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| Image illustrating a phenomenologist after reading a philosopher go on about empiricism. |
3:AM has an interview with philosopher Richard Dawid who argues that physics, or at least parts of it, are about to enter an era of post-empirical science. By this he means that “theory confirmation” in physics will increasingly be sought by means other than observational evidence because it has become very hard to experimentally test new theories. He argues that the scientific method must be updated to adapt to this development.
The interview is a mixture of statements that everybody must agree on, followed by subtle linguistic shifts that turn these statements into much stronger claims. The most obvious of these shifts is that Dawid flips repeatedly between “theory confirmation” and “theory assessment”.Theoretical physicists do of course assess their theories by means other than fitting data. Mathematical consistency clearly leads the list, followed by semi-objective criteria like simplicity or naturalness, and other mostly subjective criteria like elegance, beauty, and the popularity of people working on the topic. These criteria are used for assessment because some of them have proven useful to arrive at theories that are empirically successful. Other criteria are used because they have proven useful to arrive on a tenured position.
Theory confirmation on the other hand doesn’t exist. The expression is sometimes used in a sloppy way to mean that a theory has been useful to explain many observations. But you never confirm a theory. You just have theories that are more, and others that are less useful. The whole purpose of the natural sciences is to find those theories that are maximally useful to describe the world around us.
This brings me to the other shift that Dawid makes in his string (ha-ha-ha) of words, which is that he alters the meaning of “science” as he goes. To see what I mean we have to make a short linguistic excursion.
The German word for science (“Wissenschaft”) is much closer to the original Latin meaning, “scientia” as “knowledge”. Science, in German, includes the social and the natural sciences, computer science, mathematics, and even the arts and humanities. There is for example the science of religion (Religionswissenschaft), the science of art (Kunstwissenschaft), science of literature, and so on. Science in German is basically everything you can study at a university and for what I am concerned mathematics is of course a science. However, in stark contrast to this, the common English use of the word “science” refers exclusively to the natural sciences and does typically not even include mathematics. To avoid conflating these two different meanings, I will explicitly refer to the natural sciences as such.
Dawid sets out talking about the natural sciences, but then strings (ha-ha-ha) his argument along on the “insights” that string theory has lead to and the internal consistency that gives string theorists confidence their theory is a correct description of nature. This “non-empirical theory assessment”, while important, can however only be means to the end of an eventual empirical assessment. Without making contact to observation a theory isn’t useful to describe the natural world, not part of the natural sciences, and not physics. These “insights” that Dawid speaks of are thus not assessments that can ever validate an idea as being good to describe nature, and a theory based only on non-empirical assessment does not belong into the natural sciences.
Did that hurt? I hope it did. Because I am pretty sick and tired of people selling semi-mathematical speculations as theoretical physics and blocking jobs with their so-called theories of nothing specifically that lead nowhere in particular. And that while looking down on those who work on phenomenological models because those phenomenologists, they’re not speaking Real Truth, they’re not among the believers, and their models are, as one string theorist once so charmingly explained to me “way out there”.
Yeah, phenomenology is out there where science is done. To many of those who call themselves theoretical physicists today seem to have forgotten physics is all about building models. It’s not about proving convergence criteria in some Hilbert-space or classifying the topology of solutions of some equation in an arbitrary number of dimensions. Physics is not about finding Real Truth. Physics is about describing the world. That’s why I became a physicist – because I want to understand the world that we live in. And Dawid is certainly not helping to prevent more theoretical physicists get lost in math and philosophy when he attempts to validate their behavior claiming the scientific method has to be updated.
The scientific method is a misnomer. There really isn’t such a thing as a scientific method. Science operates as an adaptive system, much like natural selection. Ideas are produced, their usefulness is assessed, and the result of this assessment is fed back into the system, leading to selection and gradual improvement of these ideas.
What is normally referred to as “scientific method” are certain institutionalized procedures that scientists use because they have shown to be efficient to find the most promising ideas quickly. That includes peer review, double-blind studies, criteria for statistical significance, mathematical rigor, etc. The procedures and how stringent (ha-ha-ha) they are is somewhat field-dependent. Non-empirical theory assessment has been used in theoretical physics for a long time. But these procedures are not set in stone, they’re there as long as they seem to work and the scientific method certainly does not have to be changed. (I would even argue it can’t be changed.)
The question that we should ask instead, the question I think Dawid should have asked, is whether more non-empirical assessment is useful at the present moment. This is a relevant question because it requires one to ask “useful for what”? As I clarified above, I myself mean “useful to describe the real world”. I don’t know what “use” Dawid is after. Maybe he just wants to sell his book, that’s some use indeed.
It is not a simple question to answer how much theory assessment is good and how much is too much, or for how long one should pursue a theory trying to make contact to observation before giving up. I don’t have answers to this, and I don’t see that Dawid has.
Some argue that string theory has been assessed too much already, and that more than enough money has been invested into it. Maybe that is so, but I think the problem is not that too much effort has been put into non-empirical assessment, but that too little effort has been put into pursuing the possibility of empirical test. It’s not a question of absolute weight on any side, it’s a question of balance.
And yes, of course this is related to it becoming increasingly more difficult to experimentally test new theories. That together with self-supporting community dynamics that Lee so nicely called out as group-think. Not that loop quantum gravity is any better than string theory.
In summary, there’s no such thing as post-empirical physics. If it doesn’t describe nature, if it has nothing to say about any observation, if it doesn’t even aspire to this, it’s not physics. This leaves us with a nomenclature problem. How do you call a theory that has only non-empirical facts speaking for it and one that the mathematical physicists apparently don’t want either? How about mathematical philosophy, or philosophical mathematics? Or maybe we should call it Post-empirical Dawidism.
[Peter Woit also had a comment on the 3:AM interview with Richard Dawid.]
Simplicity and beauty could mean something else to a geometrist then it does to a phenomological driven individual. In my case there does seem to be a intuitive drive which could be totally misunderstood, as to the essence of this beauty that it could indeed be misconstrued as an abstraction totally devoid of the attachmentment physicality may provide to such a phenomologist.
ReplyDeleteHints of this lineage may have been understood in your previous post as a ordering of geometries that lead into realms of thought that are indeed subjectively based, but are linked later on, as we have seen in its use, as phenomological association becomes understood in physics.
All three arguments of non-empirical theory assessment work on that basis. If scientists have found no alternatives to our theory, this just means that they have no alternative solution to a specific conceptual problem that is related to a given empirical context. If we notice a record of predictive success in the research field, we just talk about predictive success at the next steps of empirical testing. None of these arguments is capable of addressing the question how many alternative theories exist that can be empirically distinguished in principle by some so far unimaginable experiments in the unforeseeable distant future. I call the limited question addressed by the three arguments the question of local underdetermination as opposed to the question of global underdetermination that would address an infinite time-horizon of empirical testing.string theory and post-empiricism
ReplyDeleteHe obviously gets to this point by breaking down how he arrived at his determination......in a way I am not sure how this could be misconstrued as a weakness, but more a deeper ontological review of the status of how things are right now.
“Theory confirmation on the other hand doesn’t exist. The expression is sometimes used in a sloppy way to mean that a theory has been useful to explain many observations. But you never confirm a theory. You just have theories that are more, and others that are less useful.”
ReplyDeleteBut in the inductive-probabilistic inferential context which Dawid appears to have adopted*, (relative) theory confirmation does exist.
* He says: “There is an influential strand of philosophy of science, called Bayesian epistemology, that identifies theory confirmation directly with an increase of the probability that a theory is true or viable.”
We can reconcile the existing theories in two dual ways: we can add new postulates to existing theories and to achieve a limited agreement in this way. Or we can build a new theory from scratch and to demonstrate, this old theories are special cases of the new model. IMO the string theory is the last attempt of modern physics in the former direction. The string theorists predicted the existence of extradimensions correctly, they just didn't expect, that our reality is hyperdimensional so much, it will kill their "elegant" ten-dimensional theory nearly completely. With compare to it, the quantum gravity phenomenologists don't pretend, they have some theory at all - they "just" want to "quantize gravity", so that they're prohibited against such a failure in the spirit of Czech proverb "Who does nothing, breaks nothing." But they all should realize too, that the formal reconciliation of theories, which are already giving a different predictions in 4D space-time is impossible in arbitrarily low number of dimensions.
ReplyDeletePaul:
ReplyDeleteSure one can define "confirmation" as "increase in probability of being true" but then that's a misleading use of the word. If I tell you I confirm that my daughters are twins, would you understand that as meaning the probability increased? The change in probability is what I would call assessment. Best,
B.
/* Physics is not about finding Real Truth. Physics is about describing the world. */
ReplyDeleteIt plays well with famous Richard Feynman's dismissal of the "WHY" questions, but I personally disagree with this stance at all. The adherence on formal description has just lead the contemporary physicists into their defensive stance, in which they're forced to ignore if not dismiss all findings, which seemingly don't play well with description based on established formal theories (general relativity and quantum mechanics). Now I have the things like the antigravity beams and drives, cold fusion, scalar waves and another findings and phenomena on mind. The physicists are supposed to do more for human society than just formal regressions of already observed and understood reality - or they're all predestined to extinct.
PNAS 14(7) 544 (1928), http://www.pnas.org/content/14/7/544.full.pdf
ReplyDeleteCox observed beta-ray parity violation. Defective theory rejected Cox.
Phys. Rev. 105(4) 1413 (1957), http://prola.aps.org/pdf/PR/v105/i4/p1413_1
Yang and Lee observed beta-ray parity violation. Nobel Prize.
How does Dawid rescue Cox? Theory was elegantly , simply mirror-symmetric. Reality said "no." "becoming increasingly more difficult to experimentally test new theories" That is diagnostic! Derivation cannot falsify an empirically defective postulate. Theory rejects external input wherein the defect is absent.
How does Dawid rescue math? Machine proofs are convenient [not(not(p or q) or not(p or not(q)) = p J. Automated Reasoning 19(3) 263 (1997)] and exhaustive (four-color theorem). They can generate immense proofs beyond understanding. Are there outputs exploiting a subtle error?
Galileo was correct. One must look.
There's a branch of Continental philosophy called "phenomenology", so your caption "Image illustrating a phenomenologist after reading a philosopher go on about empiricism" has a funny double meaning.
ReplyDeleteI'm glad your deny that "theory confirmation in physics will increasingly be sought by means other than observational evidence". When methods other than observational evidence reign supreme one might be doing mathematics, which is a noble subject with its own standards of rigor (and its own departments in universities, with their own hiring process). One might be doing philosophy. One might just be chatting. But not doing physics, I think.
For me empirical data (obtained by observing and measuring Nature) are first an efficient tool used to evaluate a theory and second a probe of Nature that can guide theoretical physicists in building their theories.
ReplyDeleteIf physicists can’t use this tool or probe, so be it; they don’t have other choice but to continue to do their work i.e. building theories or models that would bring us closer to the truth of the Natural world as humans perceive it at least. Their theories will be evaluated by the physics community according to its criteria and for some of these theories physicists may even reach a consensus.
In my view it’s that simple.
Definitions of what Natural sciences mean and the subsequent aphorisms may be interesting to discuss but are not that important in my mind.
Sabine:
ReplyDeleteYes I would understand it that way and it isn't misleading. You can call it “assessment” instead of “confirmation” if you like of course but the philosophical idea's what's important and Dawid's usage is standard.
John,
ReplyDeleteYes, I know that phenomenology is a branch of philosophy or at least used to be, but I thought for the readership of this blog, it would be obvious what I mean. I agree with you about math, it's a subject of its own right and arguably an interesting one with its own benefits, I just think one shouldn't pretend doing physics when what one actually does is math.
Paul,
ReplyDeleteThat's all fine by me, I will not fight about the definition of words, even if I don't find it particularly useful to use a word in a meaning very different from the colloquial one. If that is how you or Dawid or somebody else wants to define "confirmation" then we arrive at the stunning insight that one can "confirm" a theory without that theory ever correctly describing any observation (to some precision). In my opinion this is even worse than using the word confirmation to mean "true" (or call it having probability one), which I think is how most people would understand it. (Or, in reality they would take it to mean so close to one that nobody in their right mind would doubt it. Like, strictly speaking I don't know whether my daughters are twins with probability one.)
Be that as it may, I can phrase my point entirely without using these words simply by saying that you can never show a theory is useful to describe nature (read: is part of the natural sciences) without making predictions for observations. You can certainly collect and consider all kinds of other information about the theory, and that may be useful to decide which approach to pursue, but in the end a theory that doesn't make predictions is not about describing the natural world. Best,
B.
Hi Giotis,
ReplyDeleteI think I just don't agree that they have no other choice. Many physicists today clearly make a choice in which they prefer non-empirical assessment over making contact to observation. I think they're just plainly afraid to come to the conclusion that there isn't any phenomenology that they can think of, so they take the easy way out, which is to play with the math, a field that is infinitely rich and will continue to pay their rent. Be that as it may, most of them are tax-funded and that means they shouldn't pretend they work on describing the natural world when they don't. String theorists were pissed at Lee for calling out on them not because he was wrong but because they were afraid they would lose money should the public come to realize they're not getting any closer to understanding the world. And that mislabeling of research is the issue that I am taking with this trend. Best,
B.
Hi Sabine,
ReplyDeleteWell, there is an entire field of research called String phenomenology, with its own conference too. But as you know the problem is that the theory manifests itself at very high energies which can’t be accessed by any experiment. After certain energy scale the special features of the theory and its characteristic empirical signatures fade away. This is the problem we are trying to address here.
And I don’t think money is the issue here. A scientist (as you know better) can’t spend his entire career on something he doesn't believe in just to pay his rent. I’m sure that String theorists really believe in the theory and its explanatory power but you must have an inside view to truly appreciate that power.
OK, first of all: an oxymoron is a figure of speech. The correct term is: contradiction.
ReplyDeleteOxymoron first came into prominence because William Buckley liked to use it. He used it because it made him sound more sophisticated than simply "contradiction" or "contradiction in terms." And because he was actually not all that well educated (Yale rather than Harvard), he apparently did not know the difference.
It's an important difference, because a figure of speech is a totally different animal than a direct statement.
I may have more to say on your post after I've actually read it. :-)
"...a mixture of statements that everybody must agree on, followed by subtle linguistic shifts that turn these statements into much stronger claims." -- Unfortunately the modus operandi in many a field.
ReplyDeleteA nice rant I can very much relate to.
ReplyDeleteBTW, I think near the end you meant to write "called out as group-think".
This comment has been removed by a blog administrator.
ReplyDeleteOK, now that I've read your post, I agree with you. "Physics is not about finding Real Truth." And this goes to the heart of the difficulty between philosophers and scientists. As I see it, what science is about is the exploration of reality in all its forms. And I would stress the term "exploration," because that's the term I use in my own research on cultural evolution, which I like to think of as scientific. I have said many times that there are no assumptions in my work (very unusual for anthropology of any kind), but only examination and evaluation of evidence. In order to explore, and assess, certain possibilities.
ReplyDeleteIt is philosophers who concern themselves with truth (with the exception of Derrida I suppose) and also mathematicians and logicians. And philosophers are entitled to speculate about the viability of certain possibilities and methods even when there is no hope of empirical testing. But they should never call it "science," I agree with you 100%.
I also like your singing, Bee -- and your video production values! :-)
ReplyDeleteThank you for a stimulating posting clarifying basic notions. Theory assessment has become increasingly difficult. Philosopher Richard Dawid suggests what I would call giving up.
Why theory assessment has become so difficult? Is this really true? Or could it be that some wrong belief in our scientific belief system has caused this?
Could it be that our idea about what unified physical theory should be able describe is badly wrong. When we speak about unification, we take
the naive length scale reductionism as granted. We want to believe that everything physical above weak boson length scale is understood and the next challenge is to jump directly to Planck scale (itself a notion based on naive dimensional analysis and could lead to a totally wrong track concerning the ultimate nature of gravitation!).
In practice this means that we we drop from the field of attention entire fields of natural sciences such as biology and neuroscience - to say nothing about consciousness (conveniently reduced to physics in materialistic dogma). These fields provide a rich repertoire of what might could be seen as anomalies of existing physical theory provided we give up the dogma of length scale reductionism and see these anomalies as what
they really are: phenomena about whose physical description or correlates of we actually don't heave a slightest clue. Admitting that we do not actually understand could be the way out of blind alley.
This kind of expansion of the view about what theory should explain might be extremely useful and open up new words for theoretician to understand. Theory could not anymore be degenerated to a question what happens in Planck length scale and it would have huge number of observations to explain. What are the basic new principles needed? This would become the basic question. One candidate for them is obviously fractality possibly replacing the naive length scale reductionism. This would bring in also philosophy, but in good sense rather than as an attempt to authorise a theory which has turned out incapable of saying anything interesting about
the observed world.
Giotis,
ReplyDeleteYes, I've been at that conference a few times. That's good! I'm not saying there's no phenomenology, and just for the record I'm not talking about string theory in particular. Actually, string theory isn't that bad when it comes to phenomenology, even leaving out AdS/CFT, though the balance is clearly way off. It's most of the effort that should be on phenomenology, but it's the other way round.
I'm not saying that scientists spend their life on something they don't believe in. I'm saying scientists shouldn't base their decisions on belief to begin with. Lack of belief is certainly not a problem that string theorists struggle with.
But look, you know theoretical physicists, most of them are of the type that is interested in brainy puzzles first thing, and if you hand them a puzzle they'll start to find it interesting regardless of what it has to do with reality. I know a lot of people who can't put down a logical puzzle once they've seen it. They'll spend the night on it. I can totally relate to this (which is why I never look at these things). That is to say if you put them on any topic that leaves open questions for them to chew on for the years of their masters and PhD, they'll almost certainly find it interesting which will keep them going. Nothing wrong with that, but that speaks for the mathematical richness of a theory not for its chances of correctly describing nature. What I mean is, I'm not saying they're there only for the money.
But I maintain that money is an issue. People follow money, and the social dynamics in academia strongly encourages a rich-get-richer trend. The biggest problem is that it's hard to change fields. But money isn't the only issue though, it is also a psychological phenomenon that Gleiser touched on in his book which I recently reviewed. Somewhere along the line theoretical physicists have come to believe that they can find truth by introspection. When did this happen and why? Best,
B.
Henning,
ReplyDeleteI changed that, thanks.
Sabine you say:
ReplyDelete“Somewhere along the line theoretical physicists have come to believe that they can find truth by introspection. When did this happen and why?”
My answer is that somewhere along the way theoretical physicists gained enough confidence. Look back at all these successes in the last 100 years; from GR to QFT/SM and from Higgs to inflation. These successes permit them to extrapolate their theories to uncharted regions with much bigger confidence even without Nature’s guidance.
Theoretical Physics actually works!
Giotis,
ReplyDeleteI always start my talks with this little speech: There is to my best knowledge not a single historical example where progress in physics has come about without contact to experiment, without contact to phenomenology. Einstein had Michelson & Morley, he had the perihelion precision. The Dirac equation was preceded by a phenomenological model by two Dutch guys treating the electron as a spinning charge. So where does this unjustified faith come from?
Those philosophers better leave science they dont understand alone, instead of broadcasting deluded tirades against it in popular media channels.
ReplyDeletePeople who do not even understand the basic difference between direct and indirect observations and hints for new physics have absolutely no right to badmouth modern physics like this and delude the lay audience like this!
I guess that I am very much a phenomenologist. In my opinion quantum mechnics for example is not a theory of nature but an extremely successful theory, or model, for describing experimental results at the micro scale. I sort of agree with Einstien, no theory of nature can be delocalized.
ReplyDeleteSorry, I did not mean to be anonymous. abc=Ulf Wahlgren
ReplyDelete"There is to my best knowledge not a single historical example where progress in physics has come about without contact to experiment, without contact to phenomenology" Bee.
ReplyDeleteWhat do you do when what you have does not work? The choice is to do more or to do different. Every aspect of civilization given to professional management has become spreadsheet DCF/ROI "do more." That is why we fail.
Philosophy should be liberating. It makes its beans by being obfuscating. "Heteronormatism problematizes homosocial othering."
There is to my best knowledge not a single historical example where progress in physics has come about without contact to experiment, without contact to phenomenology. Einstein had Michelson & Morley, he had the perihelion precision...
ReplyDeleteEinstein’s friend Michele Besso wrote to Einstein in 1918 that with the theory of relativity “speculation had proved itself superior to empiricism”, but Einstein disagreed, saying no genuinely useful and profound theory has ever been found purely speculatively. He said Maxwell’s hypothesis of the displacement current was the closest case, but even there it was motivated by the need to account for the propagation of light. Interestingly, the same need, and the overall success of Maxwell’s equations, were the empirical inspiration for special relativity (rather than Michelson and Morley in particular). For general relativity the empirical fact cited by Einstein was the equivalence of inertial and gravitational mass.
The Dirac equation was preceded by a phenomenological model by two Dutch guys treating the electron as a spinning charge.
“Preceded by”, yes, but that work didn’t lead Dirac to his equation. Dirac himself said “A good deal of my research in physics has consisted in not setting out to solve some particular problem, but simply examining mathematical equations of a kind that physicists use and trying to fit them together in an interesting way, regardless of any application that the work may have. It is simply a search for pretty mathematics. It may turn out later to have an application.” He said the Dirac equation was found by just “playing around with equations”, trying to find one that was both linear and Lorentz invariant. The requirement of Lorentz invariance obviously has empirical foundation, but he said the requirement for linearity came because the transformation theory (inherently linear) was “his baby” and he couldn’t bear the thought of giving it up.
Physics is about describing the world. That’s why I became a physicist – because I want to understand the world that we live in.
ReplyDeleteBut “describing” and “understanding” are two different things. Einstein remarked that an accurate description may not give us a deep understanding: “May we hope to be guided safely by experience at all, if there exist theories (such as classical mechanics) which to a large extent do justice to experience, without comprehending the matter in a deep way?” And he later wrote: “I have learned something from the theory of gravitation: no collection of empirical facts, however comprehensive, can ever lead to the setting up of such complicated equations. A theory can be tested by experience, but there is no way from experience to the construction of a theory. Equations of such complexity as are the equations of the gravitational field can be found only through the discovery of a logically simple mathematical condition that determines the equations completely, or almost completely. Once one has obtained those sufficiently strong formal conditions, one requires only little knowledge of facts for the construction of the theory. In the case of the equations of gravitation it is the four-dimensionality and the symmetric tensor as expression for the structure of space that, together with the invariance with respect to the continuous transformation group, determine the equations all but completely.”
Somewhere along the line theoretical physicists have come to believe that they can find truth by introspection. When did this happen and why?
In 1933 Einstein wrote: “Our experience hitherto justifies us in trusting that nature is the realization of the simplest form that is mathematically conceivable. I am convinced that purely mathematical construction enables us to find those concepts and those lawlike connections between them that provide the key to the understanding of natural phenomena. Useful mathematical concepts may well be suggested by experience, but in no way can they be derived from it. Experience naturally remains the sole criterion of the usefulness of a mathematical construction for physics. But the actual creative principle lies in mathematics. Thus, in a certain sense, I take it to be true that pure thought can grasp the real, as the ancients had dreamed.”
Regarding Einstein’s later fruitless search for a “unified field theory”, Max Born wrote “He had achieved his greatest success by relying on just one empirical fact [all objects fall at the same rate] known to every school boy. Yet now he tried to do without any empirical facts, by pure thinking. He believed in the power of reason to guess the laws according to which God has built the world”.
Amos:
ReplyDeleteYes, the Goudsmit and Uhlenbeck model for all we know did not influence Dirac (much). My point is simply that the phenomenological models preceded Dirac's derivation. Best,
B.
ReplyDeleteSorry, Bee, to insist on something only tangential to your latest post. But just as with misuse of the term "oxymoron," I am concerned with misuse of the term "phenomenology."
I realize that you are not alone in the use of this term to describe a certain approach to scientific research, and by now it's probably too late to do anything about it. But "phenomenology" is an extremely dangerous term for any scientist to use as it can so easily be misinterpreted.
Here is the definition from the online Merriam Webster dictionary, which is entirely typical:
Definition of PHENOMENOLOGY
1
: the study of the development of human consciousness and self-awareness as a preface to or a part of philosophy
2
a (1) : a philosophical movement that describes the formal structure of the objects of awareness and of awareness itself in abstraction from any claims concerning existence (2) : the typological classification of a class of phenomena
b : an analysis produced by phenomenological investigation
I could not find one single definition consistent with your view of "phenomenology" as the equivalent of an empirically based approach to scientific research. And I'm puzzled why you don't simply describe your work as, simply, "empirical" as opposed to purely theoretical.
Use of this term in the manner you use it is a depressing sign of the huge rift that's developed between physics and philosophy, to the extent that scientists feel free to simply appropriate terminology associated with philosophy as though the association could be ignored.
Something similar has happened in the social sciences with the term "ontology," which has also been seriously misused in this new context.
Otto Stern got the 1944 Nobel Prize/Physics for showing the Dirac Equation failed for predicting proton magnetic moment. All the fun is in the footnotes.
ReplyDeleteDocG,
ReplyDeletePhenomenological Ontology is a perfectly good modern (20th century) terminolog from an existential stance to ideas about essence. Where QM and GR meet as a compact oxymoron is this a contradiction?
Wm. Buckley would give anyone a hundred bucks if stranded on the streets of New York. Should we judge people by what they say or by what they do?
Yes, subjective elements and terms are involved here and a little deeper ideas of what are explicit say colors A and B as the same or one class of many shades of the same color term.
What I think I see in Sabine's "scientific phenomenology is the ability to try at least to explain or bridge our less than stellar difference between physicality and our dreams. The landscape of string theory is dream if not then certainly an oxymoron as other models that make the equivalent speculation as to what is direct or indirect evidence.
one soul's contradiction is another's tautology, evidently.
Awakening to higher understanding of limits to mental or social connections can be seen as the same logical space as a conceptual Epiphany if we want to find out the how and why of our world.
Cones are sharp and spheres are blunt so Flatland can seem oxymoron space.
You forgot to capitalize that "o."
ReplyDelete:-)
Lee has long suspected LQG and string theory can be unified. His string matrix model was an attempt at such a unification. That model turns out to be dual to a certain N=2 supergravity theory containing extremal black holes with 27-dimensional charge space. Duff et al have expressed D=11 supergravity in variables that are also related to Lee's string matrix model, based on work done by Baez and Toppan et al. There's an emerging punchline just around the corner.
ReplyDeleteThere may be less of a difference between Physics and Mathematics than proposed. Mathematics has its own "empirical" problems. As I understand it, mathematicians have generated theories assuming that the (unproven) Riemann Hypothesis is true because the experimental evidence is very strong and because the assumption allows some areas of number theory to be further developed. Those areas, of course, will suffer if a counter-example is proved to exist. And just like string theory, the RH has generated its share of books for the general public. :-)
ReplyDeleteSabine,
ReplyDeleteWell it may not be colloquial usage but it is dictionary usage and that's more than can be said for many words that have a (precise) technical definition in some field (as well as a colloquial one). Anyway, I think it's more than useful to use the same meanings of words as one's opponent in a criticism of their arguments. There is no stunning insight in the ability of Bayesian Confirmation Theory to (re-)assess models/theories in the light of cogent argument or information other than (new) predicted data, but it doesn't apply to ones which never make testable predictions.
Of course you have to read this post of yours Bee in concert with many of the beliefs that are also sitting with it's writer:)
ReplyDeleteWhich comes first?
Seminar on the History of Hyperbolic Geometry, by Greg Schreiber
We began with an exposition of Euclidean geometry, first from Euclid's perspective (as given in his Elements) and then from a modern perspective due to Hilbert (in his Foundations of Geometry). Almost all criticisms of Euclid up to the 19th century were centered on his fifth postulate, the so-called Parallel Postulate.The first half of the course dealt with various attempts by ancient, medieval, and (relatively) modern mathematicians to prove this postulate from Euclid's others. Some of the most noteworthy efforts were by the Roman mathematician Proclus, the Islamic mathematicians Omar Khayyam and Nasir al-Din al-Tusi, the Jesuit priest Girolamo Sacchieri, the Englishman John Wallis, and the Frenchmen Lambert and Legendre. Each one gave a flawed proof of the parallel postulate, containing some hidden assumption equivalent to that postulate. In this way properties of hyperbolic geometry were discovered, even though no one believed such a geometry to be possible.
The value of non-Euclidean geometry lies in its ability to liberate us from preconceived ideas in preparation for the time when exploration of physical laws might demand some geometry other than the Euclidean. Bernhard Riemann
It really is that simple.:)
Thus arises the problem, to discover the simplest matters of fact from which the measure-relations of space may be determined; a problem which from the nature of the case is not completely determinate, since there may be several systems of matters of fact which suffice to determine the measure-relations of space - the most important system for our present purpose being that which Euclid has laid down as a foundation. These matters of fact are - like all matters of fact - not necessary, but only of empirical certainty; they are hypotheses. We may therefore investigate their probability, which within the limits of observation is of course very great, and inquire about the justice of their extension beyond the limits of observation, on the side both of the infinitely great and of the infinitely small. On the Hypotheses which lie at the Bases of Geometry. Bernhard Riemann
ReplyDeleteTranslated by William Kingdon Clifford
[Nature, Vol. VIII. Nos. 183, 184, pp. 14--17, 36, 37.]
Hi Paul,
ReplyDeleteYes, you are right, that was not very fair of me, mea culpa. Anyway, I think that you, I and even Dawid agree that re-assessing a theory and updating one's opinion accordingly is useful and necessary to proceed with the development of models. What I don't agree on is that non-empirical assessment ever tells us anything about the use of these models to describe the world around us. It just tells us how well the theory performs to criteria some people believe to increase the probability that the theory is useful.
One could also add though that the line between empirical and non-empirical assessment sometimes is quite blurry. As I elaborated on in earlier posts for example criteria like absence of ghosts or anomalies are actually empirical, the same goes for singularity avoidance etc, yet few would refer to these as constraints by data or observables, even if strictly speaking they are. Best,
B.
What is the difference in a mathematical and a philosophic idea? Can we imagine if isolated in a room with no knowledge of the world outside by introspection develop the physics of that imagined world?
ReplyDeleteIf we thought of this in terms of "the Chinese room arguement," how can we know if the message is more than the mechanical laws as written on but the surface in shadows of our cave like room? What can physics ultimately say but B exists in a landscape where B preceded by A or X can be followed by C or Y?
The world as science is B in this sense for A that comes before it (big bang?) And C that may follow it is in the realm of philosophy still.
But do we as science permit disembodied minds? Can we imagine anything other than "I be" (save perhaps we may not be " )that in either sense of outside or inside us both directions are external ?
Hi Sabine,
ReplyDeleteYes - and I at least agree with all of that. :-)
"...Or maybe we should call it Post-empirical Dawidism".
ReplyDeleteMaybe we should just call it pseudoscience.
"Because I am pretty sick and tired of people selling semi-mathematical speculations as theoretical physics and blocking jobs with their so-called theories of nothing specifically that lead nowhere in particular."
ReplyDeleteI really loved this line.
Thank you. I think much the same, give or take a few semantics, but I like the way you write it. (It is very humbling to realize that English is not your first language.)
ReplyDeleteWell ranted, Sabine.
ReplyDeleteMaybe part of the problem is that we don't have a good word for a theory that is mathematically consistent but doesn't correctly model nature. "Wrong" is the most accurate, but seems overly strong.
Speaking of "subtle linguistic shifts": The term "post-empirical science" 'cited' in the post appears nowhere in my interview. There is just "post-empiricism" in the header, which obviously, given that it is an interview, was not chosen by me but by the interviewer. "Post-empiricism" alludes to the philosophical position of empiricism and actually may be an adequate characterization of my position. "Post-empirical science" is a gross distortion of my position which I emphatically reject. As I say explicitly in the interview, what I call "non-empirical theory confirmation" can only work as long as empirical confirmation does happen somewhere in the research field. My claim is that a strong record of empirical confirmation in a research field under certain conditions can increase the probability of the viability of other theories in the field that have not been empirically confirmed. The currently predominant philosophical conception of theory confirmation (Bayesianism) equates confirmation with the increase of the probability that a theory is true or viable. For that reason I speak of "non-empirical theory confirmation".
ReplyDeleteRich, all evil requires to succeed is fair treatment,
ReplyDeletehttp://donsnotes.com/reference/images/pop_growth.gif
"Maybe part of the problem is that we don't have a good word for a theory that is mathematically consistent but doesn't correctly model nature. "Wrong" is the most accurate, but seems overly strong."
ReplyDeleteA 'Ptolemaic theory' might be a useful adjective/phrase in this context, since the meaning is plain to any scientist and the phrase is backed by an actual archetypal theory that was mathematically correct, but was clearly a very unnatural paradigm for both the solar system and the cosmos.
I think overall P.M Dirac sums it up quite neatly:
ReplyDelete“The successful development of science requires a proper balance to be maintained between the method of building up from observations and the method of deducing by pure reasoning from speculative assumptions.”
In my mind String theory respects the above in any conceivable sense.
You can picture all the directions in Minkowski space as the points in a three-dimensional projective space. The relationships between vectors, null-vectors and so on - - and you get at once just the relationships between points in a three-dimensional vector space. I always used these geometrical ideas for getting clear notions about relationships in relativity although I didn’t refer to them in my published works.Oral History Transcript — Dr. P. A. M. Dirac
ReplyDeleteThe type of inclination goes back in this regard to the Wunderkammern, and a idea encased, in such a space. You might remember them in Arizona?
When one is doing mathematical work, there are essentially two different ways of thinking about the subject: the algebraic way, and the geometric way. With the algebraic way, one is all the time writing down equations and following rules of deduction, and interpreting these equations to get more equations. With the geometric way, one is thinking in terms of pictures; pictures which one imagines in space in some way, and one just tries to get a feeling for the relationships between the quantities occurring in those pictures. Now, a good mathematician has to be a master of both ways of those ways of thinking, but even so, he will have a preference for one or the other; I don't think he can avoid it. In my own case, my own preference is especially for the geometrical way. Paul Dirac
ReplyDeleteI am led to these remarks by the consciousness of growing danger in Germany of a separation between abstract mathematical science and its scientific and technical applications. Such separation can only be deplored, for it would necessarily be followed by shallowness on the side of the applied sciences, and by isolation on the part of pure mathematics .... Felix Klein on intuition
What kind of space is the Planck scale that we might envision some kind of dynamics going on......? It indeed begins as subjective exploration....and in that space and place with a kind of geometry that will emerge?
Intuition and Logic in Mathematics by Henri Poincaré
On the other hand, look at Professor Klein: he is studying one of the most abstract questions of the theory of functions to determine whether on a given Riemann surface there always exists a function admitting of given singularities. What does the celebrated German geometer do? He replaces his Riemann surface by a metallic surface whose electric conductivity varies according to certain laws. He connects two of its points with the two poles of a battery. The current, says he, must pass, and the distribution of this current on the surface will define a function whose singularities will be precisely those called for by the enunciation.
Some of Wheeler's original goals remain important for this work, particularly the hope of laying a solid foundation for quantum gravity. Geometrodynamics
ReplyDeleteRichard Dawid,
ReplyDeleteYour argument that
"My claim is that a strong record of empirical confirmation in a research field under certain conditions can increase the probability of the viability of other theories in the field that have not been empirically confirmed."
seems inconsistent with the argument that the experimental inaccessibility of data relevant to string theory means new methods of theory confirmation are needed. Put differently, I don't see how you can use past success of HEP theory based on active engagement with experiment to argue for success of HEP theory unconnected to experiment.
Peter Woit
Hmmm. Well, I don't think theory confirmation will become post-empirical - yes, that philosopher's exaggeration glide mattered. Yet I do think that theory "confidence" will to a large extent become post-empirical, as many scientists and philosophers and whomever gravitate to thinking that suchandsuch is "probably true" for conceptual reasons. Note for example, Sean Carroll's defense of MWI at Why the Many-Worlds Formulation of Quantum Mechanics Is Probably Correct. The title makes the needed point (altho I and many others there disagree with him!) that there are "reasons" to believe it, even without specific empirical support.
ReplyDeleteBTW, amazing to me that so many people are attracted to an "interpretation", the basic structure of which (ratios of superpositions etc.) is fundamentally inimical to the observed Born probabilities. Indeed, MWI is arguably more a "theory" for that reason (and probably a wrong one) than merely a post-facto "interpretation."
I read Dawid's interview with real interest, but some things bothered me. First, there are many references to the "underdetermination of theories," but only one to "Occam's razor," and that from the interviewer, not Dawid. Yet the two concepts are intimately linked.
ReplyDeleteMoreover, Occam's razor is already a type of non-empirical confirmation, only "confirmation" isn't really the best term. What Occam implies is that, among all theories that account equally well for the evidence, the theory requiring the fewest explanatory elements, usually understood as the "simplest" theory, is to be "preferred."
Occam's razor is important because there is, in principle, an infinite number of theories that could account for the same evidence (i.e., the underdetermination of theories).
This is why a strictly "phenomenological" approach (to use Bee's quaint terminology) is never sufficient. Ptolemy's view of the universe accounted for the evidence just as completely as Newton's (at least in Newton's day) but since his theory was far simpler, it was quickly accepted.
So it looks to me like what Dawid is arguing for isn't really very new. The only thing new about it is the use of the word "confirmation," which is clearly a misnomer. If it's rewritten to read "nonempirical theory support," then I see no problem.
However: I see no way such an approach can be used to support, much less confirm, string theory. Because string theory violates Occam's razor in just about any way anyone can think of. It's famous for being excruciatingly complicated and difficult to understand, requiring some of the most convoluted mathematical procedures known to science.
DocG, that's a good point. OR itself is a sort of conceptual forcing tool in use for centuries. (I've long wondered, why we should believe it will pick the most likely "true" theory, in any way that isn't a circular definition.)
ReplyDeleteBTW Bee, that little visual Turing Test you got there, is mighty hard even for humans to make out ... I had to process the image. (But cute, many seem to be pics of actual house numbers ...)
Peter,
ReplyDeleteI would agree with you if either string theory were predictively empty or if the relations between theoretical structure, prediction and the arguments of non-empirical theory assessment were of a substantially different kind than in gauge theory. In string theory proper, it seems plausible to me that the theory does have empirical implications at some level (though that level may well be very difficult to access) and that the relation between the consistency arguments which motivated string theory and the no alternative argument is similar to the standard model case. Clearly, there are problems in the analogy, in particular the highly incomplete state of string theory, but with respect to the crucial question, the spectrum of possible answers to consistency problems, ST is played in the same ball park as gauge field theory. There are other contexts where I am more sceptical. For example, it seems problematic to me to extend a no alternatives argument to anthropic reasoning where the mechanism of extracting predictions from the theory’s structure is of a very different kind than in conventional scientific reasoning and no success record of comparable previous cases of anthropic arguments can indicate whether or not a no alternatives argument works with respect to this mode of reasoning.
Richard
Richard,
ReplyDeleteI'm glad we at least agree that anthropic reasoning can't be justified this way.
Where we disagree I guess is that I just don't see string theory and gauge theory as being currently in the same ball park. They may have been back in 1984/85 when there was a rather specific proposal for connecting compactified string theory to the SM, but 30 years later I think the lesson learned is that this doesn't work as hoped. Learning more about string theory led to some interesting things, but also the realization that this was an extremely complex structure that in principle one could embed the SM in in many different ways, none of which really explained anything. Back in 1984/85 one could hope that solving the moduli stabilization program would give something predictive, instead we've got the landscape.
In the last sentence of my comment, read "problem" for "program".
ReplyDeleteRichard,
ReplyDeleteThanks for letting us know that the title was not a phrase you coined, and sorry for the misunderstanding then. Alas, you've just done it again, you wrote:
"My claim is that a strong record of empirical confirmation in a research field under certain conditions can increase the probability of the viability of other theories in the field that have not been empirically confirmed."
What do you mean with "viability" of a theory in the natural science if not "usefulness to describe nature", which hinges on the power of a theory to describe nature which, again, can only be assessed by actually describing nature.
Best,
B.
Richard D.,
ReplyDeleteWords shift all the time in philosophy. The meaning for say mass shifts as well in physics, radically sometimes.
I have tried to put my mind into your views (as philosophy). It makes for some interesting models.
Perhaps when one crow learns to use a tool and at a distance all the crows know this... magic or just statistical coincidence? Science or evidence beyond experiment?
What about some of the core science concepts we do seem to pretend success in theory accumulates by belief I suppose?
What if the one universe is a string? Between two ends what is it made of if not something like the issue of such spooky action?
Ockham was a philosopher but I am not sure he applies, nor anything outside of induction or deduction held together usefully between it we call abduction now (since beam me up Scotty has been observed in the laboratory).
Is there a well, post-empirical philosophy?
Taking things seriously, trying to face these deeper questions, is exhausting and does not need the same old conflicts or side issues. We need to ask and feel a little deeper such questions than we do now.
How is it some say we have reached the end of knowing all but not what it is (Hawking once said it) and then we reach the point were we cannot know what it is as well as an end of knowing?
When I find out who and when some of these ideas in physics became fixed I almost resent the building of errors I hear repeated as informal journalistic errors. Or is Jung right we eventually reach the collective frontier?
All of a sudden such ideas seem to come back from the distance to haunt me (it is about the music of the spheres, one plan for life and the solar system or a chaos of them) I mean in learning so many songs sound like bits and pieces of what we have heard.
If you are right, and philosophy as such is more powerful than today's physics (and perhaps neutral toward mathematics). Did my tinkering in these contemplative trans-Ptolemaic realms teach you at a distance or did you somehow whisper in our dreams a question, a very zen like question perhaps, and a few sacred cows?
Dr Dawid, what you seem to be saying is that, if physics is deprived of experimental input, then physicists might nevertheless arrive at conclusions by consensus. In other words, instead of being wrong individually, they can be wrong collectively.
ReplyDeleteAnd that way of doing physics might well be taking root even as we speak. For example, there is a rapidly growing consensus that, whatever else may be right about string theory, it does not provide a sensible theory of quantum gravity. Something similar already happened to loop quantum gravity.
The thing is, though, that this post will probably trigger a strong backlash from people who claim that all of *their* friends are convinced that string theory solved this problem long ago, and that the rest of us are just idiots.
So you see that "consensus physics" doesn't really work very well. If I had wanted to argue about politics I would have studied political science, not real science.
Wow - my mind is in a pretzel! I tried to read as many of the comments - did anyone mention Popper or Kuhn? Anyway I thought the paradigm of empirical science leaned toward this realm of 'falsification' versus the old positivist school.
ReplyDeleteHere is a link to one of my favorite - ahead of his time Cambridge biologist Rupert Sheldrake - morphic resonance theory - and iconoclast against the reductionist materialist school that has ruled but in light of quantum physics yet is no longer valid. This is his banned Ted talk. A cool distinction considering what they have been putting out there lately.
http://www.youtube.com/watch?v=JKHUaNAxsTg&feature=youtube_gdata_player
“There is no quantum world. There is only an abstract physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature...”
ReplyDeleteNeils Bohr
The Planck Scale
ReplyDeleteYou know it puzzles me that the effort to identify a region of wanting foundational is somehow given too, criticisms that cannot supply any other theory to the presence of the evolving vision given a high energy regime. So the view of the black hole from the horizon becomes a play ground of sorts. I should not have to mention questions about the view from the horizon?
But it's more the that. The journey of your consciousness which can be taken into these regions is a viable question of what exists in that distance just as great as those who venture out into the stars, given their theoretical aptitude?
I just don't get it.
Plato, you're missing the whole point about the definition of science and its parameters. It's not that complicated. When you try to complete a jigsaw puzzle the first thing you do is look for the most distinct and particular feature in the picture of the puzzle that comes with the puzzle itself. It might be a small area that has a color different from the rest of the puzzle and then you try to find other pieces with that distinct color. If you tried to find two pieces just by shape alone, especially at the beginning, then you'd be lost.
ReplyDeleteThis is analogous to people working on string theory. There are at least 10^500 string compactifications in the landscape. Yet string theorists seem to think that looking just at shape of strings instead of color of the world is all that's important.
Science works just like putting a puzzle together. You do the easy stuff first and they form little islands of knowledge. Then little by little you try to extend those islands by joining together many small islands of knowledge. Pretty soon you have large continents of knowledge and the obvious task is to try to join those continents into a world.
I just don't see Dawid's philosophy addressing this in a meaningful way. It seems to me what he's saying is "Ok, look at this funny shaped piece. Let's try to find a match for it in the 10^500 pieces that we know nothing about" (and may not even exist).
Instead of trying to join the large continents of knowledge we already have as exemplified in the SM and in gravity he's trying
to redefine what science is. That shouldn't be hard for you to understand. We simply aren't at the point where there is less than 10 pieces in the puzzle left which are all the same color. That is the only time that finding pieces by shape really works.
Hi Eric,
ReplyDeleteI think I have understood the dilemma facing scientists with regard to how models can work to take existing knowledge and move it ever so slightly forward given the work they had already done qualitatively. The science had already been developed to the point they have to push theirs minds into the chasm of the deep, in order to understand at this point they have to work from the boundary, create firewall examples to further elicit some deeper insight and movement forward.
For me, the Higgs is an example. The science was developed to look for where this would exist in an energy range? So we know now. Up until that point, it was a work in progress.
The consistency with which I share is the geometry with which the fathers develop along with the requirements of the science, that by example lead to relativity, and further insights, a requirement for quantum gravity.
I do not think anyone with the fields that
I have been watching disregard the importance of the science in relation to phenomenology either.
There were a number of comments addressed to me. Rather than answering individually to each of them, let me give a general answer that, I hope will address some though surely not all points raised.
ReplyDeleteLet me start by emphasising again that my concept of non-empirical theory confirmation (let me call it NEC) does NOT imply ore even allow for something like “post-empirical science”. NEC of a theory relies on empirical confirmation of other theories in the research field. Moreover, as Sabine is absolutely right to point out, the viability of a theory is to be understood in terms of agreement with data. If NEC increases the probability that a theory is viable, it increases the probability that the theory will turn out to be in agreement with data once one will be able to test it. This means that NEC cannot be applied to theories that are in principle predictively empty. (They can be applied to theories like ST, though, whose empirical implications are not yet understood, as long as one deems it plausible that there will be some empirical implications in the end.) So NEC can never replace empirical theory confirmation across the board but can only extend the reach of scientific theory assessment to regions where empirical testing has not been achieved yet (and maybe won’t for a long time to come.)
Rastus Odinga raised the point that NEC can only work based on the scientists’ consensus with respect to their application of NEC. This seems to turn scientific conclusions into a matter of sociology. That’s a serious worry and it has been expressed by a number of commentators, not just on this blog. I want to answer by making two points.
First, the fact that subjective assessments enter NEC does not mean that there is no rational basis for NEC. Much of my work is an attempt to show that there is.
Second, deliberation and consensus-building among scientists plays an important role in empirical confirmation as well. Take the example of the supernovae measurements which indicated a cosmological constant in the late 1990s. It took years until a consensus developed that the data indeed implied a cosmological constant. That consensus was not based on a mathematical deduction of that result. Rather, it was based on considerations very similar to those which can increase the trust in an empirically unconfirmed theory: No plausible alternative explanations were found, the cosmological constant interpretation provided a coherent overall picture and the past record of similar situations made scientists confident that, in situations of that kind, they could trust their analysis to a certain degree. It may still turn out that something completely different is responsible for the supernovae data. But, based on the empirical evidence, it would just be inadequate to suggest that there is no good scientific reason for believing that there is a cosmological constant.
One might still argue that NEC involves a higher degree of subjective assessment and thus a higher degree of diverging opinions than the interpretation of empirical data. But even that is not always true. It seems open to debate whether there was less consensus around the year 2010 about the existence of a Higgs particle of some kind, which back then was based entirely on NEC, than about the existence of a cosmological constant, which was based on data and its interpretation.
Therefore, I argue that it is implausible and artificial to rule out NEC as a genuine method of theory confirmation in modern physics.
You may still argue that NEC is too weak and shaky in the case of string theory to instil trust in the theory. Fine. All I want to establish is that NEC is in principle a viable strategy for establishing trust in string theory. And if one thinks it doesn’t work in that case, she or he should discuss the arguments in the given specific case rather than reject NEC as a matter of principle.
Richard
Dear Sabine,
ReplyDeleteI think the best way to understand the roles of empiricism versus arguing from simplicity / elegance is via Solomonoff induction, a mathematical formalism that captures (in my view) the essence of how science approaches truth. According to Solomonoff induction, the probability of a theory consistent with all observations so far (formally viewed as a program for a universal Turing machine whose output is those observations) is proportional to 2^{-n} where n is the number of bits needed to describe it (the length of the program). Thus, in some sense it is possible to assign probabilities to theories according to their complexity before performing new experiments. However, in practice, given a specific theory, it is not possible to know whether there are other theories of similar or lower complexity (it is a theorem that Kolmogorov complexity - the length of the minimal theory - is uncomputable). This is the reason predictions are much more valuable than postdictions. If you made a prediction and it came true, than the posteriori probability your theory is truly the simplest explanation is much greater than if you proposed the theory with hindsight. Formalizing the later reasoning requires a theory of logical uncertainty which is unfortunately yet unknown (but there are interesting speculations by e.g. Paul Christiano and Marcus Hutter).
So, it is true that simplicity lends a theory credence (i.e. makes it more probable) but putting it to numbers is very difficult. On the other hand, successful predictions lend a theory much *more* credit. Plus, as long a nobody is actually counting the bits in those theories the latter criterion is much more objective.
Regarding people selling speculations and blocking jobs, it feels to me like going way too far. I don't work in the academia so I know little of its workings from the inside. However, it seems to me that people who can appreciate the quest for truth which is physics (from whichever angle) are already a scant minority, without fighting among themselves.
Eric,
ReplyDeletescience as a puzzle...
First in this sort of puzzle we usually find the edges first.
If we have all the parts of a puzzle we can readily see the missing piece. Once such piece may tell us the shape of the whole puzzle (if say egg like).
What if the piece is part of an infinite flat plane?
Plato is right to consider the subjective aspects as part of the puzzle if we for example try as the lady who wrote the Cosmic Cocktail imagines space expanding into higher dimensions and there not a point focus as the big bang. Her prediction of Unique early stars could be found, her interest in dark energy and so on.
Imagine then an expansion that really acts around a flatland space that it is also steady and not expanding. She holds there would be several primitive simple ideas in a groups of physicists that are such a state of mind before the theory or experiments are worked out.
We seem to be unique to see both sides of the initial thinking and to try to define the parameters as unity, or perhaps half unity.
This state of mind I cannot say is purely geometric, but I can say it is a recurring dream lately that is a new more complicated question that persists until I correctly or reasonably interpret it. But as a landscape of sorts it was a very interesting place. It raises very many new questions, sorry I cannot say it clearly at the moment.
BTW Lubos is still calling the rest of us names... I find his posts very hard to understand when he defends his idea of quantum as if he knows, and has said, string theory would not be true if QM theory shown not fundamental or complete.
I thought the string landscape problem had moved on and that its originators decided there was only one such landscape recently.
btw, 27 should really be read as 28 in that comment, let us not forget the simple algebra. Such counting structures (at least allowing for 4D so not to be ancient sacred geometry only)with a time arrow to handle complexity, would in deep informational notations suggest structures for the quark differences, qqq or q and -q types. This structure also explains the shell structures if we only concern ourselves with electromagnetic spaces.
Richard you say:
ReplyDelete“NEC of a theory relies on empirical confirmation of other theories in the research field.”
Can you be more specific?
Which are these other theories in the research field of String theory?
For example do you have in mind Perturbative/non perturbative QFT, SM, SUSY/SUGRA, GUT, GR, perturbative QG, inflation? These theories are all low energy effective limits of String theory.
In fact it’s the only theory that encompasses them in a top down fashion and in a theoretical/ mathematical consistent way; it can reproduce their gauge group content, couplings and Lagrangians. It is the only theory that can give top down the corrections to the Einstein-Hilbert action for example.
Moreover it is the only theory that has the potential to combine them in a single dS vacuum with the correct CC, which is quite amazing if you think about it.
In this rare piece of introspection a theoretical physicist Carlo Rovelli concedes, that the separation of intuitive and formal approaches in physics was detrimental to both.
ReplyDeleteOtto,
ReplyDelete"science as a puzzle...First in this sort of puzzle we usually find the edges first."
I was trying to present an analogy to a universe which is borderless. No, actually I just forgot a fact in the exposition that I would never do in actuality. It's just a special case of shape being important at the beginning. A jigsaw puzzle is just an analogy though, something to warm one's brain up for the real work.
As far as Lubos: the more he addresses our arguments directly, even if its with derision, the more happy I am. It means were getting through enough for him to feel defensive.
https://www.youtube.com/watch?v=Ug75diEyiA0
ReplyDeleteMarcusM,
ReplyDeleteWas your link referring to what I commented or to Dawid's view that one does not need empirical evidence to prove theories-just consensus.
You have a strange way of valuing arguments if it was referencing my comment. I was just trying to bring a refreshing lack of pomposity to the comments by admitting I'm human. That sure seems to me to be more important than getting things wrong and then saying to everyone "Look, I'm an important person. So you have to take me seriously when I push my views on the world."
There's all kinds of crap out there in physics today pushed by "experts".
Giotis,
ReplyDeleteGenerally, empirical confirmation of any theory in the field that was already trusted before (to a significant degree) because it provided the only or most plausible known solution to some conceptual problem supports NEC. Currently, confidence in NEC in the field is to a large extent based on the success story of the SM. If the BICEP2 confirmation of inflation survived, that would lend additional support to NEC. And if SUSY showed up at the LHC that would increase trust in NEC as well.
Confirmation phenomena, If you permit my lapse of reductionism which even some SUSY theorists have come close to suggesting the information goes to some otherworldly place. Even LM had a post hinting at this.
ReplyDeleteWhile I can imagine a scenario where we can be confident that to see a place outside the universe or our theories that tries to describe it we have to in principle be totally vanished to the laws of physics of this world. So my NEC question would be "If such a consensus caught on and scientists really took up the magical character of such reasoning and philosophy would any of us feel more confirmed of such a place, a Heaven especially if we were not among those already prone to believe?
Would it really make a difference in the work of science and scientists - life itself should have moral humanist dimensions in any case?
Oh well, perhaps given the rigid numbers or these as originating the ideas of probability and wagers (Pascal) it is perhaps just a nice thing for some to believe who dare walk in the dangers of the dark.
Eric,
ReplyDeletesorry, but I was referring to Dawid.
I mean, just look at the Higgs. Why was everybody so excited when it was detected when it was clear that it had to be there anyway ? And why do string adepts get so excited when the LHC announces a new signal that looks like supersymmetry ? In the end they all love the 5 sigma or the beef, metaphorically speaking :-)
And by the way, that's what counts in Stockholm anyway.
Richard,
ReplyDeleteI still disagree with you. I agree that an assessment takes place necessarily before data comes in. I have argued elsewhere extensively that one cannot seriously expect this to work well in the present situation for sociological reasons as Rastus hints at, but that's a different story that I want to leave aside for a moment.
What I am saying is that the assessments that you speak of are to the extent that they are useful not non-empirical and to the extent that they are non-empirical they are not useful (or, strictly speaking, there is no knowing whether they are useful).
As I wrote above the line between empirical and non-empirical is not as sharp as many people (apparently, judging by this comment section) think it is. Take an apparently simple issue like mathematical consistency. Why doesn't anybody in their right mind accept a theory that is plainly mathematically inconsistent? Because we've never ever seen anything that defies the laws of logic, that's why.
Now mathematical consistency is admittedly not a good example because a theory that isn't consistent just has too many axioms, but take anything else, eg convergence of certain series, absence of anomalies, avoidance of singularites, what have you. These are not non-empirical factors, they are based on what we know about nature. For a mathematician a diverging series is exactly that, a diverging series, nothing wrong with that. It's only a problem for the physicist who has never seen any observable giving infinity that the divergence is undesirable and will lead him to disfavor a theory that results in it.
Now what your 'non-empirical assessment' does is that it weights in these factors which are not commonly taken into account as proper observations or data in some sense, even though I suppose that at least in principle one could do this. That's all well and fine, but I maintain it is empirical.
An actual non-empirical assessment may be based on, for example, the discovery of certain symmetries that have not been observed in nature, ever. Such a factor can make a theory more interesting, but that's not something which should be taken into account to judge on its validity as a description of nature. (It's at this point where the sociology strikes in, so I'll stop here.)
Best,
B.
"non-empirical assessment" in the sciences, economics, psychology, medicine, philosophy, religion, politics...is hollow. Consensus embraced superluminal muon neutrinos at Gran Sasso . Theory copiously describes Equivalence Principle violation. No violation is observed to 5×10^(-14) relative
ReplyDeleteFive classes of EP test originate external to physics. "This is not the answer we are seeking." Empirical falsification defines science. "Non-empirical assessment" is crap - Tommy Aquinas to the Rogers Commission Report/Challenger incident (plus a glass of ice water). One must look. No lookee no cookie.
http://arXiv.org/abs/1207.2442
http://www.physics.indiana.edu/~kostelec/faq.html
http://relativity.livingreviews.org/Articles/lrr-2014-4/articlese2.html
http://relativity.livingreviews.org/Articles/lrr-2013-5/articlese4.html
http://relativity.livingreviews.org/Articles/lrr-2010-7/articlese2.html
http://relativity.livingreviews.org/Articles/lrr-2003-5/articlese3.html
http://www.gpo.gov/fdsys/pkg/GPO-CRPT-99hrpt1016/pdf/GPO-CRPT-99hrpt1016.pdf
442 pages of consensus, plus Feynman.
General Buck Turgidson, "Well, I, uh, don't think it's quite fair to condemn a whole program because of a single slip-up, sir." Dr. Strangelove The "single slip-up" sent 1400 megatons to bomb the USSR.
The only way to eat your word salad is with Sabine's dressing.
ReplyDeleteWhen you eat word salad without Sabine's dressing your expression will match the expression Sabine is wearing in her blog photo here.
So much for nomenclature.
I take away three items (without dressing) to eat. Yummy.
1.)You never confirm a theory.
2 )Science is much like natural selection.
3.)Post empirical physics is not physics.
Through no fault of Sabine proponents opposing her when feasting on their own marvel of understanding did so without their Schlabberlätze.
What a mess! Just hope the Lätzchen are washable and provided for - for the next feast of words.
Otherwise they will be wearing those stains for a long time.
Best,
from
Bob
Here more salad dressing on the feast of word salads gone astray.
ReplyDelete"I always start my talks with this little speech: There is to my best knowledge not a single historical example where progress in physics has come about without contact to experiment, without contact to phenomenology." - Bee
Don't forget your bibs. Tastes much better now, doesn't it?
Bob
This comment has been removed by the author.
ReplyDeleteThis comment has been removed by the author.
ReplyDelete74 Questionsby Clifford of Asymptotia
ReplyDeletePDF.
Some info for the philosopher.
Best,
Sabine,
ReplyDeletePart of our disagreement seems terminological. You call any assessment based on observations of any kind empirical. I define empirical confirmation as confirmation by data predicted by the confirmed theory. My main reason for using this definition is that it reflects the understanding prevalent in science and philosophy of science that the empirical method consists in comparing a theory’s predictions with empirical data. Collecting such data, according to this terminology, constitutes an empirical test of the theory; and if the predictions agree with the data this amounts to empirical confirmation. Inversely, if no such agreement has been established, a theory is taken to be empirically unconfirmed. Against this background, I point out that there are other observations which can significantly increase the probability of a theory’s viability. Since those observations do not amount to empirical tests of the theory in question, I call them non-empirical theory confirmation.
(You specifically mention a line of reasoning that relies on the observation that some characteristics of a theory tend to appear (or not to appear) in empirically successful theories. This resembles what I call the meta-inductive argument for (or against) a theory’s success and thus definitely constitutes non-empirical theory confirmation in my terminology.)
Of course one might also choose a more extensive definition of empirical confirmation that includes all kinds of observations. But that would de-emphasise the difference between confirmation by data predicted by the theory and confirmation by other observations. I do think it is important to emphasise the special status of empirical confirmation in the narrow sense of the term, but I also think for various reasons (Bayesian confirmation theory being one) that it makes sense to call the wider kind of inference confirmation as well.
Best,
Richard
Briefly: Richard, I think your point in essence is, you are not just implying we'll have to make "arm-chair" judgments of theories (like the caricature of string theory), but something more nuanced than traditional emphasis on straightforward testing is needed - ? I can work that that.
ReplyDeleteSabine you say:
ReplyDelete“Did that hurt? I hope it did. Because I am pretty sick and tired of people selling semi-mathematical speculations as theoretical physics and blocking jobs with their so-called theories of nothing specifically that lead nowhere in particular.”
So I guess you won’t agree with Greg Moore’s remark in his visionary talk at Strings 2014 conference (around 08:27):
http://physics.princeton.edu/strings2014/videos/visiontalk2moore.mp4
“If a physical insight leads to an important new result in mathematics – that is considered a great success. It is a success just as profound and notable as an experimental confirmation of a theoretical prediction.”
Giotis:
ReplyDeleteI would agree that it can be "as profound as", but just how profound depends on the case at hand. But I think you're misunderstanding me. I agree that math is important etc. The point of the statement that you quote is that I don't want maths to be sold as physics (and vice versa, but that doesn't seem to happen). Best,
B.
Are you sure you agree with this statement?
ReplyDeleteMoore means that such a physical insight (i.e. one that leads to an important new result in mathematics) is equivalent to a theoretical prediction of the theory (from which the insight was derived) that is empirically confirmed.
He establishes a short of duality if you like between Mathematical and empirical prediction...
Giotis,
ReplyDeleteAs I just said, I do of course not agree with it in general, I don't see how anybody in their right mind can agree that any "new result in mathematics" is "as profound as" some unspecified "physical insight". I agree that new math results can be relevant, but whether or not they are depends on the case. I would even agree that in some cases math result can be more relevant. Even so, my point is that one shouldn't pretend to do physics when one actually does is math. Best,
B.
I’m not sure what you mean, of course you are doing theoretical Physics but since it is difficult to discuss in an abstract way about these issues (and before you call me insane as you are obviously intending to do) let me give a concrete example of what Moore’s statement implies according to my understanding at least:
ReplyDeleteSuppose there was no Langlands program in Number theory and no geometric Langlands duality conjecture prior to the formulation of the Montonen-Olive electromagnetic duality conjecture for certain gauge theories (or of the simple Abelian case of electromagnetic duality of Maxwell theory for that matter).
Now if someone (a Physicist or Mathematician) based on this physical insight of electromagnetic duality had conjectured the geometric Langlands duality and its analogue in Number theory and the Mathematicians went on and proved independently these bundles of conjectures, then in some way this would be as important and profound *for the validity of the physical insight of electromagnetic duality* as the discovery of monopoles in Nature.
In my mind at least what Moore implies with his statement is profound and needs further careful contemplation.
Hi Giotis,
ReplyDeleteI think I finally see what you are aiming at. No, I don't think that this would be as important for the validity of the PHYSICAL insight (my emphasis) as a discovery in Nature (ie observation). As I expressed in this post very clearly, in the end it's only observation that counts for physical insight. Alas, to me that doesn't seem to be the gist of the quote you copied above - it doesn't say anything about being important for physics, it just says being important. Best,
B.
“As I expressed in this post very clearly, in the end it's only observation that counts for physical insight.”
ReplyDeleteA physical insight is an insight based on physical considerations (empirical or purely theoretical or a mix of both); its validation is a different issue.
“Alas, to me that doesn't seem to be the gist of the quote you copied above - it doesn't say anything about being important for physics, it just says being important.”
If his intention was to imply something so trivial (i.e. that is simple important) I don’t think he would had said immediately after that “I know for some of you this statement is anathema”. Check the video.
“No, I don't think that this would be as important for the validity of the PHYSICAL insight (my emphasis) as a discovery in Nature (ie observation)”
If so then in the above example and on a scale from 0 to 10, how you would rate the importance of the empirical and mathematical results for the validity of the physical insight?
Giotis:
ReplyDeleteAs I've expressed elsewhere, it doesn't matter for science just how people get their insights. It's just that over the course of time some methods have proved to be more, others less useful. Mathematical consistency has proved useful. Studying the bible hasn't. I wrote this in my post. The point is that in the end it doesn't matter how you got your insight, it only matters if it describes Nature, which is what I mean with 'validate'.
Most of what people say is trivial and superfluous. Sorry, I don't have time to watch the video, and I'm not very interested in interpreting some sentences somebody once said.
"If so then in the above example and on a scale from 0 to 10, how you would rate the importance of the empirical and mathematical results for the validity of the physical insight?"
As I said various times previously, the relevance of mathematical results for the validity of a physical hypothesis, in the sense of it describing nature is strictly speaking zero.
As I also said previously, there are empirical considerations that are not normally classified as such, ie our requirements of naturalness, consistency, absence of singularities etc are actually empirical, and thus if you show a theory scores in these terms, it does increase its likeliness of being correct, but this is not a purely mathematical statement. I don't know how I would quantify that though. Best,
B.
Dear Richard,
ReplyDeleteI'm sorry to be joining this discussion late, but I just found it. One of the weaknesses of your claims is that there will often be situations in which your three criteria can be read as supporting rival research programs. Let me give an example. You said above, " My claim is that a strong record of empirical confirmation in a research field under certain conditions can increase the probability of the viability of other theories in the field that have not been empirically confirmed." In your book you use this to argue that the success of the standard model can be used to support string theory. But I would argue that there is a much closer connection between loop quantum gravity and Yang-MIlls theory than between the latter and string theory.
LQG arises from an equivalence between GR and a certain Yang-Mills theory, furthermore the detailed techniques that led to the formulation of quantum GR in terms of loops and networks were copied from prior applications of the same techniques to quantum YM theories by Polyakov, Migdal, Wilson and others. So I would argue that if your criteria is valid, it applies even mire strongly to support LQG than it does to string theory.
My purpose in making this argument is not to make the case for LQG but to demonstrate that your criteria can be used to support rival research programs, therefor they do not resolve conflicts and disagreements between different competing research programs. Therefor they do not explain how science can progress, in the absence of emperical confirmation. Indeed, they explain only why conflicts between rival research programs will not be resolved in the absence of experimental evidence favoring one or the other.
These remarks are expanded in a review I wrote of your book that is to appear shortly that I'd be happy to send you. But in the meantime, I'd be curious how you respond.
Best wishes,
Lee
Lee Smolin,
ReplyDeleteSorry for intervening but the particular example is not very convincing in my mind. GR and YM (and thus LQG which adopts the YM formalism of Wilson loops, holonomies etc) have a resemblance only in the mathematical formalism since both are Gauge theories but with completely different Gauge groups in nature (diffeomorphism invariance VS internal symmetries). As I see it is like comparing oranges and apples.
An indication of this is that LQG (contrary to String theory) has nothing to say about the other forces of Nature, the SM and particle physics in general. The YM action is an add-on that you just add by hand. LQG is completely agnostic regarding the SM content; there is no unified framework or a deep connection between the two.
Moreover if there was such a connection LQG should be able to reproduce (as String theory reproduces) on an effective field theory level the concept of a graviton; this is the way Quantum Gravity must appear on a perturbative level and as an effective QFT within the general context of SM. This is a benchmark for connecting Quantum Gravity to the SM and LQG fails in that respect.
Is there a particular reason why my latest comment was not approved?
ReplyDeleteGiotis: No, sorry, I just didn't have time to go down the queue.
ReplyDeleteDear Giotis,
ReplyDeleteYour remarks do not reflect basic knowledge about LQG, let alone the progress of the last decade in LQG. Let me respond to them point by point:
“GR and YM (and thus LQG which adopts the YM formalism of Wilson loops, holonomies etc) have a resemblance only in the mathematical formalism since both are Gauge theories but with completely different Gauge groups in nature (diffeomorphism invariance VS internal symmetries”.
No, the gauge group that is expressed in LQG is SU(2), which is a subgroup of the local lorentz transformations. There is also diffeomorphism invariance. Indeed the action for GR-the Plebanski action- is the simplest possible which respects local SU(2) invariance and spacetime diffeomorphisms. Moreover there is a physical connection between the ideas of LQG and the ideas of Migdal, Polyakov and Wilson, which is to express the duality of the dynamics of loops and the dynamics of quantum gauge theories, at a background independent level.
“ An indication of this is that LQG (contrary to String theory) has nothing to say about the other forces of Nature, the SM and particle physics in general. The YM action is an add-on that you just add by hand. LQG is completely agnostic regarding the SM content; there is no unified framework or a deep connection between the two.”
No again. In fact Yang-Mills theory coupled to GR arises from the simplest possible extension of the Plebanski action-just enlarge SU(2) to a larger gauge group and add the unique dimension four term to the action. (See arXiv:0712.0977 and related papers by Krasnov et al.).
So LQG, like string theory, naturally unifies GR and YM theory. And like string theory, LQG has nothing to say about the choice of groups in the standard model.
“ Moreover if there was such a connection LQG should be able to reproduce (as String theory reproduces) on an effective field theory level the concept of a graviton;”
No, yet again. Spin foam models, which are the path integral formulation of LQG reproduce the correct graviton propagator (see Bianchi, Rovelli et al), moreover the correct representation of spin two fields arises from the linearization (see Abhay Ashtekar, Carlo Rovelli and Lee Smolin, Gravitons and loops, Physical Review D 44 (1991) 1740-1755.) Moreover see works by many authors showing that GR in the form of Regge calculus naturalllly emerges from a semiclassical llimit of spin foam models.
I make these points partly because one’s judgements of the promise of a research program should be based on up to date information, and partly to support my case that Dawid’s criteria for non-empirical evaluation of theories are too ambiguous to be useful.
Thanks,
Lee
Thanks for the response but I’m really baffled by it.
ReplyDeleteAre you honestly saying that LQG or some extension of it can really incorporate the SM within a larger unified framework? I don’t believe that you do; even the most vigorous proponents of the theory don’t make such claims.
The SM is QFT on a Minkowski fixed background; it has scalars, chiral fermionic matter, various gauge groups and their bosons. Can LQG or some extension of it reproduce this picture? What all these (and the subsequent success of the SM) have anything to do with LQG? Coming to GR; the low energy limit of LQG is the Einstein Hilbert action? Can you use LQG to calculate any QG corrections to it or graviton scattering amplitudes? The highly speculative and primitive ideas that you mentioned cannot be considered as concrete results or predictions of the theory.
On the contrary in String theory the field content and all the above basic ingredients that are needed for the SM and GR/perturbative QG are derived from the low energy limit of the theory (and this is a fact). It is the only known theoretical framework that can incorporate them in a natural way. That’s why people often say that for the time being at least there is no alternative theory that can do the same, and that’s why (as Dawid advocates ) someone has every right to claim that the success of the SM (and even of GR)can provide support to String theory.
Moreover even in a bottom up approach String theory is the natural extrapolation of the SM (and of GR/perturbative QG) on a conceptual level. Roughly speaking the SM field theories and perturbative QG are effective quantum field theories and they should be replaced by theories with new degrees of freedom above a certain scale; String theory provides these new dof.
Anyway the above are so trivial and widely accepted that it is truly surprising hearing you say that the success of the SM supports LQG. It is unheard of...
Dear Lee,
ReplyDeletePlease do send me your review, I’ m curious to read it, of course.
Let me begin my answer to your argument by making a general point. You seem to think that either non-empirical theory confirmation (let me once again call it NEC in brief) can offer a clear-cut and univocal algorithm for deciding between rival theories (something like a theoretical “experimentum crucis”) or it is useless. I am the first to concede that it cannot do what you demand, but I hold that that it can be important for assessing a theory’s viability nevertheless. There will indeed be different opinions on the strength of NEC in many specific cases. But I would argue that, even in those cases, NEC can tell us something significant after careful consideration. Moreover, there are cases where NEC is strong enough to generate a nearly consensual assessment. The pre-discovery judgements on the probability that a Higgs particle of some kind existed may be the best example.
Having said that, let me be more specific on your argument:
First, I agree with Giotis that, once one moves from the formal point that YM theory is used in LQG towards a physical understanding of the two theories, your claim that LQG is more closely related to the SM than ST does not look convincing. I don’t see that your recent reply answers the substance of Giotis’ point that the role of internal gauge symmetries in the SM differs from the role played by gauge symmetry in LQG, while ST treats gauge symmetry in a way that can be directly related to the way gauge groups appear in the SM.
But even if one granted you the point that LQG is at least as close conceptually to the SM as ST, your argument would not go through.
There is a specific idea behind NEC: the three main arguments of NEC are all based on observations which indicate a scarcity of alternatives to the theory one wants to assess. That scarcity, in turn, increases the probability that the theory is viable. The meta-inductive argument from the success in the research process (MIA), which you address in your argument, is one of the three main NEC arguments. It suggests that once one has noticed a clear tendency of predictive success with respect to theories that satisfy certain conditions, this provides a reason for being more confident regarding the viability of the next theory that satisfies those conditions. What conditions? Clearly, being part of the same research context is a reasonable condition. But in order to make MIA a significant argument, some criteria used in MIA should themselves indicate a scarcity of alternatives. The most immediate way of achieving that is to connect back to the other two arguments of non-empirical theory confirmation. In particular, MIA should use as a condition the no alternatives argument (NAA), which states that scientists have found no alternatives to the given theory. This means that, contrary to your claim, MIA as I define it cannot support rival research programs. If there are opposing suggested solutions to a certain problem, there is more than one known candidate solution, NAA does not apply and MIA does not get off the ground for either of the two candidate theories.
Speaking specifically about string theory and loop quantum gravity, there is, I would argue, an asymmetry with respect to NAA. String theorists can and do argue that LQG as it stands does not amount to an alternative to ST as a universal theory of all interactions (but rather aims at solving the more limited problem how to quantize gravity). To the contrary, LQG cannot deny that ST, assuming that the two approaches are distinct at all, constitutes an alternative to LQG with respect to the problem LQG aims to solve. So MIA works for ST because NAA applies. In the case of LQG NAA does not apply and no convincing MIA case can be made.
Best,
Richard
Sorry I forgot to reply to some other remarks.
ReplyDeleteRegarding the SU (2) connection:
I don’t see why you find so important that in a short reply comment I didn’t mention9 in addition to the diffeomorphism /Hamiltonian constraints) the Gauss constraints and that the holonomy is an SU (2) holonomy. I know about the Ashtekar variables and loop representation and I don’t see how my main argumentation regarding the SM and LQG is affected in a substantial way besides the fact that it brings GR closer to the YM formalism. Again we need to distinguish the resemblance in the formalism from the physical important aspects. At the end of the day you are using metric degrees of freedom and you are doing non perturbative quantization. As I see it at least that’s the essence.
Regarding the Plebanski action etc:
I checked the paper and I remembered that I have seen it before, but anyway really? You are using this to put LQG on a par with String theory and connect LQG to the SM? Same goes for gravitons. As I said in my main comment we need to distinguish wishful thinking and visions from concrete results and predictions that will allow you to make explicit calculations.
Dear Richard,
ReplyDeleteThank you very much for your reply. I can agree that, within a research community, and in the absence of a clear signal from experiment, NEC “ can be important for assessing a theory’s viability”. But let me make sure we agree on what “viability” means. I would propose that viability means “worthy of further investigation by a portion of the research community, pending experimental evidence that would justify it being considered a paradigm.”
Moreover it is useful to study how NEC work in practice, as you have done. However I disagree that, prior to their being a clear experimental confirmation “ there are cases where NEC is strong enough to generate a nearly consensual assessment.” One problem I have with this is that it is very common that in areas where experiment doesn’t yet show the way, there develop rival research communities each working on competing theories, each one of which can make a strong case for their theories “viability” based on NEC. Moreover, I follow Feyerabend in thinking that this is a good thing, and that, in the absence of clear guidance from experiment, the progress of science is best served by promoting a diversity of viable approaches to key open problems. For example, rivalries can generate new challenges and new ideas, as well as the invention of novel experimental tests.
Furthermore, NEC can become counterproductive when they are used to justify ignorance of the claims of competing research programs, because they can be used to justify groupthink and suppression of viable competitors. Indeed, this was the main point of my The Trouble with Physics for which string theory served as a case study.
This is my concern with the competition between the string and LQG research communities. So I should say here that one weakness of your book is that you follow the bulk of opinion in the string community in undervaluing both the size of the LQG community (roughly 200 contributors to semi-annual meetings) and the strength of the claims to viability based on NEC. You write as if there is a single community with a consensus about string theory being the most viable approach to fundamental physics, when actually the real story for more than 25 years has been one of more than one viable approach, based on NEC, each studied by rival communities, each with significant successes and significant failures. In my view this mistake is a major error of your book, factually as well as methodologically.
More in a minute...
Thanks,
Lee
Dear Richard,
ReplyDeleteContinuing....
Now, let me address your specific points:
“ The pre-discovery judgements on the probability that a Higgs particle of some kind existed may be the best example.”-- but surely the overwhelming empirical success of the standard model was the reason we expected there to be a Higgs phenomena-NEC had little to do with that. Moreover, the story of the theoretical expectations about what would be seen at the Higgs scale contains some cautionary lessons about the reliability of NEC. There was a near consensus that naturalness-surely a strong NEC- implied there could not be a simple SM Higgs and nothing else. The consensus based on NEC arguments was that there must be a composite Higgs, or SUSY, or technicolor or extra dimensions-few expected what has been seen so far which is an unnaturally fine tuned model with a single SM Higgs.
“ Clearly, being part of the same research context is a reasonable condition.” But this is ambiguous in this case as several of us, including myself, who contributed to LQG were trained as particle theorists or quantum field theorists while important contributors to string theory such as Candelas and Horowitz were trained as general relativists. And this would have been the wrong advice at key junctures, such as 1905 or 1911, when what was needed was a revolutionary hypothesis that broke with the dominant paradigm.
But your most important argument is “ Speaking specifically about string theory and loop quantum gravity, there is, I would argue, an asymmetry with respect to NAA.” This is I believe wrong on several grounds. First, you underrate the case that LQG offers a natural framework for unification of all four forces within a general dynamical theory of connections. ST naturally incorporates gravitational and gauge interactions and so does LQG. Each is a framework which does not explain the symmetry and representation structure of the SM, but each provides a unification of gauge and gravitational interactions. I’ll discuss more of this when I answer Giotis.
“ LQG cannot deny that ST, assuming that the two approaches are distinct at all, constitutes an alternative to LQG with respect to the problem LQG aims to solve.” No, the main problem LQG claims to have solved is to give a background independent quantization of diffeomorphism invariant gauge theories, including GR. String theory does not so far do that. String theory does give a good perturbative quantization, at leas to two loops, but that is not the same thing.
Finally, going back to general methodological issues, can I ask if you would agree that in addition to the three NEC you describe there are some negative ones? Indeed there should be reasons to abandon a research program, when it has failed to yield predictions by which it could be experimentally tested. These can only be negative NEC. Let me propose two. First, the persistence of key unsolved problems (PKUP). This happens when a key problem necessary for the viability of a theory remains unsolved despite many attempts over decades. Feynman once advised me that, “When everybody has tried and failed to prove a hypothesis, you should try instead to show that it is false.” An example in ST is the failure to prove perturbative finiteness to all orders. Second, the failure to make any experimental predictions (FEP) is itself a negative NEC. As with the positive NEC, experts may disagree about the strength of these negative NEC, which is another reason to encourage diversity of views within a research community.
Many thanks,
Lee
Dear Giotis,
ReplyDeleteThanks for your queries.
“Are you honestly saying that LQG or some extension of it can really incorporate the SM within a larger unified framework? I don’t believe that you do; even the most vigorous proponents of the theory don’t make such claims. “
Yes, after 180 papers and five books you can be assured that I do most of the time choose my words carefully to say what I mean them to say.
Regarding incorporating the elements of the standard model within the LQG framework, lets see:
Gauge fields were already discussed, but note that it is not surprising that a formulation which expresses gravity through a gauge field offers a route to a unification with the other forces. For a specific application which unifies weak and gravitational interactions and so explains the maximal parity violation of the former, see arXiv:1212.5246 [hep-th], Phys. Rev. D 89, 065017 (2014).
For the inclusion of Higgs fields in the unification of gauge fields and gravity, see arXiv:1004.4866, J. Phys. A: Math. Theor. 43 (2010) 445401
There are several routes by which chiral fermions naturally appear in LQG:
chiral topological excitations: arXiv:hep-th/0603022, Class.Quant.Grav.24:3975-3994,2007; arXiv:0710.1548, Nucl. Phys. B 796 (2008)/1-2 pp 331-359, arXiv:0804.0037. and others...
Non-local links, or wormholes: gr-qc/9404010.
Moreover, SUSY is not required in LQG, but can be easily incorporated, so there would be no conflict with LQG were SUSY observed experimentally: hep-th/9904016, Phys. Rev. D61, 044008 (2000); hep-th/0003285, Nucl.Phys. B601(2001) 191-208; hep-th/0009018, Phys.Rev. D63 (2001) 064010.
I will grant that these extensions of LQG to incorporate other dof of nature are less developed than string theory, as they indeed have not been the main focus of work by the LQG community. But I am quoting published results, which should be sufficient to make my point. In my own work, LQG developed directly out of the works of Polyakov, Migdal and Wilson and so my view has always been that these deep connections with particle physics should be emphasized and developed.
“ Coming to GR; the low energy limit of LQG is the Einstein Hilbert action?”, Yes, more specifically, the large spin limit of the elementary spin foam amplitude is the Regge action, which is the Einstein-Hilbert action for a simplicial manifold. This is by now a standard result, and has been derived several different ways.
“ Can you use LQG to calculate any QG corrections to it or graviton scattering amplitudes?” Yes, in principle, and my understanding is there are results in progress. One indirect route to this is through log corrections to the BH entropy, which have been computed.
“At the end of the day you are using metric degrees of freedom and you are doing non perturbative quantization.” The whole point of LQG is that the metric degrees of freedom are emergent and auxilliary and do not appear at all in the action. As Krasnov emphasizes, the theory of gravity is a dynamical theory of connections. And non-perturbative quantization is another thing that ties LQG to its roots in QCD, which is where those techniques were learned from.
Finally, please, re your tone: “Baffled...honestly... highly speculative...primitive.......truly surprising...unheard of....really?...wishful thinking....” etc, is all that emoting really necessary? Especially given that you are hiding behind anonymity, can I ask that you keep the discussion substantial?
Many thanks,
Lee
I will not persist; there is no point. One last thing though that indeed I think is substantial and illuminates further the discussion.
ReplyDeleteEven if I accept for a moment everything that you say you have to recognize one big difference between the two theories that distinguish them on a qualitatively manner.
Every physical concept derived from ST, from SUSY and GR/SUGRA to Gauge groups and field content/fermionic matter, is required by the internal consistency of the theory. You don’t have for example to embed arbitrary by hand the local SO(3,1) to a larger gauge group like you do in your example; instead the theory itself guides you step by step in that direction. It’s the internal mathematical and physical coherency of ST that renders these essential physical concepts necessary; they are the output of the theory and not an input to the theory. This is how a unified framework should incorporate the physical concepts in a *natural* way; this essential property is far from being trivial on the contrary it is very hard to find in a theory. Not to mention of course the dualities and all the other miracles which are revealed step by step by exploring its internal structure.
Cheers
Dear Giotis,
ReplyDeleteThanks. Of course we agree on the strong points of string theory, I make the case you rehearse here even more strongly on p 112 of The Trouble with Physics. Indeed at times I’ve been enthusiastic enough about string theory to work on it.
What you don’t mention are the persistent obstacles to realizing the promise of string theory in a well defined fundamental theory which makes predictions by which it could be tested.
What we disagree about apparently are then three things: 1) How seriously to take the failures and persistently unsolved issues of string theory, 2) How strong is the case for LQG as having also unique successes and so being also worthy of further investigation, and 3) How important it is, when we lack experimental confirmation of any theory past the SM, to keep an open mind and encourage the investigation of diverse approaches to fundamental issues including ST, LQG and several other viable research programs.
Best,
Lee
Dear Sabine,
ReplyDeleteCan I be permitted a personal remark? Today I find myself defending LQG to proponents of string theory on your blog while, simultaneously, over on Peter Woit’s blog I am defending work I did some time ago which used a version of string theory to solve a problem in foundations of quantum theory.
Apart from my advocacy of Feyerabend’s view that diversity of competing approaches should be encouraged because the competition and provocation speeds the progress of science, I’ve learned so much and had so much fun working myself on diverse approaches to solving the big problems of physics.
There are a few principles that I’ve been committed to throughout my career (relationalism,realism) but within those I’ve considered specific theories as hypothetical models to be played with and tested, which we should be ready to discard when they fail and embrace only when forced to by the evidence.
What really puzzles me and worries me are people who want to believe they are right before the evidence is in and so try to limit the playing field of ideas to the narrow realm in which they are comfortable and protected from surprise. Don’t we all do science in the hope of being surprised?
Best wishes,
Lee
Dear Lee,
ReplyDeleteI, and I am sure many of my readers and those of Peter's blog, appreciate hearing your opinion. I think that defending and explaining ones' research is a necessary part of science, and so is criticism.
Unfortunately, today criticism, if voiced at all, is often not perceived as part of the process, but as a threat. It's a by-effect of the way research is presently organized so that researchers are for financial reasons too dependent on the current opinion about their research program. They literally can't afford critical voices. And since everybody knows that, we have fallen into a pattern in which most of us ignore each other and call it live-and-let-live. That's nice, but it doesn't get us anywhere. Basically that's why there's camps barely talking to each other and if you publicly criticize the other camp somebody will stand up and accuse you of 'wanting their money'. I'm sure you recall that...
Besides that, it is a certain disease of our times that most people want to classify others into categories. You're not supposed to have no opinion and you're not supposed to change your opinion. The bolder and the simpler your positions, the better for your popularity.
This is problematic because, as you say, changing one's mind when parts are added to the puzzle is what makes science scientific to begin with.
I have noticed myself that people are not pleased when they cannot put me into either the LQG corner or the string theory corner, and I have been mistaken for both. In one rather frustrating job interview I was asked repeatedly but if you're not a string theorist and you don't do LQG, then what are you?
So what can I say when you complain that people treat unconfirmed theories like religions (yes, there, I've said it even if you didn't) and dismiss agnostics, those who want to keep their mind open, as hypocrites? The only possible response that I keep coming back to is that we'll never make progress accusing each other of faulty "non-empirical" argumentation, but that we need data, period. And that's why I work on pheno qg.
Best,
B.
Richard,
ReplyDeleteI hadn't replied to your last comment addressed to me basically because it seems quite possible that we are just using the word 'empirical' in different ways. As I said, for me 'empirical' is everything based on observation whether or not that actually comes as a set of data. Examples I gave are requirements like observables being finite values or mathematical consistency itself. For you this seems to count as non-empirical.
But now I see that you are Lee are still dancing around the same pot, so let me say that again. Renaming "theory confirmation" into "viability" doesn't make any difference. I maintain that the only thing that matters for a scientific theory is that it is useful for the description of nature and that means only criteria that are empirical (in my use of the word) matter. All other assessments are irrelevant, that includes the question whether or not a theory of everything is more aesthetic than a qg patched together with ym gauge groups, in whatever way.
What matters is that a theory be able to reproduce the Standard Model in some limit, yes. Whether it treats gauge symmetries just like the standard model or doesn't is irrelevant unless you can prove that some property is necessary to reproduce the standard model, and I am not aware such a proof exists.
From my perspective, both LQG and string theory have been similarly useless as a theory of quantum gravity. Yes, I said useless. Much of talk about black holes but nobody has ever seen a black hole evaporating, so what do I care if there's a \gamma in some observable that nobody can observe*?
String theory has it speaking for itself that it has been useful at least for mathematics and that its spin-off AdS/CFT has a good potential to become useful for condensed matter physics. The latter is what convinces at least me that it has something to do with the description of nature indeed, though one can debate how much this still has to do with 'strings' and it doesn't have anything to do with quantum gravity, unless you abuse the word I'd say. But as you have noticed though, I'm not a fan of fighting about words, I think you know what I mean.
That a useless theory doesn't have an alternative doesn't make it any more useful. So much about that argument of yours.
Best,
B.
* I find it totally possible that one might be able to prove the presence of an additional factor in the microscopic bh entropy is actually inconsistent with the absence of that factor in the spectrum observed by the Unruh detector (see recent work of Bianchi). If that was so, that would constitute, imo, a serious problem for LQG. Alas, I am not aware anybody proved this to be inconsistent. I vaguely think it clashes with the equivalence principle. Again though, note that adherence to the equivalence principle is actually an empirical requirement. This is again not a 'non-empirical' assessment.
Dear Lee,
ReplyDeletethanks for your extensive remarks. I think it’s an interesting exchange.
Let me first answer at a very general level. A worry you express – and you are not alone in this – is that a ‘soft’ form of confirmation like NEC, which can be used for decades without decisive experiments that could rule out the theory against all expectations, increases the influence of sociological aspects of the research process on a theory’s status.
I do understand this worry and I acknowledge that the problem exists. In a nutshell, my answer is that keeping the epistemological question separate from the ‘science strategic’ issue is in the interest of constructive reasoning at both levels. What I try to argue for is that NEC does have significant epistemic value. If that’s the case, however, it would be a conceptual error (one might say a category mistake) to deny it on the basis that the use of NEC carries a certain risk of ‘sociological’ distortion. Moreover, I would suggest that the problem of ‘sociology’ can be controlled better by developing a clear understanding of how NEC actually works. Only on that basis, a constructive discussion on whether or not NEC is being appropriately applied in a specific case can be carried out.
Specifically on your remarks, let me start by saying a few words on NAA and background independence: NAA, which uses the observation that scientists haven’t found any alternatives for solving a physical problem, is based on one important premise: a solution to the problem in question must be necessary for describing a substantial aspect of the observable world. So, in order to use background independence in NAA one would need a situation like:
1: Theory X is a potential alternative to our theory Y.
2: X predicts the world to be background dependent.
3: Our observations tell us, however, that the world is background independent.
4: So X is no alternative after all and we are left with Y.
But background independence does not work for LQG in this way. ST does not predict background dependent physics but merely has been developed from a starting point that does not make background independence explicit. It just does not make sense to say that ST does not constitute a possible alternative as a theory of QG because of background dependence. So no NAA can be based on this. (For everyone interested in the case of ST and background independence, Joe Polchinski has commented on this in a concise and lucid way in a review of Lee’s book “the trouble with physics” back in 2006: http://blogs.discovermagazine.com/cosmicvariance/2006/12/07/guest-blogger-joe-polchinski-on-the-string-debates/#.U-iET7GxzUg )
I’d like to avoid turning this into one more exchange on ST vs LQG though, so let me, in what follows, focus on some points you raise at a more general epistemological level.
To be continued…
Richard
Dear Lee,
ReplyDeleteLet me continue by answering directly to some of your statements.
>>But let me make sure we agree on what “viability” means. I would propose that viability means “worthy of further investigation by a portion of the research community, pending experimental evidence that would justify it being considered a paradigm.”<<
I use a stronger notion of viability: a theory is viable if it agrees with the empirical data in a given empirical regime.
>> However I disagree that, prior to their being a clear experimental confirmation “ there are cases where NEC is strong enough to generate a nearly consensual assessment.” …” The pre-discovery judgements on the probability that a Higgs particle of some kind existed may be the best example.”-- but surely the overwhelming empirical success of the standard model was the reason we expected there to be a Higgs phenomena-NEC had little to do with that.<<
The point I make is that, in order to use the success of the SM for motivating trust in the Higgs, one needs NEC. The pre 2012-empirically confirmed parts of the SM could in principle have been compatible with a mechanism of mass creation that did not predict any (fundamental or constituent) scalar particles – if there had been such a mechanism. The trust in the Higgs was based on the trust in the assessment that there was no such alternative – a classical case of NAA. And the trust in that assessment was based on the observation that similar assessments had worked in the past – a classical case of MIA.
>> Finally, going back to general methodological issues, can I ask if you would agree that in addition to the three NEC you describe there are some negative ones?<<
A very interesting question. First, let me point out that the three NEC arguments I present can also work negatively. If alternatives to a theory are found, that weakens the trust in the theory based on weakening NAA; if other trusted theories in the research field fail predictively, that weakens the trust in the theory based on weakening MIA; and if unexpected explanatory interconnections are understood to be based on more fundamental principles rather than the specific theory in question, that reduces trust in the theory based on weakening UEA.
Do I want to rule out that there are other forms of NEC (and, more specifically, arguments that focus on disconfirmation)? No I don’t. But I would argue that, in order to be substantial, such arguments should satisfy two conditions: 1) there should be a plausible conceptual connection between the observation the argument is based on and the probability that the theory in question is viable - and 2) the historical record should indicate that theories where the argument applies indeed had a tendency of (not) being viable.
Do I think that the arguments you call PKUP and FEP work in that sense? My impression is that they don’t. I see neither a conceptual nor an observational basis for assuming that longstanding unresolved problems in physics and mathematics are likely to have no solution. Clearly, those who spent a century working on the Poincare conjecture did not think so. Problems may just be difficult to solve. Moreover, some empirically well confirmed theories have unresolved mathematical issues as well – think of the convergence of perturbative series in QFT.
I see no good conceptual or observational basis either for believing that theories or ideas that don’t generate specific empirical predictions for a long time are particularly likely not to be viable. The problem is pervasive in today’s fundamental physics. And it’s not the first time it occurred. Take atomism, which, after a long history without specific empirical predictions, was reasonably successful at the end.
Best,
Richard
Dear Sabine,
ReplyDeleteI did not want to say that our disagreement is JUST terminology, I merely wanted to distinguish between what is, in my understanding, a matter of terminology and what is not.
I must admit, however, that don't fully understand your position. Your notion of 'empirical', as you previously defined it, is very extensive and includes much of what I call 'non-empicical confirmation'. But then, in your last comment, you call 'useless' theories on black holes as long as no-one has seen a black hole evaporate, which is based on a narrow notion of 'empirical'. I don't see how this fits together.
Best,
Richard
Dear Richard,
ReplyDeleteSorry about that, I was being too brief. What I meant is what I already said above, to the extent that some assessment is non-empirical it's not useful and to the extent that it's useful it's not non-empirical. Sure, we are pretty certain black holes exist and so on, we have data on that (empirical), so your theory of quantum gravity better fits to that data. So far so good.
But much of quantum gravity isn't concerned with anything we have actually observed about black holes, but about their evaporation, thermodynamical properties, microstates and so on. And I don't see why some calculation is any better than the other, as long as it's self-consistent and reproduces observation, certain properties of the classical limit, qft in the weak curvature regime and so on. So does the bh microstate counting speak for string theory and against LQG? What do you think?
My notion of empirical is broad, yes, but the problem with your notion of empirical is that it has a fuzzy boundary. I go out and tell you it rains. For me that's empirical. Do you count that as empirical? Or does it not count as empirical because I didn't deliver you a data set? See, I *could* have done that in a double-blind random controlled trial and lots of calculations with errorbars and so on. But in practice most people have so much confidence in each other's sensorial and cognitive accuracy that they don't bother. I don't see that it's a clean definition of 'empirical' to exclude data that could have been collected but wasn't because it's cumbersome or time-consuming or no two people agree on how to quantify some property etc.
If you follow that thought, then the role of the scientific community is basically to take into account the non-quantified empirical knowledge.
I totally agree with you btw that science would very much benefit if scientists were better aware of the relevance of their social interactions for the progress of science, and knew better what pitfalls can arise in that interaction that hinder knowledge discovery. It's a speech I have given many times. The problem is that the moment I tell a physicist that sociology and philosophy is important, they stop listening to me.
Best,
Sabine
Sabine’s comment about the black hole evaporation etc. reminds me Freeman Dyson’s attitude towards the quantization of Gravity and gravitons i.e. that people should be content with the existing low energy effective description of Gravity by Einstein and not try to quantize it since we have zero chance of observing a graviton.
ReplyDeleteI’m wondering what his reaction was when he heard the recent BICEP2 findings.
As Strominger said during his visionary talk in Strings 2014 (quoting John kovacs):
“It is a mistake in science to imagine that you ever know the limits to what we can see”
So I say physicists should extrapolate their theories until they reach their limits and calculate everything they can calculate regardless whether the outcome can be measured by experiment or not; and when there is nothing left to calculate, to calculate some more.
Giotis,
ReplyDeleteNo, you misread me. I did not say that one shouldn't think about black hole evaporation, entropy and so on, and I also didn't say that one should be content with the contradictions left within the classical theory. What I am saying is that without experimental evidence any consistent explanation is as good as the other. The black hole information loss problem is exactly the kind of inconsistency that is not acceptable. (Or of you think it is consistent, then that requires explanation.)
Besides this, Dyson is wrong of course in implicitly claiming that detecting gravitons is the only way to find evidence for quantum gravity, see this earlier post.
Best,
B.
Why are you saying that String theory and LQG are useless then?
ReplyDeleteAs I explained in my post, I say "useless" to mean "useless to describe the natural world". Neither LQG nor string theory describes anything we observe that could not also be described with GR and the standard model. (See above for my comments regarding AdS/CFT.)
ReplyDeleteBut then my comment holds i.e. you never know the limits to what you can observe in the natural world.
ReplyDeleteMaybe in the future you would be able to find detectable empirical signatures of QG theories but for this you need to continue the digging.
Giotis: Sure, I agree with that. The way you phrased it though I thought you thought I said otherwise.
ReplyDelete3:51 AM, August 12, 2014
ReplyDeleteDear Richard,
Many thanks for your remarks. I agree this is a useful discussion.
A key assertion you make is, “What I try to argue for is that NEC does have significant epistemic value.” At this point I want to ask you for your general theory of how science works. Here is mine, which was presented in Chap 17 of TTWP: Science progresses by three processes which are continually going on:
1) A process of generation of ideas, theories hypotheses and conjectures. This addresses the question of what MIGHT be true. At this stage it is important to encourage the generation of a diverse variety of hypotheses and competing ideas.
2) A process of refinement, challenge and debate. One aim of this process is the generation of specific experimental predictions by which a theory or hypothesis might be tested.
3) A stage of experimental confirmation and disconfirmation. At this point we want to answer, what must a rational person of good faith be forced to believe, based on public evidence. It is only when there are answers to this question that diverse and competing research programs can give way to consensus. It is only at stage 3 that we can say our knowledge of how nature works has progressed.
I draw several conclusions from this, which shape how I evaluate your claims for NEC. First, the process is healthiest and goes the fastest when there is a diverse variety of alternatives developed by competing research programs. For one thing, experimental tests are often framed to distinguish between competing theories. For another, competition between competing theories often results in the invention of new experimental tests by which they can be distinguished. And prior to experiment, competition often leads to the uncovering of weaknesses in a theory, and also it can lead to the invention of new theories inspired by the failures of the existing alternatives. Further, the way to solving a persistent roadblock in one program often turns out to be a method developed in a rival program.
So without alternatives at stage 2, many theories cannot be tested at stage 3. Thus, almost the best thing you can do for your favorite research program is to encourage the invention and development of alternatives. This is the main point of TTWP. The fact that this does not regularly occur is a great weakness of present day science which is slowing progress in many fields including, but not limited to, fundamental physics. (Indeed, I received lots of email from readers of TTWP in diverse fields such as economics, computer science, neuroscience, biology, medicine, etc thanking me for identifying sociological issues in their fields.)
This means that it is in the long run better for science if every viable research program has viable alternatives. I will call this the promote alternatives imperative (PAI) and argue it is more useful in the long run than your NAA.
The main objection I have to the criteria described in your book is that they are used (or if you prefer abused) to justify the premature suppression of viable rivals to sociologically dominant research programs, which I have argued slows the progress of science, I agree part of what you are doing is making explicit criteria that are already in common use, but that doesn’t make them right, or wise.
A final methodological point. Theories that don’t generate detailed predictions for doable experiments which are either falsifiable or unique to them cannot pass to stage three. Thus if the proponents of a theory with this failure becomes sociologically dominant and able to suppress the invention or development of viable alternatives that might be testable, the progress of science is blocked.
More in a bit,
Lee
Dear Richard,
ReplyDeleteContinuing to your remarks on background independence: “ST does not predict background dependent physics but merely has been developed from a starting point that does not make background independence explicit.”
First, by background independent we usually mean that “the definition of observable quantities does not depend on the specification of any fixed classical geometries or fields.” This is a criteria that is satisfied by a number of theories including GR with spatially compact boundary conditions, LQG, CDT, causal sets, group field theory, etc. No existing formulation of string theory satisfies it.
Second, yes, there could be a background independent formulation of string theory that satisfies this criteria. But there is not now. And aspiration counts for little compared to results, when assessing the promise of a theory.
Indeed I spent several years trying to do this, and published several papers with proposals and results which supported them. Before that, LQG was invented when I with collaborators applied to Ashtekar’s classical formulation of GR a method developed with Louis Crane in an attempt to make a background independent form of string theory. And there have been from time to time efforts by others and continue to be a few (Bars and Rychkov). Still, no approach has been completely successful or generally adopted.
Nor has the string community ever shown much interest in the goal of making a background independent string theory. When, for example, was the last talk on this subject at a Strings XXXX meeting?
Third, there is an intermediate class of theories where the only violation of background independence is on the specification of boundary or asymptotic conditions. We may call this boundary-limited background independence (BLBI): “the definition of observable quantities does not depend on the specification of any fixed classical geometries or fields, except those which appear in the specification of boundary or asymptotic conditions.”
Boundary-limited background independence is not a substitute for true background independence, because any imposition of boundary conditions renders a gravitational theory fit only for describing isolated systems, but it is useful in a limited domain. Examples of these tend to arise when truly background independent theories are truncated to describe isolated systems. One example is the boundary formulation for spin foam models which Bianci, Rovelli et al use to compute the graviton propagator.
One could ask for a version of BLBI tied to asymptotically AdS boundary conditions and investigate a version of the AdS/CFT duality in this context and there are a few papers that explore this, at least at the classical level. But to my knowledge (please correct me if I am wrong about this) there are no papers which describe a version of an AdS/CFT correspondence where the bulk is treated in a background independent but quantum manor. All the papers I am aware of that treat quantum physics in the bulk do so by computing semiclassical or perturbative corrections to strings or fields moving on one or more classical background bulk geometries.
Furthermore, any claim to base a fundamental theory on a BLBI theory would have to answer hard questions about where the boundary lives in real spacetime. This would require something like a radical version of relational quantum theory, perhaps tied to a categorical version of the holographic principle of the kind that Crane, Rovelli and myself explored in the 90s. To my knowledge no string theorist has ever worked on, let alone expressed the slightest interest in this kind of direction.
So, in summary, No, AdS/CFT cannot in principle satisfy true background independence. So to base a theory on AdS/CFT would be to strongly limit its claim to being a fully satisfactory cosmological theory. But there could be versions of AdS/CFT that satisfy the limited criteria of BLBI. I would be pleased to see more work which developed that direction.
Thanks,
Lee
Everyone knows that besides AdS/CFT we don’t have a non perturbative definition of String theory yet and everyone knows that it is notoriously difficult to quantize Strings on AdS backgrounds.
ReplyDeleteThis of course and the lack of an independent non perturbative definition of the theory is the reason you can’t test the correspondence beyond the semi-classical limit. The current view is that you take the AdS/CFT as correct and you use the CFT to give a non perturbative/ background independent definition of the String theory in the bulk.
I don’t have a clue why someone will argue that AdS/CFT is not background independent. As long as you stay in asymptotically AdS spaces you don’t have a problem and the String theory in the bulk is invariant under the diffeomorphisms of the bulk. The asymptotically AdS is a superselection sector (a parameter of the theory) which is not affected and cannot be changed by the dynamics.
The fact that the space in the bulk has to be only asymptotically AdS allows you to deal with all sorts of QG processes which are of local nature and are not affected by the asymptotic boundary conditions. Only the physical processes of global/cosmological nature are affected.
So if you accept that AdS/CFT is correct then it follows immediately that String theory is in essence a background independent theory.
Also it’s not true that String theorists are not interested in finding a background independent formulation of String theory (besides AdS/CFT) but such a construction is intimately connected to a non perturbative definition of the theory (independent of AdS/CFT). There is an entire promising field of research called Open string field theory (which ultimately is connected to Higher spin gravity) dealing with this issue that will hopefully provide such a definition. The interested reader can check Polyakov’s work for example (incidentally his latest paper is quite relevant) and of many others.
Anyway all the above are well known; the crux of the matter is that Dawid has done an amazing job in trying to identify a set of principles or criteria that would allow someone to evaluate the viability of a theory even if empirical data are not available for the time being. Under these criteria the viability of String theory as a unified framework is more that evident.
Dear Giotis,
ReplyDeleteYou say, “I don’t have a clue why someone will argue that AdS/CFT is not background independent.” Can I help? The clue would be to read the definition I gave of background independence, which is the standard definition.
“the definition of observable quantities does not depend on the specification of any fixed classical geometries or fields.”
As I explained above, by definition, the closest an AdS/CFT correspondence could come would be to satisfy the definition of boundary-limited background independence (BLBI): “the definition of observable quantities does not depend on the specification of any fixed classical geometries or fields, except those which appear in the specification of boundary or asymptotic conditions.”
With respect to this definition, to “quantize Strings on AdS backgrounds” would be not be to give a background independent definition of the theory, or even a BLBI theory, precisely because the theory would depend on the AdS background it was defined on. So even if that difficult problem was solved it wouldn’t help make the theory background independent.
Nor is it sufficient to have a theory that is “diiffeomorphism invariant in the bulk” if, by that you mean that it depends on a background metric specified up to diffeomorphisms.
The same is the case with open string field theory, which may be independent of background Yang-Mills fields, but depends on a fixed classical background metric. To be free of the latter requires a closed string field theory, which is more challenging. Indeed, it may be that you have to go to a membrane field theory-and hence M theory, which is what I was trying to accomplish with my cubic matrix models.
I agree we could just define string theory non-perturbatively to be the dual of N=4 SYM. This would give a BLBI theory. But it is not enough to just say this, a lot has to be shown. As I said, I would welcome more work in this direction.
By the way, I agree that there is a general correspondence between conformal field theories and asymptotically AdS gravitational theories one dimension up. A general argument for a limited form of a correspondence is given in arXiv:1305.6315. To the extent discussed there the correspondence doesn’t requiire string theory or supersymmetry. And this form of the correspondence does actually explain why the bulk side of the correspondence is diffeomorphism invariant.
Thanks,
Lee
Dear Giotis,
ReplyDeletecontinuing...
Anyway, what I find remarkable is that we are having the same debate we had in 2006 and could have had in 2000. This in itself shows why I disagree with Dawid’s claim to have given “ criteria that would allow someone to evaluate the viability of a theory even if empirical data are not available for the time being.” There has in fact been progress since then in supersymmetric gauge theories, but the fact that this debate is isomorphic to past debates shows that little has happenned to change the evaluation of string theory as a fundamental theory in perhaps 15 years. Now, suppose the lack of definitive progress lasts 50 years, ie it is now 2050 and our descendents are having the same argument. What troubles me about Dawid’s criteria is that they would alllow one in 2050 to argue that the 2000 version of string theory was still viable.
Now I suspect, we can agree that this is silly, but why? Because we would expect that over the next 35 years breakthroughs will occur in both experimental and theoretical physics that render the debate over string theoy as it was in 2000 moot.
Now, no one can predict where those breakthroughs will come from. Therefor the healthiest thing for science is to keep all viable options open, and to encourage the invention of novel approaches.
Now the criteria Dawid has identified are not new, as he himself admits, he is only codifying and making explicit criteria that are in common use. And what are they used for? First, to establish that string theory is interesting. I have no problem with this. But the reason there is a debate about string theory is becase proponents of string theory go further, and argue for cutting off other options by declaring string theory to be the only option worth investigating. The case for this has been often based on the criteria Dawid identifies, particularly the no alternatives argument (NAA).
In the last 15 years there has been very impressive progress in several directions alternative to string theory, including spin foam models, causal dynamical triangulations, group field theory, tensor models, casual sets, etc. If the proponents of the NAA for string theory would have had had their way back in 1999, none of that would have happenned because string theory would have been in fact and not just in aspiration, “the only game in town”. But the last 15 years show that string theory is far from the only game in town.
I am not saying this to advocate making LQG the only game in town. My point is only that the NAA and Dawid’s criteria are dangerous for the ultimate progress of science because their effect is to prematurely narrow the diversity of viable approaches at exactly a time when we need to be encouraging the search for novel alternatives.
Thanks,
Lee
Hello,
ReplyDeleteSorry I never said that “quantize Strings on AdS backgrounds” would give a background independent definition of the theory, or even a BLBI theory. Why I would say such thing?
I mentioned this (together with the lack of an independent non perturbative definition of the theory) only to highlight the reason why it is generally difficult to do calculations on the bulk side beyond the SUGRA approximation (large t’ Hooft limit) and thus to test more efficiently the correspondence in all of its limits.
Also regarding the bulk diffeomorphisms; if you use the CFT to define the theory in the bulk then the theory in the bulk is invariant under the bulk diffeomorphisms, which do not change the boundary conditions, by definition.
Regarding background independence of AdS/CFT; as I said if you stick to asymptotically AdS you don’t have a problem, no dynamical process can change the asymptotically AdS space and thus it’s not a background but a given parameter of the theory i.e. a superselection sector (something similar to initial conditions). Of course if you want to change the AdS space too then you must find a new correspondence but we are talking about AdS/CFT; so within AdS/CFT you are ok.
Finally the theory in the bulk must be a consistent theory of QG which means that it must UV complete GR and the *perturbative QG*, thus it is a String theory; (unless of course you can prove that LQG can do exactly the same).
Cheers
Just to correct something:
ReplyDeleteI meant to say “and thus to test more efficiently the correspondence beyond BPS”.
BTW Sabine, can you please turn off the moderation at least temporarily?
I write a comment and it appears after one or two days
Giotis:
ReplyDeleteI have comment moderation on for posts older than 2 weeks. Almost all submissions on older posts are spam. If I turn it off, I have to go by hand through all the pages that collected spam over night and that costs me more time than I want to waste every morning.
I normally check the moderation queue every morning unless traveling. Your comments are stuck in the queue longer than Lee's simply because you submit them during a time I'm normally offline while Lee and Richard have submitted them when I'm normally online. It's nothing personal, really. You have my email, if you think I missed a comment, send me a note.
Best,
Sabine
Dear Giotis,
ReplyDeleteWell, surely you know that spin foam models are ultraviolet finite. And there are recent results that show that in the presence of a cosmological constant they are infrared finite as well. But there is as yet no full blown description of an AdS/CFT correspondence in LQG.
Anyway, what I find remarkable is that, with respect to string theory, we are having the same debate we had in 2006 and could have had in 2000. This in itself shows why I disagree with Dawid’s claim to have given “ criteria that would allow someone to evaluate the viability of a theory even if empirical data are not available for the time being.” There has in fact been progress since then in supersymmetric gauge theories, but the fact that this debate is isomorphic to past debates shows that little has happened to change the evaluation of string theory as a fundamental theory in perhaps 15 years. Now, suppose the lack of definitive progress lasts 50 years, ie it is now 2050 and our descendents are having the same argument. What troubles me about Dawid’s criteria is that they will allow one in 2050 to argue that the 2000 version of string theory was still viable.
Now I suspect, we can agree that this is silly, but why? Because we would expect that over the next 35 years breakthroughs will occur in both experimental and theoretical physics that render the debate over string theory as it is in 2000 or 2014 moot.
Now, no one can predict where those breakthroughs will come from. Therefor the healthiest thing for science is to keep all viable options open, and to encourage the invention of novel approaches.
Now the criteria Dawid has identified are not new, as he himself admits, he is only codifying and making explicit criteria that are in common use. And what are they used for? First, to establish that string theory is interesting. I have no problem with this. But the reason there is a debate about string theory is because proponents of string theory go further, and argue for cutting off other options by declaring string theory to be the only option worth investigating. The case for this has been often based on the criteria Dawid identifies, particularly the no alternatives argument (NAA).
In the last 15 years there has been very impressive progress in several directions alternative to string theory, including spin foam models, causal dynamical triangulations, group field theory, tensor models, casual sets, etc. In fact there is now substantially more evidence that LQG is a viable approach then there was in 2000 or 2006. If the proponents of the NAA for string theory would have had had their way back in 1999, none of that would have happened because string theory would have been in fact and not just in aspiration, “the only game in town”. But the progress of the last 15 years show that string theory is far from the only game in town.
I am not saying this to advocate making LQG the only game in town. My point is only that the NAA and Dawid’s criteria are dangerous for the ultimate progress of science because their effect is to prematurely narrow the diversity of viable approaches at exactly a time when we need to be encouraging the search for novel alternatives.
Thanks,
Lee
ps. Sabine: some of this was in a post that you missed.
Dear Lee,
ReplyDeleteMuch of what I’d have to answer to your conceptual questions I’ve said already elsewhere on this blog. Therefore, in order not to get overly repetitive, let me refer back in particular to my entry from July 16 where I try to clarify my position with respect to my understanding of the relation between empirical and non-empirical confirmation and the issue of sociology.
With respect to your views on the role of sociology for the present status of string theory, my position is the following. Sociology no doubt plays a role in many scientific contexts. It also plays a role in the assessment of string theory. But you vastly exaggerate this role for the very reason that you ignore the epistemic value of non-empirical theory confirmation.
Best,
Richard
Giotis, Lee, Richard:
ReplyDeleteI will be traveling the next weeks and not sure how much I come around to check my blog. I've increased the no-moderation window to 6 weeks, so your comments should now go through again without my okay.
Lee: Sorry for missing your comment, I've found it in the spam queue, it should have appeared now.
Hello,
ReplyDeleteAs was already mentioned, String theory is not just a theory of QG but a unified framework of all fundamental fields(content and interactions) and of all fundamental physical principles and concepts.
In that respect the fact that LQG does not constitute an alternative to String theory as a unified framework is acknowledged by LQG theorists themselves. So I don’t see why you are accusing Dawid or String theorists for advocating the NAA within this context.
I read for example from Rovelli’s book ‘Quantum Gravity’ page 13:
“The basic ideas and assumptions on which LQG is based are the following:
...
iii) No Unification. Nowadays a fashionable idea is that the problem of quantizing gravity has to be solved together with the problem of finding a unified description of all interactions. LQG is a solution of the first problem, not the second.”
I’m afraid that if you claim otherwise you are a voice crying in the wilderness.
Cheers
Dear Richard,
ReplyDeleteMany thanks. I read your July 16 post and it just makes me more confused as to exactly what you are advocating.
As I mentioned above, a lot comes down to your use of the term “viable,” You said above, “ I use a stronger notion of viability: a theory is viable if it agrees with the empirical data in a given empirical regime.” In your July 16 comment you then say “ If NEC increases the probability that a theory is viable, it increases the probability that the theory will turn out to be in agreement with data once one will be able to test it. This means that NEC cannot be applied to theories that are in principle predictively empty.” OK so far, because if viability=agreement with empirical data, this is by definition.
Here is the key point: I believe we agree that string theory is so far unable to make any predictions for an experiment by means of which it could be tested. (You prefer “whose empirical implications are not yet understood,” but that amounts to the same thing. But you claim that it is sufficient that “one deems it plausible that there will be some empirical implications in the end.”
To me this is breathtakingly weak as a criteria for a theory to be taken seriously. Certainly if all that is required to satisfy NEC is that some proponent of the theory be able to “deem it plausible that there will be some empirical implications in the end.” During my career I have seen many dozens of crazy and not so crazy ideas proposed by colleagues and I can’t think of one for which the proponent didn’t, or couldn’t have if asked, put forward some speculative story about how their idea would be experimentally tested in the end. Moreover I am sure the same is true for most of the hundreds of emails, letters and phone calls I’ve gotten over the years by non- or semi-professionals with their own pet ideas to unify physics, A criteria that doesn’t rule out even the most speculative of ideas and can’t even rule out the speculations of cranks isn't worth anything at all.
But it is your closing paragraph that genuinely confuses me: “ Therefore, I argue that it is implausible and artificial to rule out NEC as a genuine method of theory confirmation in modern physics. You may still argue that NEC is too weak and shaky in the case of string theory to instil trust in the theory. Fine. All I want to establish is that NEC is in principle a viable strategy for establishing trust in string theory. “
What do you mean by “a genuine method of theory confirmation”?| Normally confirmation requires empirical tests of predictions unique to that theory. NEC by definition are non-empirical so you can’t mean that. What do you mean? Similarly, what in the world does, “establishing trust” mean as a critria? Do you mean “worth a few people working on?” Or do you mean, “we believe in it to the point of only working on it and putting aside alternative hypotheses.” It matters which one you mean.
And then you use that work “viable” again, but now not referring to a particular theory but as a criteria offered to defend a strategy. Here you cannot be using viable to mean what you said it means, “ agrees with the empirical data in a given empirical regime”-because it is now “non-empirical” criteria that are said to be viable, as a strategy. Again the whole argument comes down to what you mean by “viable.” If you mean,” in some cases will turn out to have been good advice, but in other cases not, depending on whether the theory is ever able to make predictions or how those predictions turn out,” I have no problem agreeing.. But if you mean, “always a reliable guide to how the experiments will turn out,” I have to disagree because, as I argued initially, your NEC can be used to motivate interest in competing hypotheses that cannot both turn out to be true.
Thanks,
Lee
ReplyDeleteDear Giotis,
I never claimed LQG is equivalent to string theory in requiring unification-and in fact I agree that that is string theories most attractive feature. But I do claim LQG contains natural routes to unification. There arise from the simplest possible extensions of LQG and hence constitute instances of Dawid’s criteria of “The argument of unexpected explanatory coherence (UEA).”
This supports my main argument here, which is not to rerun the strings versus loops debate but to demonstrate that Dawid’s criteria are not helpful because they can be used to support both sides of such a debate between competing research programs
Also, the results I describe are mostly from after Rovelli’s book from which you quote was published. Please don’t continue to make the mistake of ignoring recent progress. Still, you have to admit that string theory may be false so that “no unification” must be considered an alternative hypothesis to the hypothesis that the four forces of nature are of necessity unified.
Thanks,
Lee
Dear Lee,
ReplyDeleteSeveral issues you raise have been addressed already in other entries of mine in this blog. Maybe it’s time to wind down our exchange after this, before repetition fully takes over. I think our differences are clearly spelled out by now. Anyway, here are my answers.
As you point out once again, you take it to be one of NEC’s most serious problems that it can support competing research programs. I gave you a very straightforward reason in a previous comment why support for competing theories that aim to solve the same scientific question does not arise in full-fledged NEC: the observation that there are no alternatives to the theory in question is the foundation of one NEC argument (NAA) and enters as a condition in another (MIA); therefore, full-fledged NEC relies on the observation that there are no competing hypotheses, which in turn is why it cannot support competing hypotheses.
But let me say something beyond that. In fact, the situation you describe can easily arise in empirical confirmation (and is considered fairly unproblematic in that context). Take two competing theories, one predicting X and Y_1 and the other X and Y_2. If X is measured, this confirms both of the competing theories. So, actually, empirical confirmation is more prone to confirm competing theories than NEC. If confirming competing theories is anathema to you, you should actually favour NEC over empirical confirmation.
You attribute to me the position that:
< all that is required to satisfy NEC is that some proponent of the theory be able to “deem it plausible that there will be some empirical implications in the end.” >
Your wording “satisfy NEC” is ambiguous but it may be read as suggesting that I take it to be a sufficient condition for NEC to arise “to be able to ‘deem it plausible that there will be some empirical implications in the end.’ ”
This is obviously not my position. The half sentence you cite was written when addressing the question whether the three NEC arguments I describe CAN work for a theory that is predictively empty. My answer is: No they cannot. The minimal condition for them to be applicable is that physicists “deem it plausible that there will be some empirical implications in the end.” This minimal condition, which can be extracted from the structure of the NEC arguments I present, is a NECESSARY condition for NEC to work. It is NOT a SUFFICIENT condition for NEC to arise.
You ask what I mean by ‘constituting a genuine form of theory confirmation’. I mean increasing the probability of a theory’s viability. That’s standard Bayesian confirmation theory, nothing unusual about it.
You further ask what I mean by having trust in a theory. That’s closely related to the former. I mean attributing a high probability to a theory’s viability - nothing to be confused about either.
You ask for a definition of “genuine form of confirmation” in terms of deciding how many people should work on one or another research program. But this confuses the epistemic with the pragmatic level. Theory confirmation does not constitute an algorithm for generating research strategic decisions. Such strategic decisions will of course be influenced by theory confirmation. But other issues will enter, like e.g. the difficulties to develop the theory, the spectrum of scientific problems raised by the theory, the number of scientists that can most effectively deal with those problems, etc. Those aspects are entirely independent from the issue of confirmation.
Best,
Richard
Lee,
ReplyDeletethere is one more remark I should add in order to alleviate your worries that NEC is a deadly threat to diversity in physics. This is the following: NAA is based on the observation that, despite serious attempts to do so, no alternatives to theory X have been found. If no-one looks for alternatives, the fact that none show up obviously tells nothing about the actual spectrum of possible alternatives. Therefore, only continued thinking about possible alternatives can strengthen NAA. In other words, looking for alternatives is not adverse to NEC but is an important element of NEC.
This once more underlines what I've argued in a previous entry: It is well possible (and I think it is more constructive) to lead a critical discussion about a theory's status by accepting the epistemic value of NEC in principle and discussing whether a given case amounts to strong NEC or not. If someone made a case for NAA but no-one had actually looked for alternatives, the latter fact would work against the significance of NAA in that case.
In the case of ST, to be sure, there was and still is a lot of thinking about possible alternatives, from finite SUGRA over the attempts to turn LQG into a convincing unified theory of all interactions to the recent idea of Horava-Lifshitz Gravity, to mention just some examples. NAA is based on the observation that, despite all those attempts, ST to this day remains the only promising unified theory of all interactions.
Best,
Richard
Physicists who are contributing to cancer therapy are frequently asked by patients about the safe or unsafe nature of radiation treatment. I was asked by a patient if a Higgs Boson would be generated during therapy. So I wonder how patients would react when word gets out that physics doesn't depend on data to check it's theories. The beauty and consistency of a theory is not a convincing argument for my M.D.,Nursing or other therapy colleagues or the patients. It is akin to saying that physics is now not a science, but a religion and praying is the best treatment it can advocate.
ReplyDeleteScience is science because it's empirical. This is what differentiates it from mathematics, philosophy and theology. At best, if you can't test a hypothesis empirically, it's simply incomplete science, at worst it starts to take on a religious air.
ReplyDeleteI'm afraid the trend towards secularism and the uncritical reverence towards science has not escaped the power of the religious instinct and many theoretical physicists have unknowingly stepped over into territory normally occupied by prophets and priests. Yes, non-empirical science is an oxymoron, because non-empirical science is called theology.