Shamit Kachru (described by Lenny Susskind as the “master Rube Goldberg architect”) and collaborators have a new paper out this evening on flux compactifications, one that in a rational world should finish off the subject completely. Recall that Kachru is one of the K’s responsible for the KKLT construction of these flux compactifications that stabilize all moduli, and for the last couple years debate has raged over whether this sort of construction gives 10100, 10500 or even 101000 possible string theory vacuum states.
Susskind, Arkani-Hamed, and other anthropic principle aficionados have argued that the fact that this number is at least 10100 is a great triumph because it means that there are so many vacua that at least some will have small enough cosmological constant to be consistent with our existence. But if there are too many, all hope of getting predictions out of string theory disappears. With 101000 vacua, you can find not only the cosmological constant you want, but probably any values of anything particle experimentalists have ever measured or ever will measure, and the theory becomes completely unpredictive.
Even so, the study of these vacua has become more and more popular over the last year or two, with many arguing that, no matter how big the number is, at least it’s finite, so you have improved over the standard model, which has continuously tunable parameters. This argument was made in the panel discussion at the Perimeter Institute a month or so ago. Also, a finite number of vacua allows you to study their statistics, by assigning a weight one to each possible vacuum state and getting a probability measure by dividing by the total number. You can then engage in wishful thinking that this probability measure will be peaked about certain values, giving a sort of prediction.
The new paper gives a construction of flux compactifications of type IIA string theory, and in this case the authors find an infinite number of possibilities. This should kill off any hopes of extracting predictions from string theory by counting vacua and doing statistics. The authors try and put a brave face on what has happened, writing:
“we should emphasize that the divergence of the number of SUSY vacua may not be particularly disastrous. A mild cut on the acceptable volume of the extra dimensions will render the number of vacua finite.”
but then they go on to puncture their own argument by noting that:
“one can legitimately worry that the conclusions of any statistical argument will be dominated by the precise choice of the cut-off criterion, since the regulated distribution is dominated by vacua with volumes close to the cut-off.”
With this new result, the infinitesimally small remaining hope of getting predictions out of the string theory landscape framework has now vanished. It will be interesting to see if this slows down at all the ever-increasing number of string theorists working in this field.
Update: Lubos Motl has some comments about this same paper.
I said,
I don’t know the level of new students doing PhD and all of that in string theory. Do you know Peter?
By “level” i mean “the number of”
Peter said:
“No intelligent young person is going to go into this field as long as it is obviously an intellectual disaster area.”
I am not completely sure. Month ago, a joung math student contacted with me for solicintg more information in my open criticism of string theory.
He was rather misguided in a lot of points. I explained my points, but he remained skeptic. For example, he said that was not true my claim that string theory was substituing the around 20 parameters of SM by more than 10000 new ones. He claimed that Brian Greene’s “Elegant” book said that one single parameter was sufficient.
I explained to him that string equation parameter was valid for “predictions” on 10D, for real 4D one need compactification and all, a priori, predictive power is lost.
He remained skecptic. He said that if I was saiyng was true, then Brian Greene had said that in his book. !!!!!!
Some people doing PhD and after leaving the field has contacted to me and agree with my valoration of string theory like a waste of time. I abandoned my string-brane research some time.
I don’t know the level of new students doing PhD and all of that in string theory. Do you know Peter?
Hi Peter,
What makes me especially nervous, it’s the fact that almost everyone looks for physics _beyond_ the Standard Model. Everyone is eager to find its failure. This is nonsense to me. I always thought that a scientist wants to understand nature and I would never expect that he would like to see his model of the world failed. I’m afraid it’s all about money.
Offhand I can’t really think of many promising “new” fields that a post-1984 tenured string theorist could possibly defect to, other than maybe conventional particle/astroparticle phenomenology or some area in condensed matter theory.
Perhaps we should delete the last twenty years from memory and go back to the way we were then. What kid of things was people doing before the upsurge of string revolutions?
I think we were studying the non abelian anomaly in order to use it somewhere in QCD… was it because the glue? Or something of the chiral limit?
Also for sure there was someone there still thinking about flavour. Well, perhaps only H Fritzsch in Germany.
There was also detectability of new particles via their interaction with nucleus. Witten and Goodman on dark matter for instance. As well as some low-energy theorems for the Higgs boson.
I certainly agree that the whole string theory phenomenon is due to HEP being a victim of its own success. Until someone does an experiment which disagress with the standard model and gives a clue how to get beyond it, things are going to be very tough.
But this is no excuse for getting stuck in an endless investigation of one speculative idea about going beyond the standard model, one that has clearly failed. It is amazing to see how unwilling people are to abandon an idea they have a lot of time invested in, no matter how clear it is that the idea can’t work.
Hi everyone,
don’t you think that all the problems of string theorists are mostly due to overall stagnation of HEP as a field. There is nothing really new found in an experiment (beside maybe the mass of neutrino, which hardly changed anything) and I doubt that anything can be found at LHC beside maybe Higgs. Without experimental data people are just doomed to either leave the field until any intersting data is available or do “math”. It’s clear that we are way too far from energies when quantum gravity effects can be of any significance. So overall I don’t see why string theory approach is better or worse than any other quantum gravity theory.
But even this is not a big problem. What really looks bad is a typical career path that one has to follow to stay in physics. There is no room for mistakes. The competition for a permanent faculty position is so tough that hardly anyone who doesn’t have tenure would risk to switch a field just because he thinks that the field is going in a wrong direction. It takes many years to get a certain level of compitence to do anything sensible. I’m afraid we just work too much and don’t have much time to think.
In a comment to his string theory blog “Game Over”, Peter says “… string theory … is obviously an intellectual disaster area.”.
I am reminded of a story mentioned in another of Peter’s blog entries about Hilbert and Heisenberg. According to Thall’s History of Quantum Mechanics, at http://mooni.fccj.org/~ethall/quantum/quant.htm :
“… Hilbert suggested to Heisenberg that he find the differential equation that would correspond to his matrix equations. Had he [Hesenberg] taken Hilbert’s advice, Heisenberg may have discovered the Schrödinger equation before Schrödinger.
When mathematicians proved Heisenberg’s matrix mechanics and Schrödinger’s wave mechanics equivalent, Hilbert exclaimed,
“Physics is obviously far too difficult to be left to the physicists …” …”.
Since the string theorists seem to be becoming an obstruction to the advance of physics, and since JC said a comment on Peter’s blog:
“… Only … scenario … which could possibly cause a huge landslide exodus from string theory, is if the government grant agencies (ie. DOE, NSF, etc …) all decide to stop funding …”,
I have a suggestion. Perhaps the black-budget programs of the USA might be expanded to include a well-funded space exploration and colonization program in which a large human colony is sent into space to contact other civilizations on some of the newly discovered extrasolar planetary systems. Since the colonizers will be the ones who form the aliens’ first impressions about humans, the colonizers should be only the best and the brightest so that the aliens will be dazzled by the brilliance of humanity. Obviously that means that the ship should carry all the most outstanding superstring theorists, who would be honored to be chosen. In order to impress the aliens even more, the aliens should be deceived into thinking that humanity back on earth included some who were even more brilliant than the best-and-brightest superstring theorists. Therefore, the ship carrying the superstring colonists should be modestly named something like, for example, the B Ark.
Tony Smith
http://www.valdostamuseum.org/hamsmith/
Peter,
Only other scenario I can think of offhand which could possibly cause a huge landslide exodus from string theory, is if the government grant agencies (ie. DOE, NSF, etc …) all decide to stop funding any string theory research.
It would be interesting to see what types of future papers will cite this particular Kachru et. al. paper hep-th/0505160
Offhand I can’t really think of many promising “new” fields that a post-1984 tenured string theorist could possibly defect to, other than maybe conventional particle/astroparticle phenomenology or some area in condensed matter theory. I can’t really see many string folks suddenly defecting to loop quantum gravity, nor to many of the other camps working on various partisan approaches to “quantum gravity”.
Hi JC,
What’s really amazing to me is how string theorists refuse to give up, no matter how bad it gets. At this point it’s completely clear that the idea of string theory based unification is dead, but no one seems to be giving up anyway. The attitude is “we’re going to keep doing this until someone gives us a new fad to work on”, but there is no encouragement at all for anyone to try and find something new. String theorists still will only hire string theorists.
I don’t see anything changing unless Witten comes up with something new. Increasingly the people who got tenure pre-1984 and know about something other than string theory are getting old. Those who got tenure post-1984 more and more often don’t know about anything except string theory, and have no interest in learning. No intelligent young person is going to go into this field as long as it is obviously an intellectual disaster area.
So I somewhat marvel that people aren’t more interested in the old fashioned stringy models or even the more modern brane world stuff. No one has outputed a no go theorem on the small/positive cc for those classes of theories, so why aren’t people still looking for whatever *that* may be.
I think that no-go theorems more or less exist. If you want to use AdS/CFT, it is certainly a problem if the CC is positive, since that rules out the AdS part. People have tried to invent some kind of dS/CFT, but AFAIU the CFT must then live at temporal negative infinity, which apparently is problematic and usually a discarded possibility.
Don’t forget that there are other problems, too. Without flux compactifications you have at least one unbroken SUSY and unstabilized moduli, i.e. new long-range forces, in disagreement with experiments, right?
While not defending the Landscape approach to phenomenology, the point is that string theory contains these flux fields, they may be turned on, and so the number of possible supersymmetric vacua is much larger than previously imagined. As far as other approaches are concerned, people use flux vacua to construct brane worlds that are on a more solid theoretical footing, i.e. with all moduli stabilized and with an acceptable final cosmological constant. Once you’ve found the possibility of turning on flux, you can’t pretend that it doesn’t exist. What this indicates, to me at least, is that finding a useful (testable) string phenomonology will involve more than finding a proper vacuum, and will most likely involve cosmological dynamics. Finally, Occam’s razor is fruitfully applied to starting points (two examples being Einsteins equations or the replacement of particles with strings) and really doesn’t apply to solutions (all gravitational solutions in one case or all possible vacua in the other)
What I have never understood about the landscape business. Why exactly do people take flux compactifications so seriously if this is what it outputs, eg an unpredictive mess?
There are many potential models in String theory, many Brane inspired models and what not. I take it the former is the only one (to date) that has outputed a small and positive CC. However typically the tradition in physics is, if its too messy move on and find something else. Typically (a variant of Occams razor) that turns out to be the simplest and invariably the correct answer (even if nothing has been discovered that fits the bill, we usually assume the universe is governed by simplicity).
There have been many theories that have been discarded in physics b/c of this premise, even before whatever else replaces *it* has been discovered.
So I somewhat marvel that people aren’t more interested in the old fashioned stringy models or even the more modern brane world stuff. No one has outputed a no go theorem on the small/positive cc for those classes of theories, so why aren’t people still looking for whatever *that* may be.
It seems to me String theory is still alive and well, its just that many of its practioners have abandoned a perfectly sensible attempt at understanding qg, with a weaker phenomenological theory that clearly doesn’t cut it.
I have a theory that Quantoken is a monkey. For proof, look at his typing skillz.
Correction.
I said: “Most of the monkey patents would look like completely garbage. But it’s OK. We can eliminate most of them by the anthropic principle.”
On a careful thought, I would replace it with Monkey Principle. That would also be what I call what string theoretists call anthropic principle. I call it monkey principle 🙂
Quantoken
Peter said:
“Susskind, Arkani-Hamed, and other anthropic principle aficionados have argued that the fact that this number is at least 10^100 is a great triumph because it means that there are so many vacua that at least some will have small enough cosmological constant to be consistent with our existence.”
Hey I would suggest something much better than 10^100 cavuas, I call it the monkey theory, a true theory of every thing. And this theory is absolutely correct and permanently safe from being falsified.
Very simple, you just allow a monkey to hit a keyboard arbitrarily for a little while, and then repeat again, and try again. The possible number of monkey patents it may come up with is definitely limited, something between 4^4^4 and 6^6^6, which definitely look better than 10^1000 vacuas.
Most of the monkey patents would look like completely garbage. But it’s OK. We can eliminate most of them by the anthropic principle. The correct monkey patents would at least make some sense in English. And certainly, once in a while it may come up with something that reads like “F=MA” or “E=MC^2”, which happen to be the correct physics theory.
What’s the odd of a monkey type 6 letters and it happen to be “E-MC^2“? It’s certainly not zero, and roughly one out of 10^11. That’s certainly a much better odd than one in 10^100 vacuas being the correct one!!!
Just allow the money keep typing, it eventually give you all monkey patents that is conceiveable. Any correct and incorrect theories we human can think about in the past and in the future million years, would all eventually come out of the monkey typing machine. Theory of every thing, every theory of thing, every theory of every thing, every every theory of thing, they will all come out with pretty good odds, not just a TOE.
And it is verifiable experimentally!!! Actually as I have demonstrated I can make “very sharp predictions” out of this theory. I predicted that “E=MC^2” can come out of it with an odd of roughly 1 in 10^11. It’s not observed experimentally yet, but no one will doubt it. It is only that we do not have enough monkeys, (or in another word we do not have enough string theorietists to study all of the 10^100 cavuas).
You see, my monkey theory definitely beats string theories already 🙂
Quantoken
there are more (vacua) in heaven and earth than are dreamt of in your philosophy.
JC,
“How fast do you think people will abandon the field?”
I replied to this in another part.
With each new failure of stringy endeavour, string adherents begin a new, more arrogant, folk tale.
The history that i write is not exact but one could say that with the failure of ST like a theory of the strong, they claimed that also was a theory of gravity. With the failure of first versions of “superST”, claimed that was also a theory of rest of interactions and particles. With the failure, they claimed that M theory was the theory of everything, from particles or gravity to cosmology, big bang, and other universes newer observed but “living” in some “part”. M-theory was also the basis for some eccentric topics like aliens (Kachu), extrasensorial perception, would reformulate QM eliminating its present weird state (Witten), etc.
I think that they will interpret the failure of M theory like a symptom of that the theory was conservative in excess. Probably it was a theory of more than everything and that would explain the current failure 🙂
String Theory appears to be a toaster. M-theory however, though lacking in real physics, is nonetheless going somewhere.
Peter,
If this is indeed “game over” and string/M-theory is not a mysterious space ship but really a toaster, how fast do you think people will abandon the field?
But these are vacua where SUSY is unbroken, right? Shouldn’t one expect infinitely many, since there are moduli spaces of SUSY theories? Isn’t what matters the number of non-SUSY vacua?
April is the cruelest month, breeding
Didacts out of the dead landscape, mixing
M-ory and D-sire, stirring squareroots with string pain.
Remarkable how much trouble one can get into by taking the simplest object beyond a point, a string and applying the constaints of quantization and relativity.
“This is how String Field ends,
Not with a Bang, but
With a Whimper.”
[Sorry T.S. Elliot]
The CC is zero. It’s an artifact of decoupling of light and gravity.
-drl
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