String Theory and the Scientific Method

There’s a new philosophy of science book out, Richard Dawid’s String Theory and the Scientific Method (available online here if your institution is paying Cambridge University Press appropriately or if you have a credit card). It comes with endorsements from string theorists David Gross and John Schwarz, with Schwarz writing:

Richard Dawid argues that string theory plays a novel role in the scientific process that has been neglected by philosophers of science. I believe that this book is a valuable contribution to the philosophy of science, which should interest practicing scientists as well as those who are more interested in the methodology of science.

Dawid is a particle theorist turned philosopher, and as you might guess from the endorsement, he approaches string theory from an enthusiast’s point of view. The fundamental question addressed is how one can reconcile string theory’s failure in terms of conventional methodology of science with its continuing hold on at least part of the physics community. He explains how the book came about as follows:

This book has been on my mind ever since I left physics and turned to philosophy in the year 2000. A core motivation for making that step at the time was my feeling that something philosophically interesting was going on in fundamental physics but remained largely unappreciated by the world outside the departments of theoretical physics – and underappreciated even within. Twelve years of grappling with the specification of that general idea have considerably changed my perspective on the issue but left the overall idea intact. This book is the attempt to present it in a coherent form.

Reading the book in an odd way reminded me of my recent experience reading Gordon Kane’s reissued book on supersymmetry and string theory written in 2000, especially Witten’s essentially unchanged introduction. The degree of self-confidence of string theorists at that time was much different than now: AdS/CFT was a new idea, with a solution to QCD on its way, SUSY a sure thing at the LHC if not at the Tevatron or LEP, and at least half of the new jobs in the field going to string theorists. No landscape or multiverse pseudo-science was around to sow dissension in the ranks. No failure of SUSY to show up anywhere. No discouraging numbers like those for the last two years which show, in the US at least, 9% of jobs going to string theorists, with more jobs going to lattice gauge theorists in 2011 than to string theorists. And of course, a uniformly positive press, with no naysayers like Smolin and Woit causing trouble.

In Dawid’s description, string theorists are still partying like it’s 1999:

String theory has attained a pivotal role in fundamental physics and has been treated as a well-established and authoritative theory for quite some time by the community of string theorists and by physicists in related fields. As we have described above, large parts of fundamental physics are influenced by string theoretical analysis. The string community is one of the largest communities in all of theoretical physics and for many years has produced the majority of the field’s top-cited papers. Moreover, many string theorists express a remarkably strong trust in their theory’s viability.

For the actual list of last year’s top-cited papers in HEP, see here, and “remarkably strong trust in their theory’s viability” seems to me more 2000 than 2013. He does go on to mention skeptics, but to him a majority of the field is behind string theory, with the skeptics only coming from outside particle theory:

On one side of the divide stand most of those physicists who work on string physics and in fields like inflationary cosmology or high energy particle physics model building, which are strongly influenced by string physics. That group represents a slight majority of physicists in theoretical high energy physics today. Based on an internal assessment of string theory and the history of its development, they are convinced that string theory constitutes a crucial step towards a better and more genuine understanding of the world we observe. On the other side stand many theoretical physicists of other fields, most experimental physicists and most philosophers of physics. They consider string theory a vastly overrated speculation.

Dawid’s main thesis is that string theory critics fail to recognize that a new paradigm of scientific methodology is now needed:

String theory thus should not be taken to announce an end of science but rather to represent a new phase of scientific progress. In this new phase, progress in fundamental physics is no longer carried by a sequence of limited, internally fully developed theories, but rather by the discovery of new aspects of one overall theoretical scheme whose general
characteristics identify it as a candidate for a final theory, yet whose enormous complexity bars any hope of a full understanding in the foreseeable future.

What is the reason you should accept this final theory that no one can understand? Obviously the lack of any empirical support is a problem, so Dawid turns his attention to a detailed study of the subject of “non-empirical theory assessment”: how do you assess scientific progress absent connection to experiment? This is a real and serious problem, which Dawid studies in detail, although from a point of view which just naively accepts all arguments made by string theorists. He considers three main reasons for studying a theory with no empirical support:

  • The No Alternatives Argument. This is the best argument for string theory: there aren’t a lot of viable unified theories out there. Of course, the way science progresses is that there always are unsuccessful ideas with no good alternatives, until the day someone come up with a better idea.
  • The Unexpected Explanatory Coherence Argument. This is the idea that if a theory holds together better after you start studying it and understand it better, that’s a good thing. Dawid repeats uncritically claims of some string theorists that this is the case for string theory. I think you could make an equally good case for string theory unification becoming a more and more dubious idea as it became better understood (see, the Landscape).
  • The Meta-Inductive Argument. Here the idea is that if a theoretical research program worked before, so will a similar later one. Dawid claims that the string theory research program is just like the research program that led to the Standard Model:

    Given the entirely theoretical motives for its creation, the lack of satisfactory alternatives and the emergence of unexpected explanatory inter-connections, the standard model can be called a direct precursor of string theory.

    Honestly, this I just find bizarre, and have no idea what he’s talking about, with the history of the Standard Model and the history of string theory two radically different subjects.

In one crucial respect, this book is very different though than Kane’s. Kane is well aware that the idea of an inherently experimentally untestable theory is something he can’t sell to his colleagues and the public, so he devotes his book and its argument for string theory to supposed experimental tests. More savvy string theorists than Kane though are seeing the writing on the wall: no SUSY at 8 TeV means almost surely no SUSY at 13 TeV, and thus no prospects for experimental evidence for SUSY during any of our lifetimes. To prop up the string theory unification program past SUSY null results from the 13 TeV LHC in 2016 is going to require relying on Dawid’s “non-empirical theory assessment” and convincing people that string theory and the multiverse represent a new paradigm for how to pursue fundamental science. This book will be welcomed by those pursuing such a goal.

Update: For a different take on the book you can see Lubos Motl’s review (as you might expect, he’s a big fan). The case of the most prominent string theorist blogger reminds me of one of the funnier things in the Dawid book that I forgot to mention, this footnote:

It should be emphasized that physicists on both sides of the divide are aware of the slightly precarious character of the “non-physical” arguments deployed in the debate. Lee Smolin has applied the concept of groupthink to the community of string physicists (which, incidentally, seems a quite accurate representation of what many critics of string physics do think about string physicists) but is careful not to present it as a core argument. String theorists, when entering a discussion with their critics (see e.g. Polchinski in his reasoning against Smolin), try to keep the debate at an entirely physical level.

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47 Responses to String Theory and the Scientific Method

  1. Bill says:

    I just went to a conference attended by a mix of mathematician and physicists. Since I started reading this blog (recently) I was curious to ask a few physicists what they think about string theory. My motivation was pretty simple: I just find it a bit doubtful that one guy arguing against so many of the top physicists in modern times can be right. But to my surprise I consistently got nearly the same answer: “it is clear that predictions of string theory have no chance to ever be observed experimentally”. It is truly bizarre to me that such as state of affairs is possible in physics. And, by the way, none of the people I talked to knew who Peter Woit is.

  2. Bob Jones says:

    I think Dawid is right about string theory being treated as a well-established and authoritative theory.

  3. Cliff says:

    These posts are so predictable and shallow. You just state your conclusions as facts, and then act shocked when someone “fails” to “reason” to your answers, when they obviously do not agree with your premises at all.

    Nobody is forcing you, or anyone, to “accept” string theory, Peter. It is a project that a lot of brilliant people choose to work on out of their own free will, for reasons that are become pretty clear to someone with the right preparation who bothers to investigate it. There is no sane reason to complain about the top people in theoretical physics doing what they obviously see as the most productive use of their talent. Nobody is suggesting that string theory be presented as fact to be “accepted” – that’s just a ridiculous straw man – it should be presented honestly for what it is: an extremely promising and insightful yet unproven framework.

    If a superior idea ever emerges that is demonstrably more promising to address the big mysteries of physics, then the attention and status will shift accordingly. In the meantime trying to maximally tear down and obfuscate all the promising properties and insights that motivate the study of string theory does nothing to help advance either the public understanding or science.

  4. chris says:

    Cliff,

    it’s the intrinsic notion of “top” you have that needs to be dragged out of the closet and publicly debated. In the past it meant those who came forward with predictions that were later verified by experiment. i still like this definition best. You obviously don’t.

  5. Roger says:

    This must be the only field that justifies itself by bragging about how smart its leaders are, and claiming to have the only theory that attempts to have a theory of everything while actually explaining nothing.

  6. phmer says:

    As I see no reason why the Universe would not be infinitely complex, isn’t the idea of “theory of everything” a far-away dream? Is not the investment of resources into such a business an extremely risky gamble? It is my impression that Nature suprised us over and over again during the history of high-energy physics, each time with new structural layers, new forces, unexpected mixings, etc., which could not be predicted before they were actually found and measured, and which revealed that some successful models were in fact low-energy approximations of more advanced (but not necessarily simpler) constructs. Examples: Who could have imagined such a thing as the weak interaction before the observation of beta decay? Who could have devised a theory of nuclear interactions when nuclei were not even discovered? Who could have described QCD before the interior of nuclei were probed? Now we have 15 more orders of magnitude in energy to explore until we reach the Planck scale, surely there can be quite a few unforeseen phenomena with little to do with our current theories to be revealed out there… Science without experimental guidance and evidence, to me that sounds more like faith.

  7. Jeff Moreland says:

    Peter,
    I’m curious why you think that no SUSY at 8 TeV means almost surely no SUSY at 13 TeV. 5 TEV seems a big gap; is there some reason I’m missing why there won’t be any evidence for SUSY in this range?

  8. Peter Woit says:

    Jeff Moreland,

    By the standard arguments for SUSY, it was supposed to appear at energy scales of 100 GeV. Roughly, the Tevatron probed energy scales up to a couple hundred GeV, so one expected SUSY to be there, but the factor of 4 in going to the 8 TeV LHC should definitely have done the trick. There’s just no argument for why SUSY should appear if one goes up by an extra factor of 13/8.

    This is kind of off-topic though, the point of the book is to give a justification for string theory research assuming no relevant experimental data.

  9. Bernhard says:

    I did not read the book yet, but judging from the same old arguments you’ve listed, what is surprising to me is that this is still material for a new book.

  10. Joel Rice says:

    It would be a lot easier if they would just stop calling it a theory. At least electroweak includes QED. If they can not similarly include the standard model, then in what useful sense can one refer to it as a theory ? I have no problem with speculation. Just don’t call it a theory.

  11. Thomas says:

    this fundamental belief in string theory is nothing more than a fundamental belief in a religion. thank you, and good night science

  12. Peter Woit says:

    Joel Rice,

    In string theory, the argument is that you can include the Standard Model. The problem is that if so you can probably include just about anything else, getting a theory of everything, just not in a good way. It’s definitely a theory, but has turned out to be an empty one.

  13. francis says:

    Peter,
    AFAIK in ST, all they can do is getting something that looks like the SM, but not the right SM (or any extension of it).

  14. Peter Woit says:

    francis,

    I think a more accurate description of the situation is that you can’t do reliable calculations in ANY realistic string theory model (e.g. one that gets the CC and basic SM structures right). There’s no known reason though why, if you could do such calculations, you couldn’t get the SM (and just about anything else…)

    All: please, if you have something to say about the book, that’s great, if you just want to discuss string theory in general, or rant pro or con, please resist temptation.

  15. Bob Jones says:

    “this fundamental belief in string theory is nothing more than a fundamental belief in a religion. thank you, and good night science”

    Every time Peter writes a blog post on string theory, we see ridiculous comments claiming that string theory is a religion. It’s fine to criticize string theory, but I think you first have to understand why so many people see it as a promising direction for research. There are some very good reasons for studying this theory. For example, string theory gives the right answer when used to calculate black hole entropy, and it has some general features that are expected to hold in any successful quantum theory of gravity. I don’t see how you can criticize string theory without at least addressing these points, and I’m sure they must have been discussed in Dawid’s book…

  16. Peter Woit says:

    Bob Jones,

    I agree that the “string theory is a religion” arguments aren’t either accurate or helpful to understand what is going on. To all, enough of this kind of thing.

    Dawid’s book doesn’t pretend to be a serious evaluation of the arguments pro and con about string theory. Basically he just repeats uncritically arguments used by string theorists, with his interest not whether they make sense or whether there’s a good counter-argument, but just what sort of general framework for “non-empirical” arguments they fit into.

  17. Bob Jones says:

    Peter,

    I haven’t read Dawid’s book, so I don’t know exactly what he says. But the strongest reasons for studying string theory are scientific and mathematical reasons, not sociological ones. I think it’s unfortunate that so many laypeople misunderstand this point.

  18. Peter Woit says:

    Bob Jones,

    The point is that some of the main reasons that people keep working on and promoting string unification schemes are not scientific, but sociological. To take an extreme example, Kane’s recent “update” of his book violates standard scientific norms of how you are supposed to evaluate scientific theories, and what he is doing I think can only be understood in sociological (or psychological) terms.

    What I think Dawid completely misses in his book is that a large part of the story of the scientific community’s assessment of string theory unification is a completely conventional one: the idea didn’t work out, but a lot of the people with their time and reputations invested in it deal with this by refusing to admit it. This doesn’t require any new methodology of science to understand, it’s a well-known phenomenon.

  19. Koray says:

    I don’t have access to the book. I came here for the philosophy of science arguments presented by the book.

    Does Dawid present any prior examples for the No Alternatives argument? Did any other branch of science struggle for decades with a very complex theory with no empirical support because there was nothing better? Does he recommend that they do so now since this is the “new” phase of scientific progress? Would he prefer, say, for cancer research, that if some biologists devise a complex model that feels like the right one to those who understand, yet is expected to yield no fruit for decades, the entire field should stick with it?

  20. Joel Rice says:

    I have to disagree with Dawid’s idea that it is acceptable to change the idea of theory so as to throw Feynman under the bus. He calculated the Lamb shift and that is what made it a real theory – as opposed to a mathematically sensible thing that looks like a theory but numbers don’t work out. OK, granted, Weinberg had a theory in 1967 before any numbers were in, but there was never any doubt about connecting with experiment, for better or worse. It becomes a ‘real theory’ by passing tests. If Dawid can find himself persuaded otherwise then we are reduced to who thinks which theory is mathematically prettier than the rest, and it becomes a matter of opinion. A bunch of physicists bet money that Parity was the truth. Opinion was worth zilch.

  21. Peter Woit says:

    Koray,

    There’s nothing much in the book about other sciences, and little about history (no specific parallels are given). To some extent Dawid is arguing that the situation with string theory is an unparalleled one (a “final” theory that is impossibly hard to test), justifying new scientific methodology. He’s not claiming that such methodology is necessarily justified in other fields.

  22. Cliff says:

    phmer,

    Your view is a common one, but its not a truly accurate portrait of how these developments have gone. Nature has surprised us with new manifestations of the basic principles of relativity and quantum mechanics, but none of the surprising developments you mention has altered these basic principles. It took time to fully appreciate, but electromagnetism and its non-abelian generalizations are the only possible ways to have an interacting spin-1 field consistent with relativity and quantum mechanics. Many people were impressed with this idea of generalizing electromagnetism but were discouraged because the lack of new long-range forces seemed to rule them out. It turned out that new mechanisms were required to implement the ideas – the Higgs mechanism for electroweak and confinement for the strong force – but it was still based on the one unique option that existed to generalize electromagnetism. There is a big difference between finding surprising and novel ways to implement well-established principles of physics versus a development that actually requires abandoning them. A priori, it would be totally conceivable that nature would select a genuinely radical departure, as you seem to think, but it just didn’t.

    So, sure, there is always some small chance that around the next bend everything we know about physics will just go out the window. But speculation based on these principles that are backed up by 100+ years of evidence will almost always beat speculation that is totally random and baseless. And thats exactly what string theory is, the one fully-consistent way to talk about quantum gravity while incorporating the principles of relativity and quantum mechanics. (If the extrapolation seems dubious, remember that GRB090510 verified the principle of Lorentz invariance up to Planckian energy scales, where many of the “discrete spacetime” people were predicting something else.) Unless there appears solid evidence to the contrary, the idea that preserves those principles will remain the most promising. Especially as long as it remains such a fantastically productive idea for thinking about physics in general as Maldacena’s #3 ranking in Inspire’s 2012 most-cited list indicates.

  23. Peter Woit says:

    Cliff,

    Hype such as “a fantastically productive idea for thinking about physics in general” isn’t any more convincing than what you are responding to.

    All: No more comments not about the book. Just stop.

  24. book says:

    How do you expect comments about the book since most people will not have read read it?

  25. Peter Woit says:

    book,

    Some people do have access to the book itself via the CUP page I linked to. Also, Dawid has been writing about this with similar arguments in quite a few places, he has links to such papers on his website, see here.

    http://homepage.univie.ac.at/richard.dawid/Homepage-Publications.htm

    From such materials and the posting it should be clear what the topic of the book is.

  26. paddy says:

    I risk failing the “purely on the book dictum”, since I have not read it but only gathered excerpts here and elsewhere on the web as well as perused the authors papers. ‘Twould seem though from what I have gathered that the argument is that we should change our (empirically derived) standards of what is or is not considered to be a useful empirical scientific model just because (1) a “promising” field of research has failed as of yet to meet those standards and (2) there is a paucity if not a complete absence of alternatives (note: though no uniqueness theorem or conjecture is posited). Is this a fair assessment?

  27. Peter Woit says:

    paddy,

    Kind of, although your formulation leaves open what “promising” means. Given the lack of progress towards making any predictions with string theory, it’s hard to argue that it’s “promising” in terms of moving towards a predictive, testable theory. Dawid is interested more in other reasons string theorists see the theory as “promising”, reasons that have nothing to do with testability or prospects for testability.

    I actually think this is an interesting question. When you are starting thinking about a speculative idea, the reasons for examining it more closely often are not that you see some potential way of testing it. Instead, the idea may be attractive for other reasons: it embodies some powerful and beautiful mathematical concepts, it’s related by analogy to some other ideas that have worked well, etc. etc. You can think of a lot of good reasons why people decide to pursue one speculative idea rather than another.

    The problem here is that these things are very slippery, and easy to fool oneself about or be less than honest about, with one’s vague argument for why one should look at something evolving into a protective armor of hype as one keeps arguing with those who are skeptical your idea is going anywhere.

    Unfortunately I don’t thing Dawid really comes to terms with the real problems of this kind of “non-empirical theory assessment”, since he sticks to taking at face value things which are heavily hype-ridden.

  28. Lee Smolin says:

    Dear Peter,

    I am shocked that the no alternative argument still gets a hearing given the major progress on key issues in loop quantum gravity and spin foam models. Does the book acknowledge this progress? Ten years ago it was possible to be skeptical of LQG because of open issues such as getting the 1/4 right in black hole entropy and deriving general relativity as the low energy limit. However the last five years there has been major progress on both of these and other issues including having a detailed and credible account of the onset of inflation following a quantum bounce. If it was valid to deny LQG the status of a full alternative approach to quantum gravity because of these issues any honest account must acknowledge the progress made.

    The no alternative argument fails on sociological as well as scientific grounds. This summers upcoming LQG meeting has already reached more than 200 registrations.
    Its fair to say that LQG is now after 25 years a healthy and vibrant large established research community. This doesn’t mean its right but it does puncture the no alternative argument.

    There is considerable progress as well on other alternative approaches to quantum gravity including causal dynamical triangulations and causal sets.

    I would be curious to read the book and see if the author has an up to date account of of the alternatives he claims do not exist.

    Thanks,

    Lee

  29. Peter Woit says:

    Hi Lee,

    Dawid discusses LQG on pages 91-94, with a very string theory-centric point of view. The oddest part is this

    “Leading exponents of loop quantum gravity tend to be fairly confident regarding their theory’s chances of success. However, compared to the way the status of string theory is assessed by that theory’s leading exponents, it may be fair to say that assessments of loop quantum gravity are significantly more timid. While the sentiment that their theory is “too good to be false” is widespread among string physicists, adherents to loop quantum gravity are more inclined to emphasize that their approach constitutes one possible solution that has some attractive features but may well turn out false in the end.”

    which kind of argues against you on the grounds that you are insufficiently arrogant. Other than that, he evaluates things by his three kinds of arguments I explained in the posting. For “No Alternatives” (which he calls AAA), string theory is supposed to be a promising way to unify with the SM, while LQG doesn’t really address this. For “Unexplained Explanatory Coherence” (his UEA) he explains the nice explanatory features of both approaches to quantum gravity, then somehow decides string theory is better. For “Meta-Inductive” (his MIA), again he’s using the argument that we should believe string theory because it’s like the SM (an argument that just baffles me), whereas LQG is like GR, which somehow is less desirable.

  30. bsm says:

    What testable BSM predictions do LQG and/or spin foam make, in particular at LHC scales? Have ATLAS and CMS published results of searches, or excluded regions of parameter space, for the BSM predictions of LGG/spin foam?

  31. Peter Woit says:

    bsm,

    Neither string theory nor LQG/spin foam make any predictions about LHC scale physics.

  32. Alex says:

    We all agree that it is important to think about what the correct model of quantum gravity is, right?
    Demanding that there are hard TeV scale predictions of something that by necessity involves the scale 10^19 GeV, that is basically a lamp post argument. There is no reason to think that dis/favouring approaches based on the amount of predictions they make *at the weak scale* can be a very misleading strategy. Of course one should try this (a la ADD and so on), but other than the hierarchy issues, there is no reason to think that quantum gravity should be so nice to us.

    Quite the contrary, the fact that something as baroque as the Standard Model is to come out of this at low scales, makes it for me unlikely that there should be anything fundamental to the observed low-scale physics. I don’t think anyone can seriously expect that the SM gauge group and particle content with such and such parameters are the unique consistent model that can come out of the correct theory of quantum gravity.

    Given this, I find it disingenuous to criticize string research for the lack of predictive power at the weak scale. There is a lot of predictive power near the fundamental scale, smoking gun signatures if you will – it is merely a technical reason why we can’t observe them, not a philosophical one.

    @Joel Rice
    Arguing about the name is silly, you could just as well criticize quantum field theory for its name. The names of stuff are all over the place for historical reasons and don’t conform to the terminology we should impose in discussions with the general public (in order to avoid arguments like “Evolution is just a theory” from the anti science crowd).

    The Standard Model is a Theory
    Quantum Field Theory is a mathematical framework
    String Theory is a mathematical framework
    Any explicit realization of the Superstring is correctly called a “Model” in the literature.

  33. Alex says:

    That was supposed to read:

    There is no reason to think that dis/favouring approaches based on the amount of predictions they make *at the weak scale* is a sensible strategy to find the correct theory of quantum gravity.

  34. bsm says:

    Unlike ST, do LQG/spin foam make any testable predictions at all?

  35. Alex says:

    IANALQGE, but I think you would expect to see some violation of Lorentz Symmetry at gignormous Energy Scales.

  36. Krzysztof says:

    Peter,

    From what you write about the book it seems to promote a real ‘scientific revolution’ – a huge change of the scientific paradigm. And, in a way it has some religious connotations, or at least philosophical ones. The main goal in that respect is to explain or motivate physics by itself – even more at the end, to explain all the reality, including its roots and reason, by science, and by science only. S. Hawking and other ‘top theorists’ since long have been voicing dreams about the ultimate theory which should explain also itself. As a side remark, I wonder what they say about the Goedel’s theorems in that context…

    To me, an experimental particle physicist, string theory as such is a purely mathematical project, having (almost) nothing to do with physics, so far.

  37. Lee Smolin says:

    bsm:

    LQG is a framework for the quantization of diffeomorphism invariant theories. But there are striking consequences if not falsifiable predictions for experiment. One comes from the existence of a new parameter necessarily in the gravitational action, analogous to the theta angle of QCD: the Immirzi parameter. When this takes complex values there are parity odd quantum gravitational effects. These imply a parity odd component to the polarization in the CMB, possibly visible in the B-T channel. This could be seen in upcoming measurements at Planck and other detectors. This is not a falsifiable prediction but its detection would be a striking confirmation of the framework. To put this another way, Planck polarization measurements will constrain the Immirzi parameter.

    See papers of Magueijo et al for details.

    btw I am not aware that string theory makes any falsifiable predictions for doable experiments.

    Thanks,

    Lee

  38. Pingback: Why I Still Like String Theory | viXra log

  39. Peter Woit says:

    bsm/Alex,

    The whole point of this book is that it starts from the assumption that string theory (and also LQG) can’t make any testable predictions, so the author is coming up with a new methodology of science to evaluate untestable theories.

    The problem with string theory is not that it can’t make testable predictions about physics at the weak scale, but that it can’t make testable predictions about physics at any scale whatsoever.

  40. Alex says:

    Peter,

    “The problem with string theory is not that it can’t make testable predictions about physics at the weak scale, but that it can’t make testable predictions about physics at any scale whatsoever.”

    Are you seriously claiming that the superstring does not make any testable predictions about physics at *any* scale?
    What about the 6 extra dimensions, the string spectrum, Regge excitations, measuring open string and closed string scattering amplitudes explicitly? Come on, if we could by some surprising feat built a Planck scale collider, there would be a wealth of stuff to observe.
    As far as the first point is concerned, it could be that there is no real 10D supergravity regime because the compactification scale is at the string scale or so, but that is an extreme situation.

  41. JG says:

    Philip Gibbs in his quasi-review (the book is above his price range, as it is mine) says the following:

    “The more evidence there is against SUSY, the more evidence there is in favour of the multiverse and the string theory landscape” and “the standard model succeeded because it was based on consistency arguments such as renormalisability which reduced the possible models to just one basic idea that worked. The same is true for string theory so we are on firm ground.”

    OK, one thing I thought was true was that string theory rises and falls on SUSY. And, what is the “one basic idea” that works in string theory?

    Is this as crazy as I think it is?

  42. Peter Woit says:

    Alex,

    This one has been gone over a million times (and has nothing to do with the book). Yes, we would learn something from a Planck scale accelerator, no, string theory makes no falsifiable predictions about it, since we don’t know what non-perturbative string theory is: would there be black holes produced? would it be six extra dimensions or seven (according to M-theory)? But wait, we don’t know what M-theory is…

    Sorry, but I’m just going to delete further comments not about the book.

  43. Peter Woit says:

    JG,

    Please argue with Philip about his posting on his blog, not here.

  44. Neil says:

    Of his three principles of “non-empirical assessment”, I find the “no alternatives” one disturbing and destructive. The other two seem reasonable. You can never know there are no alternatives, so it is silly to presume such. By this reasoning we should always stay on the path we are on because we cannot imagine another. But why would we try if a presumption of no alternatives is part of our assessment package?

    And of course, as Smolin points out, in fact there are alternatives.

  45. fuzzy says:

    i think that such a philosophical position if perfectly ok if we want to relocate string theory out of natural sciences; in a sense, dawid blesses the idea of string theory becomes a branch of math and philosophy, and its physical origins can be forgot. in this sense, the position of joel rice can be agreed upon, simply adding a bare word to his statement: “string theory is not a *physical* theory”. of course, here i argue that we should maintain the vintage position of old isaac: “to be termed scientific, a method of inquiry must be based on empirical and measurable evidence subject to specific principles of reasoning” — this should remain the rule of natural sciences, without implying any derogative position toward math and philosophy. however, i feel that if the position of dawid will be accepted, mathematicians should be ready to hear statements as “since we will explain anything, stop working on riemann hypothesis–this is our stuff”

  46. Raisonator says:

    Joel Rice,
    “It would be a lot easier if they would just stop calling it a theory. ”
    A good point. I thought about this too. A big problem to me seems to be that when you call it “theory” in the media, lay people tend to think that it is comparable to the theory of relativity or quantum theory which have been tested to incredible accuracy in so many ways.

    David Gross likes to call it a “framework”, which I find a very good idea. Or “the string hypothesis” could also do.

    Best.

  47. Adrian_H says:

    I can think of one good reason why this new version of string theory + landscape would be attractive to someone who has some philosophy behind them: it is essentially equivalent to the model theory of modern logic.

    In that way of thinking, which philosophers tend to associate with the name of Leibniz, but that goes back to Duns Scotus, there are a set of logical truths, which are essentially a set of mathematical constraints that are common to all models; and there are sentences that are allowed to vary from one model, or possible world, to another — the contingencies. If one increases the set of “logical/mathematical truths” that are invariant then you decrease the size of the “possible worlds”. If logic is science I suppose that this can all be considered science too — but logic would be a better name for it. (And it would be falsified if one of the constraints is shown to be false.)