Causes of loss of interest in String program

[Aidyan]

In fact. As everyone knows the aristotelian cosmogony turned out to be dead wrong (and no, between Ptolemy and Copernicus almost nobody was working on it). Would there have not been the church and its inquisition who dogmatically insisted to pursue that path we could perhaps have avoided the 'dark ages'. I hope really that string theoreticians will not take that as an historical reference case. This would only discredit them. And I don't want to wait another 2000 years ...

 

[MTd2]

Hmm, MTd2, I think that you have misread Aidyan question. He asks for heavy involvement, no results during a long period, and then suddenly it happens to be right. I doubt you are claiming that Aristotle biology happened to be right at the end, nor even a huge involvement of resources (by biologists, aka veterinaries and doctors, not by teologists).

Oh, yeah! I misread! I just noticed that!

 

[MTd2]

In fact. As everyone knows the aristotelian cosmogony turned out to be dead wrong (and no, between Ptolemy and Copernicus almost nobody was working on it).

No! Thousands of people indeed researched the Ptolomaic model! It indeed achieved a great accuracy during the Islamic period. In fact, the accuracy was so great, that the muslim astronomers came up first with the heliocentric model, or close to it:

"Ibn al-Shatir, the Damascene astronomer (1304–1375 AD) working at the Umayyad Mosque, wrote a major book entitled Kitab Nihayat al-Sul fi Tashih al-Usul (A Final Inquiry Concerning the Rectification of Planetary Theory) on a theory which departs largely from the Ptolemaic system known at that time. In his book, "Ibn al-Shatir, an Arab astronomer of the fourteenth century," E.S.Kennedy wrote "what is of most interest, however, is that Ibn al-Shatir's lunar theory, except for trivial differences in parameters, is identical with that of Copernicus (1473–1543 AD)." The discovery that the models of Ibn al-Shatir are mathematically identical to those of Copernicus suggests the possible transmission of these models to Europe.[14] At the Maragha and Samarkand observatories, the Earth's rotation was discussed by al-Tusi and Ali Qushji (b. 1403); the arguments and evidence they used resemble those used by Copernicus to support the Earth's motion.[15][16]"

http://en.wikipedia.org/wiki/Geocentric_model#Geocentrism_and_Islamic_astronomy

 

[negru]

I could mention several technical reasons why SS theory leaves me cold, but am still a layman in QFT and don't dare to go into technical details I'm still learning. But from a simple historical perspective, I'm wondering if there is a single example in the history of physics where hundreds, if not thousands, of top physicists worked on for more than three decades without producing a concrete result, and then turned out to be a correct theory? I can't think of any. People are slowly realizing that if a theory, despite all the efforts, does not produce tangible results after say 15, max. 20 years, then it must be wrong. And I'm afraid that this holds for LQG too.

The history of things is irrelevant here. String theory and its alternatives have a minimal amount of external data to work with. This was usually not the case before. People were observing various phenomena then trying to explain them. They were guided by data. Now we're not observing anything new, we're just trying to make the theory we have prettier. Any new predictions we could make will very likely be at unobservable energies anyway (unless we're extremely lucky and there is low energy susy, or dark matter detection says anything). So even if string theory somehow made a prediction around i don't know say 100-1000 Tev, no one would take it seriously anyway for another 50 years or so. Almost everyone working on string theory now would be dead by then.

 

[marcus]

In regards testability (mentioned above) some readers might be interested in:
http://arxiv.org/abs/1204.1288
Perturbations in loop quantum cosmology
Ivan Agullo, Abhay Ashtekar, William Nelson
(Submitted on 5 Apr 2012)
The era of precision cosmology has allowed us to accurately determine many important cosmological parameters, in particular via the CMB. Confronting Loop Quantum Cosmology with these observations provides us with a powerful test of the theory. For this to be possible we need a detailed understanding of the generation and evolution of inhomogeneous perturbations during the early, Quantum Gravity, phase of the universe. Here we describe how Loop Quantum Cosmology provides a completion of the inflationary paradigm, that is consistent with the observed power spectra of the CMB.
4 pages, ICGC (2011) Goa Conference proceedings

and in the earlier paper (cited 45 times), simply as an example:
http://inspirehep.net/record/812301?ln=en
Cosmological footprints of loop quantum gravity.
J. Grain (APC, Paris & Paris, Inst. Astrophys.), A. Barrau (LPSC, Grenoble & IHES, Bures-sur-Yvette).
Feb 2009
7 pp. Phys.Rev.Lett. 102 (2009) 081301

You shouldn't lump Loop in with String. Loop is just beginning to get broad attention from researchers, more-than-token representation at major conferences. Even the biennial Loops conference only goes back to 2005. Their arcs of historical development are quite different.
===============

As I mentioned before, 6 or 7 days ago the Munich organizers of Strings 2012 posted the list of 39 invited speakers, but the titles of the talks are all blank except for one. So it has been for nearly a week. The only talk, out of 39, whose title is listed is
Alternative approaches to quantum gravity: a brief survey
http://wwwth.mpp.mpg.de/members/strings/strings2012/strings_files/program/talks.html
It's hard not to conclude that leading string folks and likely participants are interested in hearing about and discussing this. And this, I think, is relativey new. I don't recall much attention to non-string QG, at past conferences.

I'm pointing out a subtle change in climate, or perhaps just a shift in the weather pattern.

 

[Aidyan]

No! Thousands of people indeed researched the Ptolomaic model! It indeed achieved a great accuracy during the Islamic period. In fact, the accuracy was so great, that the muslim astronomers came up first with the heliocentric model, or close to it...

MTd2, these are only isolated historical examples (and you surely can find more), but can not in the least be compared with the effort, the people, the machinery and the money spent today on string theory. In string theory there are hundreds of "Ibn al-Shatirs" who produce an amount of papers, books, articles and whatever documents in few month, perhaps even only few weeks, comparable to what humanity did in 20 centuries (just compare what pops into existence daily on arxiv...). Modern organized science in the form we know exists only since three max. four centuries. And since then I can't think of another theory in physics that was so revered, cherished and honored for a so long time without producing concrete results.

The history of things is irrelevant here. String theory and its alternatives have a minimal amount of external data to work with. This was usually not the case before. People were observing various phenomena then trying to explain them. They were guided by data. Now we're not observing anything new, we're just trying to make the theory we have prettier. Any new predictions we could make will very likely be at unobservable energies anyway (unless we're extremely lucky and there is low energy susy, or dark matter detection says anything). So even if string theory somehow made a prediction around i don't know say 100-1000 Tev, no one would take it seriously anyway for another 50 years or so. Almost everyone working on string theory now would be dead by then.

I wouldn't call QM, GR, the SM and all the modern particle physics and astrophysical observations "minimal amount of external data to work with". And what "data" had three guys as Copernicus, Kepler or Tycho Brahe to work with? Only those of the extremely limited human senses, and yet they produced something. The "unobservable energies" argument is acceptable provided that a research along the "unobservable energies" line will sooner or later lead to "observable energies" data. Or at least a minimal hint, an allusion, a scratch of evidence. History suggests that "sooner or later" means about a couple of decades, not centuries, and not to say millenniums.

 

[arivero]

Kepler

Hmm perhaps we could have a better example here, with the theory of indivisibles/fluxions... it is a whole lifespan of development, the initial players, such as Kepler or Cavalieri, never see the final physical results (Newtonian Dynamics). Kepler himself -whose treatise is mostly numerical- was never considered a player, except perhaps by Cavalieri, who insisted on showing his work to Galileo (and failing to attract attention). Cavalieri atoms run into all kinds of problems, until Newton and Leibnitz got the final formulation.

 

[negru]

I wouldn't call QM, GR, the SM and all the modern particle physics and astrophysical observations "minimal amount of external data to work with".

Of course not, but the relevant data was already used to give precisely QM, GR and the SM. if you want a bigger theory, you need more data than was already used, that was my point. Just like Newton used all the data he knew to get classical gravity. Even if he saw hints of things beyond classical gravity, the data he had wouldn't have been anywhere near of helping him.

And what "data" had three guys as Copernicus, Kepler or Tycho Brahe to work with? Only those of the extremely limited human senses, and yet they produced something.

Yes, and the data they had was enough to produce what they did. A bunch of yearly measurements is all that's needed to derive Kepler's laws. A bunch of particles is all that's needed to derive the SM. To derive a TOE, you need data comparable to the scope of that goal.You might that the combination of all of GR and SM data should be enough. Not necessarily. If Kepler only had data from one of whatever he was measuring, it's very possible that wouldn't have been enough. Or if we had only detected half the particles we did before i don't know EW unification, maybe that wouldn't have happened either. Sure with hindsight a minimal amount of data seems required to derive a new theory, but it doesn't work that way. Same with string theory. Perhaps all that's needed is one low energy susy particle, or missing energy, or who knows, to guide us towards the correct formulation.

 

[MTd2]

Modern organized science in the form we know exists only since three max. four centuries. And since then I can't think of another theory in physics that was so revered, cherished and honored for a so long time without producing concrete results.

The scientific method, as we now it was first used by al Haytham, in the X century.

http://en.wikipedia.org/wiki/History_of_scientific_method#Ibn_al-Haytham

Anyway, I think you are not considering the quantity of data and the works that was not preserved.There was no printing and paper was hard to acquire. So, even important texts were erased, when not destroyed, for random uses. Take a look at this:

"Archimedes lived in the 3rd century BC, but the copy of his work was made in the 10th century AD by an anonymous scribe. In the 12th century the original Archimedes codex was unbound, scraped and washed, along with at least six other parchment manuscripts, including one with works of Hypereides. The parchment leaves had been folded in half and reused for a Christian liturgical text of 177 pages; the older leaves folded so that each became two leaves of the liturgical book. The erasure was incomplete, and Archimedes' work is now readable after scientific and scholarly work from 1998 to 2008 using digital processing of images produced by ultraviolet, infrared, visible and raking light, and X-ray.[1][2]"

http://en.wikipedia.org/wiki/Archimedes_Palimpsest

 

[marcus]

Since we've turned a page, I'll remind readers what the basic input data are that we are considering how to explain

The decline itself is clear from the available indices: there has been a downtrend in the rate of first-time faculty hires, starting around 2001. This is visible both in terms of absolute numbers (from average about 9 per year down to around 1 per year) and also in terms of string as a fraction of total Particle Theory. It used to be that around HALF the first-time faculty hires in HEP theory were in string, now it's more like a tenth.

A physicist at the U Toronto (Erich Poppitz) charts first time faculty hires in High Energy Physics Theory (Usa and Canada) by year and keeps track of what fraction of these are in string, which fraction are in lattice field theory, and so on.
http://www.physics.utoronto.ca/~poppitz/Jobs94-08
His chart shows 11 HEP theory hires in 2011 of which one was string.
Here annual rates have been smoothed by averaging over 3 years intervals.

period                 1999-2001    2002-2004   2005-2007    2008-2010    2011
annual HEP theory hires   18             24            23             13            11 
annual string hires           9              8              6               2              1

The source is http://particle.physics.ucdavis.edu/rumor/doku.php
A new webpage has been started that reports on postdoc fellowships in a broad category (gen. rel. and quantum cosmology) which includes quantum gravity. Also something to keep an eye on:
http://sites.google.com/site/grqcrumourmill/

There has been a decline in annual citations to recent string research by the theorists themselves.
Number of recent string papers making the top fifty in the annual Spires HEP topcite list

year (some omitted for brev.)   2001    2003    2005    2007    2009    2010
recent work highly cited in year  12         6         2         1         1        0

Here a paper is counted as recent if it appeared in the previous five years. This gauges the quality/significance of current work by how much other researchers in the field currently refer to it. A kind of community self-evaluation, if you will, concerning the perceived value of current and recent work.

Several ideas have surfaced in this thread regarding possible reasons for the decline in interest. It's conceivable that reasons might be found in the physics of string itself. As an approach to reproducing the Standard Model, say, it might conceivably be fundamentally flawed on physical grounds. Arivero made the point that we should consider it separately as particle model and as a candidate theory of the quantum geometry of the universe.
In that second role, does it offer a promising way to resolve the cosmological singularity and model conditions leading up to the start of expansion? Is it testable by astronomical observation? This seems to be the main thing one wants a QG theory for. So there may or may not be valid physics reasons inherent in the theory.

Or it could simply be that newer approaches to QG and explaining the SM have arisen, and that researchers have some natural tendency to spread out seeking fresh ideas and new areas to work on.

We might get some good out of a special String retrospective issue of the journal Foundations of Physics edited by Gerard 't Hooft. He invited a reputable bunch of string and other theorists to contribute articles for an issue called Forty Years of String Theory.
http://en.wikipedia.org/wiki/Foundations_of_Physics
Some of the articles which 't Hooft invited to be in this special issue of the journal are available online:
http://arxiv.org/find/grp_physics/1...+co:+AND+string+AND+Forty+years/0/1/0/all/0/1

Additional help may be found by checking to see what topics interest String researchers these days, as indicated by the titles of invited talks which the the Strings 2012 conference organizers have put online:
http://wwwth.mpp.mpg.de/members/strings/strings2012/strings_files/program/talks.html
One assumes these are the topics which active researchers, the likely participants, are interested in hearing about and having discussed at the main annual conference. So we can get an idea of what they have in mind. For the past six days the list has had only one topic, but we can expect to see more appear shortly.

 

[MTd2]

Or it could simply be that newer approaches to QG and explaining the SM have arisen, and that researchers have some natural tendency to spread out seeking fresh ideas and new areas to work on.

This is a more likely explanation. But with a caveat: people are getting tired.

 

[negru]

For a rigorous analysis to prove that statement you should keep track of total number of citations in het+qg. Also h-index. In the past few years more and more garbage is showing up on the arxiv, from instituions i'll call sketchy at best.

I'd like to see evidence that papers and citations that in past came from string theory are now coming from alternatives. Just counting isn't enough. My own impression is that string people are doing SCFT's(amplitudes, localization, index stuff, a/c/f theorems), while newcomers especially from Europe are doing the alternative stuff. Also jobs are going to phenomenology related stuff, which is of course natural because of the LHC.

I'd also be curious to find out what job situation is in CMT to compare.

 

[mitchell porter]

But from a simple historical perspective, I'm wondering if there is a single example in the history of physics where hundreds, if not thousands, of top physicists worked on for more than three decades without producing a concrete result, and then turned out to be a correct theory? I can't think of any.

What is your opinion of grand unified theories and supersymmetric field theories?

 

[Aidyan]

A bunch of yearly measurements is all that's needed to derive Kepler's laws. A bunch of particles is all that's needed to derive the SM. To derive a TOE, you need data comparable to the scope of that goal.

How do you know what data threshold is needed? The data might well be already in front of our eyes but we can't see it because probably we don't want to give up our still too classical mindset. That's what happened to those who insisted on epicycles like Tycho Brahe, or to Poincaré who had all data and couldn't see relativity as Einstein did, or to Einstein himself with QM, just to mention some. I don't think it is only about available data, but about a message from nature we still don't want to swallow.

The scientific method, as we now it was first used by al Haytham, in the X century.
http://en.wikipedia.org/wiki/History_of_scientific_method#Ibn_al-Haytham
Anyway, I think you are not considering the quantity of data and the works that was not preserved.There was no printing and paper was hard to acquire. So, even important texts were erased, when not destroyed, for random uses...

You can't compare with the actual state of affairs the exceptional individual cases of some people who showed up from time to time throughout a centuries long period and that otherwise had almost no scientific progress. Organized science began with Galilei, Newton, perhaps even later. And since then, and also before that, there is nothing in history like the effort in terms of people, research and money set behind a single project like string theory *AND* with no concrete results.

What is your opinion of grand unified theories and supersymmetric field theories?

As I wrote, I'm not in a position to express too technical judgements apart of my doubts from the historical perspective (and BTW, if someone wants to help me: https://www.physicsforums.com/showthread.php?t=594293 ). I spent several years on applied physics and only recently turned my interests to more theoretical issues. But this happened just because of the "string crises". Intuitively I always perceived string theories as nonsense. I can only see in it the attempt of human mind to impose its naive classical aristotelian and anthropomorphic understanding of the macro-cosmos on a micro-cosmos that obviously refuses to be imprisoned in such narrow limits. But on the other side I always told myself: "those guys know better than you, they have certainly good reasons to believe in it, let me see...". But now, enough is enough... As to GUT they appeal certainly much more to my aesthetic sense. However, since they didn't produce concrete results either, this might be a lesson too: beauty is not a criterion. But something tells me that nucleons aren't stable, as predicted by several GUTs. I would keep an eye open on experiments looking for that.

 

[mitchell porter]

there is nothing in history like the effort in terms of people, research and money set behind a single project like string theory *AND* with no concrete results.

This is why I asked your opinion of GUTs and supersymmetric QFT - to see if you thought that they differ from string theory in this regard.

Let's recall another historically unprecedented situation: the existence of a single theory which does explain almost all of physics. This is the standard model, which has existed since the 1970s and has only needed the addition of neutrino masses, and a dark sector about which there is almost no data, to remain valid.

GUTs and supersymmetry and string theory have all grown up in the era of standard model dominance. GUTs are held to explain certain features of the standard model, like the hypercharge assignments; supersymmetry is supposed to give us dark matter, GUT coupling unification, and stabilization of the Higgs mass. Specific theoretical constructions give us, not the exact particle masses, but ratios between them with the right order of magnitude.

Nonetheless, none of these beyond-standard-model theories has yet become the new standard. It is a mathematical fact that there are innumerable possibilities to explore, even just within the framework of supersymmetric GUTs, because there are innumerable possible field theories which reduce to the standard model at accessible energies.

String theory has also turned out to contain innumerable possibilities, but they do have one new feature (apart from containing gravity): these distinct stringy possibilities do not come with continuously adjustable parameters, unlike field theories. Therefore, they are potentially more predictive than field theory. Unfortunately, like QCD, in practice it has proven very difficult to extract the predictions. The ability to calculate in string theory does progress, but this progress takes years to occur, and requires new mathematics.

There is continuity between the field-theoretic research program of unification and supersymmetry, and the research program of string theory, because the field-theory limit of string theory is typically a grand-unified supersymmetric theory. It has also been discovered that some field theories are simply equivalent to string theory on the specific corresponding background; the strings are essentially flux-lines in the field theory, and the extra dimensions emerge from scalars. It's likely that QCD itself is equivalent in this way to string theory on a particular background.

So reality does look a lot like string theory, because string theory looks like gauge theory plus gravity, and increasingly we also learn that gauge theories, like the standard model, look like string theory! It may be that some of the dominant physical hypotheses about how string theory works are misguided. Perhaps there's no supersymmetry, or no supersymmetry until ultra-high energies; perhaps the "extra dimensions" are algebraic rather than geometric. But it's also still very possible that the central hypotheses of the field are entirely correct. We might be living in a heterotic compactification with weak-scale supersymmetry, neutrino masses coming from the GUT scale, and so on.

When you say string theory has "no concrete results", I can't agree. What it has given us is a very large number of models which incorporate and complete the field theories that non-string theoretical physicists were already using, and which have the potential to explain the quantities which are just input parameters for something like the standard model. We know that string theory can get close to reality in various ways. One has every reason to hope it can go all the way.

 

[MTd2]

You can't compare with the actual state of affairs the exceptional individual cases of some people who showed up from time to time throughout a centuries long period and that otherwise had almost no scientific progress.

It was not casual. We lost a lot of information on those people. Only the very best survived because, as I said, the availability of recording media was extremely scarce.

 

[negru]

We know that string theory can get close to reality in various ways. One has every reason to hope it can go all the way.

Just an example off the top of my head, Heckman and Vafa compute the CKM matrix to within something like 1% from F-theory http://arxiv.org/abs/0811.2417

 

[arivero]

Organized science began with Galilei, Newton, perhaps even later. And since then, and also before that, there is nothing in history like the effort in terms of people, research and money set behind a single project like string theory *AND* with no concrete results.

If you are happy with 50 years without concrete results, then my previous example, the quest for quadratures of areas and cubatures of volumes, holds. Note that Kepler http://www.matematicasvisuales.com/english/html/history/kepler/doliometry.html Nova Stereometria doliorum vinariorum is from 1615, Cavalieri atoms, "Geometría indivisibilibus continuorum quadam nova ratione promota" are from 1635 and the final "concrete" results, Newton' "Analysis per aequationes número terminorum infinitos" and then the Principia, are from from 1669 and 1687. During this time, most of the Natural Philosophers (ie MathPhys), from Glasgow to Rome, were putting a lot of resources on this, and before Newton all they got was to confirm the Greek results and to add some extra examples.

Now I agree, that String Theory is near to break this record (and we will see if it gets something "concrete" out of it).

 

[Aidyan]

When you say string theory has "no concrete results", I can't agree.

With "concrete" in the case of ST I obviously meant "experimental evidence" which supports ST against other candidates, not just mathematical developments.

What it has given us is a very large number of models which incorporate and complete the field theories that non-string theoretical physicists were already using, and which have the potential to explain the quantities which are just input parameters for something like the standard model. We know that string theory can get close to reality in various ways. One has every reason to hope it can go all the way.

That's precisely what I find unconvincing. There are "various ways" to build a general theory that reduces to a previous one and yet turns out to be wrong. Especially if one is free to chose among a "very large number of models". Bohr's atomic model (which did "not come with continuously adjustable parameters" too) got 'close to the reality' in some respect. And Sommerfeld could refine it making it even closer to reality. But soon broke down because it couldn't account for the spectra of atoms much beyond Hydrogen. One can shows that it is possible to describe the observed planets trajectory on the sky with arbitrary precision all the way in a geo-centric model by adding epicycles to epicycles (very reminiscent of today's perturbative approaches...). But then Galilei brushed all this aside by observing the phases of Venus. Where would physics have ended by insisting on these paths because "reality does look a lot like..."? As long as you don't have the observational anomaly that can be explained only by one theory alone where all the others fail and that makes a minimum amount of testable predictions where all the other models predict something else, the argument of coming "close to reality in various ways" is week.

If you are happy with 50 years without concrete results, then my previous example, the quest for quadratures of areas and cubatures of volumes, holds.

As far as I know very concrete results were already obtained by a single philosopher like Archimedes with his exhaustion method. Cavalieri made some progress in between, and he furnished also some results. And Leibniz, Descartes and Newton followed giving us integral and differential calculus. These were steps where someone could do something out of it, not just a complicate theory about the world that was unclear if it was correct or not.

Note that Kepler http://www.matematicasvisuales.com/english/html/history/kepler/doliometry.html Nova Stereometria doliorum vinariorum is from 1615, Cavalieri atoms, "Geometría indivisibilibus continuorum quadam nova ratione promota" are from 1635 and the final "concrete" results, Newton' "Analysis per aequationes número terminorum infinitos" and then the Principia, are from from 1669 and 1687. During this time, most of the Natural Philosophers (ie MathPhys), from Glasgow to Rome, were putting a lot of resources on this, and before Newton all they got was to confirm the Greek results and to add some extra examples.

Now I agree, that String Theory is near to break this record (and we will see if it gets something "concrete" out of it).

What is there more "concrete" than estimating the prize of wine barrels? But it is interesting that to justify ST's supposed "slow success" one has to resort to dubious examples that are more than four centuries old. Do you have an idea in what miserable material, cultural and even more academic and scientific conditions was the world at those times? I live in the city where Galileo observed for the first time the Milky Way, the sun spots, and Jupiter's satellites. The historical documents tell that there was almost nothing here, apart from a hill with few houses, and that thing they called a "university". He did all alone by himself. There was nothing like large scale collaborations on a project, the universities, the laboratories, the institutions and organized science we have today. It is quite natural that scientific progress proceeded extremely slowly in those times. And yet, it is a miracle that these people could produce something tangible almost alone in the time span of a lifetime. I believe that string theoreticians should refrain from pointing at such examples, that doesn't make them look well...

 

[arivero]

I believe that string theoreticians should refrain from pointing at such examples, that doesn't make them look well...

Disclaimer, I am not a string theoretician. I just happen to be intrigued by the theory and my still current opinion, developed in other thread here , is that most of the important work was done in less than five years, say 1968-1973, and then they did a wrong turn towards Planck energy.

 

[marcus]

Hi Arivero, Aidyan, Mitchell, MTd2 and others thinking about the causes of observed string decline.
(on that, see post #340 https://www.physicsforums.com/showthread.php?p=3854410#post3854410 )

I'd been favoring the "no-fault" idea that there's nothing wrong that wasn't already known over 10 years ago and the cooling of interest could be attributed to the appearance of non-string alternative approaches to QG. But Matt Visser posted a paper yesterday that I think could represent real substantive trouble.

Visser cites stringy black hole work by people like Strominger, Horowitz,... and calls their results/conjectures into question as unphysical. In other words he finds actual physical fault, not merely failure to be predictive. I'd appreciate any comment on this. Does anyone see reasons to dismiss or minimize Visser's argument?

http://arxiv.org/abs/1204.3138
Quantization of area for event and Cauchy horizons of the Kerr-Newman black hole
Matt Visser (Victoria University of Wellington)
(Submitted on 14 Apr 2012)
Based on various string theoretic constructions, there have been repeated suggestions that the areas of black hole event horizons should be quantized in a quite specific manner, involving linear combinations of square roots of natural numbers. It is important to realize the significant physical limitations of such proposals when one attempts to extend them outside their original framework. Specifically, in their most natural and direct physical interpretations, these specific proposals for horizon areas fail for the ordinary Kerr-Newman black holes in (3+1) dimensions, essentially because the fine structure constant is not an integer. A more baroque interpretation involves asserting the fine structure constant is the square root of a rational number; but such a proposal has its own problems. Insofar as one takes (3+1) general relativity (plus the usual quantization of angular momentum and electric charge) as being paramount, the known explicitly calculable spectra of horizon areas for the physically compelling Kerr-Newman spacetimes do not resemble those of currently available string theoretic constructions.
15 pages

Here are papers Visser cites, which he appears to be shooting down:
[1] G. T. Horowitz and A. Strominger, “Counting states of near extremal black holes”, Phys. Rev. Lett. 77 (1996) 2368 [hep-th/9602051].
[2] E. Keski-Vakkuri and P. Kraus, “Microcanonical D-branes and back reaction”, Nucl. Phys. B 491 (1997) 249 [hep-th/9610045].
[3] G. T. Horowitz, J. M. Maldacena and A. Strominger, “Nonextremal black hole microstates and U duality”, Phys. Lett. B 383 (1996) 151 [hep-th/9603109].
[4] E. Halyo, B. Kol, A. Rajaraman and L. Susskind, “Counting Schwarzschild and charged black holes”, Phys. Lett. B 401 (1997) 15 [hep-th/9609075].
[5] G. T. Horowitz and J. Polchinski, “A Correspondence principle for black holes and strings”, Phys. Rev. D 55 (1997) 6189 [hep-th/9612146].
[6] F. Larsen, “A String model of black hole microstates”, Phys. Rev. D 56 (1997) 1005 [hep-th/9702153].
[7] M. Cvetic and F. Larsen, “General rotating black holes in string theory: Grey body factors and event horizons”, Phys. Rev. D 56 (1997) 4994 [hep-th/9705192].
[8] M. Cvetic and F. Larsen, “Greybody Factors and Charges in Kerr/CFT”, JHEP 0909 (2009) 088 [arXiv:0908.1136 [hep-th]].
[9] M. Cvetic, G. W. Gibbons, and C. N. Pope, “Universal Area Product Formulae for Rotating and Charged Black Holes in Four and Higher Dimensions”, Phys. Rev. Lett. 106 (2011) 121301 [arXiv:1011.0008 [hep-th]].
[10] A. Castro and M. J. Rodriguez, “Universal properties and the first law of black hole inner mechanics”, arXiv:1204.1284 [hep-th].

 

[Physics Monkey]

I believe "shooting down" is way too strong a phrase to use!

Many of the references singled out by marcus concern themselves with supersymmetric situations not encountered in the real world. Supersymmetry can affect, among other things, the running of the coupling constants which happens to be one of Visser's first criticisms.

Let me take pains to emphasize that I am not saying the Visser article is not interesting, I merely suggest that way more parsing of the works involved needs to be done before anyone has any right to claim that Visser is shooting down anyone.

For example, a simple explanation would be that Refs. 1-10 mostly consider susy models (or very nearly susy models) while Visser mostly considers very non-susy models. I'm only half joking when I suggest that "general" to a string theorist could mean "true among susy models".

 

[mitchell porter]

It looks to me like Visser hasn't asked any of the string theorists he cites what they make of his observation - and that's foolish. They could probably set him straight in five minutes. He's acting like one of those people who hope to show that the whole of particle physics is a fallacy because of some single calculation they made. I don't doubt that there are challenges to understanding the entropy of real black holes in stringy terms, but I'm sure this isn't one of them. I'm just a string-theory amateur, but if I figure out what he's overlooking (and whether he nonetheless has a valid point somewhere), I'll post about it.

 

[MTd2]

He's acting like one of those people who hope to show that the whole of particle physics is a fallacy because of some single calculation they made. I

String theory might be a fallacy, so, what s the problem? Developing string theory as a physical theory can indeed be as tricky as programming a very complicated computer game, and that s all. N

 

[mitchell porter]

The specific problem is that Visser frames his paper as a criticism of a string theory formula, but he doesn't understand string theory and didn't consult with anyone who does.

Most of his paper elaborates on non-string formulas found in references 19-22, and I think not in a very sophisticated way. Those formulas relate black hole horizon areas to spin, mass, and charge. What Visser then does is to reexpress the charge in terms of the fine structure constant, also using the fact from particle physics of charge quantization. But he just does this at the level of elementary algebraic substitution. If he's going to talk about the impact of charge quantization on black hole entropy, shouldn't he be using quantum field theory - maybe something like 't Hooft's brick-wall model from 1985?

Anyway, most of his paper is devoted to these slight elaborations of non-string formulas. But in the paper he has released, he starts out by quoting a few string formulas (or conjectures) in which horizon areas are functions of integers. His thesis here is that these formulas can't be valid for the real world, because (so he says) they would imply that the fine structure constant equals 2, not approximately 1/137. And besides, alpha runs, so it has to pass through irrational values.

So here is the most obvious gap in what he writes: he says nothing about how to interpret the significance of a varying alpha for his own new formulas, the ones which he advances as the correct alternative to the string formulas. Is the reader to assume that black hole entropy runs with the energy scale? He's just silent on this issue. If he had bothered to develop his new formulas within a proper QFT framework, he would have an answer. As things stand, apparently the reader has to figure this out for themselves.

Similarly, he doesn't even raise the question of how running coupling constants figure in string theory. In string theory, the tree-level coupling constant depends on the VEV of the dilaton. My ignorance is such that I don't know whether this is already taken into account in the string formulas for horizon area, whether it's an invisible normalization factor, or what. But again, Visser says nothing about this issue, he evinces no awareness of it. And that is precisely why I can say that he's been sloppy in relating his new formulas to string theory - he hasn't bothered to find out how the string formulas work, he's just relying on his own personal guess as to how they work.

 

[MTd2]

I am aware that you are studying string theory for quite some time. You seem to be a smart person, yet, these details, which seem to be not so subtle, still are hard to find and even to study. More over, there is no empiricism involved here.

So, that reinforces my thoughts about giving up on strings because they are too hard with little practical reward. Perhaps, other theories are also hard, but you can cut the loose buds and simplify the teaching/exposition literature, for the reason that you can do experiments.

 

[marcus]

Since we've turned a page, I'll recap the basic input we are trying to explain. There's been a decline in string interest and activity that shows in various ways. One is a downtrend in the rate of first-time faculty hires, starting around 2001. This is visible both in terms of absolute numbers (from average about 9 per year down to around 1 per year) and also in terms of string as a fraction of total Particle Theory. It used to be that around HALF the first-time faculty hires in HEP theory were in string, now it's more like a tenth.

A physicist at the U Toronto (Erich Poppitz) charts first time faculty hires in High Energy Physics Theory (Usa and Canada) by year and keeps track of what fraction of these are in string, and which fractions are in other branches of theory.
http://www.physics.utoronto.ca/~poppitz/Jobs94-08
His chart shows 11 HEP theory hires in 2011 of which one was string.
Here I've smoothed annual rates by averaging over 3 years intervals.

period                 1999-2001    2002-2004   2005-2007    2008-2010    2011
annual HEP theory hires   18             24            23             13            11 
annual string hires           9              8              6               2              1

The source used is http://particle.physics.ucdavis.edu/rumor/doku.php

There's also been a decline in annual citations to recent string research by the theorists themselves.
Number of recent string papers making the top fifty in the annual Spires HEP topcite list

year (some omitted for brev.)   2001    2003    2005    2007    2009    2010
recent work highly cited in year  12         6         2         1         1        0

Here a paper is counted as recent if it appeared in the previous five years. Citations gauge the quality/significance of current work by how much other researchers in the field currently refer to it.

It could be that the decline in String research is not primarily due to any flaw or inadequacy in stringy physics that was not evident already, say, by 2001. It could simply be that newer approaches to QG and explaining the SM have arisen, and that researchers have a natural tendency to spread out seeking fresh ideas and new areas to work on. The String program is some 40 years old and there has been plenty of time for new ideas to germinate and new research directions to develop.

On the other hand we can try to identify inherent shortcomings in the physics which might be responsible. Arivero made the point that we should consider String separately as a source of particle models (where it seems to have limited utility) and of candidate theories of the quantum geometry of the universe.
In the latter role, does it offer promising ways to resolve the cosmological singularity and model conditions leading up to the start of expansion? Are these testable by astronomical observation? Such seem among the main things one wants from a QG theory. In short, it's still debatable whether there are valid physics reasons for the decline.

 

[marcus]

The other topic that just came up (on the previous page) is this recent paper by Matt Visser.
Visser call some stringy black hole work into question as unphysical.
http://arxiv.org/abs/1204.3138
Quantization of area for event and Cauchy horizons of the Kerr-Newman black hole
Matt Visser (Victoria University of Wellington)
(Submitted on 14 Apr 2012)
Based on various string theoretic constructions, there have been repeated suggestions that the areas of black hole event horizons should be quantized in a quite specific manner, involving linear combinations of square roots of natural numbers. It is important to realize the significant physical limitations of such proposals when one attempts to extend them outside their original framework. Specifically, in their most natural and direct physical interpretations, these specific proposals for horizon areas fail for the ordinary Kerr-Newman black holes in (3+1) dimensions, essentially because the fine structure constant is not an integer. A more baroque interpretation involves asserting the fine structure constant is the square root of a rational number; but such a proposal has its own problems. Insofar as one takes (3+1) general relativity (plus the usual quantization of angular momentum and electric charge) as being paramount, the known explicitly calculable spectra of horizon areas for the physically compelling Kerr-Newman spacetimes do not resemble those of currently available string theoretic constructions.
15 pages

==quote from the first paragraph of the introduction==
Various string theoretic constructions have led to the suggestion that black hole event horizon areas might follow the quantization rule [1–10]
...
...
These specific string-inspired proposals are conjectured to have universal validity, far beyond the realm in which they were originally conjectured. It is this conjecture of universal validity which will be addressed in this current article.
==endquote==

Here are papers [1–10] which Visser begins by citing in his lead paragraph.
[1] G. T. Horowitz and A. Strominger, “Counting states of near extremal black holes”, Phys. Rev. Lett. 77 (1996) 2368 [hep-th/9602051].
[2] E. Keski-Vakkuri and P. Kraus, “Microcanonical D-branes and back reaction”, Nucl. Phys. B 491 (1997) 249 [hep-th/9610045].
[3] G. T. Horowitz, J. M. Maldacena and A. Strominger, “Nonextremal black hole microstates and U duality”, Phys. Lett. B 383 (1996) 151 [hep-th/9603109].
[4] E. Halyo, B. Kol, A. Rajaraman and L. Susskind, “Counting Schwarzschild and charged black holes”, Phys. Lett. B 401 (1997) 15 [hep-th/9609075].
[5] G. T. Horowitz and J. Polchinski, “A Correspondence principle for black holes and strings”, Phys. Rev. D 55 (1997) 6189 [hep-th/9612146].
[6] F. Larsen, “A String model of black hole microstates”, Phys. Rev. D 56 (1997) 1005 [hep-th/9702153].
[7] M. Cvetic and F. Larsen, “General rotating black holes in string theory: Grey body factors and event horizons”, Phys. Rev. D 56 (1997) 4994 [hep-th/9705192].
[8] M. Cvetic and F. Larsen, “Greybody Factors and Charges in Kerr/CFT”, JHEP 0909 (2009) 088 [arXiv:0908.1136 [hep-th]].
[9] M. Cvetic, G. W. Gibbons, and C. N. Pope, “Universal Area Product Formulae for Rotating and Charged Black Holes in Four and Higher Dimensions”, Phys. Rev. Lett. 106 (2011) 121301 [arXiv:1011.0008 [hep-th]].
[10] A. Castro and M. J. Rodriguez, “Universal properties and the first law of black hole inner mechanics”, arXiv:1204.1284 [hep-th].

It may be that what he is finding fault with, or opposes, is what he considers an unwarranted claim of generality--an overextension of some results beyond where they were originally derived. So, for example, see Alejandra Castro's http://arxiv.org/abs/1204.1284. But this overextension might not apply to some of the earlier work. As I recall Castro is one of Alex Maloney's associates (postdoc?) at McGill. Finn Larsen (see [7-8]) was her PhD advisor. References [8-10] are all to recent work, since 2009.