Frank Wilczek has a new Reference Frame piece in this month’s Physics Today. It’s about the question of whether the parameters of our fundamental physical theory are uniquely determined by abstract principles, or “environmental”. He gives two reasons for suspicion about the idea that these parameters are calculable from a fundamental theory:
1. They have complicated, “messy” values and, despite much effort, no one has come up with a good idea about how to calculate them (an exception is the ratio of coupling constants in a supersymmetric GUT). He writes:
Could a beautiful, logically complete formulation of physical law yield a unique solution that appears so lopsided and arbitrary? Though not impossible, perhaps it strains credulity.
2. Some of the values are fine-tuned to make complex structures and thus life possible:
It is logically possible that parameters determined uniquely by abstract theoretical principles just happen to exhibit all the apparent fine-tunings required to produce, by a lucky coincidence, a universe containing complex condensed structures. But that, I think, really strains credulity.
Personally I don’t see the same degree of believability problems that Wilczek sees here. On the first point, it seems quite plausible to me that there are some crucial relevant ideas we have been missing, and that knowing them would allow calculation of standard model parameters, by a calculation whose results would have a complicated structure.
On the second, it’s not at all clear to me how to think about this. Sure, the fact that our universe has highly non-generic features means that it is incompatible with generic values of the parameters, but there’s no reason to expect the answer to a calculation of these parameters to be generic. I guess the argument is that there would then be two quite different ways of getting at some of these parameters: imposing the condition of existence of life, and a fundamental calculation; and if two different, independent calculations give the same result one expects them to be related. But the question is tricky: by imposing the condition of the existence of life in various forms, one is smuggling in different amounts of experimental observation. Once one does this, one has a reason for why the fundamental calculation has to come out the way it does: because it is has to reproduce experimental observations.
Wilczek avoids any mention of string theory, instead seeing inflationary cosmology and axion physics as legitmating the idea that standard model parameters are fixed by the dynamics of some scalar fields, or something similar. This dynamics may have lots of different solutions so:
We won’t be able to calculate unique values of the parameters by solving the equations, for the very good reason that the solutions don’t have unique values.
The fundamental issue with any such anthropic or environmental explanation is not that it isn’t a consistent idea that could be true, but whether or not it can be tested and thus made a legitimate part of science. It’s easy to produce all sorts of consistent models of a multiverse in which standard model parameters are determined by some kind of dynamics, but if one can’t ever have experimental access to information about this dynamics other than the resulting observed value of the parameters, why should one believe such a theory? It is in principle possible that the dynamics might come from such a simple, beautiful theory that this could compel belief, but the theories of this kind that I have seen are definitely neither simple nor beautiful. If you want me to believe in a complicated, fairly ugly theory, you need to produce convincing evidence for it, some sort of testable predictions that can be checked. Wilczek does believe that multiverse theories may provide such predictions:
Of course, the very real possibility that we can’t calculate everything in fundamental physics and cosmology doesn’t mean that we won’t be able to calculate anything beyond what the standard models already achieve. It does mean, I think, that the explanatory power of the the equations of a “theory of everything” could be much less than those words portend. To paraphrase Albert Einstein, our theory of the world must be as calculable as possible, but no more.
One can’t argue with this: if a model make distinctive predictions, and these can be compared to the real world and potentially falsify the model, one can accumulate evidence for the model that could be convincing. Unfortunately I haven’t seen any real examples of this so far. The kind of thing I would guess that Wilczek has in mind is his recent calculation with Tegmark and Aguirre that I discussed here. I remain confused about the degree to which their calculation provides any convincing evidence for the model they are discussing.
Unlike many theorists, Wilczek personally seems to be an admirably modest sort of person, and perhaps this has something to do with why the multiverse picture with its inherent thwarting of theorist’s ambitions to be able to explain everything has some appeal for him. Over the years during which particle theory has been dominated by string theory, Wilczek has shown little interest in the subject, perhaps partly due to its immodest ambitions. But I see two sorts of dangers in the way his article ignores the string theory anthropic landscape scenario which is what is driving the interest of much of the theory community in these multiverse models. As his advisor David Gross likes to point out, accepting this scenario is a way of giving up on the perhaps immodest goal he believes theorists have traditionally pursued, and one shouldn’t give up in this way unless one is really forced to. None of these models is anywhere convincing enough to force this kind of giving up.
The second danger is that what is happening now is worse than just giving up on a problem that is too hard. The string theory landscape anthropic scenario is being used to avoid acknowledging the failure of the string theory unification program, and this refusal to admit failure endangers the whole scientific enterprise in this area.
Update: It has been accurately pointed out to me that Wilczek does mention string theory briefly at one point in the article (“Superstring theory goes much further in the same direction”), and alludes to it at another place (when he talks about a “theory of everything”).
Regarding Wilczek’s point 2: what Schellekens says is that if the equations of some fundamental theory managed to produce all of these numbers, then the notion that the laws of physics seem to be specially designed to produce life would be replaced by the notion that the “laws” of *mathematics* seem to be specially designed to produce life. And that would be far *worse*! I urge everybody to re-read Schellekens’ paper to see what he is saying about this.
The classical physicist’s expectation, far from being trivial, is wrong. E. Schroedinger, 1945
This quote is from the famous book What is life? based on a series of lectures that Schroedinger gave in Dublin at the end of the war. Geneticists have a high regard for the place of this book in the history of biology. Anyway, there is no reason whatsoever to think that the parameters for life are anything special, except from the anthropological point of view. What is terrifying is the thought that the new laws of physics should say something about biology. But Schroedinger recognised that this was inevitable over 50 years ago!
Of course, I say that (the above) as someone that does think these parameters are calculable. What is so wrong with the idea that biology become more quantitative? It already has.
I don’t think the degree to which biology is quantitative is the issue. Besides, that any subject can be made quantitative is trivial, unless one asks what the numbers mean. What is interesting are quantities and quantitative arguments that have deep qualitative implications. Supposing that certain physical constants of the observed universe are “anthropically” determined—that is, by a selection effect—tells us little or nothing we didn’t already know (or think we know) about either life or the laws of physics.
Consideration of the anthropic principle won’t get anywhere until it divests itself of the connotations of the word “anthropic” (and for that matter, “terrestrial”). The question is this: Does allowance for the existence and natural evolution of autonomous, self-reproducing physical systems somewhere in the universe impose any constraints on the laws of physics, or in any sense dictate their form?
Does allowance for the existence and natural evolution of autonomous, self-reproducing physical systems somewhere in the universe impose any constraints on the laws of physics, or in any sense dictate their form?
Or conversely: do new laws of physics naturally imply the existence of self-reproducing molecules, say via their appearance in a periodic table of structures?
Yea I agree with this idea in general. If you resort to anthropic reasoning (and I like how you mention that it is often understated that it requires somewhat tautological preexisting empirical output since we only have one universe with life in it that we can measure things in) then you face Occams razor.
eg Pick the simplest theory then that has the least amount of arbitrary continously adjustable free parameters (whether in solution space or theory space) and thats probably what you should go with. Unfortunately at this time, thats more or less the standard model + generic nonrenormalizable GR + maybe a few simple and well understood extras, like GUTs.
I mean the whole starting point of ST and most modern particle physics is to get rid of the naturalness problems, giving up on that most important goal, is premature, badly motivated and frankly annoying to the majority of physicists.
“We won’t be able to calculate unique values of the parameters by solving the equations, for the very good reason that the solutions don’t have unique values.”
See Dirac’s large numbers work. There is no reason to expect them to have determined values, rather, some inherent relation to be found out (I think a conformal one). Example – in Weyl’s theory one could in principle connect the value of the background radiation with G.
-drl
It’s “ecobalanced”…
All of the anthropic coincidences are balanced “just-so”, in a “goldilocks” manner, between diametrically opposing runaway tendencies. This goes way beyond the standard model to apply to every anthropic coincidence.
“Coincidentally”… ecosystems are also the most effecient means for uniformly disseminating energy, because they spread the process out over numerous “topological hotspots”, over an extended period of time. There are other facets to this…
Given the physical necessity for dissipative structuring, this is the most natural, (the only), configuration that our expanding universe could have. The balance is fixed, in other words.
The expansion process can’t maximize the entropic effort per the least action principle if the universe is not economically restricted to dissipate energy in the most “energy-efficient” manner possible.
Energy is not conserved if work isn’t maximized, so an expanding universe assumes the form that conserves energy and the second law of thermodynamics via an ecobalanced configuration that maximizes energy.
Dirac’s Large Numbers Hypothesis is flawed by his choice to fix the electric force rather than gravity. The mechanism for the AP becomes clear when you reverse this physics.
Is there a reference for any systematic study of low energy behavior over the Standard Model parameter space? It seems like a very hard problem to determine the volume of this space (in some reasonable measure) that is life-viable. At least with any kind of rigor. There is the issue of what happens in this space right near where we are — and then there is the seemingly much harder issue of totally distinct life-viable regions.
One admires Wilczek for a lot of reasons, including his flair for winging it philosophically (which a person with his originality can safely do). But since he is talking about philosophical issues in physics and cosmology, I would have suggested he draw on what should become a standard handbook reference:
http://arxiv.org/abs/astro-ph/0602280
Issues in the Philosophy of Cosmology
George F. R. Ellis
To appear in the Handbook in Philosophy of Physics, Ed J Butterfield and J Earman (Elsevier, 2006).
“After a survey of the present state of cosmological theory and observations, this article discusses a series of major themes underlying the relation of philosophy to cosmology. These are: A: The uniqueness of the universe; B: The large scale of the universe in space and time; C: The unbound energies in the early universe; D: Explaining the universe — the question of origins; E: The universe as the background for existence; F: The explicit philosophical basis; G: The Anthropic question: fine tuning for life; H: The possible existence of multiverses; I: The natures of existence. Each of these themes is explored and related to a series of Theses that set out the major issues confronting cosmology in relation to philosophy.”
Science and the philosophy of science being collective cumulative efforts, what’s the use of paying GFR Ellis to write a thoughtful 60-page handbook article about the very issues Wilczek addresses if he doesn’t use it? I havent yet seen the Physics Today opinion piece, but it sounds as if (characteristically) Wilczek is winging it.
Maybe the signature fresh outlook is something to be celebrate, and one shouldnt care. But when I get hold of a copy I will check to see if he cites Ellis.
Who,
I think Wilczek is someone whose motivations are primarily from very practical and phenomenological considerations, without taking a lot of interest in abstract philosophical or formal points of view. He certainly doesn’t refer to Ellis or anything like it. In any case, this was a short column, a semi-popular piece of science writing, not a serious scientific paper.
In that case what matters is that it be entertaining and provocative, which I feel sure it is. I’ll be at the library presently and have a look.
“The second danger is that what is happening now is worse than just giving up on a problem that is too hard.”
Sure, that`s the big concern about anthropic reasoning. If it were only giving up on something that appears to be too hard, the problem would be rectified the moment somebody demonstrates that one can do better. But if this perception is allowed to poison the organizing principles of theoretical physics, it can become a real obstacle to future progress.
That`s precisely why we must understand what string theory is, even if the remote possibility is taken seriously that it might not be a theory of nature. Comprehensively understanding the theoretical possibilities of unifying gravity with quantum mechanics is a necessary step in determining the amount of ad hoc input needed before a theory can become predictive.
Anthropic reasoning is based on the statement that a lot of ad hoc input is needed. Not surprising that this idea is taken seriously by some, while our understanding is still limited. The smart money is on the landscape going away eventually…
In reply to Michael’s comment
http://www.math.columbia.edu/~woit/wordpress/?p=396#comment-11077
I would agree that
“Comprehensively understanding the theoretical possibilities of unifying spacetime with quantum mechanics”
would be a necessary step for a number of reasons, some perhaps more significant than the one Michael mentioned but including his.
I note that the theory of spacetime dynamics that we have to work with is GR, so that would mean understanding what is involved in unifying quantum mechanics with GR or with some variant of GR—a theory of spacetime geometry exhibiting at least the salient features of General Relativity in an explicit up-front way.
As a minimum, something in the theory must represent the spacetime metric as a dynamic variable—or an equivalent surrogate of the metric–because that is the geometry. And the quantum state must be a state of that metric, alias the geometry.
what makes me doubtful of Michael’s reasoning (suspicious that it is mere apologetics) is that saying
“Comprehensively understanding the theoretical possibilities of unifying GRAVITY with quantum mechanics” allows “gravity” to work as a weasel word—so that we suddenly find ourselves talking about some theory which does NOT present a straightforward quantum model of the geometry of spacetime and does not actually quantize General Relativity. May even lack primary features of GR such as the explicit absence of a fixed background metric.
=======================
In case anyone wants to inspect Michael’s persuasive argument to motivate further string study I will try to paraphrase:
A. Anthropic reasoning is a poison dangerous to theoretical physics.
B. To guard against the harmful effects of this poison we must understand “the amount of ad hoc input needed before a theory can become predictive.”
(This would vary quite a bit: he doesnt say what theory or what kind of theory. Some types of QG have different requirements from string and are already falsifiable. I dont fully understand what he means by “input needed” since a theory either does or does not make predictions which would allow it to be ruled out—-it does not make CONDITIONAL predictions which allow it to be CONDITIONALLY ruled out based on some further assumptions. That would regress to testing those further assumptions. But for the sake of argument let this pass. Michael’s “a theory” probably means a stringy theory if it means anything definite.)
C. Therefore to guard against the harmful effects of this poison we must diligently study string theory. Because only in this way will we be able to discover how much “ad hoc input [is] needed before [it] can become predictive.”
I’m somewhat puzzled here. How many free parameters are okay? Is the ultimate goal to have a testable theory in which all numerical values are functions of pi, e, i, etc. with no observational input? In order for that to happen, you’d have to have a theory with no empirical free parameters which explained the known data but made predictions about currently unknown but discoverable phenomena. Good luck with that, but I wouldn’t hold my breath.
On the other hand, if some “brute facts” are allowed to remain unexplained in the ultimate theory, how do you know when you’ve reached the irreducible minimum? My guess is that it will come down to taste, faith, and the resources available to keep looking, since there seems not to be any reliable inductive method for knowing when to quit.
Steve
The question is about the parameters of the Standard Model and GR. If we can derive these, and there is every reason to believe it is possible, then we have a complete theory of SM+GR. This does not mean that future investigations will not reveal the necessity of more, as yet unknown, parameters of a post SM physics. So, no theory of everything – we are only human – but from our limited perspective the next breakthrough might well have the semblance of something grand.
Newyear 2007: Lenny Susskind conjectures that the consequences of String Theory are not understandable for the homo sapiens sapiens. He calls it the finite-brain conjecture.
January 2007: String Theorists all over the world realize that the f-brain conjecture naturally supports their believe that String Theory is the Theory of Everything, and moreover, it successfully explains the current crisis. The conjecture is strongly criticized for relating two not fully understood subjects, String Theory and the human mind.
Summer 2007: Ed Witten proves that the conjecture can not be proved. String Theorists realize that their quest is over. Either String Theory is not the Theory of Everything, or it is, and then they can never understand it. Gary Horowitz generalizes the statement by attaching bubbles of nothing to the f-brain. Lee Smolin points out that the conjecture fails for independent brains, but is widely ignored by the community.
End 2007: Thousands of String Theorists retire. They have fulfilled the task of finding the Theory of Everything. They have revealed what was possible, and have shown that the full beauty of the theory is to vast to fit into the human brain. They declare the end of theoretical physics, until intelligent designers improve the human f-brain.
January 2008: Those who are left focus on brain-independent theories.
I think I’ve said this before on this weblog, but I will say it again. I don’t understand why string theorists are working on the landscape and the anthropic principle, which as far as I can tell has virtually no mathematically well-defined content, when they could be working on the perfectly well formed, although probably unverifiable experimentally question, of “exactly what happens to the information inside it when a black hole evaporates.” (Some of them undoubtedly are; let me apologize to these string theorists.)
In other words, if you don’t want to work on physics (i.e., stuff you can get at by experiments), at least work on mathematics.
(Some of them undoubtedly are; let me apologize to these string theorists.)
I think you’ll find that the majority of them are; just look at hep-th on an given day. The landscape people just happen to be louder.
Peter Shor, irrespective of one’s opinion on the anthropic principle, it is a sociological fact that this idea as an approach to cosmology predates the string landscape and is still practiced mostly by non-string theorists (such as Wilczek), not that I think such sociological issues are that crucial…
\
Also, again irrespective of one’s opinions on the physical content of the anthropic principle, the study of the landscape certainly motivated lots of interesting and well-posed mathematical problems (e.g. see the work of Douglas and collaborators).
I am not sure about Nostradamus here’s predictions. FWIW, here are my own:
2006: “I can’t believe that you guys are so impatient,” say leading String Theorists. “Here we are, about to discover the answer to the Ultimate Question – the answer to Life, the Universe, Everything and you are demanding that we connect or theories to the real world. Of course we will do that. That and more. You just have to be patient.”
2026: “I can’t believe that you guys are so impatient,” say leading String Theorists. “Here we are, about to discover the answer to the Ultimate Question – the answer to Life, the Universe, Everything and you are demanding that we connect or theories to the real world. Of course we will do that. That and more. You just have to be patient.”
2040: Ed Witten dies and within six months is canonised Saint Edward of New Jersey.
2046: “I can’t believe that you guys are so impatient,” say leading String Theorists. “Here we are, about to discover the answer to the Ultimate Question – the answer to Life, the Universe, Everything and you are demanding that we connect or theories to the real world. Of course we will do that. That and more. You just have to be patient.”
2066: “I can’t believe that you guys are so impatient,” say leading String Theorists. “Here we are, about to discover the answer to the Ultimate Question – the answer to Life, the Universe, Everything and you are demanding that we connect or theories to the real world. Of course we will do that. That and more. You just have to be patient.”
Kea said:
“The question is about the parameters of the Standard Model and GR. If we can derive these, and there is every reason to believe it is possible, then we have a complete theory of SM+GR.”
Just out of curiosity, what gives you confidence that it is possible to derive unique values for the parameters of the SM+GR?
I’m sure it would be wonderful if that were true. But I have no idea, one way or the other, whether it is true (either in string theory or in some other, as yet unknown, approach).
All physicists are equal. But some are more equal than others. Be kind. Open the exit door for String Theorists, and offer them a helpful hand. They know it’s time to go.
Moshe,
I think justifying landscape work by its application to mathematics is a real stretch. Sure, it has generated some well-posed mathematics problems, but very few interesting ones, especially in comparison with other areas of string theory (e.g. topological strings), which have generated a lot of interesting mathematics. I spend a lot of time talking to many different mathematicians, especially ones interested in physics, and I can think of exactly one who has ever had an interest in anything generated by landscape studies (in a problem that asked about asymptotics of numbers of sections).
Douglas has a review promoting this kind of work
http://www.arxiv.org/abs/math-ph/0508019
Notice that the only references to work by mathematicians is to that of two of them who have collaborated with him on the problem of asymptotics of sections.
nostradamus said:
Newyear 2007: Lenny Susskind conjectures that the consequences of String Theory are not understandable for the homo sapiens sapiens. He calls it the finite-brain conjecture.
Chris Oakley said:
2066: “I can’t believe that you guys are so impatient,” say leading String Theorists. “Here we are, about to discover the answer to the Ultimate Question – the answer to Life, the Universe, Everything and you are demanding that we connect or theories to the real world. Of course we will do that. That and more. You just have to be patient.”
Nostra, it’s already happend. But we guys have to be patient, it’s far too early…
“This raises the possbility that we might someday convince ourselves that string theory contains candidate vacua which could describe our universe, but that we will never be able to explicitly characterize them. This would put physicists in a strange position, loosely analogous to that faced by mathematicians after Gödel’s work. But it is far too early to debate just what that position might be, and we repeat that our purpose here is simply to extrapolate the present evidence in an attempt to make preliminary statements which could guide future work on these questions.”
Computational complexity of the landscape I
Authors: Frederik Denef (KU Leuven), Michael R. Douglas (Rutgers and IHES)
http://lanl.arxiv.org/abs/hep-th/0602072
*sigh* I know. It’s more an extrapolation than a prophecy. (That’s because my brain is finite.)
http://lanl.arxiv.org/abs/hep-th/0602286
Statistics on the Heterotic Landscape:
Gauge Groups and Cosmological Constants of
Four-Dimensional Heterotic Strings
Keith R. Dienes
p 57
“By contrast, the second danger can be called the “Gödel effect” — the danger that no matter how many conditions (or input “priors”) one demands for a phenomenologically realistic string model, there will always be another observable for which the set of realistic models will make differing predictions. Therefore, such an observable will remain beyond our statistical ability to predict. (This is reminiscent of the “Gödel incompleteness theorem” which states that in any axiomatic system, there is always another statement which, although true, cannot be deduced purely from the axioms.) Given that the full string landscape is very large, consisting of perhaps 10^500 distinct models or more, the G¨odel effect may represent a very real danger. Thus, since one can never be truly sure of having examined a sufficiently sizable portion of the landscape, it is likewise never absolutely clear whether we can be truly free of such Gödel-type ambiguities when attempting to make string predictions.”
The invocation of Godel incompleteness is pretentious and absurd since there is nothing deep, subtle, or fundamental going on here. Lots of speculative ideas about physics turn out to be useless once you look into them because they can’t be used to actually predict anything about the real world. String theory unification is just one more such useless idea, and the only strange thing about it is the sociological phenomenon of serious scientists refusing to abandon a failed project.
A continually stalling project is actually a very safe territory to work on. If string theory was in danger of closing shop by producing the ‘final theory’ tomorrow, it would be hazardous to base a career on string theory.
On any large project, when success arrives the project workers are out of jobs, because far fewer researchers are needed to continue working on the completed product. If and when the much-touted ‘final theory’ arrives, a vast change in careers goals will be required.
I think that, far from celebrating, most people will be enraged that the fundamental physics will reach completion. Anyone who say climbs a mountain for the first time removes the opportunity for anybody else to do so, and in that sense is very selfish.
Kea: I’m still not getting it. Any unification of GR + SM (assuming that’s possible) will still have some number of parameters. Either these will be empirical parameters with no further justification OR they will all be fundamental math constants such as pi. My question is: How do you know when you’ve reduced the number of empirical parameters down to the bare minimum, i.e. when is further unification pointless? And how do we know that point hasn’t already been reached?
How do you know when you’ve reduced the number of empirical parameters down to the bare minimum, i.e. when is further unification pointless?
When you have none within the theories that were being unified. Of course, you will probably be introducing new ones, because that’s what usually happens. But there is no need to focus initially on the new ones when just understanding the unification is a big enough problem.
And how do we know that point hasn’t already been reached?
Well, that depends what you mean by the word know. Most good physicists that I know would bet their life on the fact that we haven’t reached that point with the anthropic principle. And the idea that no one has any idea about any alternatives is ludicrous.
Peter Shor: as has been pointed out, there is probably more work being done on the fate of information in black holes than on the landscape. However, I am mystified by Aaron B’s remarks. Surely if it is indeed true that string theory inevitably leads to a landscape, this is something that we want to know. Conversely, any discovery of a mechanism that selects a point or a region in the landscape would be an enormous advance. The problem is precisely that there are *not enough* people working on these things, and way too many working on essentially trivial technical exercises justified by the feeble hope that they will teach us “what string theory really is”.
Peter Shor again: “In other words, if you don’t want to work on physics (i.e., stuff you can get at by experiments), at least work on mathematics. ”
Sorry, this was tried for a long time and it did not work very well at all. There was a time when physicists would rush out and learn a new mathematical technique [K-theory, even category theory…] at the drop of a hat. It didn’t really get us anywhere at all.
The interest among physicists in pure mathematics has collapsed for a good reason. Nowadays people pin their hopes on the field where the data are, viz cosmology. And work on the landscape should be part of that. I’m not saying by the way that all of these developments are good, just that there is a reason for what has happened.
Sorry, this was tried for a long time and it did not work very well at all. There was a time when physicists would rush out and learn a new mathematical technique [K-theory, even category theory…] at the drop of a hat. It didn’t really get us anywhere at all.
Lambchop, of course random new math does not help. You have to learn, and perhaps invent, the right kind of new math. K-theory and category theory wouldn’t have helped Einstein finding GR or Dirac finding his equation. Tensor calculus, and the representation theory of SU(2), did the trick. And that was new math (at least new to physicists) at the time.
It has been obvious to me for almost two decades which kind of new math is needed to quantize gravity; since spacetime diffeomorphisms play an fundamental role in gravity, we need to understand the diffeomorphism group and its projective representations. This is why I started to search for, and later discovered, how to generalize the Virasoro algebra to several dimensions.
It really baffles me that others don’t want to look in this direction. Urs Schreiber even independently made the same observation, but then lost interest when he realized that I agreed with him.
Peter, fair enough, I made a mistake by adding the word “interesting” which represents an opinion. Strike it then, it is not essential to my response to Peter Shor’s remark.
There’s two issues here. The first is whether it means anything to make statistical predictions. I don’t believe it does. The second, however, is that, as best I can tell, there’s this huge region of parameter space over which we have absolutely no control. And, even in the vacua about which we can say something, it is almost always in the context of effective field theory with a conjectural nonperturbative scaffolding. So, at best we’re learning about some subset of vacua with the hope that there isn’t some unknown phenomenon that ruins the whole game. Studying these examples might be useful in that they could inspire new phenomenological scenarios, but I don’t think there’s much hope of applying string theory to the real world if we don’t even know what it is. My personal opinion is that that’s a much more useful question to research (and do “trivial technical exercises”) than to create increasingly complicated tinker-toy vacua that still bear very little resemblence to the world as we know it. I think one of the reasons you’re seeing a resurgence of interest in things like AdS/CFT is that it’s one of the few things in string theory that, if you kick it, it’ll actually hurt your foot. And, for what it’s worth, those categories you deride give the best description of gauge theories on D-branes at a singularity and, hence, AdS duals of field theories other than N=4 SYM. Even if string theory doesn’t turn out to be the theory of everything in our world, given that it does appear to be a theory of quantum gravity, we can at least try to learn how it solves the usual problems associated with that.
But that’s just me. I’ve been wrong before (lots), and I don’t have a job anyways.
You’ll get a job — you just need to switch to cosmology. 🙂
Come on, don’t you think that something like
http://arxiv.org/abs/hep-th/0510046
[which, by the way, invokes the landscape]
is far more worthwhile than hopeless calculations aimed at finding out what string theory really IS, but which never seem to lead anywhere? True, they didn’t really achieve all that much, but at least they did something that goes in the right direction, towards the real world. Historically [yes, I know this sort of argument is often crap, but anyway….] people almost *never* knew what their theory really WAS until much later. Schroedinger didn’t know about probability. Einstein thought that SR could not really handle acceleration. Everybody made all kinds of idiotic mistakes, but in the end they found out what their theories really WERE long *after* they made some connection with the real world. Yes, trying to find out what the theory really IS sounds very noble. But Don Quixote felt the same way about attacking those windmills. And as for categories — forget it! Even if they are the key to the Universe [like quaternions? 🙂 ] nobody will pay any attention.
Ludicrous is the right word.
I think that it is quite possibly relevant that quantum mechanics isn’t inherently able to describe dissipative structuring since it depends very much on Hamiltonian mechanics… except by way of the “Master Equation in the special, Lindblad form, which derives that flatness acts as a natural harmonic damper mechanism that keeps the imbalanced universe from evolving inhomogeneously, so this is the most natural configuration… if the universe is finite and closed… given inherent asymmetry in the energy. This will necessarily maximize the time that the expansion process takes, and that’s what a flat universe accomplishes via anthropic structuring.
Peter Woit Says: […]
and the only strange thing about it is the sociological phenomenon of serious scientists refusing to abandon a failed project.
I don’t find that so strange. I guess they just don’t know what else to do. Front research in physics has fallen apart into specialized subclasses, and it takes time and effort to change subject. Even for a postdoc it’s become hard to change the field. (Even more so since knowing the relevant people is an non-negligible factor.) If you have worked for some decades on String Theory, you just don’t drop the pen and say: Hey, the landscape sucks, lets go make spin foam models instead.
Or, to put it differently, someone should think about what we ought to do with all the String Theorists.
Best, B.
The attitude of “LambchopofGod” encapsulates well everything that is wrong with what is going on in particle theory these days. The idea that “too much math” is what caused the problematic state of the field has caused a backlash against investigating new ideas about mathematics and fundamental physics and this is both unfortunate and extremely unhealthy for the future of the subject.
The current prejudice seems to be that the problem isn’t string theory, but all that nasty math stuff, and by doing more “physical” calculations in string theory, one will manage to get closer to reality. This is nonsense. There are very well-understood reasons by now why string theory can’t tell you anything useful about anything collider experiments or cosmology-related experiments are going to see in our lifetimes. Pretending this isn’t so is just going to lead to completely useless work and the continued destruction of this field.
I don’t happen to believe that trying to think about “what string theory really is” is the best way to learn anything, but it’s a lot more promising than wasting ones time trying to connect string theory to cosmology or LHC physics because that sounds good. At least there’s a chance of learning something.
Aaron,
Sorry to hear you’re having job problems, the job situation in this field has sucked for a very long time, and in some ways is worse now than ever, especially for anyone who thinks interesting new math and physics go hand in hand. Undoubtedly you’ve thought about this, but you might have better luck looking in math departments. Good luck!
It is sad to see that virtually all the Millenium Nobel laureates in particle physics left their critical mind at the wardrobe to the string club where the new reality is being manufactured.
The following is an illustration for how facts are manufactured in String theory.
Witten’s introduction of the Maldacena conjecture:
“Recently it has been proposed by Maldacena that large N-limits of certain conformal field theories in d dimensions can be described in terms of supergravity and string theory on the product of d-+1 dimensional AdS space with a compact manifold.”
(Note the “proposed”)
After more than two thousand citations the Witten passage changed to
(Berenstein, Maldacena and Nastase):
“The fact that large N gauge theories have a string descirpition was believed for a long time. These strings live in more than 4 dimensions….”.
The conjecture has been manufactured into a correspondence. The answers to why such things happen are sociological and have nothing to with science (only the the sociology of scientists). String theory is a community and then all the researchers in such a social setting are compelled to accept things like that; no one can refuse to recognize it without undermining the veracity of the whole construct.
Yesterday I listened to one of the available online talks of David Gross. I didn’t believe that this is the same Gross whom I met (and discussed physics with a long time ago in Aspen) when he claimed that string theory cannot be proven wrong because it is linked via the Maldecena conjecture to the standard model. What I find so incredible is that the audience in a place like Princeton (where Pauli and other critical minds spend many years) receives such statements with applause.
Having experienced such a weird video, the fact that Wilszeck has not a single profound word of critique for this millenium circus was almost expected.
I should say by the way, that if my previous comment came across as bitter, it wasn’t meant to be. I made a conscious decision about what I wanted to do, and I wasn’t expecting to get a physics position given my choice of research topic and productivity. Unfortunately, the idea of applying for math jobs occurred to me too late in the game.
For lambchop, actually I like that paper precisely because it is in AdS/CFT. As for the rest, I don’t really see where these vacuum contraptions have gotten us thus far. It hasn’t given us any new insight into the cosmological constant problem, and there’s next to nothing being said about neutrino decay or proton decay from dimension five operators. The best prospects I see are for new mechanisms for inflation (which really is a lot ickier than it’s made out to be even ignoring the question about the initial conditions) and supersymmetry breaking (assuming supersymmetry even exists at the weak scale given that current experiments either seem to indicate a fine tuned MSSM or something a bit more non-minimal). I’m not denigrating this, by the way; outside of mathematics, string theory has been most successful in inspiring new ideas in field theory and phenomenology. The odds of this leading towards some sort of smoking gun for string theory, however, seem rather long to me. Of course, I’ve always been a formalist at heart (closet mathematician, it’s been accused), so there’s a lot of my personal prejudices speaking here.
And on the mathematics front, in the realm of actually trying to construct vacua like our world (as opposed to, say, immediately postulating gadzillions of them), the constructions are all rather mathematical, (0512177 and 0512149 or 0512170 where they try to do SUSY-breaking).
Bee wrote in a constructive simpatico spirit (IMO) as follows:
I saw a sign that someone may have been thinking about it. Baez left a trail of crumbs leading to spinfoam when he titled his last two papers
Quantization of strings and branes coupled to BF theory
and
Exotic Statistics for Strings in 4d BF Theory
Now we will see if the ants find the sandwich.
http://arxiv.org/find/grp_physics/1/au:+baez/0/1/0/all/0/1
4D beef means no extra dimensions.
Best to you too.
said who?
I have a summary of the first of these two signs here:
.
Notice, though, that not everything that looks like a shoestring is necessarily an F-string.
But, as someone else already pointed out, there might be a relation here to some sort of solitonic strings.
Hm, I am always having problems with hyperlinks in this comment section. Where there is nothing in the above comment it should read
http://golem.ph.utexas.edu/string/archives/000777.html
Aaron,
You should come and work in the software business. The money is better than academic research, it is genuinely creative, people are more interested in what you do and if you get something wrong you will normally know about it straight away. Of course, not everyone would consider the last one an advantage, but I do. In theoretical HEP as currently practised if you get things wrong then you can patch them up ad infinitum, or – if the worst comes to the worst – just invoke the landscape. This is not very satisfying.
Chris, I dont know about you or Aaron but I respect it a whole lot when children are curious about where babies come from and when physicists are obsessed to find the fundamental degrees of freedom of spacetime and matter. so I find it jarring when somebody says, to one of these obsessed ones, go do software. it sounds dismissive. I looked up Nature in the dictionary and it comes from the word for “birth”. Asking what the world is made of is a sacred question (if any question is).
And maybe the whole scientific enterprise has some elements of high comedy (like self-delusion, hubris, the failure of the best, over and over—or maybe I mean tragedy). Anyway I want to say to whoever might be listening: Don’t stop looking for the sandwich!
Who,
If this curiosity is leading most of these grown-up kids into exploring ever more complex mathematical neverlands then I would say that they would be better off without it.
Besides, the search for answers to ultimate questions – done my way – resulted in no academic job. Maybe Aaron is finding the same thing.
No, modern theoretical physicists are not driven (mainly) by curiosity, but by the joy of solving problems.
Who:
It is quite possible to “look for the sandwich ” and work for a software company (or a patent office) at the same time. This has a great advantage of being free to choose your own “crumb trail” and stay out of the crowd.
Who
Did you put some category theory butter on the sandwiches?