Freed on Chern-Simons

Posted on August 20, 2008 by woit

Dan Freed has a wonderful preprint out on the arXiv this evening, based on a talk he gave at the celebration of MSRI’s 25th anniversary, entitled Remarks on Chern-Simons Theory. It’s mainly about the current state of attempts to better understand the mathematical significance of the Chern-Simons-Witten quantum field theory.

This is a truly remarkable and very simple 3d quantum gauge theory, the significance of which Witten first came to understand back in 1988. He quickly showed that the theory brought together in an unexpected way several quite different but important areas of mathematics and physics (3d topology, moduli spaces of vector bundles, loop group representations, quantum groups, 2d conformal field theory among others). This work was the main reason he was awarded a Fields medal in mathematics in 1990. While Witten and others worked out many important aspects of this story back then, many important puzzles still remain, and it is these that Freed concentrates on.

Perhaps the biggest puzzle is that of how to actually define the theory in a local manner. The standard definition thrown around is that this is just the QFT with Lagrangian given by the Chern-Simons number CS[A] of a connection A, so all one has to do is evaluate the path integral
$$\int [dA] e^{i2\pi k CS(A)}$$
While this is a good starting point for a perturbative expansion at large k, it doesn’t appear to make much sense non-perturbatively. Freed points out that it is known that the theory must depend on additional topological structure on the 3-manifold (e.g. a 2-framing), whereas the path integral looks like it only depends on the orientation. If you try and think about how you would actually calculate such an integral numerically, by discretizing it and taking a limit, it looks like you will end up with something hopelessly dependent on the details of the discretization and the limit. For a much simpler toy example with some of the same problems, consider the path integral on closed curves on a sphere, taking as Lagrangian the enclosed area.

Freed describes in detail the state of attempts to rigorously define the theory without dealing with the path integral, but instead exploiting the fact that it is supposed to be a topological qft, and thus may have an abstract definition in terms of generators and relations. He describes the current situation as follows:

  • There is a generators-and-relations construction of the 1-2-3 theory via modular tensor categories for many classes of compact Lie groups G. This includes finite groups, tori, and simply connected groups, the latter via quantum groups or operator algebras.
  • There are new generators-and-relations constructions – at this stage still conjectural – of the 0-1-2-3 theory for certain groups, including finite groups and tori.
  • There is an a priori construction of the 0-1-2-3 theory for a finite group.
  • There is an a priori construction of the dimensionally reduced 1-2 theory for all compact Lie groups G

    • The bottom line is that we only have a local construction of the theory for the case of finite groups, where one can make perfectly good sense of the path integral. For the case of a 3-manifold that is a product of a circle and a Riemann surface, one can define things in terms of a 2d theory, and Freed explains the connections to the Freed-Hopkins-Teleman theorem.

    To convince mathematicians that there is something to the path integral, Freed writes down the asymptotic expansion for large k that it leads to, and shows that this gives a highly non-trivial conjecture relating quite different mathematical objects associated with a 3-manifold. He shows strong numerical evidence for this conjecture.

    Finally, he ends with some extensive and interesting comments about the relationship between quantum field theory and mathematics, as it has been pursued by both physicists and mathematicians over the past quarter-century, with some speculation about what direction this might take in the future.

    Posted in Uncategorized | 10 Comments

    Strings 2008

    Posted on August 17, 2008 by woit

    Strings 2008 starts tomorrow at CERN, with about 400 physicists in attendance. CERN will be providing a live webcast for the rest of us. The timetable of the talks is here. The first afternoon will be devoted not to string theory, but to the LHC.

    Those in attendance without their own blogs are encouraged to report on the goings-on by writing comments here when they get bored by the talks. I’ll try and watch some of the talks (or at least look at the slides), and use this posting to write about them.

    Update: I’m not likely to be up early enough to catch the morning talks on the webcast, but Lubos is, so you can follow his virtual live-blogging.

    Update: Live, the conference seems to be suffering from not always being up to the technology of displaying slides on a Mac to the audience. But slides of the previous talks are now beginning to be available here.

    Update: After looking through the slides of the talks and hearing a few of them, the thing that strikes me most about Strings 2008 is how little there has been about strings. Particle theory may be moving to a model where the big annual conference is labeled “STRINGS”, and speakers make nods of respect toward string theory, but actually talk about something else.

    The three big hot topics of the conference are

  • the LHC (talks by Evans, Engelen and Buchmuller), which has nothing at all to do with string theory
  • New 3d superconformal quantum field theories (talks by Lambert, Maldacena and Mukhi). One motivation for these is that they can be fit into a pattern of dualities, much like the famous 4d superconformal theories that have dominated particle theory research since Maldacena.
  • Scattering amplitudes, especially those of N=4 SYM and N=8 supergravity (talks by Veneziano, Kallosh, Dixon, Cachazo, Green, Sokatchev and, to come, Alday). Some of this looks a lot like particle physics from the mid-60s, based on the study of the analytic S-matrix, including the presence of Veneziano. While there has been a lot of progress in studying certain kinds of QFT S-matrix amplitudes in recent years, some of it coming out of string theory, the most dramatic news is that about the possible finiteness of perturbative N=8 supergravity. Remember all those talks you’ve heard where someone draws a Feynman diagram and a string diagram, then explains how this shows that perturbative QFT has deadly divergence problems due to point-like interactions, while perturbative string theory doesn’t? Well, it appears that you can forget about all that now. In a rear-guard action, some speakers point out that you need to understand non-perturbative N=8 supergravity, and maybe this can’t be done in a QFT context. Unclear why non-perturbative string theory is supposed to help here, since the only viable non-perturbative version of it is, by duality, a QFT itself…

    • Looking at the talks that actually are about string theory unification, you quickly see why most people are talking about something else. Ibanez starts off by asking whether string theory makes physical predictions, then claims that it does, with one of them being exactly the reason it doesn’t make predictions about physics: “There is a large landscape of string vacuum solutions…”, which he then goes on to describe. Donagi’s talk, about Heterotic Standard Models, was remarkable in how much the situation there hasn’t changed since 1985. You can come up with such models with the right quantum numbers (and actually, just about any quantum numbers you want…), but to get anything else, you have to address how to stabilize moduli and break supersymmetry, and Donagi just mentions these problems at the end as tasks to address in the future. For more about the F-theory-motivated models reported on, see the comments at this posting, where “anonymous” has an informed discussion with him (or her)self.

    Posted in Strings 2XXX | 24 Comments

    The Landscape at CERN

    Posted on August 14, 2008 by woit

    The current plan at CERN is to celebrate my birthday by trying to circulate the first beam around the LHC on September 10 (actually my birthday is September 11, but in recent years my family, like CERN, has tended to celebrate on the 10th, feeling that 9/11 has too unfortunate connotations). One can follow this at a special web-site set up by CERN called LHC First Beam, which now is running a daily countdown.

    String theorists have been flocking to CERN this summer trying to somehow connect their subject with the LHC. The big yearly Strings 08 conference will be starting there next week. The organizers don’t seem to have a lot of sympathy for anthropic pseudo-science, with no talks scheduled on anthropics, the landscape, or the multiverse. Instead they’ll be wisely sticking mostly to talks on topics related to better understanding more formal issues in string theory and quantum field theory.

    In the weeks leading up to the conference though, CERN is hosting a theory institute on String Phenomenology. The web-site of the institute has a section on its “Scientific Case”, which, with remarkable chutzpah makes the claim that:

    … the past few years have provided a drastic improvement on the potential for string theory models to be confronted with low-energy data

    a claim that is diametrically opposed to reality.

    For a look at the reality of what the landscape has meant for the “potential for string theory models to be confronted with low-energy data”, one can take a look at the slides of talks by Wati Taylor and Michael Douglas. Taylor describes the importance of distinguishing two possibilities he calls A (anything goes) and B (constraints), and finds in IIA intersecting brane models that the evidence favors A. It seems that such a landscape can give one pretty much any kind of low energy physics, with the things one can compute (the gauge group and number of generations) randomly and independently distributed. He looks for some hope in cosmology, noting that a large class of IIA models are incompatible with slow-roll inflation, while at the same time also pointing out that there are lots of potential ways around this particular constraint, although most of them involve uncontrolled approximations.

    Douglas’s talk was entitled String Landscape: A Status Report, and in it he describes evidence for the existence of order 10500 “quasi-realistic vacua”. If you don’t impose some constraints from experiment, you’d have an infinite number of possible vacua. He claims that there is no way to rule out any of these vacua, other than to try and compute detailed predictions of each one (something no one has a clue about how to do). Douglas explained why it isn’t possible to make even the crudest prediction that initially he and others had hoped for, that of whether the SSYM breaking scale would be at observable or Planck energies. There’s an odd speculative section about how since SU(2) and SU(3) have shown up on energy scales of 100 MeV to 100 GeV, maybe one gets two new gauge groups for every factor of 1000 in energy (which he calls the “jungle scenario”, as opposed to the conventional “desert scenario”). There’s a final “No Conclusions” section, admitting that “at this point it seems likely that we will not have definite conclusions of predictions before LHC data comes in.” He ends with the standard piece of wishful thinking that now is all that is left of the project of connecting string theory unification models with physics:

    Let us hope that discoveries here at Cern will reveal enough about the real world to make contact [with string theory] possible.

    Yesterday there was a discussion session on “the string theory landscape and its impact on particle physics and cosmology”, but it doesn’t appear to be online. I wonder what conclusions the participants reached…

    Update: Jester at Resonaances has a posting up about this. His impression of the Vafa et al. recent claims about “F-theory phenomenology” seems to match mine:

    For the neutrino physicists the important piece of information is that the neutrinos are Dirac or Majorana and their masses are roughly of the order of what is observed. I heard some sceptics saying that back in the old days phenomenology meant a different thing, but such grumbling should not be taken seriously.

    Posted in Uncategorized | 9 Comments

    Grothendieck’s Later Years

    Posted on August 8, 2008 by woit

    Alexander Grothendieck’s 80th birthday was this past March, and the September Notices of the AMS has several articles about his later years. There’s a long piece entitled Who is Grothendieck?, by Winfried Scharlau, who is writing a three-volume biography. The first volume (in German) is available here and mainly deals with the stories of his parents. The article contains the only pictures I’ve ever seen of the post 1970s Grothendieck and a wealth of information about his activities after leaving the mathematical research world.

    The same issue contains a short piece Memories of Shourik, by Valentin Poenaru reminiscing about his friendship with Grothendieck during the 1960s. The most shocking thing in it to me was actually the part about Barry Mazur’s wife, who Poenaru describes as being only 17 when he met her living with Mazur at Bures-sur-Yvette.

    Note added: Mazur’s biography here mentions just one wife, Grace Dane, a Harvard biology postdoc he married in 1960. If she was, as Poenaru claims, 17 in 62-63, that would have made her a 15 year-old postdoc when they married….

    Finally, there’s a piece by Allyn Jackson about Grothendieck and the IHES, which is having its 50th birthday this year. Evidently Grothendieck has recently been in communication with the IHES:

    Six months to the day before the start of the IHES anniversary celebration, Grothendieck wrote to the institute with a request for books. The IHES sent him the books as quickly as it could. But the exchange of letters between Grothendieck and the IHES administration culminated in his writing a furious “open letter” recounting his view of the exchange, which he took as deeply insulting towards him. He requested that copies of the open letter be sent to all members of the IHES Scientific Council and explicitly states that this letter is public (though he also says he will make no efforts on his own to publicize it). Having seen the open letter, I can say that it conveys an extreme outrage that indicates how difficult it would be to conduct reasonable communication with him.

    At the same time, the open letter reveals the vivid personal tie that Grothendieck clearly still feels to the IHES. The letter also reveals an isolated individual who is reaching out in the only way he is able. In one place he speaks of his open letter as being a letter of farewell (“adieu”) to a world with which he no longer has anything in common. He ends on a note of apocalyptic foreboding, saying “that the time is near when…this letter, this cry will be known by all. In a world of the living.” This cry does not seem to concern misunderstanding over his original request for books. Rather, it speaks of anguish in the heart of one of the great mathematicians of modern times.

    The IHES is having Recoltes et Semailles, Grothendieck’s long meditation on mathematics and his withdrawal from it, published this summer. Articles about this are beginning to appear in the French press, see here and here.

    Posted in Uncategorized | 24 Comments

    Furby, Tamagachis, string theory…

    Posted on August 8, 2008 by woit

    Things don’t seem to be going well these days for string theory in the “marketplace of ideas”. From an article about gasoline-saving pedals:

    The 1990’s were the host of many great fads. Furby, Tamagachis, string theory, the examples are as numerous as the many incarnations of Prince.

    Posted in Uncategorized | 43 Comments

    FQXI and Templeton News

    Posted on August 5, 2008 by woit

    The FQXI organization has just announced the details of $2.7 million dollars in grants that it will be handing out. The winners and their projects are described here. As usual, one of the main topics funded by FQXI is multiverse studies. There’s also another news story on the topic from them here, which examines the question: “Are we in danger of a fatal crash with another universe?”

    At the same time, FQXI announced an essay contest on the topic of “The Nature of Time”, first prize is $10,000.

    FQXI is funded by the Templeton Foundation, an organization whose goal is to bring science and religion together. The founder of the Foundation, Sir John Templeton, died last month at the age of 95, leaving his son in charge of the place. While the father seems to have been a rather Unitarian sort, the son Jack is the money behind the right-wing PAC Let Freedom Ring. Sir John’s death will provide Jack Templeton with a lot more money to spend. The Chronicle of Philanthropy has a story about this, which explains that the plan is to hire new vice-presidents, with the goal of coming up with new ideas of how to spend more money to support free enterprise and virtue. Not clear yet what this means for FQXI, or for some of the other physicist beneficiaries of Templeton largess over the years.

    Posted in Multiverse Mania | 45 Comments

    ICHEP 2008

    Posted on August 4, 2008 by woit

    A major HEP conference, ICHEP 2008, is taking place in Philadelphia at the moment, and many of the talks are already available online here. This is mostly a conference devoted to experimental HEP, and the big news is the joint announcement by CDF and D0 that they are just barely able to exclude, at 95% confidence level, the possibility of a Higgs with mass of 170 GeV. This is the first new information about (ignoring neutrinos…) the one remaining parameter of the Standard Model since LEP showed that the Higgs mass can’t be below 115 Gev. For more about this, see Sunday’s ICHEP plenary talk by Matthew Herndon.

    Also announced at ICHEP and providing constraints on the possible Higgs mass are new fits using precision electroweak measurements. Tommaso Dorigo has a nice explanation of this story in a new posting here. Don’t miss the comment section, which has a hilarious exchange between Lubos and an anonymous physicist who can’t believe what is going on, asking Tommaso to check IP addresses to see if someone is impersonating Lubos. The point of physics being discussed is an extremely interesting one, but the mode of discussion ensures that enlightenment will not result.

    Lyn Evans of the LHC gave a report on its progress. They expect to first try to inject a beam about a month from now, with first collisions and data maybe two months later, at 10 GeV center of mass energy. Evans is guessing that luminosity in 2008 will be about 10 pb-1.

    This morning, Joe Polchinski will give the plenary talk on “Recent Progress in Formal Theory”, and Witten gave a public lecture Monday night. Nima Arkani-Hamed was supposed to give a “Concluding Inspirational Talk”, but that appears to have been canceled.

    Update: It’s worth noting that the Higgs mass getting excluded is right in the middle of where Alain Connes’s prediction from his NCG model comes in. Connes has a new blog posting about this here, where he admirably notes how discouraging this is for his model. Jacques Distler has a quite good new posting about the NCG model here.

    More about this from Gordon Watts here.

    Posted in Experimental HEP News | 11 Comments

    Blogging Heads Science Saturday

    Posted on July 26, 2008 by woit

    Today’s “Science Saturday” on Bloggingheads features me and Sabine Hossenfelder, supposedly talking about What’s wrong with string theory. Actually, we both agreed that we were pretty tired of that topic, so tried to discuss some more interesting related issues we both have an interest in. Here’s a clip from the full thing, I promise to not start regularly embedding video in this blog:

    I hope this thing came out all right. It was recorded a couple weeks ago, in a process involving no trouble on my end, but heroic efforts on Sabine’s. While Sabine had to set the whole thing up on her end, and ended up crouched in an attic since it was the only place she could get a connection of good enough quality, I just sat at my office chair and someone from Bloggingheads took care of everything. Unfortunately we couldn’t see each other while talking. I can’t really bear the thought of watching myself on video, so I guess I’ll never see exactly how this turned out, but I’m glad to see that the turtles on the bookcase behind me made it into the frame.

    Sabine has her own posting about this here, and the full thing is here.

    Posted in Uncategorized | 60 Comments

    Gauge Theory and Langlands Duality

    Posted on July 21, 2008 by woit

    At the KITP in Santa Barbara there’s a wonderful program on Gauge Theory and Langlands Duality starting up this week, with some of the talks beginning to become available. The main topic will be the relations between S-duality in quantum field theory and geometric Langlands duality that Witten and collaborators have been working on the past few years.

    I started trying to watch the talks, but the fact that the video quality is such that one can almost but not quite tell what is being written on the blackboard makes this a bit of a trial. I’m hoping that David Ben-Zvi or someone else will make available notes, which would help a lot. I did very much like Edward Frenkel’s description of the Langlands story as a “Grand Unified Theory of Mathematics”, and was interested to hear that he still feels that there are two different stories about the relation to QFT here, whose relationship is not at all understood (S-duality in 4d QFT is one, 2d CFT and vertex algebras is the other). It seems that A.J. Tolland is there, maybe he or someone else will do some blogging. As I get time to take in the lectures, I hope to write some more about them here.

    Update: Notes for the talks are now also being posted, making following them on-line much more feasible. The quality of the talks is excellent, with Ed Frenkel so far giving a beautiful introduction to the roots of the Langlands program in number theory, David Ben-Zvi explaining the structures in topological quantum field theory that mathematicians are trying to exploit, David Morrison and Paul Aspinwall explaining mirror symmetry, D-branes, and the relation to N=(2,2) superconformal field theory, with examples, and Anton Kapustin starting on the 4d N=4 TQFT used to turn S-duality into a mirror symmetry.

    Posted in Langlands | 11 Comments

    The Emperor’s Last Clothes?

    Posted on July 21, 2008 by woit

    Bert Schellekens has posted on the arXiv an extended 87 page argument for the anthropic string theory landscape, entitled The Emperor’s Last Clothes? While most string theorists find the existence of the landscape and the corresponding inability to get any predictions out of the theory about particle physics rather discouraging, Schellekens instead sees this as an argument in its favor:

    Initially, when string theory was touted as the “theory of everything” around 1984, there were hopes it would lead to exactly the opposite: a unique derivation of all the laws of physics. Evidence that quite the opposite was true started emerging almost immediately after 1984, but most people chose to ignore it. In 2003, after important additional evidence had been found, Leonard Susskind published a paper [2] entitled “The Anthropic Landscape of String Theory”, which finally started a debate that should have started fifteen years earlier. What is at stake in this debate is not only the uniqueness of our universe, but also the fate of string theory as a fundamental theory of all interactions.

    In my opinion string theory gives the right answer, and the fact that it does adds to the evidence in its favour. I can say this without being accused of trying to put a positive spin on the recent developments, because I actually wrote in 1998 [3] that I hoped string theory would ultimately lead to a huge number of possible choices for the laws of physics, a point of view I have been advocating since the late eighties. I reached that conclusion after having been involved in one of the first papers [4] pointing out that the number of possibilities was humongous…

    We all hope to live during a time when big things are happening in our field, and I have never doubted that this is one of those things. I have spent the last twenty years trying to convey my sense of excitement to my colleagues, but with little success. But in the last few years I have been delighted to see more evidence coming in supporting this point of view, so that the mood has started to change. I hope this is the right time to make one more attempt.

    Schellekens describes in great detail the anthropic argument and the arguments for the string theory landscape. He addresses some of the counter-arguments, especially in three appendices. He doesn’t explictly deal with the main counter-argument that I’ve made repeatedly here: the anthropic landscape is not science (since it is not testable), rather it is just an elaborate excuse for the failure of the speculative idea of getting the SM out of a 10/11d string/M-theory.

    Schellekens has the following comments about “string phenomenology”, noting that he worked in the area around 1987 and recently, finding not much has changed:

    I have been active in this are around 1987 (which led me to the conclusions presented here) and again in the last few years, and to me the similarities are more striking than the differences. There has certainly been progress: we can obtain string solutions that are more similar to the Standard Model than twenty years ago, and we have more methods to construct them. There has been major progress in moduli stabilization and supersymmetry breaking. There is more interest in “landscape statistics”. But very little seems to have changed in the way many people view the problem we are facing. Although many of my string phenomenology colleagues claim that it was clear to them a long time ago that there are many solutions, I cannot help noticing that they still talk about their most recent “model” as if it would actually have a chance to be the Standard Model. And even nowadays one still hears the occasional expression of hope for the unknown and elusive dynamical principle that will select the vacuum. The most common way of dealing with the large vacuum degeneracy is to say “I do not care about the other 10500vacua, I only care about the one that describes our universe”. That may sound reasonable, and fact it may sound like the very definition of phenomenology, but it is actually an escape from reality.

    First of all, if indeed there are 10500 vacua, it is highly unlikely that anyone will find “the Standard Model” in string theory. One should expect to find a huge number that satisfy all current experimental constraints. In addition, although we now have many techniques at our disposal to construct string theories in four dimensions, it is quite clear that we are just scratching the surface. Statistically speaking, our chances of finding even one of the expected huge number of Standard Model realizations is essentially zero. Furthermore, even if we do find one, we can only make predictions about novel phenomena if we know all the other solutions and their predictions for the same phenomena. This is a crucial change in comparison to the state of the art about ten years ago: with 1020 solutions (the largest number anyone may have expected), if one is found that agrees with all current data, the probability that there is a second one is extremely small. With 10500, the same probability is astronomical. So we should forget about the idea of finding the Standard Model and then making predictions based on it.

    As for LHC predictions, Schellekens argues against the idea that it will see supersymmetry:

    One could say that supersymmetry is a non-solution to a non-problem: the large weak scale hierarchy is already understood anthropically, and supersymmetry by itself does not even explain it…

    With the start of the LHC just months away (at least, I hope so), this is more or less the last moment to make a prediction. Will low energy supersymmetry be found or not? I am convinced that without the strange coincidence of the gauge coupling convergence, many people (including myself) would bet against it. It just seems to have been hiding itself too well, and it creates the need for new fine-tunings that are not even anthropic (and hence more serious than the one supersymmetry is supposed to solve). But even if evidence for low energy supersymmetry emerges at the LHC, in the context of a landscape it will not be the explanation for the smallness of the weak scale. The explanation will in any case be anthropic. The landscape will undoubtedly allow a distribution of values for the weak scale, including values outside the anthropic window.

    Schellekens ends up making the currently fashionable argument that it doesn’t matter that string theory doesn’t predict anything testable about particle theory, that the important thing is that it is a theory of quantum gravity:

    During the last two decades there was some reason to hope that we might be able to do that [get experimental confirmation of string theory] by means of some prediction of a Standard Model feature. That hope is fading now. I am not saying that this will never happen, but I have seen too much wishful thinking to make an optimistic statement about this. Essentially, we came to that conclusion already in 1986 [4]. We are dealing with a theory of gravity. Getting information about it through the back door of particle physics is a luxury that we once had good reasons to hope for, but that may not exist. Rejecting a theory of gravity that makes no particle physics prediction may be like rejecting the theory of continental drift because it does not predict the shape of Mount Everest

    He then goes on to acknowledge that we’re not going to get any experimental tests out of the quantum gravity aspect of string theory either:

    One cannot count on any direct experimental check of a theory of quantum gravity, since any observable consequences it might have are extremely small, unless we are extremely lucky.

    In the end, he seems to argue that the only evidence for string theory we may ever get is its consistency, something which is a very long ways from being shown. He does argue that string theory is in principle falsifiable, but the example he gives (that string theory would be wrong if coupling constants varied observably on astronomical scales) is not an uncontroversial one since other string theorists have argued that varying coupling constants would be evidence for string theory. There’s also the usual “who knows?” argument used against anyone who points out that evidence against an idea is overwhelming:

    On longer timescales, it is clearly ridiculous to pretend that what we currently know will be the state of the art forever. When Darwin formulated his theory of evolution he was unaware of Mendel’s results on inheritance, and could not even have imagined DNA.

    The truly peculiar thing about this is to see a scientist almost gleeful at the idea that a theory they have worked on their entire professional lives doesn’t predict anything:

    To me, what is emerging looks very appealing. It fulfills and even exceeds the hopes I expressed in 1998. It is has been amazing to see this theory leading us in the right direction, sometimes even against the initial expectations of most of the people working on it. We should continue to follow its lead, and do everything in our power to strengthen its theoretical underpinnings. The emergence of a huge landscape” makes this more worthwhile then ever before.

    Unfortunately, Schellekens is far from alone in this. At the FQXI web-site there’s an article about the string theory/cosmology couple Andrei Linde and Renata Kallosh entitled A Perfect Match (“How do you tie down the physics of the multiverse? With string.”) In it, Kallosh explains how “string cosmology” is now the hot topic:

    These days, in fact, collaboration be-tween string people and cosmology people is all the rage.
    “To give you a funny example, I had an invitation to give a talk at the Strings 2008 conference at CERN,” Kallosh says. “The way the invitation was writ-ten was, ‘Of course you are welcome to speak about any topic . . . but we would be very happy if you would give us a mini-review on string cosmology!’”

    Suddenly, everyone is interested in their kind of union.

    “I’m also working on other very formal, very stringy topics, which were always part of my skills,” Kallosh says. “But, at this moment, people want to know about string cosmology. I’m happily working on it . . . with Andrei’s help.”

    Cosmology is now ascendant, with Kallosh arguing that it will be needed to explain what is seen at the LHC:

    “Soon the LHC will start giving new information on particle physics,” she says. “But we know it will be difficult to interpret this data unless you also can digest all the data from the sky—all the observations from astrophysics and cosmology.”

    The article ends with a large picture of one of the LHC detectors, captioned “Cradle of Collaboration: Will the LHC provide evidence for string theory?”

    FQXI is funded by the Templeton Foundation, the goal of which is to bring science and religion together. Cormac O’Raifertaigh is at another Templeton funded event, a conference in Cambridge on From the Big Bang to the Brain: Current Issues in Science and Religion. This Wednesday will be devoted to cosmology, featuring talks on the anthropic principle, fine-tuning, God and time, and God and the Big Bang.

    For another take on cosmology, this October the ENS in Paris will host a conference on Evolution and Development of the Universe. For more about this parallel universe of cosmologists who also study anthropics and the multiverse , see EvoDevoUniverse.

    Posted in Multiverse Mania | 25 Comments