Quantum Field Theory, As Seen By Mathematicians

Posted on February 11, 2008 by woit

In recent years, interest in quantum field theory among mathematicians has gone through ups and downs, in a sub-field dependent manner, as ideas rooted in quantum field theory have turned out to be mathematically useful in a variety of contexts. At Berkeley, it appears that there’s now more interest in quantum field theory in the math department than in the physics department, so much so that last fall three senior faculty (Nicolai Reshetikhin, Peter Teichner and Richard Borcherds) offered courses on various QFT topics. Luckily, Berkeley graduate students seem to be very industrious, and they have accumulated quite a few tex-ed lecture notes from these and other courses, gathering together the QFT ones here and here.

Another popular topic at Berkeley has been geometric Langlands, a subject where Witten’s QFT approach has intrigued many mathematicians. Witten has a new preprint aimed at mathematicians promoting the QFT point of view, and he explains in more detail claims he made in talks last fall that the use of 4d QFT corresponds in a sense to the use by mathematicians of “stacks”. Stacks are a mathematical device useful for handling non-free quotients, situations where one wants to keep track not just of the quotient space (which is often singular), but of more structure, for instance the varying stabilizer groups at different points of the quotient. Witten notes that if one just uses mirror symmetry of the Hitchin moduli space to study Langlands duality, one doesn’t know how to handle various singularities. Mathematicians have dealt with these singularities by invoking stacks, Witten instead argues that one should use a 4d gauge theory QFT perspective to see how to study the issue in a way that does not involve these singularities (they only appear when you dimensionally reduce and work with the 2d topological sigma models).

Last week Witten gave a talk to the mathematicians at the IAS on “Duality from Six Dimensions”, which is to be continued this week. He explained how the existence of a 6d superconformal theory implies SL(2,Z) symmetry and thus duality (Montonen-Olive duality) in the 4d N=4 supersymmetric topological gauge theory he uses in his approach to geometric Langlands. This is an old story by now, from the mid-nineties duality days, and Witten wrote up some of it here, for his contribution to the proceedings of the conference in honor of Graeme Segal’s sixtieth birthday back in 2002. David Ben-Zvi was at the talk taking notes, and I hope he’ll be adding to his extensive collection of on-line notes this semester since he’ll be at the Institute attending this year’s program there.

Note added: David has started posting his notes, the notes from the Witten talk are here.

At MIT this semester there’s a “pre-Talbot” seminar being run that will lead up to a Talbot workshop in March. The topic is something that might be called “quantum geometric Langlands”, involving not Witten’s QFT ideas, but a version of geometric Langlands that uses quantum groups due to Dennis Gaitsgory and Jacob Lurie. Scott Carnahan discusses this at Secret Blogging Seminar, and has notes from his overview talk available.

In March Lurie will be giving the Marston Morse lectures at the IAS, on the topic of “Topological Quantum Field Theories in Low Dimensions”.

Posted in Favorite Old Posts, Uncategorized | 7 Comments

Is Big Physics peddling science pornography?

Posted on February 7, 2008 by woit

There’s a new round of nonsense about theoretical physics making its way through the media, especially the British tabloids. The original source is a preprint from a few months ago by Aref’eva and Volovich entitled Time Machine at the LHC (it refers to another earlier one by other authors If LHC is a Mini-Time-Machines Factory, Can We Notice?). These papers discuss the possibility that the LHC will produce not just black holes, but also wormholes that would be “Mini-Time-Machines” (MTMs).

New Scientist now has a cover story based on this which begins:

As you may have heard, this will be the year. The Large Hadron Collider – the most powerful atom-smasher ever built – will be switched on, and particle physics will hit pay-dirt. Yet if a pair of Russian mathematicians are right, any advances in this area could be overshadowed by a truly extraordinary event. According to Irina Aref’eva and Igor Volovich, the LHC might just turn out to be the world’s first time machine.

The article invokes work by Nima Arkani-Hamed and others to justify the idea that the LHC will produce black holes and possibly wormholes, and Kip Thorne to justify the possibility of time travel. Several physicists are quoted in favor of the plausibility of the underlying idea, it not its practicality.

The story has now made it to the Sun, which has two stories: Time Travel Russia’s in and Visits From Crack to the Future. According to the Sun, the LHC will be switched on in May (not true….) and from that time on time travel will be possible:

The laws of physics suggest that no one from the future will be able to travel back any further than when the machine was switched on — with 2008 being Year Zero.

According to the Daily Mail:

Time travel could be a reality within just three months, Russian mathematicians have claimed. They believe an experiment nuclear scientists plan to carry out in underground tunnels in Geneva in May could create a rift in the fabric of the universe.

The Telegraph has Time travellers from the future ‘could be here in weeks’, but the article at least has some skeptical quotes, for instance from David Deutsch, who describes the idea as “not cranky”, but unlikely to work.

New Scientist does seem to realize that this kind of silliness may have gone too far, publishing an article by Michael Hanlon entitled Is Big Science peddling science pornography?. I think Hanlon raises extremely important questions that the physics community needs to address, although he makes a mistake by pinning this on “Big Science”. The people working hard to make projects like the LHC a reality are not the culprits here, irresponsible theorists are. Hanlon writes:

Physics and cosmology stories are like this these days. Once it was all hard sums and red-shifted galaxies; awesome enough one would have thought. Now it’s time machines and universe-eating particles.

Does any of this bear any relation to reality? Or is Big Physics guilty of some serious sexing-up, drifting away from the realm of hard data and into the softer universe of science pornography?

As well as accidental time machines we are told of cosmic strings – gigantic filaments of super-stuff that warp and tear space-time like ladders in a pair of celestial stockings – and crashing branes, titanic slabs of maths that give rise to the big bang in the exotically lovely ekpyrotic universe of Neil Turok.

Not crazy enough for you? What about the multiverse? One of the biggest sell-out lectures at last year’s Hay-on-Wye festival in Wales starred the UK’s astronomer royal, Martin Rees, who entertained his audience with a discussion of the possibility, indeed the probability, of multiple worlds – endless parallel realities existing in a gargantuan super-reality that makes what we think of as the universe as insignificant as a gnat on an elephant’s backside. Or there’s the simulation argument, philosopher Nick Bostrom’s delicious idea that since it should be possible to replicate an entire universe in a computer, and that this could be done countless times, statistical cleverness proves that we are not the real McCoy but the figments of some electronic entity’s imagination.

…Scientists, and people like me who stick up for science, are happy to pour scorn on astrologers, homeopaths, UFO-nutters, crop-circlers and indeed the Adam-and-Eve brigade, who all happily believe in six impossible things before breakfast with no evidence at all. Show us the data, we say to these deluded souls. Where are your trials? What about Occam’s razor – the principle that any explanation should be as simple as possible? The garden is surely beautiful enough, we say, without having to populate it with fairies.

The danger is that on the wilder shores of physics these standards are often not met either. There is as yet no observational evidence for cosmic strings. It’s hard to test for a multiverse. In this sense, some of these ideas are not so far, conceptually, from UFOs and homeopathy. If we are prepared to dismiss ghosts, say, as ludicrous on the grounds that firstly we have no proper observational evidence for them and secondly that their existence would force us to rethink everything, doesn’t the same argument apply to simulated universes and time machines? Are we not guilty of prejudice against some kinds of very unlikely ideas in favour of others?

Update: The time travel story has even made it to the Chronicle.

Posted in Uncategorized | 46 Comments

Worth Reading

Posted on February 6, 2008 by woit

The latest issue of the Cern Courier contains a wonderful article entitled From BCS to the LHC by Steven Weinberg. It is based on a talk he gave at a recent conference celebrating the 50th anniversary of the BCS theory of superconductivity, and explains the relation between electroweak symmetry breaking and superconductivity, by way of telling about some of the history, in which he played a central role.

From the Mathematical Intelligencer, there’s an excellent review by Leila Schneps of a book which contains much of the correspondence over the years between two of the greatest mathematicians of the last century, Grothendieck and Serre. The review covers not just the mathematics, but also the very different personal styles that were part of what was such a fruitful interaction. She refers to the existence of “a much larger collection of existing letters” from the later period in his life when he had begun to stop regularly doing mathematics which are still unpublished, one of which answers Serre’s question about why his mathematical research program had come to a halt. She ends with the summary:

In some sense, the difference between them might be expressed by saying that Serre devoted his life to the pursuit of beauty, Grothendieck to the pursuit of truth.

Barry Mazur has a new article giving his very personal take on the philosophy of mathematics: Mathematical Platonism and its Opposites.

MSRI celebrated its 25th Anniversary last week, and Dan Freed gave a talk on Chern-Simons-Witten theory (slides here). He is careful to put a warning label in red on the standard path integral definition of the theory, writing “this path integral is only a motivating heuristic”. Together with collaborators Mike Hopkins and Constantin Teleman he has been working on coming up with a very abstract definition of the theory, far removed from the path integral, but at the end he notes that in the stationary phase approximation one can make sense of the path integral, putting up a page from one of his old papers where this was shown calculationally.

The latest Physics Today has a long article about the disastrous budget situation for HEP in FY2008. The politics of this are described as follows:

Congress and the administration took turns blaming each other for the bad news. The omnibus bill “turned its back on Congress’s concern for competitiveness,” Marburger said, by wiping out most of the increases for science and technology that had received strong bipartisan support in the America COMPETES Act, which was signed into law in August 2007.

But the White House was hardly without fault. Bush’s 11th-hour refusal to negotiate with Democrats on a spending ceiling he had imposed forced lawmakers in the dead of night to trim back spending bills that had been assembled and approved in a far more thoughtful process. In doing so, they unsurprisingly took their red pen to presidential priorities. The increases for the physical sciences were part of Bush’s American Competitiveness Initiative to revitalize US technological leadership. Marburger said he had little doubt that Congress has deliberately chosen the science programs for the budget-cutting scissors.

Ironically, House Speaker Nancy Pelosi’s (D-CA) “Innovation Agenda” proposed to double nondefense R&D spending over 10 years. Admitting that funding levels this year fall short of the 7% annual increases needed to meet the goal, Pelosi assured the scientific community in a letter that her commitment to growing the physical sciences budgets “remains strong and steadfast.”

In the Chicago Tribune, Fermilab director Oddone describes what he thinks about the budget process. He now has to fire 200 people, while a huge budget increase is proposed by the administration, which the Congress probably won’t act on until deep into the next fiscal year, with no indication now of what they will do:

This is not the way a developed country manages a scientific enterprise… It’s more like a banana republic.

Update: One more. A popular talk by Richard Taylor about reciprocity laws and density theorems (such as Sato-Tate) in number theory.

Posted in Experimental HEP News, Uncategorized | 2 Comments

This Week’s Hype

Posted on February 6, 2008 by woit

This week’s media hype promoting a new observational test of extra dimensions is based on the recent arXiv preprint Transient Pulses from Exploding Primordial Black Holes as a Signature of an Extra Dimension. Stories about it have appeared already in Nature and in New Scientist.

Some of the authors are part of a group at Virginia Tech that is working with a radio-telescope array they call the Eight-meter-wavelength Transient Array (ETA). The possible astrophysical sources they are looking for include primordial black holes. The press articles however, aren’t about this, but about the new preprint, which makes claims not about conventional primordial black holes, but about ones involving extra dimensions:

For a toroidally compactified extra dimension, transient radio-pulse searches probe the electroweak energy scale (∼0.1 TeV), enabling comparison with the Large Hadron Collider. The enormous challenges of detecting quantum gravitational effects, and exploring electroweak-scale physics, make this a particularly attractive possibility.

In the New Scientist piece, astrophysicist Avi Loeb makes the comment:

There are a lot of layers here of nonstandard assumptions… If nothing could be observed in this context, then it would not surprise me.

According to the ETA web-site and the New Scientist article, as far as the extra-dimensional business is concerned, the project is led not by the faculty members involved, but by first author Mike Kavic, a graduate student in the department. Unlike most recent examples of such hype, which appeared in conjunction with the acceptance or publication of a paper in PRL, this one is based solely upon the submission of a paper to PRL.

Posted in This Week's Hype | 6 Comments

Microsoft Research New England

Posted on February 4, 2008 by woit

Microsoft announced today that they’ll be opening a new research lab, in Cambridge, which will be called Microsoft Research New England. The director of the lab will be mathematical physicist Jennifer Chayes, with deputy director her husband Christian Borgs, who is also a mathematical physicist. For an interview with them, see here, for a story in today’s New York Times, see here.

Jennifer and her ex-husband Lincoln Chayes (also a mathematical physicist, now at UCLA) were my class-mates during graduate student years in Princeton, as well as frequent companions on trips down to City Gardens in Trenton to see bands like the Ramones. The two of them at the time had even more impressive leather outfits than the Ramones.

Update: There’s more about this at the Xconomy web-site.

Posted in Uncategorized | 17 Comments

Steinhardt: The Anthropic Landscape Has Run Its Course

Posted on February 3, 2008 by woit

Over at John Horgan’s blog, he quotes an e-mail from Princeton cosmologist Paul Steinhardt, who corrects Horgan’s account of a recent conversation between them, writing

I said that I thought that the idea of a string landscape and the notion of anthropic selection had run its course. I think it is too early to give up on string theory.

While Steinhardt sees anthropic selection of our universe out of a multiverse as an idea that has run its course and is on its way out, it’s still quite popular in certain quarters. The Templeton Foundation, through the FQXI organization, is a major source of funding for anthropic multiverse research. FQXI’s web-site has a new story up entitled Philosophy of the Multiverse, which asks “On what side of the borderline between science and philosophy are multiverses?” The writer evidently couldn’t locate anyone to take the “it’s philosophy, not science” side of the argument, quoting Sean Carroll, Anthony Aguirre, Alexander Vilenkin and Aurelien Barrau as supporters of anthropics as science. Barrau suggests that we may need to change the definition of science to accomodate the multiverse.

Whatever Steinhardt says, at least the Mormons are getting on the multiverse bandwagon, with their journal Dialogue recently publishing a long article entitled Eternal Progression in a Multiverse: An Explorative Mormon Cosmology. The article begins:

This article is an examination of the Mormon doctrine of eternal progression within the context of big-bang cosmology, a description of a finite universe that appears to contradict that doctrine. I argue that a multiverse cosmology, a theory that posits a multiplicity of universes, resolves many of the problems posed by big-bang cosmology.

and goes on to explain how the multiverse agrees well with the doctriine of “eternal progression” in Mormon theology:

In a Mormon multiverse cosmology, God does indeed manifest his infinite creative prowess in the respect that God (any god along the infinite chain of gods) creates children, some of whom progress to become gods, who in turn create their own universes and children, some of whom progress to become gods, and so on, forever. Each universe in the ensemble of universes becomes an extension and continuation of the creativity of every “ancestral god” in an eternal family of deities. The creativity and glory of each god increases exponentially with the production of new universes. In this cosmology, the multiverse is a hallmark and witness of the infinite work and glory of God and the dwelling place for an infinite number of eternal progressing beings.

While solving the problem of justifying eternal progression, the multiverse idea leads to all sorts of new possible research directions:

In a Mormon multiverse cosmology, many questions remain open. Are there communication and movement of the gods and other premortal and postmortal beings between universes? When a universe experiences a big crunch or big freeze, does the god of that universe generate a new universe or “relocate” to another universe fit for carrying out the “great plan of happiness” for a new household of spirit children? Did God, our Father in Heaven, achieve godhood in this universe or a prior one? If God was exalted in a prior universe, how many universes has he governed? Jesus Christ is the redeemer for this universe, but is he the redeemer for others? Are some universes “stillborn” in the sense that they do not have the required values of the physical constants for a universe capable of sustaining life? Because the multiverse is infinite, are there replicas of us in other universes as postulated by the replication paradox? Cosmologists speculate whether the physical laws are the same across the ensemble of universes, but what about the spiritual laws? Are the spiritual laws “multiversal” or just “universal”? As multiverse cosmologies develop scientifically, these questions and others will stimulate much discussion.

The author ends the piece with a quote from Andrei Linde: “Universes can have babies — it’s nice.”

Posted in Uncategorized | 24 Comments

US HEP News

Posted on February 1, 2008 by woit

Today and yesterday at Fermilab there is an HEPAP meeting designed to gather information necessary to prioritize decisions on how to spend the US HEP budget over the next few years. Many of the talks there are on-line and give a good idea of what future possibilities look like. The main issues being discussed are:

  • Whether to go ahead with project X at Fermilab, a proposal for a high-intensity proton source.
  • The state of the ILC project, given that it was zeroed out in this year’s US and UK budgets. Barry Barish emphasizes the continuing goal of being ready to make a decision about whether to build such a thing soon after LHC results arrive, presumably starting in 2010. The state of CLIC and other multi-TeV lepton collider possibilities is reviewed by Tor Raubenheimer of SLAC, who puts a likely date for a multi-TeV electron collider at 2030-40, a muon collider after 2050. These things are a long ways away…
  • Whether to run the Tevatron in FY 2010, with presentations about how the Tevatron is currently performing, and from CDF and D0 advocating for a run past FY2009. Both experiments make the case that they are getting close to being able to either see evidence of the Higgs or rule out its existence over most of the expected mass range. More about this from Tommaso Dorigo of CDF here. Since the Tevatron is about the most successful and exciting thing going on in US HEP, I personally don’t see the case for planning on shutting it down until solid results are in from the LHC about the Higgs, which should be sometime in FY2010 at the earliest. Who knows, maybe the LHC will see something that the Tevatron is a good tool to study further. Seems more likely than that it will see black holes…

    • The involuntary furloughs of Fermilab employees begin today. No news regarding the supposed efforts by the Illinois Congressional delegation to lobby for a supplemental appropriation to keep Fermilab from having to layoff around 200 people. At least one of the relevant people is undoubtedly too busy with other things to pay attention to this. The Congress and the White House are negotiating an emergency bill to deal with the recession and job losses that have started recently. Since government spending is bad and tax cuts are good, their plan seems to be to continue to throw people out of their jobs with budget cuts in HEP and elsewhere, while handing out cash to as many voters as possible.

    For a presentation by DOE Undersecretary Orbach about the DOE budget problem, see here, and analysis from Richard Jones of the AIP here. The FY 2009 budget request from the White House will come out on Monday, and Orbach promises that

    The President’s request for FY 09 will be wonderful, again, for the physical sciences. While I can’t go into details here, I can say that it will continue the funding request consistent with the American Competitiveness Initiative and the America COMPETES Act. The problem for all of us is that, faced with essentially flat funding for the physical sciences in FY 08, the President’s Request for FY 09 will appear as a very large percentage increase for the three ACI agencies. The danger is that basic research in the physical sciences will again be ‘donors’ to other programs.

    meaning I guess that Congress will be tempted to strip these out in order to fund other things.

    Gordon Watts notices that in Bush’s State of the Union speech he explicitly advocated increased funding for basic physical science research, something which is extremely unusual in such a speech:

    Last year Congress passed legislation supporting the American Competitiveness Initiative, but never followed through with the funding. This funding is essential to keeping our scientific edge. So I ask Congress to double federal support for critical basic research in the physical sciences and ensure America remains the most dynamic nation on earth.

    The physics community seems to have done a great job of convincing the administration to support basic physics research in general and HEP in particular, which normally would be a very good thing. But the same was true last year, and it seems to just have had the effect of painting a big fat bullseye on HEP funding for someone in Congress looking for a place to cut. At least this year people are aware of what might be coming, and maybe something can be done to head off a repeat of this year’s disaster.

    The general budget politics don’t look favorable at all though, with the Bush Administration evidently proposing to heavily cut Medicare and Medicaid spending. Congress has very different priorities, and it seems all too likely that they will fund restoration of the health-care cuts by cutting things like the DOE basic research budget. This fall will be different though, with a new Congress and president elected at the beginning of November, but not taking office until January. I wouldn’t be surprised to see the government run on a continuing resolution at FY2008 levels until after a new president takes office.

    Update: The proposed FY2009 budget is out, DOE here, NSF here. The DOE budget contains a huge increase for HEP, from $688 million in FY2008 to $805 million in FY2009. The NSF budget doesn’t break out the HEP component, but the total budget for math and physics is supposed to go from $1167 million in FY2008 to $1403 million in FY2009. These are huge and very healthy proposed increases, but unfortunately it is not at all clear that they will actually make it into the final budget.

    Update: There’s a story today in the New York Times about this. Also a message from the Fermilab director, saying he has no choice but to go ahead with the plan to start laying off employees of the lab. In practical terms, the proposed budget increases appear to be meaningless, with the likely situation no increase at all in FY2009 of any kind until a budget gets passed, which most likely will not happen until already deep into the fiscal years. He writes:

    …every Washington expert tells me to prepare for a continuing resolution that might last into the new administration. Such a continuing resolution would extend the present difficult budgets well into FY09. At the same time, relief in FY08 in the form of a supplemental appropriation is not guaranteed and is at best several months away.

    Posted in Experimental HEP News | 5 Comments

    Today’s Hype

    Posted on January 31, 2008 by woit

    The rate of appearance of press releases hyping string theory has now passed the the one-per-week mark. Today’s example is from the press office of the University of Wisconsin, and again is based on the appearance of a paper in PRL. The preprint of the paper appeared 8 months ago on the arXiv. Since that time, it has been cited exactly once by later papers, in another paper by some of the same authors.

    Posted in This Week's Hype | 5 Comments

    Last Week’s Hype

    Posted on January 30, 2008 by woit

    I was concerned that my “this week’s hype” headlines might be less than accurate, counting only 3 separate over-hyped string theory stories during the past month rather than four. Turns out that I missed one (although a commenter here didn’t), involving yet another university press release based on a PRL-published paper about cosmic strings. To be fair to the authors, the press release and paper don’t contain that much hype, nothing about how they are “testing string theory”. What they do is fit the CMB data using an additional parameter they call f10, which has to do with the fractional contribution of cosmic strings to the temperature power spectrum at multipole l=10. They claim to get a slightly better fit to the data with a non-zero version of this parameter and power-law tilt ns=1, versus the usual fit with gives a ns less than one. When they also take into account non-CMB data, the effect goes away.

    This isn’t really convincing of anything, so it’s unclear why it deserves a press release. According to the New Scientist story on this, which is pretty reasonable and hype-free, the chief scientist for WMAP, Charles Bennett thinks it’s a statistical fluke:

    Calling it a detection is odd… I’d be very surprised if cosmologists were excited about this at this stage.

    For other press stories about this, featuring misleading headlines, see String Theory Gets A Boost at physorg.com, and String Theory slightly preferred… or at least, not disfavored! at Canada Free Press, where the author does note:

    To listen to people speak about string theory is a lesson in ambiguity. No one is willing to commit to a solid opinion, on either side of the coin, and they dance upon the fence as if they were auditioning for a Garfield strip.

    Posted in This Week's Hype | 3 Comments

    This Week’s Hype

    Posted on January 28, 2008 by woit

    This week’s press release trumpeting a bogus “test of string theory” comes from the University of Illinois at Urbana-Champaign, which is headlined Scientists propose test of string theory based on neutral hydrogen absorption, and informs us that

    Ancient light absorbed by neutral hydrogen atoms could be used to test certain predictions of string theory, say cosmologists at the University of Illinois. Making the measurements, however, would require a gigantic array of radio telescopes to be built on Earth, in space or on the moon.

    String theory – a theory whose fundamental building blocks are tiny one-dimensional filaments called strings – is the leading contender for a “theory of everything.” Such a theory would unify all four fundamental forces of nature (the strong and weak nuclear forces, electromagnetism, and gravity). But finding ways to test string theory has been difficult.

    Now, cosmologists at the U. of I. say absorption features in the 21-centimeter spectrum of neutral hydrogen atoms could be used for such a test.

    One peculiar aspect of this press release is that it seems that the relevant paper is not yet publicly available. Supposedly it has been submitted to PRL and accepted, but it has not yet appeared in PRL, and I don’t see a preprint on the arXiv (the authors do have a PRL paper with an arXiv preprint from last year on a different topic, one that also came with a press release, but this one didn’t mention string theory).

    As far as I can tell from the press release the idea behind this “test of string theory” is the same as lots of other similar ones that invoke cosmic strings. Among the huge variety of string theory backgrounds and the many possible ways to try and use such backgrounds to model the big bang, some will (just like some non-string theory GUT models) produce macroscopic “cosmic strings”. Astronomers have looked hard for evidence of such things and found none, but one can always imagine that, miraculously, such things exist, with characteristics exactly such that they wouldn’t have shown up so far, but would in some new, improved astronomical observations. In this case, I guess to come up with some new possible observation not already ruled out, the authors of the paper invoke a possible radio telescope with an area of a thousand km2.

    There seem to be at least a couple reasons for the recent flood of bogus “we’ve found a test of string theory” press releases. One is that PRL evidently encourages authors to issue press releases whenever they have a paper appearing in PRL. Another reason is that string theorists are on the defensive, and some of them have decided that finding some way to claim that string theory really is testable, no matter how dubious, is the way to fight back. Earlier this month, one such claim hyped in New Scientist carried the headline “slammed for their failure to explain how our particular universe came to exist, string theorists are fighting back.” In an interview with string theorist Thibault Damour in today’s edition of the Swiss paper le Temps, he promotes three possible tests of string theory. One is the possibility (which he describes as “very speculative”) that one might observe extra dimensions at the LHC, another is cosmic strings, and finally there are his claims that string theory leads to violations of the equivalence principle. Lubos Motl strongly disagrees. Lubos also has a posting about this latest hype, where he comments:

    Such possibilities highlight that creative people may often solve questions that look too difficult at the beginning. They also emphasize how incredibly idiotic are the aggressive crackpots’ proclamations that modern theoretical physics in general and string theory in particular is untestable.

    Not clear who it is who believes that “modern theoretical physics” is untestable. While at Lubos’s blog, you might want to see what you can make of his posting on his new book The Bogdanov Equation: the secret of the universe?

    Update: This story is appearing lots of places, including the UPI newswire, and at Wired, where the writer seems to realize that the bogosity level here may be problematic, including the unusual disclaimer:

    Disclosure: I have no idea whether this makes sense.

    Update: A correspondent points me to another recent “test of string theory”, one where for some reason the authors don’t seem to have issued a press release. The article is Toward a test of string theory using Rydberg atoms, and it begins by referencing my book and then claiming that

    … measurable effects are predicted by String Theory on normal quantum scales, which the current criticisms have apparently overlooked.

    What is discussed in the paper is actually not string theory, but just the idea of adding spatially non-commuting terms to the Heisenberg commutation relations. Certainly such terms should have experimentally observable effects. I suppose you can claim that such terms, of any size you want, come from a “string theory background”, but, as with all these “tests of string theory”, what is going on here just reflects the fact that you can pretty much get anything you want out of string theory, which is why it’s not testable…

    Posted in This Week's Hype | 65 Comments