says:

    Really? I’m promoting the idea of the multiverse as a new Copernican revolution? That’s news to me (although I don’t have a subscription, so I can’t read the article). Of course, I have been known to say that we have no reason to believe that the universe we don’t see looks just like the universe we do see, out the edges of infinity — but that’s pretty trivially true, I hope nobody would disagree with it. If that’s a “Copernican Revolution,” then so be it.

  13. Chris Oakley says:

    Look on the bright side, Peter. Statistical analysis of the Landscape prepares PhD students for a career on Wall St.

    Not really. Wall Street interviewers will in general find an applicant with a Ph.D. in a highly speculative subject less appealing than one with a Ph.D. in a hard science or mathematics.

  14. MathPhys says:

    But future stringy PhD’s will know a lot more about data analysis, inference, sampling theory, etc, than PhD’s who worked on, let’s say, lattice gauge theory.

  15. woit says:

    Hi Sean, here’s part of the section quoting you and Wilczek:

    But, he says, the idea that the known universe is only a small part of something much bigger should not come as so much of a schock. “Again and again in the history of cosmology, we’ve been shown that the little pieces we’ve been looking at are not the whole story,” Carroll says. At the time of the Copernican revolution, the supposed whole universe was just the solar system. But the sun eventually was revealed to be just one star in a vast galaxy, and in the 20th century, that galaxy became just one speck in space among billions and billions of others.

    As Wilczek observes, the string landscape and the multiverse merely suggest that the same story is happening again. “This is going one step further,” he says. “We should be used to it by now.”

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  17. Juan R. says:

    Sean Carroll said:

    “Of course, I have been known to say that we have no reason to believe that the universe we don’t see looks just like the universe we do see, out the edges of infinity — but that’s pretty trivially true, I hope nobody would disagree with it. If that’s a “Copernican Revolution,” then so be it.”

    Well, may be “pretty trivially true” also that the universe we do not see belong to metaphysics.

    Even there exist doubts that the study of the part of universe we can see (so-called observable universe) can be considered Science since not all of scientific method applies therein; e.g. crucial distinction between observation and experimentation.

    String theorists, certain loop theorists and rest of fans would be valiant by recognizing that Landscape and those “novel” ideas (idea of a multiverse is not characteristics of 20th century, of course) and “revolutions” are just pure nonsense (of interest for philosophers and film makers of course) from a purely scientific point of view.

    In the case of string theory, the anthropic attitude is just the proof that string theory is a fiasco as scientific discipline (how was pointed by several Nobel laureates: e.g. P.W. Anderson)

    Juan R.

    Center for CANONICAL |SCIENCE)

  18. Sean Carroll says:

    Okay, I’ll happily stand by that quoted statement. I don’t really think it’s controversial.

  19. Matthew says:


    But future stringy PhD’s will know a lot more about data analysis, inference, sampling theory, etc, than PhD’s who worked on, let’s say, lattice gauge theory.

    Lattice gauge theory teaches you lots of those sorts of skills. Given that the primary tool is monte-carlo simulation. It’s pretty good prep for “Wall street”

  20. Okay, I’ll happily stand by that quoted statement. I don’t really think it’s controversial.

    You might not think so, but the reality is, you guys are starting to sound like the guy from timecube.com. This isn’t ad hominim. You really are.

    When Copernicus proposed the heliocentric model he did so only after years and years of careful observation and data aquisition. Kepler law’s proposed his laws only after years of analysis of Brahe’s data, which itself took decades to gather. The Cophenhagen interpretation was not simply thrown together from mathematical equations. It too was only reached after decades of experimental data that supported it. And finally the standard model was only proposed and accepted after countless meticulous and detailed experiments gathered vast amounts of cold hard data.

    In light of this, when people deriving results from mathematical equations, using pertubation theory I might add, start declaring that a multiverse landscape exists and start making anthropic arguments about “why we are here”, and all with no data of any kind whatsoever, it means you sound like the guy at timecube.com.

    Science is the experiment. If you haven’t got an experiment, you’ve just got a few mathematical symbols on paper. I’m a mathematician, but I know that without experimental confirmation, my equations and relations, no matter how beautiful, are just that. Equations and relations of mathematical constructs. And in light of this, without experiment, I would not be inclinded to go around making predictions about multiverses, landscapes or timecubes.

    Get some data, then get back to us.

  21. D R Lunsford says:

    I can’t help but see parallels with this nonsense and the twin monsters of postmodernism and neoconservatism. One should read John Dean’s book “Conservatives without Conscience” – the arguments can be taken over directly and applied to “leading” (or should I say “fuehring”) academics and their relation to science, rather than politics. The key point is the utter compulsion, among a large number of people, to follow – to be a follower of somebody, anybody who can assuage their fear. I consider string theory, the multiverse, etc. to be profoundly conservative ideas in a bizarre sense – because they seem to hearken back to an innocent time when Aristotle and the Pope decided how the world really worked. (Comparing the multiverse to the Copernican worldview is not only utter nonsense, it is just plain contemptible.)

    -drl

  22. Who says:

    “Again and again in the history of cosmology, we’ve been shown that the little pieces we’ve been looking at are not the whole story,” Carroll says.

    [there might be dragons in piece next to ours.}

    As Wilczek observes, the string landscape and the multiverse merely suggest that the same story is happening again. “This is going one step further,” he says. “We should be used to it by now.”

    [sea serpents also are a possibility]

  23. nigel cook says:

    “The Copenhagen interpretation was not simply thrown together from mathematical equations. It too was only reached after decades of experimental data that supported it. And finally the standard model was only proposed and accepted after countless meticulous and detailed experiments gathered vast amounts of cold hard data.” – Obsessive Maths Freak

    But the Copenhagen interpretation is an ad hoc philosophy not a mathematical prediction technique, and it doesn’t make unique predictions that have been tested, so you can’t lump it with the Standard Model that does make predictions, has been tested.

    There is an industry within physics run by full time science fiction writers who do mathematical philosophy of physics part time, and after about 1916 that was what Bohr did. OK, he did some useful applied nuclear physics theory such as determining u235 is the fssioning nuclide in natural uranium, but he just sprouted content-less, ad hoc, abjectly speculative philosophy when writing about the nature of reality and the future of theoretical physics. He claimed the Copenhagen Interpretation in 1927 solved everything completely for all time by separating and so outlawing any progress understanding of how classical and quantum electrodynamics can be reconciled:

    ‘… the view of the status of quantum mechanics which Bohr and Heisenberg defended – was, quite simply, that quantum mechanics was the last, the final, the never-to-be-surpassed revolution in physics … physics has reached the end of the road.’ – Sir Karl Popper, Quantum Theory and the Schism in Physics, Rowman and Littlefield, NJ, 1982, p6.

    ‘… the Heisenberg formulae can be most naturally interpreted as statistical scatter relations [between virtual particles in the quantum foam vacuum and real electrons, etc.], as I proposed [in the 1934 book ‘The Logic of Scientific Discovery’]. … There is, therefore, no reason whatever to accept either Heisenberg’s or Bohr’s subjectivist interpretation …’ – Sir Karl R. Popper, Objective Knowledge, Oxford University Press, 1979, p. 303.

  24. andy says:

    When I was at Oxford Rudi Peierls told me [words perhaps slightly disremembered] “we theorists need experimental results. Otherwise we’re only speculating.”

    There was more, over coffee and chocolate cake at Brown’s, but that’s the gist.

    Pity that this lesson has been forgotten.

    A.

  25. Chris W. says:

    Andy,

    Indeed. Unlike Rudolph Peierls, some prominent (and not so prominent) members of the last two generations of theorists don’t really give a shit. Knowing theory, and producing more theory for their students to master, is all they seem to care about. It’s kind of like a defense contractor who produces some massive system that doesn’t work, and then gets the government to write yet another contract to fix it, and so on…

    Analogies with out-of-control software development projects seem most apposite.

    There is one kind of theoretical activity that is absolutely essential, with or without experimental results, and that is careful and penetrating examination of problem formulations. To the extent that’s happening at all these days, it’s happening at the margins, and is being mostly ignored as mere “philosophy”.

    (Pardon the bile in these remarks. I’m a bit cranky right now.)

  26. Who says:

    (Pardon the bile in these remarks. I’m a bit cranky right now.)
    You didn’t sound cranky or bilious, Chris: the preceding post sounded reasonable to me—-comparisons seemed apt, fair and so on.

    we wouldn’t necessarily agree on other issues but what you say here strikes me as uncontroversial. “out of control software development project” says it well.

  27. Kea says:

    Speaking of nails, there is also the calculation of lepton masses, as discussed on this thread.

  28. nigel cook says:

    Chris, that Time mag article concludes with Sean Carroll stating:

    “It’s true that nobody has any good idea of how to test string theory, but who’s to say someone won’t wake up tomorrow morning and think of one? The reason so many people keep working on it is that, whatever its flaws, the theory is still more promising than any other approach we have.”

    Similarly, if you flog a dead horse enough, it may decide to spring to life. I can’t believe the amount of shit tha comes from theories held together by imaginary branes and bits of string. Call that a theory?

  29. Chris Oakley says:

    Statement about dead theory generator in Visual Basic:

    Function StatementAboutDeadTheory(ByVal theory As String) As String

    StatementAboutDeadTheory = “It’s true that nobody has any good idea of how to test ” & theory & “, but who’s to say someone won’t wake up tomorrow morning and think of one? The reason so many people keep working on it is that, whatever its flaws, the theory is still more promising than any other approach we have.”

    End Function

  30. Chris Oakley says:

    … and here is the same thing in APL

    ╛≥─╜╝♣┠╞╟♥╠╡∏┴╢╣∑╤▒◊♪−╥▓○

  31. D R Lunsford says:

    CO – I just spit coffee all over my machine, damn you you Englishman! Come back and I shall taunt you a second time! (Did someone say “a second time”?)

    Funniest comment ever on NEW.

    -drl

  32. L. Riofrio says:

    Kea and Chris, right on. Einstein said that the definition of insanity is trying something repeatedly and expecting a different result. We are seeing growing acceptance of approaches (LQG, Kodama states, and my little Type Ia contribution) with testable Results to satisfy MathFreak. The Copernican revolution was preceded by cosmologies held together by epicycles and imaginary energies. This is a very exciting time to be in science.

  33. Chris Oakley says:

    Hi Danny,

    I do my best. Resorting to cheap humour is, as you will have seen, my usual strategy when I have nothing useful to say on the topic. The APL gibberish, though, comes from the heart having had to decode the incomprehensible scripts that the New York office used to write for valuing exotic interest-rate derivatives when I worked for UBS.

  34. John Rennie says:

    You seem very negative about Wati Taylor’s talk, but it seems to me to be a valid program to pursue. If no correlations can be found then this is worth knowing, and worth the effort.

  35. Rickkkk says:

    Quote “It’s true that nobody has any good idea of how to test string theory, but who’s to say someone won’t wake up tomorrow morning and think of one? The reason so many people keep working on it is that, whatever its flaws, the theory is still more promising than any other approach we have.”

    I’m so sick of seeing this type of logic that I believe anti-nausea medication will soon be in order. Sean happens to be the one saying it here, but my anger isn’t directed toward him. It’s more toward the “only game in town” people.

    If the only game in town is crap, and the -best- explanation is crap, so what? Spending your time on crap because it’s the best crap there is doesn’t remove the fact that you’re working on crap.

    I’d propose that it’s better to be doing nothing, than wasting one’s time working feverishly on something wrong or not even wrong.

    When I see this “if you’ve got a better explanation let’s see it” rebuttal it seems to be begging for the answer “ANY explanation is better” especially a clearly wrong one. A vacuous, unpredictive body of complexity is clearly much worse than ANY other explanation. The aether, the book of Genesis, etc. are all better explanations than string theory….and this is the beauty of this blog….because at least they’re wrong, which is much more than the yarners have going

  36. Rickkkk says:

    Addenda, I think it’s best summed by this analogy I’ve thought of.

    Even THE MOST complex and contrived search for food in an empty room is a bad thing. No matter how elegant or theatric or difficult the methods employed, even giving up and starving from the get-go is a better approach. Leaving the room and searching elsewhere is of course the brightest thing to do.

    So “what’s your better explanation?” It’d be almost impossible to find a worse one, even the spaghetti monster is better.

  37. Peter Woit says:

    John,

    I think Taylor gives a reasonably accurate description of the state of affairs as regards the possibility of ever predicting anything using string theory. He argues that the only hope at this point is to find this kind of correlations, but acknowledges that realistic calculations are impossible (you can only calculate in special cases, in an unrealistic approximation, and are trying to say something about all string theory vacua when you only know about a set of measure zero of them).

    If the only hope for your theory having even a very small amount of predictivity is a very unlikely one, and you have no way of ever even checking this very unlikely possibility, why don’t you give up and do something else?

  38. Who says:

    Tom Siegfried’s Science magazine article “A Landscape Too Far?” has been made available at the SUSY 06 conference site
    [url]http://susy06.physics.uci.edu/press/susy06_science_naturalness.pdf[/url]

    or go here and select it from the “susy06 on the web” offerings
    http://susy06.physics.uci.edu/proceedings.html
    which include a recent posting from N.E.W.

  39. Michael Edwards says:

    Trying to calculate things in string theory is like looking for your keys under the streetlamp in front of your house, even though you know perfectly well you dropped them on the next block where it’s pitch dark. This is not always as stupid as it sounds. If you are accustomed to finding things exclusively by sight, then you need to train your sense of touch before you stand any chance of finding your keys by feeling around where you dropped them. Perhaps you should spend some time feeling around under the light so that you can distinguish an actual dropped object from the surrounding landscape.

    QFT as it stands today is a keychain dropped in the dark – a morass of heuristic prescriptions developed one by one to relate a string of symbols we call a “model” to calculations that match the experiments we know how to set up. Most of the major advances in the state of the theory have simplified the model at the expense of an added heuristic. (The examples I have in mind, roughly in historical order: Lorentz invariance, canonical quantization, the spin-statistics theorem, adiabatic coupling at infinity, Wick rotation, Ward identities, dimensional regularization, CPT invariance, gauge invariance, renormalizability, BRST invariance. Some of these are rigorous mathematics in their own right, but in the QFT context they function as heuristics for the selection of acceptable models and their elaboration into computable integrals.)

    It does not seem to be widely recognized that the BRST _transformation_ is a different sort of theoretical advance. Viewed from a geometric perspective, it relates several of these heuristics (canonical quantization, Ward identities, gauge invariance, renormalizability, BRST invariance) to one another, and connects all of them to the intrinsic geometry of fiber bundles. It comes tantalizingly close to explaining why the entire framework of “second quantization” works as a method of perturbative expansion, almost irrespective of the chosen model — as long as that model is expressible as a BRST invariant Lagrangian density. And more concretely, it explains why the Faddeev-Popov gauge fixing procedure results in (some) anomaly-free QCD calculations.

    Unfortunately, this leaves quite a bit of unfinished business: the apparent flatness and Minkowski signature of the metric, the presence of Dirac fermions and the nature of the Grassmann algebra they inhabit, the Wick rotation prescription for propagators, the nature and empirical values of dimensionless coupling constants at Planck scale, and the origin of mass and its relationship to broken C, P, and T symmetries. This last is the only one that seems to be remotely within the reach of experiment. But the current state of QFT is that these bits of “unfinished business” are every bit as much part of the _model_ as the mix of gauge groups and representations.

    To demand under such circumstances that mathematical physicists focus exclusively on making falsifiable predictions is to misunderstand the role of theory in scientific advance. It so happens that the last couple of theoretical advances in QFT showed up in phenomenology largely as relationships between the measured values of coupling constants and angles. The next one probably will not; in fact, it may not show up in phenomenology at all, if its principal contribution is to relate (say) Wick rotation to the fact that only left-handed fermions carry representations of the electroweak SU(2).

    Nobel prizes may be reserved for “visible” progress (if Nature cooperates on schedule), but it is only fair to say that work on the foundations is science too. It is rarely realized except in hindsight that this sort of “non-falsifiable” advance can reshape the landscape of plausible models, ruling some out and suggesting others that could not have arisen under the previous framework of heuristics. Quantitative predictions may have to await the next theoretical advance after that – say, obtaining three families of SU(3) triplets and singlets as an effective theory for one SL(3,R) triplet+singlet, obtained in turn as the centralizer of the discrete time reversal symmetry within GL(4,R).

    What does this have to do with string theory, you ask? There is no reason whatsoever to think that the universe we live in has a compact S^1 dimension, any more than there is a reason to think that magnets are made of little arrows with their tails nailed to a lattice and springs between their tips. But many important phenomena general to phase transitions in statistical mechanics are more tractable in the Ising model than elsewhere, shedding light on which approximation techniques and other heuristics will be needed to obtain valid results for more realistic models. As I understand it, string theory began as an effort to train mathematical physicists’ cohomological sense of touch, in the light of the (relatively) tractable mathematics surrounding the streetlamp of diffeomorphisms on S^1.

    Even ten years ago, one could still reasonably hope for similar insight into QFT from studying the Nambu string action. Perhaps this hope is now extinguished in many observers, and in some ostensible practitioners it seems to have been replaced by the bravado born of despair. Yet even if string theory has produced little that I would call insight, some string theorists have – or at least some of those known to the public almost exclusively as string theorists. Obviously I have in mind Ed Witten here, one or two of whose contributions I understand well enough to call a genuine insight into what a keychain in the dark would feel like. A working physicist could probably name others.

    Doubtless the “community” of string theorists includes a fair number of charlatans, thugs, and complacent riders on the academic gravy train. Perhaps the proportion of dubious characters is even higher than elsewhere in this imperfect world of ours. If so, and if the careerists crowd out or drive out those who march to a different drummer, and if you care about whether physics transcends the standard model in our lifetimes, then you ought to be outraged. Not because string theory can’t predict the mass of the Higgs boson, but because it’s time to admit that the landscape under this particular streetlight isn’t telling us much about what keychains do and don’t feel like.

    Cheers,
    – Michael

  40. John Rennie says:

    Peter,

    It seems to me that the real criticisms of String Theory come down to it’s unfair(?) level of funding. If money were no issue few of us would worry what the String Theorists got up to in their corner. Suppose you’re the one holding the purse strings. Surely you’d put some of the money into String related research (though probably not at the current levels) and you’d need to decide where to focus the effort. Here you have Wati Taylor pursuing a program to decide in concrete terms whether further investment in landscape research is justified. That seems to me an excellent idea and one that I’d pay for, even if I suspect I already know the answer. Isn’t this sort of research badly needed in String Theory?

    It would be interesting to see if any other areas of ST research could be addressed in a similar way i.e. rather than pursue details take a step back and ask some basic questions about the feasibility of the approach. We industrial scientists are pretty good at spotting where research programs are going to cost our shareholders too much, even though they might ultimately be successful. This doesn’t seem to happen in academia. Of course even in industry we fund some blue sky work because it doesn’t cost too much and occasionally something intersting happens.

    John Rennie

  41. Peter Woit says:

    John,

    The problem with string theory is not specifically the level of government research funding. It’s more that a young researcher interested in mathematical approaches to particle theory basically will find it extremely difficult to get a job and have a research career unless they decide to do string theory. This has more to do with the hiring decisions being made by theory groups than grant funding.

    Taylor is not pursuing a program designed to decide where to focus effort. He’s put forward an argument that shows that what other people are doing can’t work, that the only remaining possibility he can think of doesn’t work either, but he intends to continue with it anyway. I don’t understand why this should be encouraged.

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