There’s a review of Susskind’s book The Cosmic Landscape in this Sunday’s New York Times book review section. The reviewer does a reasonably good job of laying out what the Landscape controversy is about, characterizing Susskind’s attitude as “braggadocio” with “an air of smugness”, and noting that “He allows remarkably little doubt about string theory considering that it has, as yet, not a whit of observational support.”
This week’s Village Voice has a profile of Susskind.
Update: More about this over at Uncertain Principles.
With respect to finding a conventional superstring model that has no obvious fundamental flaws (moduli etc) AND agrees quantitatively with a significant subset of the Standard Model parameters:
Peter said “… This problem with the moduli has been around since the beginning, and all attempts I’ve seen to get around it have had huge problems of one sort or another. … everything I’ve seen in following this more than 20 year history and looking at what people are doing now leads me to strongly believe that this is just wishful thinking. …”.
Urs said “… Currently, claims that there is a phenomenologically viable solution in … the space of solutions … are just as plausible or implausible as claims that there cannot be any. …”.
So,
Peter sees the failure of many very smart people working over 20 years to find a “phenomenologically viable” conventional superstring model as an indication that it might be a bad bet to expect success from similar people doing similar work over the next few decades,
and
even Urs agrees that there is no more reason to expect success than to expect failure from continued work on conventional superstring theory.
Given that,
it seems to me absurd to continue to devote 90% of theoretical physics funding and jobs to conventional superstring theory,
and
it seems sensible to divert half of those funds and jobs to alternative approaches, such as exceptional math structures, emergent spacetime, J3(O) spin foam, etc,
and
it seems to me that such a diversion is exactly what NSF, DOE, and university administrators should undertake NOW.
While I expect that conventional superstring theorists would cry in pain and outrage at losing money and jobs (just look at how rabidly they defend their turf nowadays),
why should they be treated any differently from USA manufacturing and IT workers who lost jobs that were outsourced to China and India ?
If conventional superstring theorists are really “the smartest guys in the room”, then they should have no trouble retraining and adapting to a new environment.
Tony Smith
http://www.valdostamuseum.org/hamsmith/
Regarding the reviewer´s comment on Susskind’s book, as well as the set of very interesting comments on this post, I´d like to mention that I have recently found this talk from Dr. Andrew Chamblin (dated Feb. 24, 2004). A further (brief) search on the net (arxiv, etc) did not allow me to find a transparancy of his talk or a related paper (if you know about it, please let me know). His assertion (see full abstract from the link above) seems fragile to me because it is as if one is blindly relying on the “reality” of the cosmic acceleration in order to use it as a valid guideline for the correctness of the approach (I would like to wait a lot more to rely on this, see, e.g., astro-ph/0601377 and astro-ph/0511628, as well as the delay on 2nd year WMAP data release; there are several rumors on this). If it turns out that the cosmic acceleration is not confirmed then it seems that string theory can be simply “adjusted” to fit that (negative) observation as well. I think this is just a practical example on some points that are being discussed here.
If I understand things remotely correctly, testing hypothetical GUT-scale physics has typically involved staring (with photomultipliers, of course) at vast quantities of ultra-pure water for years, waiting for the signature flash of light that will reveal proton decay. Presently, no protons have been observed to decay. One could conceivably build a much bigger tank, so maybe there’s still some hope for testing some of the GUTs, but the outlook seem less optimistic than it once did, so I’m told.
Testing Planck-scale physics, being the energy realm virtually all agree is where gravity must be just as important as Standard Model forces, is apparently going to be a lot more difficult.
We’re told one might not need galaxy-sized machines to probe physics relevant to the quantum gravity realm if, and only if, some best-case scenerios of various speculative q.g. approches pan out (e.g., compactified dimensions are a lot bigger than the Planck length, and hence a humanly-constructible accelerator can achieve the energies required to see the new physics such not-so-small extra dimensions give rise to).
It seems what’s being said is that experimental contact with quantum gravity might only be possible if we are lucky enough to be living in a universe where things not only aren’t what they seem to be, they aren’t what they seem to be in a terribly fortuitous way, something perhaps to the tune of tens-of-orders-of-magnitude in terms of a particle’s energy.
Otherwise, maybe quantum-gravitational effects only manifest at Planckian energies.
Watching from the seat in the bleachers provided by popularizers of physics, I’ve come to wonder if Unification is something mere mortals can reasonably aspire to any time in the next millennium or so. Is there presently a rational reason to presume otherwise? When does it become clear this is or is not physicists’ predicament?
D. B.,
There is a counterargument that should be mentioned. When modern physics began, atomism lay firmly in the realm of metaphysical speculation, inherited from certain thinkers of antiquity. It gradually became grist for the theoretical mill of early physics and chemistry, and only after two centuries or more assumed an unassailable role in science. This happened because atomism proved to be an extraordinarily fruitful basis for framing a great variety of questions about matter, many of which led to the formulation of precise and testable hypotheses. The point is that atomism began to show its value long before we had incontrovertible empirical evidence that the atomic structure of matter was a fact. (You will note strong echoes of this in some central ideas of modern biology.)
I strongly suspect that something like this will happen with many of the problems that currently fall under the headings of quantum gravity, the unification of fields and forces, cosmology, and the foundations of quantum theory (and quantum field theory). To many people string theory feels like—or, at least, used to feel like—such an idea. I rather think it is more like a muddled hint that such an idea exists, but is not the idea itself. Nevertheless, I think such an idea is needed; we can’t even clearly identify the relevant observations and paths of experimental as well as theoretical investigation without it. With it, we may see the relevance and importance of questions that the presuppositions of the Standard Model and it close relatives (GUTs) never prompted us to ask. In a number of ways I think this has already begun to happen.
Dumb Biologist (actually, maybe a biologist, but certainly not dumb) said:
“… Presently, no protons have been observed to decay. …”.
That is clearly the consensus view, but it may or may not be correct.
Adarkar, Krishnaswamy, Menon, Sreekantan, Hayashi, Ito, Kawakami, Miyake, and Uchihori, authors of a paper hep-ex/0008074 entitled
Experimental evidence for G.U.T. Proton Decay
say:
“… in Kolar … an experiment to detect proton decay has been carried out since the end of 1980. Analysis of data yielded … the life time of the proton is about 1 x 10^31 years …
A number of other experiments have also looked … The present consensus among these other experiments seems to be that they have not found any evidence for proton decay yet, and that the lower limit on the lifetime of proton is of the order of 10^33 years. …
The apparent contradiction between these conclusions does not mean a complete disagreement between the observations. … In our opinion, there are many points of agreement between the observations in other experiments and ours …
Since the total number of events to be analyzed and discussed is rather small, we have not fixed any special criterion to select the candidates for nucleon decay at the very beginning and we have tried to understand each event as it is. …”.
It seems to me that the validity of the consensus view of proton decay rests upon choices made in analysis of the experimental data, which consists of only a small number of candidate events. If the analysis choices made by Adarkar et al were to turn out to be correct, then some types of SU(5) GUT models might not in fact be ruled out by experiment.
As an illustration of how different analysis choices affect results, here is an excerpt from the Adarkar et al paper:
“… The IMB group has reported … that they have found 4 candidate events for e+ pi0 during the observation of about 4 kty. Out of these,
two events have been rejected because of their association with muon decay signals.
The other two events, according to their analysis also have some difficulty to be considered as due to proton decay phenomenon.
One of them has a concentrated Cerenkov light cone which may come from a slow
proton and
the other event has an extra light cone due to a lower energy particle.
However, if these features are ascribed to fluctuations in cascade showers, these two events may remain as candidates for proton decay. Assuming such an interpretation, their observed rate of candidate event becomes close to our results. …”.
It is my opinion that the experimental validity of proton decay by SU(5) GUT should remain an open question until all reasonable alternative analysis choices are taken into account.
Tony Smith
http://www.valdostamuseum.org/hamsmith/
DB – to risk echoing Tony, the proton may yet decay but the cool theory with proton decay, the SU(5) gauge theory, is ruled out because not enough of them decay in a given interval. It’s wrong by something like a factor of 100. I think everyone was surprised by this failure, since the SU(5) theory has a lot of nice features. That it failed, in a sense cast doubt on the structure of the standard model itself, to be sure mostly unspoken. It’s just a nagging “physicist’s feeling” that if SU(3)xSU(2)xU(1) were really correct, and you assumed that the strong and electro-weak forces are just parts of a whole, then SU(5) should work.
(It may yet work, if say the theory of the electro-weak interaction changes fundamentally, something that is certainly possible, given current neutrino research.)
-drl
About SU(5):
I haven’t looked carefully at the argument that the analysis of the proton decay experiment is wrong that Tony mentions, but I’m very skeptical for purely sociological reasons. Georgi and Glashow have a potential Nobel prize riding on this, so I find it hard to believe that they or their collaborators would be ignoring or downplaying evidence that they might be right.
I was never such a big enthusiast for GUTs like SU(5), because they have nothing to say about the big problem, where electroweak symmetry breaking comes from, and they require an even more elaborate Higgs sector. You “unify” things into SU(5), but then you have to break the unified symmetry back down to SU(3)xSU(2)XU(1) by putting in an adhoc Higgs sector. Not aesthetically convincing….
I think D.B. has it exactly right that the problem with quantum gravity is that it looks all too possible that there’s no way to measure its effects. My own point of view is that an interesting solution to quantum gravity has to also tell us something about particle physics. That would be real unification and allow testing of the idea, whatever it was. The fact that string theory might potentially do this is why people got so interested in it. Too bad it doesn’t work…..
Urs,
Unless you know what the background is, even if you have arbitrarily high energies available, string theory can’t predict what will be seen. The problem is that the theory is unpredictive, not that we don’t have the energy to check its predictions.
Didn’t know there was any controversy about proton decay results. Perhaps a larger detector could resolve it. At any rate, from what I’ve read, an instrument of that nature also makes a great neutrino observatory, so cosmologists and particle physicists still win, GUTs or no. It’s a worthwhile project, and I’d heartily endorse it…
I guess I’d like to say, witnessing the plight of q.g. theorists is hardly a source of schadenfreude, or any other satisfaction, for me. Whether they fail or succeed, I’m at least intelligent enough to recognize their brilliance, and admire them for it. I do admit I get more than a little disturbed when some of them appear to be promoting the idea that experments can wait 1000 years if that’s what it takes. It, uh, bums me out, but after my blood pressure returns to normal, I’m inspired to write my congressman and ask him to give these people a pile of money to build yet a bigger machine more than anything.
As for atomism: I thought the idea started to become much more than spurious physics, or a philosphical curiosity, when things like the ideal gas law, and other concepts dependent on statistical mechanics, started doing a very good job of describing what we see…not to mention some earlier insights from the development of stoichiometric rules in Dalton’s day, and so forth. Probably there were earlier evidential hints of atomism I’m ignorant of or forgetting, but if we go back in time much further, we’re entering a period where what we know as the scientific method was still in its nascent stages, and it seems hardly fair to judge those thinkers by our standards for empiricism. At any rate, many decades, maybe even well over a century before Einstein’s paper on Brownian motion, it seems like there were very good, experimentally verified reasons to think matter was composed of “elemental” particles.
Perhaps I’m wrong, but sometimes I look at q.g., and it reminds me a bit of the plight of scientists exploring the origins of life. I mean, really, the entire field is predicated on the notion that there’s a naturalistic, and relatively unexotic (compared to, say, aliens seeding the early Earth, or even panspermia) explanation that will rise from the primordial soup, so to speak. Given the alternatives, it’s certainly the most attractive bias, and some preliminary results with autocatalyzing ribozymes certainly lend credence to some models of pre-biotic processes. Too bad RNA is so fragile. Whatever came before it (and it’s generally thought something self-replicating probably must have), we’ve nothing but conjecture. At best we can say what, in principle, might have been possible. Beyond that, convincing verification of abiogenesis hypotheses, or, more ambitiously, a bona fide theory about how life arises, seem virtually unattainable. The evidence was lost billions of years ago, and we’ve only got our own planet to study, with a paltry n=1 informing all of our data about “life”. Lots of good, ideas; no definitive way to test them. Fortunately, there’s lots of other things to work on.
Anyway, please forgive the wet-and-squishy bio-hijack.
“Didn’t know there was any controversy about proton decay results.”
There’s no controversy. The damn thing just hasn’t decayed yet. This pretty much rules out ordinary SU(5), and, IIRC, susy SU(5) is hanging by a thread at best. SO(10) GUTs aren’t ruled out yet, as I understand it, and has some attractive features in relation to neutrino masses.
Thomas Larsson said,
Fantastic resume!
People -specially young one- does not know the history of the field. Since the very beggining of string theory in the strong force (last 1960s) until TODAY, string theory has been a complete failure.
It is often claimed that string theory cannot be tested. This is just untrue. All direct and indirect experimental verifications of string theory (including cosmic strings or mm-range esxtradimensions) in last near 40 years have obligated to string theorists to rewrite the theory in many ways. This has been denunciated by a number of physicists such as Nobel Prize Laugling.
And what is the final outcome?
A theory with hundred of hundred of hundred of unspecified parameters (instead of the few experimentally measured parameters of the SM), that cannot explain anything (it is not predictive) and in clear contradiction with other well-versed fields of science and with experimental data.
For example:
1) usual world is non-masless, still string theory only can rigorously deal with non-masless states.
2) The only gravity contained in typical superstring is a gravition over a flat classical spacetime. This is not GR, because GR is not a gravition over a flat spacetime with causal structure defined on the background. Precisely this is the main criticism of LQG and the search for one future M-theory…
3) Far from conjetures and half-trues the SM cannot be derived from string theory.
4) String theory requires lot of unobserved things (SUSY) but explain none of oberved things. If SUSY is observed at HLC last years, this is not a predicition of string theory not indicates that string theory is correct.
It is not a prediction because one may introduce the previously known SUSY on the old-stringy framework by pure consistency of the theory, not because was predicted from. Moreover, In nature SUSY, if observed at high energies, is not observed at usual energies.
String theory claims SUSY to all energies and therefore is in clear contradicition with experiment. No string theorists has proved how at high energies universe is SUSY but at low energies it looks non-SUSY and we observed SM of particle physics.
Conclusion: We obtain a theory that is not defined, is not scientific (not predicitive), contradicts our current scientific knowledge, ignores theorems proved on other fields of science (thermal science, complexity, decoherence and quantum measurement, etc.) deals with 10^500 ‘universes’ but none of the hypotetical universes looks like our universe, is mathematically very deficient (math is very outdated in several ways: HSs, Calaby Yaus and G2), and aestetically very ugly (take for example the ‘compactification’ of the bosonic 26D into the superstring hibrid), etc.
—
Juan R.
Center for CANONICAL |SCIENCE)
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