Non-empirical Physics

I haven’t been paying much attention in recent years to the philosophers of science studying “Non-empirical” or “Post-empirical” physics or theory confirmation. At various times I did write fairly extensively about this, see for instance here, here and here. By 2015 there was a conference in Munich on the topic, which led in 2019 to a volume of papers entitled Why Trust a Theory?

There’s a new paper out along similar lines, String theory, Einstein, and the identity of physics: Theory assessment in absence of the empirical, evidently to appear in a journal special issue from a 2019 conference on Non-Empirical Physics from a Historical Perspective.

The reaction of most physicists to this sort of thing is exemplified by Will Kinney’s tweet about the paper:


In the past few years I’ve been writing less and less here and elsewhere about the issue of evaluating string theory as physics, for several reasons:

  • String theory has effectively gone completely post-empirical, decoupling from any possible relation to experiment. This Week’s Hype used to be a regular feature here, devoted to debunking the numerous bogus claims regularly being made for how to “test string theory”. One rarely sees these anymore, with the string theory community now having given up on this and somehow comfortably moved into a completely post-empirical mode.
  • I’m actually much more sympathetic than most people to the idea that there is a serious and very interesting question about how to evaluate ideas about theoretical fundamental physics in the absence of viable experimental tests. But I haven’t had much luck finding others who share my views. The reaction to blogposts like this recent one tends to be pretty uniformly scornful, that I’m just Lost in Math. The post-empirical philosophers of science deal with me differently, pretty much doing their best to ignore me (I don’t make it into the extensive bibliography of the new paper on the arXiv).
  • There are two other projects that seem to be a much better way to spend my time (the twistor unification stuff, and improving the textbook on QM and representation theory).

By the way, I notice that there is an arXiv trackback already for another blog entry about this paper, wondering if trackbacks here are still censored.

Well, that’s all about this for now, best to take my own advice and go think about something else.

Update: I just ran across this AIP interview with John Schwarz from last year. Schwarz seems to feel that string theory unification is a huge success, despite the testability problem. On the failure to find the superpartners he and other string theorists expected, that’s a problem for experimental physics, not for string theory:

As I said, if supersymmetry is not discovered, there’s a danger that experimental particle physics will die. If that happens, it would be tragic, but it wouldn’t be the end of string theory. String theory will continue, regardless, and will continue to advance.

On the topic of answering those who argued that superpartners would not be found back in the 2000s, and who have put forward detailed criticisms of string theory unification, here’s what he has to say:

There were a couple popular books that attacked string theory about a decade or so ago. The authors clearly had chips on their shoulders. For people without a physics background it’s not possible to assess whether what they’re reading makes sense or not. But anyone with at least an undergraduate education in physics I think can recognize that they should not be taken seriously.

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27 Responses to Non-empirical Physics

  1. Sabine says:

    There’s also a new book called “On The Fringe” by Michael Gordin about the demarcation problem. It has a paragraph or two about string theory, but only to say “look, sometimes even scientists can’t tell if it’s science or pseudoscience” (not an actual quote, I paraphrase). The book is mostly about astrology, alchemy, bigfoot, and so on.

  2. Peter Woit says:

    I don’t think arguing over whether “string theory” is “science” or “pseudo-science” is worthwhile. Even before you get to the demarcation problem, your problem is that these days “string theory” has no specific meaning.

    What’s accurate to say is that, even if you agree to put string theory unification on the science side of your science/pseudo-science demarcation, it’s a failed idea about science. My problem with what most of the “post-empirical physics” philosophers of science are doing is that they’re just producing excuses for failure. They are starting from the assumption that this can’t be failed science, since its proponents are leaders of the field, rewarded with multi-million dollar prizes. So, it must be a new way of doing science.

  3. André says:

    The last sentence of the conclusion of the paper arxiv:2105.14342 reads: “let’s … keep funding it as generously as before.” The author thus states clearly that he is making money out of his paper. This is appalling. Were it politics, not science, this would not be called a conflict of interest, but simply corruption.

  4. Alessandro Strumia says:

    Entire published papers are not appearing on arXiv. Is it wise to leave such a resource, important for the whole international field, in the hands of a few individuals and private donors?

  5. Peter Woit says:

    I think the “keep funding it as generously as before” plea makes explicit that what’s going on here is what I described in my response to Sabine: an attempt to evade the unpleasant implications of failure (with losing funding just the crudest of such things).

  6. Peter Erwin says:


    The author of the paper is a philosopher/historian of science, not a physicist working on string theory, so encouraging people to continue funding things like string theory isn’t going to give him any money. (Arguably there is a slight conflict of interest in that he finds the topic interesting, so he’d presumably be disappointed if it was shut down; but since he’s written a number of papers on Einstein, I suspect he’d do fine academically even if string theory was shut down.)

  7. Peter Woit says:

    Alessandro Strumia,

    I don’t want to try and host here a discussion of the general topic of arXiv moderation (from dealing with comments, I know moderation is difficult…). To the extent the problem is with them censoring politically incorrect views (whether about string theory or anything else…), it’s a problem larger than a few individuals, would likely be there whatever their institutional structure is.

    To describe my experience in dealing with the arXiv over the trackback matter, it was essentially impossible to communicate with anyone there, or even find out what decisions they were making and on what basis. After a huge effort involving a lot of time and asking for help from a lot of people, all I ever got was a message from a Cornell administrator saying a decision had been made by unknown parties based upon unknown criteria. To this day I have no idea who decided what about trackbacks, based on what information and what policy, or what their current policy is.

  8. Sabine says:


    “My problem with what most of the “post-empirical physics” philosophers of science are doing is that they’re just producing excuses for failure”

    Well, yes, kind of. Some of them, anyway. The problem is that most philosophers don’t actually understand the topic (string theory or quantum gravity or naturalness) in any depth, are afraid to put forward an original analysis of it, and then end up doing sociology more than philosophy. Unfortunately, they then don’t factor in what we actually know about the sociology of science.

    Having said that, it actually is difficult to sort out the wheat from the chaff if you can’t do it by way of experiment because that’d take centuries. So we have to change our methods, and philosophers have a role to play in that.

    Merritt did a pretty good job for MOND. I mean, as I write in my review, I have some objections to his conclusions, but this isn’t the point. The point is that this kind of analysis is very important. But Merritt is an astrophysicist who only recently switched to philosophy. I think we’d need someone like this in string theory. Or, preferably, several people.

    Having said that, the book by Gordin I mentioned above makes a good point, which is that it often takes time for scientists to sort out the demarcation and also, the judgement changes over time. There are quite a few ideas that we currently regard as pseudoscience but that were once considered adequate.

    All of which means, basically, you are making scientific history 😉

  9. Sabine says:

    And while I am at it, let me echo Alessandro’s concerns about the arXiv moderation. I have personally never had an issue with them, but then I am a soundly boring person. However, I wrote a blogpost some years ago about the arXiv moderation issue (brought to my attention by others) and ever since people have contacted me asking for help. Every once in a while I try to actually do that, but it never leads anywhere. I have found it impossible to figure out who is even making a decision on what, and in the end they’ll fall back on saying “if it gets published in a journal, we’ll accept it on the arXiv” which amounts to refusing to take responsibility. Most people are afraid of saying anything about it because their good standing with the arXiv moderation decides on their career. This is not a good situation. I really think the community should do something about it.

  10. Alessandro Strumia says:

    It seems to me that we now have two big problems at the same time:
    High-energy physics wants to keep its historically large level of funding despite lack of new physics, while institutions are affected by an ideology that denies objectivity and views science as a system of power.
    Will the field survive to a short-sighted compromise?

  11. Peter Shor says:

    The arXiv certainly needs moderation, otherwise it would fill up with papers that are written by crackpots and become completely useless.

    I haven’t had any problem with it myself, but I think making the system more transparent (it being completely opaque now) would be a considerable improvement.

  12. maciej says:

    If you criticize string theory on arxiv your work is likely to be rejected. They can even disable your submission rights if you don’t stop submitting your criticism. The situation is very concerning, reminds me a kind of censorship of totalitarian systems. What arxiv needs is transparency but that comes with objectively chosen committee which for decades has not been objective at all
    (The only hep-th related members of arxiv committee are pro-string-theory Jacques Distler and Paul Ginsparg

  13. Peter Woit says:

    About my problems with the arXiv, all I can do is guess what they might be. A good guess seems to be the attitude towards this blog taken by a certain arXiv moderator right at the beginning. Those interested in history might want to take a look at the discussion in the comments right at the beginning of the blog, here

  14. “I’m actually much more sympathetic than most people to the idea that there is a serious and very interesting question about how to evaluate ideas about theoretical fundamental physics in the absence of viable experimental tests.”
    Could you expand on this a little more. I have spend quite some time over the last 4 years thinking about how to judge the potential of a theory by its mathematical ingredients but so far I haven’t really come to a conclusion that goes beyond gut feeling and a set of pitches that catch the attention of physicists. (given we have to decide which approaches to unification should be funded, I think it is crucial that we do have a better framework to gauge the potential of new ideas).

  15. Peter Woit says:

    Claudio Paganini,

    I think this is a difficult and complex question, with no easy answer. A couple aspects of it are:

    1. Initially, speculative ideas are hard to evaluate, since there is a lot about their implications that still has to be worked out. Most speculative ideas don’t work out, and it’s not that one could tell this at the beginning, but as you work things out and understand them better, typically the more you learn, the more you find problems with the idea. Only in rare occasions do you find that the more you learn the better and more solid the idea looks. In some sense, the fundamental problem with the string theory unification idea is just exactly this: you could argue about how promising it was in 1984, but everything learned about it since then makes clearer and clearer the deadly problems with the idea. In slogan terms: the absolute value of the significance function of an idea may be very hard to evaluate, the derivative in time a lot easier.

    2. Absent experimental confirmation, you need to actually understand ideas and their evolution to evaluate them, there’s no easy way around this. If a highly complex and obscure set of ideas accurately computes the details of something you can observe, you know there is something right about it, even if you don’t understand the set of ideas. If you decouple from experiment, you have no external evaluation of the ideas, have to really understand and engage with them to evaluate them.

    3. Psychologically, once people have a certain amount of their time/energy/reputation invested in working on a set of ideas, it is very difficult for them to honestly evaluate whether the ideas are working.

    The combination of 2 (a lot of effort needed to understand something well enough to evaluate) and 3 (if you put a lot of effort into an idea, you have a lot invested in it) creates a huge problem, and I think explains a lot about some of the pathology we’ve seen in fundamental theoretical physics

  16. The combination of 2 (a lot of effort needed to understand something well enough to evaluate) and 3 (if you put a lot of effort into an idea, you have a lot invested in it) creates a huge problem

    Not to be bleak, but does this leave room for a way out other than what one might postulate as the inverted Planck’s principle? (“A failed scientific venture does not wane by disappointing its proponents and making them see the light, but rather because its proponents eventually die and a new generation grows up that is familiar with its ineffectiveness.”)

  17. Peter Woit says:

    Aristotle Pagaltzis,
    Actually, the situation is even bleaker than that. Once a complex failed research project gets institutionalized, absent a new successful one coming along and displacing it among the younger generation, the younger generation just gets trained in the complex failed project, reproducing the problem. To this day, lots of the best young students in theoretical physics are being trained by being told to spend years reading the canonical multi-volume superstring theory treatises.

  18. Jackiw–Teitelboim says:

    Dear Peter,
    Suppose you are talking to a person belonging to the set of “best young students in theoretical physics” from some reputable university according to all standard metrics, and have been told to “spend years reading the canonical multi-volume superstring theory treatises”.

    What would *you* tell such student to spend their time on then?

    An advice I have being often told, which I rejected based upon personal experience, is that of doing a math PhD instead of a physics one. Nevertheless, the kind of interests and standards of “rigor of proof” in a typical top math PhD program will possibly consume much more energy as reading a 2-volume Polchinski’s textbooks, however with the additional risk of also losing physical intuition.

  19. Peter Woit says:

    There really isn’t a good answer to give students in this position right now. HEP theory/quantum gravity is not a healthy research area and hasn’t been for years. The first obvious piece of advice is to consider instead working in a healthier research area. There are a lot of them in mathematics, many with significant overlap with fundamental physics. But, sure, if what interests you is just physics and not math, getting a math phd. is problematic.

    Students are inescapably highly dependent on faculty and their advisor, this can’t be solved by them getting advice from the internet or figuring out themselves the problems with their advisor’s research direction. I do think though that good advice at the moment is that if you’re a student being told to spend a lot of time mastering the quantization of the 10d superstring, you should be asking questions and looking around for other options.

  20. Peter Shor says:

    Jackiw-Teitelboim: if the actual theory of quantum gravity requires math that physicists currently don’t know, then if you don’t learn more math you will never find that theory.

    On the other hand, it’s clearly much safer to read through all Polchinski’s textbooks, because it’s very possible that if you get a math PhD, the math you learn is not going to be the math you need for quantum gravity. And if you’re not interested in proving theorems rigorously, but in using advanced math to study physics, you may not get a good academic job. [This is something that maybe could be fixed.]

    However, if no physicists ever learn any more math, then it’s quite possible we’ll never find the theory of quantum gravity.

    Looking back in history, finding the theory of general relativity needed knowledge of differential geometry. But Einstein was smart enough that he realized he needed to learn this, and he had a friend, Marcel Grossmann, who helped teach it to him. And after the theory of GR, differential geometry was added to the physics curriculum (at least for relativists).

  21. Peter Shor,
    An alternative approach is for mathematicians to learn more physics, so that a mathematician who actually does know the mathematics that posterity will discover is needed, can bring that mathematics to the attention of physicists. Of course, the mathematician will need to do a lot of work explaining a lot of physics in terms of a new mathematical model, before any physicists will listen. But if physicists don’t know what mathematics they need, perhaps mathematicians can help?

  22. lun says:

    Peter Shor, at least from a historical point of view things are a bit more subtle.
    Heisenberg did not know matrices, and Einstein did not know differential geometry.
    Learning the required maths can be accomplished while developing the theory, after having “found it”. “finding it” was about physical insight, not knowing the right maths.
    Perhaps post-empiricism will change that.

  23. Ricardo says:

    Somebody please comment on advising a young student to choose condensed matter physics as a field of study. TIA.

  24. JE says:

    If you ask me, I would say that the guiding principle for advancement in theoretical physics should not be beauty, but physical intuition. The quest for beauty can easily lead you astray in physics, because beauty is quite a debatable question. Boldly put, beauty is fine for fine art, but physical intuition will more likely keep you linked to physical reality. The quest for beauty can rapidly entice you to supersede the SM with a larger theory of which it merely is a subset, while physical intuition can tell you that such a successful theory may have become a victim of its own success by obfuscating the fact that it may not even be “right”.

  25. Peter Woit says:

    The problem with the argument that “physical intuition” or “physical insight” is the answer to figuring out a new layer of fundamental physics is that there’s no good reason to believe our physical intuitions based on earlier theories are relevant. Quantum mechanics famously violated all previous physical intuitions and took a lot of getting used to (with a lot of help from mathematics). Curved space-time also violates all previous physical intuitions, and Einstein could only pursue that idea and work with it by learning a lot of very sophisticated new mathematics.

  26. Low Math, Meekly Interacting says:

    It’s been ages since I’ve been around bachelor’s anything, but my sense is that an undergraduate physicist is going to have to go out of their way to learn much more than the basics of GR and QFT. Most won’t take dedicated courses on either, even if they’re on the curriculum. I know Schwarz isn’t trying to be fair, but is his dismissal as absurd as it looks to me?

  27. Peter Woit says:

    Yes, it’s absurd. Also kind of sad that Schwarz feels it necessary to make over the top ad hominem (chip on my shoulder?) attacks on an argument he has no good answer to. Back in 2006 the point of view of my book and Smolin’s on string theory already had a lot of support in the theoretical physics community. By now, with the collapse of hopes for a SUSY extension of the SM and the multiverse debacle, the idea that string theory has not worked out is I think a majority one among physicists. Schwarz and some others may comfort themselves with the idea that criticism from their colleagues is based purely on ignorance, incompetence and resentment, but I don’t think this helps his case.

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