String Theory Visions

Posted on June 27, 2014 by woit

Strings 2014 ended today, with five separate “vision” talks, giving a good picture of where the leaders of the string theory community see the subject going. I saw the talks on streaming video, presumably they should appear on the conference website in the next few days.

  • Michael Green led off by noting that string theory had at one point been intended as a unified theory, but now has “blossomed into something much more significant”, a framework covering all sorts of things. He went on to say that he would avoid discussing the grand questions, and instead just give a summary of what he found interesting about work reported at the conference. The main area that he covered in the talk were the many different kinds of results about scattering amplitudes that are under study. He seemed to be somewhat of a skeptic about Arkani-Hamed’s widely publicized “Amplitudehedron”, saying it had some ways to go before it was useful for computations (unlike other methods).
  • Juan Maldacena gave a talk that had nothing to do with string theory, mainly about the conceptual issues of black holes and quantum theory. He claimed that the BICEP2 results showed that quantum gravity was now an experimentally-based subject, answering those who were skeptical about studying an untestable subject.

    At the end of the talk he gave an answer to the question “What is String Theory?”:

    Solid Theoretical Research In Natural Geometric Structures

  • Andy Strominger gave his own answer to the “What is String Theory?” question:

    anything that anybody in this room or any of their friends has ever worked on.

    He did note that there were hardly any strings anywhere to be seen at recent string theory conference talks.

    About the LHC and any conceivable follow-on higher energy accelerator, his comment was that it was now highly unlikely that string theory could make predictions relevant to them, and that he didn’t want this to be a defining goal of the field. Clearly, the failure to find SUSY at the LHC has now pretty much killed off most hopes that string theory unification is relevant to particle physics in any testable way. Like Maldacena, he pointed to BICEP2 as showing that quantum gravity was now an experimental subject.

    He ended by explaining that he had sent around emails to a hundred people asking for their suggestions about what problems there would be progress on over the next 5-10 years. He got 80 responses, and quickly put up some slides with them. No time to really read these, but he says that they’ll be posted online soon, and that should be a quite interesting document

  • The last talk was by David Gross, who pointed out that he has given many of these things before. He then went on to discuss Paul Steinhardt’s impassioned talk earlier in the week, which included a video of Richard Feynman discussing “Cargo Cult Science” and theories that were too vague to be testable. Steinhardt had been arguing that inflation was so vague and flexible a theory that it could not be tested and so was not science. Gross like many others realized that you could replace “inflation” by “string theory” in Steinhardt’s argument. He then gave a long and very defensive discussion of why string theory might still be science, invoking the recent book by Richard Dawid and telling the audience they needed to read it so they could defend their subject against the accusations it is facing.

    I wrote here last year about the Dawid book, including an explanation of Dawid’s three main arguments for string theory. Gross went through these in detail, and I think what I wrote last year also responds to what Gross has to say. He did include in the “Meta-Inductive Argument” the argument that SUSY is a related research program to string theory and that it will be vindicated at the LHC in the next few years. It will be interesting to hear what he has to say at a future Strings 20XX after this hasn’t worked out. He announced that Strings 2015 will be in Bangalore, Strings 2016 in Tsinghua, Strings 2017 in Israel, Strings 2018 in Japan and Strings 2019 in Belgium.

    He explicitly addressed the fact that many in the field were experiencing depression and anxiety due to things not working out, pointing out that even if the first derivative of progress in a field is negative, there can be jump discontinuities. So, although things don’t look good, maybe a big piece of progress will come along out of nowhere.

There was one more vision talk, but I’ll discuss that in a separate posting.

Update: Strominger’s slides are available here, and include the 80 responses he got from others about the open problems of the field.

Update: Videos of the talks are now available.

Posted in Strings 2XXX | 18 Comments

Pierre van Baal 1955-2013

Posted on June 23, 2014 by woit

I only recently heard about the death late last year of Dutch particle theorist Pierre van Baal. Pierre was my office mate when we were both postdocs at Stony Brook during the mid-eighties, and he was one of the people I most enjoyed talking with about physics during those years. He arrived at Stony Brook after completing a Ph.D. with Gerard ‘t Hooft, and later went on to CERN and ultimately a professorship in Leiden. I last saw him at a conference in Stony Brook in 2008 (described here) where he told me that he had suffered a serious stroke in 2005. Pierre was quite modest, and always a cheerful and optimistic presence in the room. In 2008 he was still very much himself, but more halting in his speech. From what I remember, he told me that he was resuming teaching, but was frustrated that he was no longer capable of engaging in research work.

The lecture notes of his class on quantum field theory are available (an online version here, a published version here). Like Pierre himself, they’re a model of clear and concise thinking and exposition. Last year a book with a selected collection of his papers was published, see here.

A major theme in Pierre’s work was the study of quantum gauge theory via semi-classical methods, for the case of a system in a “box”, i.e. finite extent in space and time dimensions. In the Euclidean picture, periodic boundary conditions in time correspond to doing computations at non-zero temperature, inversely proportional to the size of the time dimension. As a result, this work is quite relevant to the study of QCD at finite temperature, including the expected deconfining phase transition.

While Pierre was not really a lattice gauge theorist, his work was highly relevant to lattice gauge theory, where computer simulations inherently take place in a finite box, and understanding the effects of this on the physics is crucial. As a result, Pierre was well-known in the lattice gauge theory community. This week Columbia University is hosting Lattice 2014, the big yearly meeting for lattice gauge theorists (plenary talks are streamed on livestream.com). This morning I attended the talk by Michael Mueller-Preussker on Recent results on topology on the lattice, which was given in memory of Pierre. The slides have a lot more information about Pierre and his work, as well as surveying the latest on lattice results involving the topology of gauge fields.

For more about Pierre, see this site, which has an appreciation written by Chris Korthals Altes (in English here), as well as pieces by ‘t Hooft and Hans van Leeuwen (in Dutch).

Posted in Obituaries | 2 Comments

2015 Breakthrough Prizes in Mathematics

Posted on June 23, 2014 by woit

The first set of winners of the $3 million Milner/Zuckerberg financed Breakthrough Prizes in mathematics was announced today: it’s Donaldson, Kontsevich, Lurie, Tao and Taylor. There’s a good New York Times story here.

When these prizes were first announced last year, I was concerned that they would share a problem of Milner’s Fundamental Physics Prizes, an emphasis on rewarding one particular narrow area of research. I’m happy to say that I was wrong: the choices made are excellent, including a selection of the absolute best people in the field, working in a wide range of areas of pure mathematics. The prize winners are mathematicians who are currently very active, doing great work. It’s clear that there was an effort to avoid making this a historical prize, i.e. giving this to people purely for great work done in the past (which to some extent the Abel Prize is doing). The recipients are on average in their 40s, at the height of their powers.

One oddity is the award to Kontsevich, who already received $3 million from the Fundamental Physics prize. Given my interests, I suppose I shouldn’t criticize a prize structure where physicists get $3 million, mathematicians $3 million, and mathematical physicists $6 million.

While this prize doesn’t suffer from the basic problem of the Physics prize (that of rewarding a single, narrow, unsuccessful idea about physics), it’s still debatable whether this is a good way to encourage mathematics research. The people chosen are already among the most highly rewarded in the subject, with all of them having very well-paid positions with few responsibilities beyond their research, as well as access to funding of research expenses. The argument for the prize is mainly that these sums of money will help make great mathematicians celebrities, and encourage the young to want to be like them. I can see this argument and why some people find it compelling. Personally though, I think our society in general and academia in particular is already suffering a great deal as it becomes more and more of a winner-take-all, celebrity-obsessed culture, with ever greater disparities in wealth, and this sort of prize just makes that worse. It’s encouraging to see that most of the prize winners have already announced intentions to redirect some of the prize moneys for a wider benefit to others and the rest of the field.

Update: Among the private reactions I’ve heard from prominent mathematicians this morning, one is the desirability of funding a new “sidekick” prize for collaborators of the $3 million winners…

Posted in Uncategorized | 24 Comments

Smoking Gun No Longer Smoking

Posted on June 19, 2014 by woit

The BICEP2 paper is now out in Physical Review Letters, with major revisions to its conclusions from the preprint/press conference version of last March. For another sort of associated revision, compare this (from a March 17 Stanford press release):

Linde, now a professor of physics at Stanford, could not hide his excitement about the news. “These results are a smoking gun for inflation, because alternative theories do not predict such a signal,” he said. “This is something I have been hoping to see for 30 years.”

to this (from an interview with Linde in the latest New Scientist):

I don’t like the way gravitational waves are being treated as a smoking gun.

If we found no gravitational waves, it wouldn’t mean inflation is wrong. In many versions of the theory, the amplitude of the gravitational waves is miserably small, so they would not be detectable.

Last month, Resonaances broke the news that there was a problem with the BICEP2 claims, specifically with the bottom line (and punch line) of their preprint abstract:

Subtracting the best available estimate for foreground dust modifies the likelihood slightly so that r=0 is disfavored at 5.9σ.

Back then the BICEP official reaction to the Resonaances claim that they were admitting to a mistake was “We’ve done no such thing.” Post-refereeing, there have been extensive changes in the paper (for example, the “DDM2” dust model based on scraped Planck data is gone), and the bottom line of the abstract has been changed to:

Accounting for the contribution of foreground, dust will shift this value [non-zero r at 7.0 sigma] downward by an amount which will be better constrained with upcoming data sets.

If the BICEP collaboration is still not admitting a mistake in their treatment of Planck data or the bottom line of their preprint, then it seems that referees have told them they can’t publish these in PRL.

Back in March the BICEP2 results made the front page of the New York Times with a Dennis Overbye story Space Ripples Reveal Big Bang’s Smoking Gun, but today the NYT has Astronomers Hedge on Big Bang Detection Claim, which explains well what has been going on.

Update: Nature has a story out about this, which includes the news of a recent presentation at a Moscow cosmology conference by Jean-Loup Puget of the Planck collaboration:

Using for the first time the newest Planck maps available, Puget and his collaborators have directly examined the polarization of dust in these high galactic regions rather than extrapolating from dustier regions in the plane of the Milky Way. Averaging over some 350 high-galactic-latitude patches of sky similar in size to the region observed by BICEP2, Puget reported that polarization from interstellar dust grains plays a significant role and might account for much of the BICEP2 signal that had been attributed to inflation-generated gravitational waves. Puget told Nature that an article detailing these findings would be published in about six weeks.

Update: I’ve been watching Paul Steinhardt’s talk at Strings 2014, where he’s giving a dramatic attack on the way inflationary cosmology is being pursued as in violation of the scientific method. One thing he does is put up exactly the Linde quotes from this posting.

Posted in Uncategorized | 47 Comments

Strings 2014

Posted on June 15, 2014 by woit

This coming week and the next Princeton will host both the big yearly string theory conference Strings 2014, and Prospects in Theoretical Physics 2014, a program designed to train young physicists in string theory.
Princeton is definitely the right place for this, since it now is very much a singular point in the world-wide theoretical physics research community. At the IAS the director is a string theorist, so is the past director (now faculty member). Of the other four senior HEP theorists, three are string theorists and one might be described as a fellow-traveller. Over at the university, of the nine faculty in HEP theory, all are string theorists except for one junior faculty member.

One will be able to follow the Strings 2014 talks live here, and video and slides should be posted here.

The Strings 20XX conferences provide a good place to see what the latest trends in string theory are, with the talks chosen to highlight what some of the most influential people in the field consider the most interesting work. I’ve written posts on the blog here about previous such conferences, which one can compare to this year’s to see how the field has evolved. Looking at the list of over 70 talks and their topics, some things that strike me (in many cases, much the same things as in other recent years):

  • Talks actually about strings are a small minority (20%), something that has been true for quite a few years. The percentage may have grown from a minimum back in 2011 when some of the speakers were mentioning the small role strings were playing at a string theory conference.
  • AdS/CFT and holography remain a dominant theme, as they have for many years. Possible applications of this to condensed matter physics are a continuing hot topic. The previous hot topic of this kind, applying AdS/CFT to heavy ion physics, now seems to be dead, something people would rather not talk about anymore since it never worked out as advertised.
  • Amplitudes are the other big hot topic.
  • Discussion of the LHC and hoped-for LHC results in the past was often a major topic at these conferences. Now that the LHC results are in and a huge disappointment (no SUSY or extra dimensions), it looks like there’s a chance the LHC will not be mentioned at all at this year’s conference, with “string phenomenology” in general the topic of only a very few talks.
  • String phenomenology does have its own yearly conference (see here), but at least as far as the US participants go, the top US research institutions are not represented there, whereas they are heavily represented at the Princeton conference. Whatever “string phenomenology” is these days, it’s not popular at all among the Princeton crowd. It’s no longer being done at the most prestigious US institutions, and in Europe is concentrated in certain places (popular in England for some reason, not at all in France).
  • While research into string theory unification schemes now seems to be very unpopular at Princeton, for some reason it’s a topic that the young must still be trained in. The PiTP program includes a series of lectures on string compactications, for which the Princeton people needed to bring in Martijn Wijnholt from Munich, one of the places still doing this kind of thing.
  • To the extent there’s anything about connection to experiment, B-modes are the hot topic.
  • There was a time when mathematicians were sometimes invited to Strings 20XX, but that’s over and done with. It seems most prominent string theorists no longer want to hear anything from mathematicians.
  • Finally, zero about the multiverse or the landscape. Clearly some on the organizing committee still have strong opinions and are not going to tolerate that kind of nonsense.

    • Witten will just give a 15 min welcoming speech. In the past, David Gross has ended the conference with a “vision” speech. This year there will be five “vision talks”, and it may be interesting to see a wider range of opinions on where the field is heading.

Update: One more notable thing about this version of the yearly conference is that (as far as I can tell), it’s the first one in many years that has not included a promotional public talk about string theory. It may very well be that this was considered unnecessary in Princeton.

Update: Martin Wijnholt’s lectures to the students and postdocs in Princeton about string compactifications are available here. Lots of nice material on Calabi-Yaus and algebraic geometry, nothing at all about extracting the standard model from all this. One thing that has always surprised me is how little most string theorists know about the state of the art of getting particle physics out of the theory. This is less surprising now after seeing the kind of lectures they get on the subject.

Posted in Strings 2XXX | 44 Comments

Large Hadron Collider Physics Conference

Posted on June 9, 2014 by woit

While I was away last week Columbia was hosting the Large Hadron Collider Physics (LHCP) conference here on campus. Talks are available here. Matt Strassler posts about some of the new Higgs results, which basically see some of the inconsistencies in Higgs mass measurements disappearing. Right now everything is quite consistent with a pure Standard Model Higgs.

In the final plenary session, the theory talk from John Ellis ended by claiming the LHC results as a success for SUSY (the “success” is that simple classes of SUSY models said the Higgs couldn’t be too heavy, also that the Higgs couplings should be much like those of the SM, so any SM success is a SUSY success). Another argument was that “SUSY is increasingly the best solution [of the hierarchy problem] that we have” (here he was following Nathaniel Craig’s summary talk), illustrated by two discouraged soldiers under bombardment in a foxhole, one saying to the other “Well, if you knows of a better ‘hole go to it!”. It’s interesting to note that the arguments from Ellis work just as well if SUSY is not found at Run 2, a likely possibility he’s getting ready for.

The conference included a Friday afternoon panel discussion that you can watch here. This began with an excellent presentation from Fabianola Gianotti about the possibilities for next-generation colliders. The discussion moderated by Dennis Overbye of the New York Times focused to some extent on the budgetary challenges facing US HEP, with Steve Ritz, the chair of the P5 panel, commenting on the tough situation reflected in that panel’s recent report. Many speakers expressed frustration over the US budget level for HEP and what to do about it. Enlist the public? Do a better job of convincing Congress? Get billionaires to help fund HEP? Get billionaires to fund a Super PAC that would buy us a Congress with a better attitude?

Most of the discussion was about the experimental side, but Arkani-Hamed also had comments about the theory side, noting that the job market for theorists, which improved after his grad school days in the mid-90s, has now worsened and gone back to that level. He also noted that successful young theorists are increasingly ending up in faculty jobs outside the US after starting their careers as students and postdocs here.

Posted in Uncategorized | 7 Comments

Evidence in the Natural Sciences

Posted on June 9, 2014 by woit

I recently spent a day at the Simons Foundation in midtown, attending a symposium on Evidence in the Natural Sciences. Of the scientific program talks, I got the most out of the one by Thomas Hales on the question of checking the proof of the Kepler conjecture. For the latest on the project to produce a formal, computer checkable version of the proof, see the Flyspeck Project page.

The program ended with a discussion/debate featuring Brian Greene, Peter Galison and Jim Baggott, with the contentious issue basically “has physics gone too far?” in a speculative direction, unable to get back to a point where connection can be made to experiment. Baggott gives a summary of what he had to say at Scientia Salon, which would be a good place to discuss these issues (so I’m leaving comments off on this posting). Both Greene and Galison were much more taking the position that things haven’t gone off the rails, that one needs to trust the leaders of the field and the physics community to do the best they can. This blog’s readers shouldn’t have much trouble guessing which side of this I’m more sympathetic to. I didn’t notice the event being recorded, perhaps it was.

The symposium was co-sponsored by the Templeton Foundation, with no theology or religion in sight. I think they’re mostly these days keeping the physics/math and theology apart, with this symposium and FQXI two good examples, and I’m happy to see that. My other main complaint about Templeton was always that they were pushing multiverse research since that fit into their agenda. These days I don’t see them doing so much of that, with multiverse mania being driven by much more dangerously influential sources. But maybe I’m less critical of them because they invited me to a very nice dinner after the talks…

Update: Videos of the talks are now available here.

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Past the End of Science

Posted on June 8, 2014 by woit

I haven’t yet seen a copy of Marcelo Gleiser’s new book, but this weekend the Wall Street Journal had a review by John Gribbin, author of the 2009 multiverse-promotional effort In Search of the Multiverse. I don’t know how Gleiser treats this, but Gribbin emphasizes the multiverse as new progress in science (for some reason he’s now calling it the “metaverse”):

Within the metaverse, the story goes, there are regions that form inflating bubbles. Our universe is one such region or bubble. As Mr. Gleiser explains, the implication is that there are other universes, other bubbles far away floating across an inflating sea.

This seemingly speculative idea counts as a genuine scientific hypothesis, because it makes testable predictions. If other “bubble universes” exist in the metaverse, it is possible that, long ago, one or more of them may have collided with our universe, like two soap bubbles touching and moving apart. One effect of such a collision, Mr. Gleiser points out, would be to make ripples in the space of both bubble universes; they would leave a distinctive if faint ring-shaped pattern, known as a “cosmic wake,” in the background radiation that fills the universe. Data from the Planck satellite is being used to test this prediction right now. Is the metaverse real? We may well know in the next year or so.

This seems to be a reference to work by Matthew Kleban and collaborators, which I saw Kleban talk about recently (see here). My impression from that talk is that the actual state of affairs with Planck is that it has already looked for and ruled out most hoped-for signals of “bubble collisions”. I don’t know anyone besides Gribbin who believes that the next round of Planck data is going to answer the question “Is the metaverse real?”.

The really odd thing about the review is that Gribbin uses the multiverse to argue that John Horgan’s claims about physics in The End of Science are wrong. This is just bizarre. Gribbin and his multiverse mania for untestable theories provides strong ammunition for Horgan, since it’s the sort of thing he was warning about. Actually, I don’t recall anything in Horgan’s book about the multiverse, and suspect the idea that physics would end up embracing such an obviously empty idea was something that even he didn’t see coming. As the multiverse mania gains strength, physicists are blowing past the “End of Science” to something that has left conventional science completely behind.

Update: I took a look again at a copy of The End of Science, and, as I remembered, the chapter on “The End of Physics” has no mention of the multiverse pseudo-explanation of why one can’t ever understand the parameters of the Standard Model. Horgan ends the chapter with a vision of physics descending into “ironic science”, endlessly studying untestable string theory models and interpretations of quantum mechanics. With the multiverse we may already have gone past that point.

In the next chapter though, “The End of Cosmology”, there’s a long section about Linde and his “self-reproducing universe theory”, so Horgan more than 20 years ago already was writing about the place we’re ending up. I was interested to see the comment he got at the time from Howard Georgi about this kind of model:

quite amusing. It’s like reading Genesis.

Georgi also is quoted as describing inflation as:

a wonderful sort of scientific myth, which is at least as good as any other creation myth I’ve ever heard.

Of course what is different now is that 20 years ago the theory establishment saw Linde’s multiverse as kind of a joke, not at all part of science. Things have changed…

Update: While my favorite local bookstore doesn’t have a copy of the Gleiser book The Island of Knowledge, you can see parts of it on Google Books. Searching on “multiverse” you can read chapters 15 and 16 of the book which deal with the issue of the testability of the string theory multiverse. Reading these shows that Gribbin seriously misrepresents what Gleiser has to say about the multiverse. The context of his discussion of “Cosmic Wakes” and the possibility of seeing them in the Planck data is to argue that even if this happened (which he describes as having an “extremely small” probability), all that would show is evidence for a neighboring universe, not a multiverse:

However, I stress again that even a positive detection of a neighboring universe would not prove the existence of a multiverse. Within the present formulation of physics the multiverse hypothesis is untestable, however compelling it may be. [Page 129]

Posted in Multiverse Mania, Uncategorized | 15 Comments

Big Bang Blunder Bursts the Multiverse Bubble

Posted on June 4, 2014 by woit

This week’s Nature has an article by Paul Steinhardt, with the title Big Bang blunder bursts the multiverse bubble. The subtitle of the piece describes the BICEP2 frenzy of last March as “premature hype”, and the description in the body of the article is:

The results were hailed as proof of the Big Bang inflationary theory and its progeny, the multiverse. Nobel prizes were predicted and scores of theoretical models spawned. The announcement also influenced decisions about academic appointments and the rejections of papers and grants. It even had a role in governmental planning of large-scale projects.

Given recent arguments that BICEP2 may be seeing dust, not primordial gravitational waves, the March media frenzy quite possibly was highly premature, if not completely misguided. Steinhardt goes on to argue that in the future

announcements should be made after submission to journals and vetting by expert referees. If there must be a press conference, hopefully the scientific community and the media will demand that it is accompanied by a complete set of documents, including details of the systematic analysis and sufficient data to enable objective verification.

He also takes the occasion to note the odd fact that while BICEP2 results have been claimed to be proof of inflation and the multiverse, if they turn out to be wrong, that’s fine too:

The BICEP2 incident has also revealed a truth about inflationary theory. The common view is that it is a highly predictive theory. If that was the case and the detection of gravitational waves was the ‘smoking gun’ proof of inflation, one would think that non-detection means that the theory fails. Such is the nature of normal science. Yet some proponents of inflation who celebrated the BICEP2 announcement already insist that the theory is equally valid whether or not gravitational waves are detected. How is this possible?

The answer given by proponents is alarming: the inflationary paradigm is so flexible that it is immune to experimental and observational tests. First, inflation is driven by a hypothetical scalar field, the inflaton, which has properties that can be adjusted to produce effectively any outcome. Second, inflation does not end with a universe with uniform properties, but almost inevitably leads to a multiverse with an infinite number of bubbles, in which the cosmic and physical properties vary from bubble to bubble. The part of the multiverse that we observe corresponds to a piece of just one such bubble. Scanning over all possible bubbles in the multi­verse, every­thing that can physically happen does happen an infinite number of times. No experiment can rule out a theory that allows for all possible outcomes. Hence, the paradigm of inflation is unfalsifiable…

Taking this into account, it is clear that the inflationary paradigm is fundamentally untestable, and hence scientifically meaningless.

Steinhardt was on a panel last Friday night here in New York at the World Science Festival, which can be watched here. The panel included Guth and Linde (who earlier in the week got $1 million for their work on inflation), as well as John Kovac of BICEP, and Amber Miller, Dean of Science here at Columbia. The last part of the video includes an unsuccessful attempt by Steinhardt to pin down Kovac on the significance of the BICEP2 evidence for primordial gravitational waves claim, as well as an exchange with Guth and Linde. They both defend inflation as the best model of the alternatives.

Multiverse promotion continues apace, with Steinhardt one of a rather small number of physicists publicly objecting. On Monday Alexander Vilenkin will explain to the public at the American Museum of Natural History that “the Big Bang was not a unique event in cosmic history and that other Big Bangs constantly erupt in remote parts of the universe, producing new worlds with a great variety of physical properties” (see here). A recent story on livescience has Brian Greene on the multiverse. Over at Massimo Pigliucci’s Scientia Salon Coel Hellier is starting a multipart series arguing against multiverse skeptics with The multiverse as a scientific concept — part I. Nothing in Part I about the problematic issues (untestable claims that fundamental physics is “environmental”), maybe in Part II…

Posted in Multiverse Mania | 27 Comments

This Week’s Hype

Posted on May 25, 2014 by woit

About every three years KEK issues a hype-filled press release announcing that Jun Nishimura and collaborators have used a supercomputer to get evidence for string theory. Back in 2008, the announcement was of a numerical simulation on a supercomputer of a supersymmetric QM system that supposedly showed that superstring theory explained the properties of black holes (press release here, preprint here, blogging here). In 2011, the claim was of a numerical simulation on a supercomputer that used superstring theory to understand the birth of our universe (press release here, preprint here, blogging here). Both of these papers were published in PRL.

The 2014 press release is now out (see here), based on this preprint from last December. The latest claim is that the authors have solved the black hole information paradox, have shown that we live in a hologram, as well as showing that string theory provides a self-consistent quantization of gravity, all by doing a numerical simulation of a QM system. Even better, they have made the quantum gravity problem just as well-understood and tractable as QCD:

In short, we feel that problems involving quantum gravity have become as tractable as problems involving the strong interaction. The latter can be studied by simulating a gauge theory on a four-dimensional (4D) lattice, and such a method has recently been used to reproduce the mass spectrum of hadrons (28) and the nuclear force (29). We can now apply essentially the same method to study quantum gravity, which has been thought to be far more difficult.

This latest version of the KEK-hype has gotten a lot more attention than the previous two versions. Based on the preprint, late last year for some reason Nature covered this with a story about how Simulations back up theory that Universe is a hologram and this got a lot of media attention (see here for example).

The paper has now been published, and this time it’s not in PRL, but in Science magazine (submission there was a month after the preprint came out, could it be that PRL wouldn’t have it?). Science is giving it a high profile, including together with it a piece by Juan Maldacena, which claims the paper as “further evidence of the internal consistency of string theory”. Science provides the following one-line summary of the Maldacena piece:

A numerical test shows that string theory can provide a self-consistent quantization of gravity.

One obvious problem with this is that even if you take the most optimistic view of it all, what is being described is quantum gravity in 10d space-time. The Japanese authors deal with this problem with a footnote:

Theoretical consistency requires that superstring theory should be defined in ten-dimensional space-time. In order to realize our four-dimensional space-time, the size of the extra six dimensions can be chosen to be very small without spoiling the consistency.

Remarkably, Maldacena has another answer: the multiverse, which now he seems to take as accepted fact.

Of course, the 10-dimensional space under consideration here is not the same as the four-dimensional region of the multiverse where we live. However, one could expect that such holographic descriptions might also be possible for a region like ours.

Absurd hype about string theory is a continuing problem, and it’s not one that can be blamed on journalists, with this latest example getting help from HEP lab press releases, a highly reputable journal, and an IAS faculty member.

Posted in This Week's Hype | 18 Comments