String theory and post-empiricism

18208_Peter_Woit_HD_Wallpaper_Pic.jpgby Peter Woit

Last month’s conference in Princeton included two remarkable talks by prominent physicists, both of whom invoked philosophy in a manner unprecedented for this kind of scientific gathering. On the first day, Paul Steinhardt attacked the current practice of inflationary cosmology as able to accommodate any experimental result, so, on philosophical grounds, no longer science [2]. He included a video clip of Richard Feynman characterizing this sort of thing as “cargo cult physics.” On the final day, David Gross interpreted Steinhardt’s talk as implicitly applying to string theory, then went on to invoke a philosopher’s new book to defend string theory, arguing that string theorists needed to read the book in order to learn how to defend what they do as science [3].

The book in question was Richard Dawid’s String Theory and the Scientific Method [4], which comes with blurbs from Gross and string theorist John Schwarz on the cover. Dawid is a physicist turned philosopher, and he makes the claim that string theory shows that conventional ideas about theory confirmation need to be revised to accommodate new scientific practice and the increasing significance of “non-empirical theory confirmation.” The issues of this kind raised by string theory are complex, so much so that I once decided to write a whole book on the topic [5]. A decade later I think the arguments of that book still hold up well, with its point of view about string theory now much more widespread among working physicists. One thing I wasn’t aware of back then was the literature in philosophy of science about “progressive” vs. “degenerating” research programs, which now seems to me quite relevant to the question of how to think about evaluating string theory.

I’ve written a bit about the Dawid book and earlier work of his [6], although as for any serious book there’s of course much more to say, even if I lack the time or energy for it. Recently an interview with Dawid appeared, entitled “String theory and post-empiricism,” which summarizes his views and makes some claims about string theory critics which deserve a response, so that will be the topic here. In the interview he says:

I think that those critics make two mistakes. First, they implicitly presume that there is an unchanging conception of theory confirmation that can serve as an eternal criterion for sound scientific reasoning. If this were the case, showing that a certain group violates that criterion would per se refute that group’s line of reasoning. But we have no god-given principles of theory confirmation. The principles we have are themselves a product of the scientific process. They vary from context to context and they change with time based on scientific progress. This means that, in order to criticize a strategy of theory assessment, it’s not enough to point out that the strategy doesn’t agree with a particular more traditional notion.

Second, the fundamental critics of string theory misunderstand the nature of the arguments which support the theory. Those arguments are neither arbitrarily chosen nor uncritical. And they are not decoupled from observation. String theory is indirectly based on the empirical data that drove the development of those theories string theory aims to unify. But more importantly for our discussion, the arguments for the viability of string theory are based on meta-level observations about the research process. As described before, one argument uses the observation that no-one has found a good alternative to string theory. Another one uses the observation that theories without alternatives tended to be viable in the past.

Taking the second part of this first, Dawid seems to be claiming that Smolin and I don’t understand what he calls the “No Alternatives Argument” (discussed in detail in his book, as well as in a paper in The British Journal for the Philosophy of Science [8]. In response I’ll point out that one of the concluding chapters of my book was entitled “The Only Game in Town” and was devoted explicitly to this argument. To this day I think that a version of such an argument is the strongest one for string theory, and is what motivates most physicists who continue to work on the theory. The version of this argument that I hear often privately and that has been made publicly by theorists like Edward Witten goes something like:

Ideas about physics that non-trivially extend our best theories (e.g. the Standard Model and general relativity) without hitting obvious inconsistency are rare and deserve a lot of attention. While string theory unification hasn’t worked out as hoped, we have learned a lot of interesting and unexpected things by thinking about string theory. If they see a new idea that looks more promising, string theorists will shift their attention to that.

This is a serious argument, one that I tried to carefully address in the book. Beyond that, more naive versions of it seem to me to have all sorts of obvious problems. Of course, if you really can show that alternatives to a given model are impossible, that is a convincing argument for the model, but this is rarely if ever possible. Working scientists beating their heads against a hard problem are always in the position of having “no alternatives” to some flawed ideas, until the day when someone solves the problem and finds the alternative. The only example I can recall seeing from Dawid of a successful example of the “no alternatives argument” is the discovery of the Higgs, and I find that very hard to take seriously. Pre-2012, the Standard Model was a very precise and exhaustively tested theory, providing a huge amount of indirect evidence for the Higgs. There were plenty of alternatives (technicolor, SUSY, etc.), all much more complicated and with no evidence for them. Making a “no alternatives argument” for a theory with overwhelming experimental evidence behind it is something completely different than trying to do the same thing for a theory with zero experimental evidence.

As for the other mistake that Dawid thinks string theory critics make, that of believing in some unchanging notion of empirical theory confirmation, the first thing to point out is that of course every theorist is well aware that one can can’t just demand experimental predictions and confirmation for ideas, that one spends basically all one’s time working on better understanding ideas that are far from the point where empirical confirmation comes into play. The second thing to point out is that I agree completely with Dawid that as experiments become more difficult, one needs to think about other ways of evaluating ideas to see if they are going anywhere. The last chapter of my book was devoted to exactly this question, arguing that physicists should look carefully at how mathematicians make progress. Mathematics is certainly “post-empirical,” and while logical rigor is a constraint, it is not one that necessarily points mathematicians to fertile new ideas. There is a long history and a deeply-ingrained culture that helps mathematicians figure out the difference between promising and empty speculation, and I believe this is something theoretical physicists could use to make progress.

The epigram from that last chapter though was something that kept going through my head when thinking about this, a line from Bob Dylan’s “Absolutely Sweet Marie”:

But to live outside the law, you must be honest.

Yes, theoretical particle physics is in a stage where empirical results are not there to keep people honest, and new and better “post-empirical” ways of evaluating progress are needed. But these must come with rigorous protections against all-too-human failings such as wishful thinking and Lee Smolin’s “groupthink,” and I just don’t see those anywhere in Dawid’s proposal for new kinds of theory confirmation.

_____

I’d like to thank Massimo Pigliucci for the opportunity to write something here at Scientia Salon, and hope it will generate an interesting discussion. Contributions from philosophers to this kind of debate in physics I believe are very much needed, on this issue and others. Don’t even get me started about the multiverse…

 

Peter Woit is an American theoretical physicist. He is a Senior Lecturer in the Mathematics department at Columbia University. Woit is especially known for his criticism of string theory in his book Not Even Wrong, and also for his widely-read blog of the same name. Peter was one of the first guests on the Rationally Speaking podcast.

[1] Strings 2014 conference.

[2] Paul Steinhardt’s presentation.

[3] David Gross’ presentation.

[4] String Theory and the Scientific Method, by Richard Dawid.

[5] Not Even Wrong: The Failure of String Theory and the Search for Unity in Physical Law for Unity in Physical Law, by Peter Woit.

[6] Woit on Dawid: here and here.

[7] String theory and post-empiricism, interview with Richard Dawid.

[8] The No Alternatives Argument, by Richard Dawid.

156 thoughts on “String theory and post-empiricism

  1. Hi schlafly,

    You wrote down: “Sorry, but Tyson is right. It is nearly impossible to find any philosopher who has anything worthwhile to say about 20th century physics”.

    Well, as Robin Herbert said: “On the contrary, the early 20th century was when physics went into a mind meld with philosophy”.

    This is the point, some physics ─not many─ adopted a philosophical view about physics, let me say Bohr, Einstein and Erwin Schrödinger. We should not be surprised about it, there is a long tradition of philosophers of nature ─physicists─, a venerable tradition that go back to the pre-Socratics, Aristotle, Giordano Bruno, Copernicus, Kepler, Isaac Newton, Immanuel Kant, etc. I think it’s a fertile crucible that helps us to understand the epistemic lines that join philosophy and psychics.

    With regard to string theory I’m cautious and I also have the greatest respect for stringers, but I feel more confident about the physic developed by Newton, Descartes, Faraday, Maxwell, Boltzmann, Rutherford, Einstein, Planck, Emmy Noether, Dirac, Fermi and some theorists of quantum mechanics. I don’t really know what is beyond the Kaluza’s theorem, extra dimensions, etc. Right now I think there is no need to focus on strings to discover new physical data. Indeed, some stringers would think that string theory is a crucial insight to flash the facts of nature, this becomes part of the debate though for me is not an essential point. I’m aware that my point of view is classical but for better or for worse it doesn’t bother me.

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  2. Hi Coel,

    Surely the whole point is that the volume you start with (before infinite decomposition) and the volume you end with (after reconstruction) are indeed normal and sensible volumes. That’s why it is paradoxical. If it were only about infinite fractal spaces then that would be rather different.

    Surely they are infinitely divisible volumes which are only normal and sensible if you are a pure mathematician. It is not like they are talking about bowling balls.

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  3. @ Nigel Cook. I’m sorry, but I don’t think your post makes sense. The Ashtekar variables does exactly what you are requesting – and without breaking any taboo that I know of: formulating general relativity as a gauge theory, where the kinematics is identical to that of a Yang-Mills theory but with different dynamics.

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  4. Hi Robin,

    Maths describes the way the real world works but it is not limited to describing how the real world works.

    But isn’t B-T a statement that is supposed to apply to ordinary Euclidean 3-space, and thus apply to the real world? It wouldn’t be a “paradox” otherwise.

    And in fact, according to you and DM it is only pot luck that reality is such that Banach-Tarski objects are not instantiable as actuals (since they are entirely logically consistent).

    How do we know that? Didn’t Godel show that that could not be proven? In fact, isn’t the whole issue here whether the treatment of volume through the B-T process is indeed consistent?

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  5. But if mathematics can study types of reality that don’t happen to be the case then how could you say it is empirically based?

    The claim is that the axioms map to real-world behaviour, even if not all possible mathematical structures buildable out of those axioms actually exist.

    As an analogy, it is entirely sensible to consider things such as the set of all possible DNA combinations in the next generation, even though only a tiny proportion of the set will then come to be.

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  6. Surely they are infinitely divisible volumes which are only normal and sensible if you are a pure mathematician. It is not like they are talking about bowling balls.

    But normal physical space is usually taken to be continuous and infinitely divisible (rather than, say, quantised). You’re right that we’re not talking about a material object (such as a bowling ball), but we are talking about volume, which is a normal, real-world, physical concept.

    Thus the question is whether B-T is held to apply to the concept of “volume” that is used in everyday life and in physics. If it’s not about that sort of volume then what sort of volume is it about?

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  7. Hi Coel,

    Surely the whole point is that the volume you start with (before infinite decomposition) and the volume you end with (after reconstruction) are indeed normal and sensible volumes. That’s why it is paradoxical. If it were only about infinite fractal spaces then that would be rather different.

    Sure, the beginning and ending volumes are normal and sensible. The intermediate stages are not. It’s like dividing 1 by 0 to get 2 (or whatever value you like). You start and end with perfectly sensible values, but do something weird in between which makes no sense in the real world.

    but we are talking about volume, which is a normal, real-world, physical concept.

    Right, but the idea of dividing up and rotating empty space does not make sense in the real world either. Empty space is not a substance that can be manipulated, especially if we’re talking about a pure Cartesian space and not the quantized quantum foam of real space.

    Besides, the creation of new empty space from nothing should not be that surprising, since that actually does seem to be happening in the real world as the expansion of the universe accelerates (not that that has anything to do with B-T, of course).

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  8. Jesper: what doesn’t make sense is your reference to Ashtekar variables, which don’t convert spacetime curvature into rank-1 equation for field lines. What they do is to introduce more obfuscation without any increase in understanding nature. LQG which resulted from Ashekar variables has been a failure. The fact is, there is no mathematical description of GR in terms of field lines, and no mathematical description of QED in terms of spacetime curvature, and this for purely historical, accidental reasons! The two different descriptions are long held dogma and it’s taboo to mention this.

    (For a detailed technical discussion of the difference between spacetime curvature maths and Maxwell’s field lines, please see my 2013 paper “Einstein’s Rank-2 Tensor Compression of Maxwell’s Equations Does not Turn Them Into Rank-2 Spacetime Curvature”, on vixra).

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  9. Hi Coel,

    But isn’t B-T a statement that is supposed to apply to ordinary Euclidean 3-space, and thus apply to the real world? It wouldn’t be a “paradox” otherwise.

    Are there any ordinary Euclidean 3-spaces in the real world? And B-T is not really a paradox although it is often termed this.

    How do we know that? Didn’t Godel show that that could not be proven? In fact, isn’t the whole issue here whether the treatment of volume through the B-T process is indeed consistent?

    Good point, but Godel’s theorems apply just as much to axiomatic systems that don’t use the Axiom of Choice so the question of logical consistency applies just as much to the mathematics that describe the real world as it does to mathematics that describe B-T type worlds.

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  10. Yes, Einstein made an argument that quantum mechanics was philosophically unsatisfactory. Bohr and others defended it as a scientific theory. Even today there are people who argue that Einstein was right. Those people have gone down a gigantic dead end, and nothing good has come from their work.

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  11. What’s with the discussion of Banach-Tarski? That is a theorem about non-measurable sets. It does not apply to a potato. A potato is made of atoms.

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  12. “Nobody bothered to try to replace Maxwell’s field line description of electrodynamics with a spacetime curvature description, or vice-versa to express gravitational fields in terms of field lines” – Ok so you haven’t heard of Misner and Wheelers geometrodynamics, or the literature by Thorne et al on visualizing spacetime curvature via frame-drag vortexes and tidal tendexes.

    ” If gravity is quantized in quantum field theory, the gravitational force will then be mediated by graviton exchange (gauge bosons), just like any Standard Model force” – yes there are always alternative effective theories to describe any physical effect, the issue is which is the more fundamental one. That quantum field theory description can be an effective result of various competing quantum gravity theories. Which fundamental theory is correct cannot be established simply by making dogmatic statements that dismiss out of hand major well developed research programmes (“LQG which resulted from Ashekar variables has been a failure”). This is just a statement of personal prejudice.

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  13. http://vixra.org/abs/1407.0088 “MOND and the Photon Underproduction Crisis”
    “… TeVeS for a specific choice of F is in principle falsifiable. Dark matter is less falsifiable because of the essentially unlimited choice of halo models and choices of their free parameters.” — Jacob Bekenstein, p. 22 of “Relativistic gravitation for the MOND paradigm”

    Click to access 0403694v6.pdf

    My guess is that dark matter particles, the string landscape, and eternal cosmological inflation cannot be falsified because D-brane adjustments might allow these theories to model any plausible or implausible physics. I say that string theorists have blundered by ignoring MOND and the idea of Fernández-Rañada and Tiemblo-Ramos that atomic time might be different from astronomical time.

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  14. But when I said that science and philosophy were in a mind meld I had people like Bohr very much in mind.

    Einstein was a skeptic of the prevailing philosophy of science of the time, Bohr was very much in tune with it. Bohr’s defence of QM as a scientific theory was due to his philosophical position about what constituted a good scientific theory.

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  15. Geometrodynamics doesn’t express electrodynamics’ rank 1 field lines as spacetime curvature, any more than vortices do, or any more than Ashtekar variables can express spacetime curvature as field lines.

    The point is, if you want to unify gravitation with standard model forces, you first need to express them with the same mathematical field description so you can properly understand the differences. You need both Maxwell’s equations and gravitation expressed as field lines (rank 1 tensors), or you need them both expressed as spacetime curvature (rank 2 tensors). The existing mixed description (rank 1 field lines for QED, spacetime curvature for GR) follows from historical accident and has become a hardened dogma to the extent that merely pointing out the error results in attacks of the sort you make, where you mention some other totally irrelevant description and speculatively claim that I haven’t heard of it.

    The issue is not “which is the more fundamental one”. The issue is expressing all the fundamental interactions in the *same* common field description, whatever that is, be it rank-1 or rank-2 equations. It doesn’t matter if you choose field lines or spacetime curvature. What does matter is that every force is expressed in a *common* field description. The existing system expresses all SM particle interactions as rank-1 tensors and gravitation as rank-2 tensors. Your comment ignores this and and you claim it is “personal prejudice” to choose “which fundamental theory is correct” which “cannot be established by making dogmatic statements”. I’m not prejudiced in favour of any particular description, I am against the confusion of mixing up different descriptions. That’s based on dogmatic prejudice!

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  16. On the contrary – Bell’s theorem http://en.wikipedia.org/wiki/Bell's_theorem followed from the Einstein-Rosen-Podolsky (EPR) paper, and then a huge amount of further work including experimental tests of Bell’s inequalities and the CHSH inequality http://en.wikipedia.org/wiki/CHSH_inequality and tests for hidden variables, also the Legget-Garg inequalities http://en.wikipedia.org/wiki/Leggett%E2%80%93Garg_inequality. This is real physics deriving from philosophical explorations.

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  17. Bell’s theorem showed that certain experiments could distinguish quantum mechanics from hidden variable theories. The experimental tests confirmed quantum mechanics. Had they falsified quantum mechanics, Bell’s theorem would have been a big deal. As it turned out, the work just confirmed what was thought by everyone except Einstein and a few other fringe skeptics.

    Bohr is an example of a scientist who made some philosophical remarks in defense of a scientific theory. No one has given an example of a philosopher who had anything worthwhile to say about 20th century physics. (Maybe Popper did, but very few others.)

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  18. “Yang-Mills theory (Maxwell, QED, QCD etc.) is a theoretical framework of connections (rank 1 tensor) and curvature of connections (rank 2 tensor).”

    Wrong: rank 2 field strength tensor is not spacetime curvature! as I prove in my paper on fibre connections, see http://vixra.org/pdf/1301.0187v1.pdf “Einstein’s Rank-2 Tensor Compression of Maxwell’s Equations Does not Turn Them Into Rank-2 Spacetime Curvature”, on vixra:

    Maxwell’s equations of electromagnetism describe three dimensional electric and magnetic field line divergence and curl (rank 1 tensors, or vector calculus), but were compressed by Einstein by including those rank-1 equations as components of rank 2 tensors by gauge fixing as I showed there. The SU(N) Yang-Mills equations for weak and strong interactions are simply an extension of this by adding on a quadratic term, the Lie product. As for the connection of gauge theory to fibre bundles, I as I showed in that paper, Yang merely postulates that the electromagnetic field strength tensor equals the Riemann tensor and that the Christoffel matrix equals the covariant vector potential. These are efforts to paper over the physical distinctions between the field line description of
    gauge theory and the curved spacetime description of general relativity. I go into all this in detail in that 2013 paper.

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  19. This comment does not make much sense. Yang-Mills theory (Maxwell, QED, QCD etc.) is a theoretical framework of connections (rank 1 tensor) and curvature of connections (rank 2 tensor). General relativity formulated in terms of Ashtekar variables uses a SU(2) connection (rank 1 tensor) and curvature of this connection (rank 2 tensor). The only difference is in the dynamics – as already stated.

    Also, LQG does not not result from Ashtekar variables. It employs them, yes, but that is a different statement.

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  20. Einstein carefully read the work of Hume and Descartes. Erwing Schrodinger was a clear example of a physicist very much interested in philosophy. In 1955, in an important lecture during the World Energy Conference, refused to talk about the atomic energy because of his skepticism about the subject. Instead he gave a talk on philosophy. On the other hand, I don’t quite understand what “anything worthwhile to say” means.

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  21. Harry Ellis: “While I argue strongly for sticking to a traditional definition for science methodology, I agree that we should not view science as a sole road to truth or understanding. … Again, I am a good Popperian, opposing positivism.
    I consider all science a branch of philosophy: Natural Philosophy, or “Philosophy of Nature” … And I think it is dangerous when scientists stop recognizing that their methodology is a sub-field of a greater seeking after understanding.
    Maybe there WILL arise a post-science methodology which represents an improved route to understanding.”

    Thanks for speaking out on such a great insight with open-mind.

    Popperianism (with falsifiability as a principle) has been very successful for the past 400 years. Yet, successful does not guarantee it being the best or being correct. The stone-tool was very successful for over half-a-million years, and it must give way to better tools.

    In physics (or science), ‘theory’ is defined with ‘hypothesis’, that is, a guesswork. Thus, by definition, it has a big chance to be wrong. Yet, for every guesswork, it should still give out some ‘consequences’, the so-called ‘predictions’. Then, testing these predictions can be the criterion for this theory (guesswork) confirmation. Thus, this Popper’s empirical falsification doctrine was not only making sense but was a great tool.

    But, any true truth by definition can and must not be falsified. That is, Popper’s empirical falsification doctrine is fundamentally and principally wrong as a ‘truth’-confirmation criterion. The key point here is that there is the world’s difference between the truth and theory. Theory is a humanly built model with hypothesis (guesswork), and it is by definition not a truth but trying to model a truth. Thus, almost all theories are wrong (being not truth), but some of them are very useful as they might be as approximations of the truths. Furthermore, as only a hypothesis based, a theory is only one ‘point’ in the field of truth. That is, its validity is hinged on its ‘connection’ to, at least, another point on this truth field; that is, the validity of the ‘prediction’. Thus, theory (in Popperian sense) is an ‘isolated’ point in the truth field, and its only connection to any other truth point is its prediction.

    Yet, we now have passed the critical mass in the truth-field. We now have many established ‘anchors’ (accepted knowledge) in this truth-field. In this anchored-truth landscape, ‘theory’ becomes the stone-tool with a glory history. The new tool is the ‘framework’ which is no longer hypothesis-based but is ‘axiom’-based. A framework does not make any prediction but must produce a ‘set’ of theorems. And, this set of theorems must ‘match’ with ‘all’ (no exception) the known anchors and answer all open-questions. While a theory hangs in the truth field with only a thin thread (its prediction), a ‘framework’ must ‘cover’ the entire anchors of this truth field, see http://prebabel.blogspot.com/2011/10/super-unification-in-fictitious.html and http://prebabel.blogspot.com/2012/04/axiomatic-physics-final-physics.html . With this new truth (not theory)-confirmation pathway, I must agree with the first part of Dawid’s claim that Popperianism is no longer to be a major pathway in the physics-epistemology.

    But, I do disagree with all his other claims, especially the ‘no alternative argument’. I also totally disagree with his support on the M-string theory, as it has simply failed the ‘anchor-matching’ criterion. M-string theory has failed matching with any single ‘anchor’ (string-unification, nature constants, Planck data, etc.) thus far, while the other ‘framework’ has succeed.

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  22. Ed Witten: “… well, you know, the falsifiablity picture of science is a little narrow. A lot of what scientists do has to do with either discovering things or confirming theories… the Higgs particle was discovered, which you can describe by saying that the Standard Model wasn’t falsified. But… the people who actually did it thought they were searching for the Higgs particle.”

    50:20 https://www.youtube.com/watch?v=N2XerpjV_AA

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  23. “Unfortunately, it doesn’t invalidate the philosophical objection against the atomic hypothesis”

    I don’t mean to claim it does. What I said about strength of evidence and induction was aimed at Larson’s hypothesis, not at your objection. I don’t know enough about the philosophical arguments related to the atomic hypothesis (is “atomism” a fair description, philosophically?) to comment there.

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  24. Even today there are physicists who are interested in reading the philosophy of past centuries. But philosophers turned antagonistic to physics about 50 years ago. Define “worthwhile” any way you want, and modern philosophers come up short. The previous post on Tyson explains this fairly well.

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  25. Witten’s defense of string theory was particularly lame. There is no such “falsifiablity picture of science”. The question was about the testability of string theory, and all he could say was that string theory was related to supersymmetry, and if supersymmetry existed, then maybe people would not complain about string theory so much.

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  26. I think we are not in actual disagreement, but I would go further on the limits – yet strengths – of the role played by “theory” in science. A theory is usually much more than a simple guess since, as you say, it must account for all to-date observations. AND it must imply predictions of new observations, which can then be used to “prove” IN THE ORIGINAL SENSE OF THE WORD, I.E., TEST the theory. (Thus the proverbial “exception that proves the rule” – thus establishing the limits of the rule’s applicability. Also “proving grounds” where hardware is tested to its limits.)

    Mathematical theorems can, of course, be “proven” in a different sense – dating from Aristotle and Euclid. But these have axioms/postulates as “IF” parts, so, once again, the proof is conditional – the theorem is valid contingent on the conditions. Attempts by Russell, Whitehead, and others to achieve condition-free logical proof have apparently failed, and Godel has shown that they must.

    In science, observation provides the constraint (condition) on the logic. No theory in science is ever “proven” in the sense that doubt vanishes. A theory will always be a theory, and as our ability to “prove” (TEST) it expands, it is almost certain to eventually fail. Science acts as a filter, as theory after theory fails. The most that can ever be said for a theory is that it has not failed TO DATE. A “theory” which CANNOT fail, which can explain any conceivable empirical result, is simply not a theory. My favorite examples are creation science (in any of its forms) and the Idea of “The Matrix” from the (first) movie.

    All this is straight Popper as I understand his contribution, but some of it (e.g., that science doesn’t “prove” theories in the popular sense of removing doubt) comes as a shock to most students and some scientists. Thus the oft-heard phrase “it’s just a theory” by which the speaker (I can only hope) means a yet-untested or inadequately tested theory.

    I am a physicist, but an experimentalist who makes no claim to understand string theory. The fact that ST has not produced a testable prediction does not mean that it never will and can’t, but I do question the effort and expense of continuing to push deeper into the esoteric and pretty clearly speculative/untestable areas until there is some hope of testing the ideas with observation.

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  27. I think there is great danger connected with this idea of post-empirical science. Physics ideas have a history of being important for ways of thinking about about other intellectual challenges. Newton’s Principia was important for the Enlightenment. Einsteins ideas in relativity was similarly important in philosophy, psychology and other endeavors, whether the connection was valid or not. The notion of post empirical science offers a lead in for Fox News , Dick Cheney, Ramesh Ponnuru and other frauds to justify their challenge science , their creation of their own facts, and offer Creationism as an acceptable alternative to the Big Bang and evolution .

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  28. Bohr is an example of a scientist who made some philosophical remarks in defense of a scientific theory.

    Where do you think that philosophy came from? Did you ever hear of the Vienna Circle, that collaboration of philosophers, mathematicians and scientists?

    Bohr collaborated with people like Schlick, Neurath, Godel and others on this philosophical approach. This was a completely new way of looking at science, the suspension of the automatic assumption that it was about a ‘real world’ or ‘external reality’.

    This is not to say that they denied an external reality (although some, like Schrodinger did) but that it was not a hypothesis that physics needed.

    You could certainly argue that this is one of the things that enabled physics in the 20th century to make such bold leaps.

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  29. Will this post-empiricism apply to medical practices, engineering and flying airplanes? Just asking. Will it also include post-everyday language usage – mainly academic English?

    Why are philos obsessed only with extreme physics and cosmology and not chemistry, engineering and animal ethology? Where is the philosophy of engineering?

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  30. Hi DM,

    Sure, the beginning and ending volumes are normal and sensible. The intermediate stages are not. It’s like dividing 1 by 0 to get 2 (or whatever value you like).

    OK, so if we say that B-T is doing something mathematically undefined to volume through the process, and thus that we cannot track volume through the process, and thus there is no relation between volumes going in to and out of the process, then we get round any violation of real-world behaviour. If we do that then I’m fine with it.

    Besides, the creation of new empty space from nothing should not be that surprising, since that actually does seem to be happening in the real world as the expansion of the universe accelerates …

    This shows that it is meaningful to talk about “volume” and changes in volume in the real world, and thus we know that the behaviour supposedly entailed by B-T (volumes increasing through rotation) does not happen.

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  31. Bell’s theorem … This is real physics deriving from philosophical explorations.

    Is it really? Or is it real physics that derived from explorations that could be labelled either “physics” or “philosophy” according to taste (and that when “philosophy” on such topics is done properly the philosophy is really just a fancy name for thinking about certain questions which are still entirely within the domain of physics)?

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  32. I understood that you were only commenting on Larson’s scientific objection, not the philosophical one. I just wanted to clarify to readers that the two kinds of objection don’t stand or fall together.

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  33. My guess is that there is no philosophy of engineering because there isn’t much interesting to say about engineering from a philosophical perspective. It is a (philosophically) boring discipline…

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  34. See “Geometry of Electromagnetic Systems” by Baldomir and Hammond. Wheeler got his geon wrong, the confinement is electromagnetic, and we call it an electron. The electromagnetic field is curved space whilst the gravitational field is inhomogeneous space aka curved spacetime. Combine the radial “electric” field lines with concentric “magnetic” field lines to visualize electromagnetic field lines, and then you appreciate why charged particles move in a linear and/or rotational fashion. See this depiction.

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  35. Hi schlafly,

    What I want to mean is that once Einstein read the work of Hume he got a philosophical background to launch the quantum ideas. He didn’t turn antagonistic to physics, though he certainly had to meet with the mainstream. Thus, Einstein was the transmission belt between the new ideas exposed by David Hume and the quantum phenomena discovered by Planck. It means that (indirectly) some philosophers of past centuries are still alive in the epistemic sense. In this context is difficult to understand that philosophers turned antagonistic to physics, at least not all of them.

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  36. “Yang-Mills theory (Maxwell, QED, QCD etc.) is a theoretical framework of connections (rank 1 tensor) and curvature of connections (rank 2 tensor). General relativity formulated in terms of Ashtekar variables uses a SU(2) connection (rank 1 tensor) and curvature of this connection (rank 2 tensor). The only difference is in the dynamics – as already stated.”- Jesper Møller

    The only way to respond to this is mathematically: http://vixra.org/pdf/1301.0187v1.pdf

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  37. Thanks for your reply.

    Harry Ellis: “… theory … it must account for all to-date observations.”

    What do you mean ‘account for’ here? Standard Model encompasses the Alpha (Fine structure constant) but cannot ‘account for’ it. SUSY encompasses the zoo of Standard Model particles but cannot ‘account for’ them. Is M-string a theory? It cannot account for the both above. So, what do you mean that “… it [theory] must account for ‘all to-date observations’.” Are all theories account for the Planck data?

    Harry Ellis: “But these have axioms/postulates as “IF” parts, so, once again, the proof is conditional – the theorem is valid contingent on the conditions.”

    The ‘framework’ which I described in my previous comment is ‘axiom’ based. Thus, it subjects to the rigor constrain of mathematical rules (the conditional and all the whatnot). But the key point goes way beyond that mathematical rigor. It must (must, …, must …) makes ‘contacts’ to (a true ‘account for’) the physics-anchors. The string-unification must be completed. The Alpha must be derived, etc.

    Harry Ellis: “The fact that ST has not produced a testable prediction does not mean that it never will and can’t, …”

    This can easily become a string- parousia, waiting for its first-coming. ST is a failed ‘physics’-theory because it has failed to ‘account for’ any (any, any, …) the known physics (Standard Model, Planck data, Alpha, etc.). If one of its ‘prediction’ (if any) were confirmed, it will still be a failed theory if it cannot make contact to the known reality, as a ‘prediction’ is often not truly related to the core of a theory. One good example is that ‘claiming the observation of CMB gravitational wave’ which is the confirmation of the ‘inflation’ is just a hype (see, http://profmattstrassler.com/2014/05/30/the-bicep2-dust-up-continues/ ).

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  38. Ed Witten: “… well, you know, the falsifiability picture of science is a little narrow. A lot of what scientists do has to do with either discovering things or confirming theories… the Higgs particle was discovered, which you can describe by saying that the Standard Model wasn’t falsified. But… the people who actually did it thought they were searching for the Higgs particle.”

    I do agree with Witten that the falsifiability picture of science is a little narrow and the ‘discovery’ (by accident or an intentional search) can be a pathway of advancing the knowledge of science. But, the ‘Higgs particle discovery’ is really a very bad or totally wrong example for this case.

    Pauline Gagnon (a physicist at CERN) reported on July, 11, 2014 (two years after the announcement of the discovery of Higgs boson), “The question is still open though to see if this is the unique Higgs boson that was predicted by Robert Brout, François Englert and Peter Higgs in 1964 in the framework of the current theory, the Standard Model. But it could also be the lightest of the five Higgs bosons predicted by a more encompassing theory like Supersymmetry that would fix some problems of the Standard Model and open the door to the so-called “new physics, (see http://www.quantumdiaries.org/2014/07/11/happy-birthday-dear-boson/ )”.

    Gagnon’s statement does not give an impression that ‘SM Higgs boson’ is ‘discovered’ in a ‘proper’ sense.

    Nigel Lockyer (Fermilab director) posted a statement on April 24, 2014 (almost two years after the Higgs discovery announcement) at (http://www.quantumdiaries.org/2014/04/24/massive-thoughts/ ), saying, “As just about everyone now knows, the Higgs boson is integrally connected to the field that gives particles their mass. But the excitement of this discovery isn’t over; now we need to figure out how this actually works and whether it explains everything about how particles get their mass.”

    Indeed, the Higgs mechanism (giving ‘some’ particle’s mass) is the hard core about this model while the Higgs ‘boson’ is only a sidekick of the story. How can this core (mechanism) not yet be understood while claiming that the sidekick was discovered? Seemingly, two years after the discovering of this sidekick, this great discovery is of no use for understanding its master (the mechanism).

    In the past two years, physics has gained many great new knowledge (Planck data, EDM (electric dipole moment) data, LUX data, BICEP2 (?), etc.), but nothing from the great Higgs discovery yet. In fact, there are two scenarios on this great discovery.
    1. If it is truly a SM Higgs boson, the ‘physics’ will be half-dead for long time to come. In fact, this worries many physicists now.
    2. If it is not a SM Higgs boson, this great discovery will become a good comic story.

    With the above statements (Lockyer and Gagnon) and the scenario analysis, I will bat my bottom dollar on the fact that this ‘discovery’ will be a great example of how science is fallible, that is, the new 126 Gev boson is after all not a Higgs of any kind. So, the ‘discovery’ is always great but is definitely not a surefire scientific tool until we are totally certain that what the heck we have discovered.

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  39. And the generalizations from animal ethology to human behaviour and culture has been systematically awful. And philosophers have had to sit down and clean up that mess. That said, empirical investigation of animals has led to a major innovation in philosophy: animal rights. Singer’s philosophy depends on considering how humans should relate to other species on the planet as if their suffering mattered. I don’t think any chimps or shrimps are worried about working out that utilitarian calculus, but they might breathe a little easier because of a thoughtful homo sap.

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  40. Einstein also went back and considered early philosophical objections to Newton. Now, that said, translators, librarians, and scholars kept those materials available to that a scientist could draw on them to do the thinking he needed to do his work. Was philosophy really a Humean underlabourer to the science, or simply one resource among many that one particular scientist found useful and another might non have found useful at all?

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  41. A Consitent Quantum Theory of Gravity describing Dark Energy, Dark Matter and galaxy rotation curves and evolution can be downloaded from. http://www.worldscientific.com/worldscinet/ijgmmp

    For those of you interested in falsifying the theory at least when it comes to describing galaxy rotation curved the Nexus Paradigm of quantum gravity predicts the rotation curves and evolution of galaxies using the simple expression

    v^4=GM(r)Hc.exp(4Ht)

    You will observe that the predictions are inagreement with observation thus making the Nexus paradigm the only quantum theory of gravity that is falsifiable in accordance to Karl Popper’s view of science.
    The full equation for gravitational acceleration in the weak field limit is

    g=GM/r^2 +Hv-Hc

    The MoND like regime begins when GM/r^2=Hc=v^2/r
    from which the Tully -Fisher relation can be obtained if we substitute for r to obtain
    v^4=GM(r)Hc

    In this regime the weak field equation becomes
    vdv/dt=Hv
    such that
    v=Vexp(Ht)

    Here V^4=GM(r)Hc

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  42. Note that the same expression for galaxy evolution can be applied at cosmic level to explain late time cosmic acceleration. This happens when the condition GM/r^2 =Hc is met from which we can explain the Coincidence Problem inwhich baryonic energy density is equal to dark energy density at cosmic level.

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  43. Are you there George? Would you like to come and talk about the varying speed of light here? When it comes to empiricism, it is exemplar. And when it comes to conviction, it is disturbing.

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  44. Einstein turned antagonistic to quantum mechanics, for philosophical reasons. But he still believed that physics was making progress towards truth. It was the philosophers after his death who turned antagonistic to physics.

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  45. “… in-line with mainstream physics …” The book “Not Even Wrong” contains no mention of Milgrom. Are we to understand that as a vote of no confidence in MOND?

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  46. Karl Popper’s 1935 correspondence arguments with Einstein are vital reading. See, in particular, Einstein’s letter to Karl Popper dated 11 September 1935, published in Appendix xii to the 1959 English edition of Popper’s “Logic of Scientific Discovery,” pages 482-484. Einstein writes in that letter that he has physical objections to the trivial arguments of Heisenberg based on the single wavefunction collapse idea non relativistic QM. Note that wavefunction collapse doesn’t occur at all in relativictic 2nd quantization, as expressed as Feynman’s path integrals, where multipath interference allows physical path interference processes to replace metaphysical collapse of a single indeterminate wavefunction amplitude. You instead integrate over many wave function amplitude contributions, one representing every possible path, including specifically the paths that represent physical interactions with a measuring instrument.

    “I regard it as trivial that one cannot, in the range of atomic magnitudes, make predictions with any desired degree of precision … The question may be asked whether, from the point of view of today’s quantum theory, the statistical character of our experimental statistical description of an aggregate of systems, rather than a description of one single system. But first of all, he ought to say so clearly; and secondly, I do not believe that we shall have to be satisfied for ever with so loose and flimsy a description of nature. …

    “I wish to say again that I do not believe that you are right in your thesis that it is impossible to derive statistical conclusions from a deterministic theory. Only think of classical statistical mechanics (gas
    theory, or the theory of Brownian movement). Example: a material point moves with constant velocity in a closed circle; I can calculate the probability of finding it at a given time within a given part of the
    periphery. What is essential is merely this: that I do not know the initial state, or that I do not know it precisely!” – Albert Einstein, 11 September 1935 letter to Karl Popper.

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  47. There is one very important distinction that always seems to get lost in these debates, always clearly to the detriment of the non-expert readers. It seems clear to me that the reason it gets lost is because it allows one to make dramatic arguments like Peter’s dismissing string theory as “not even wrong”, but no serious and meaningful discussion of this issue can proceed without dealing clearly with this distinction.

    The distinction I refer to is between the actual specificity of scientific theories – how precisely all of their aspects are fixed in a proposed scenario, so as to make the predictions definite – versus the ability or ease of the underlying theory to be deformed or otherwise changed. Its the former that must be associated with the Popperian criterion for falsifiability and thus potential scientific meaning. To make the mistake of trying to apply Popper’s criterion to the latter is demonstrably absurd: One can’t take seriously a would-be standard of science that presumes to order nature to obey structural properties designed to make things easier for us. It’s also absurd due to the fact that our best empirically verified laws of physics do not possess this property: the Standard Model is just a representative of the general laws of quantum field theory: a hugely infinite dimensional space, and a framework that in general makes no predictions. Yet this has has never prevented quantum field theory from succeeding at describing nature in every way we have a right to expect, since obviously it’s representatives of QFT that are tested and confirmed in experiments.

    These rather basic and inevitable observations imply we can’t just accept these claims at face value that string theory or inflation must be disqualified because they represent a class of scenarios that in full generality are too broad to be scientifically useful. In the case of inflation, the alleged “unscientific” quality boils down to the fact that its just a simple mechanism involving a scalar field, and like most simple mechanisms it can be incarnated in a variety of ways. But its universally obvious that this does not prevent nature from utilizing such a mechanism! The sane response to this situation, and the way science actually works in practice, is to acknowledge that we need a certain level of specificity in order to meaningfully test almost any idea. To embrace this argument that inflation should be disqualified from science is to truly depart from an unbiased scientific effort to understand nature, you’re now in the business of telling nature what it’s allowed to do.

    The claim about string theory is similar, and here the situation is very much like quantum field theory. The main difference is that instead of choosing a ‘representative theory’ from the broader framework, there is just one theory from which one needs to choose a vacuum. The conditions for getting predictions from the underlying structure are directly analogous. The other difference is of course the fact that there is ample empirical confirmation of field-theoretical phenomena and no such empirical confirmation for string theory, but a simple exercise in hypotheticals completes the analogy: There are scenarios where all this talk about non-empirical assessment could rapidly become moot if we observed some clearly string-theoretical phenomena (like string resonances) or other string-predicted physics (extra dimensions, SUSY), and similarly we could also imagine a scenario where pre-quantum science authors might rail against the attack on scientific standards from the “not even wrong” quantum field theorists. One of the best expositions on this crucial point comes from a field theory expert, Matt Strassler, prompted by what he regards as Peter’s unrealistically rosy account of the situation in quantum field theory that he uses to make his case against string theory. It starts here:
    http://profmattstrassler.com/2013/09/23/quantum-field-theory-string-theory-and-predictions/

    The bottom line is that there needs to be some subtlety and measure when assessing the status of these theories. People like Steinhardt seem to be impressed by the fact that inflationary models could be made unreasonably complicated, and the only solution to this, he says, is to disqualify the entire class. But even complicated models can be viable candidates to describe nature. Scientists have always had to exercise some intuition regarding when a particular model becomes too contrived to be believable. There is no acceptable way to redefine science that could eliminate the need for this kind of assessment.

    Broadly I agree with much of what Dawid says, but I think its important to emphasize that the current situation is only quantitatively different, not qualitatively different. Empirical data is and will always be the foundation of science, but it has never been and could never become the only component of it. The very notion of deriving predictions is an inherently logical aspect, and so is the requirement of consistency, without which no true predictions are possible. It’s only natural that non-empirical aspects are in a period of heightened relative importance today, due to the fact that we have a complete renormalizable QFT description could be in principle be valid all the way up to the Planck scale. We also know that field theory is ultimately insufficient, but the measurable departure from this framework might also not occur until the Planck scale. This puts us in an uncomfortable position, but its important to keep a cool head and realize that something like this isn’t all that surprising in light of the continual organized efforts to understand fundamental physics.

    String theory remains “the only game in town” according to well-justified criteria for candidate successor frameworks. In particular, like Dawid mentions, it’s the only theory that resolves the short-distance pathologies of quantized general relativity while also verifiably reducing to quantum field theory (particularly Yang-Mills-Dirac-Higgs field theory) plus GR at sufficiently long distances. Its notable for being the only theory to give a satisfactory, natural account of the entropy of black holes, where other theories have generally offered ad-hoc hacks. Its also in the historically unique position of being fully equivalent and captured by certain field theories, not just reproducing field theory in a special limit, thus suggesting that this would-be “successor” is deeply tied, and in some sense identifiable with, the framework we already have. Given all this, combined with the fact that it remains an invaluable source of insights into other areas of physics and math, its very natural that string theory should remain an active topic of study for some time. Peter says we need “rigorous protections” from wishful thinking and groupthink. As far as I know, no one has ever devised a “rigorous protection” against wishful thinking and groupthink. Instead we should probably be content to let arguments stand or fall based on the strength of their reasoning and their viability to explain known empirical data. It’s okay if not everyone agrees on the exact outcome of those assessments.

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  48. immediatism,

    About what you say “always seems to get lost”, I’ve addressed this “string theory is just in the same situation as QFT and the Standard Model” claim so many times that it’s a FAQ on my blog.

    http://www.math.columbia.edu/~woit/wordpress/?wp_super_faq=isnt-string-theory-just-as-predictive-as-quantum-field-theory

    If you want to engage in a discussion of this, that could be interesting, but you might start by acknowledging that the argument you are making has been addressed by me, often.

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