Latest From the LHC

Posted on June 9, 2009 by woit

Last week was the annual Fermilab User’s Meeting, for all sorts of interesting talks see here. These included a talk by Sergio Bertolucci giving recent news about the LHC status. This week CERN is hosting a CERN-Fermilab Hadron Collider Physics summer school, talks here, including one from Jorg Wenninger about the LHC status.

The main concern now involves bad soldering of some of the 1700 or so bus-bar inter-connections between magnets. One of these seems to have been at the origin of the accident last September. For the sectors (four of them) that are warm, such bad joints can be identified relatively easily, by their higher-than-normal resistance, and repaired. Unfortunately, for the four sectors that are now cold, identifying such bad splices is much more difficult. Warming up these sectors and cooling them back down is a time-consuming process that could significantly push back the LHC schedule.

Late last week the decision was made to start warming up sector 45. Measurements at 80K had identified 3 cases of anomalously high resistance. The plan is to warm up the sector, take measurements which can be compared to the measurements made when the sector was cool, and fix splices as necessary. For this particular sector, things can be rearranged so that warming it up and cooling it back down will not seriously impact the schedule.

For the other three cold sectors though, the situation remains unclear. They’re gathering more data and analyzing it, trying to understand better what is going on, as well as analyzing the question of whether it’s possible to go ahead and find ways to run the machine safely, even given the possible existence of somewhat iffy interconnections.

The latest version of the schedule, from mid-last week, has powering tests ending in mid-October. So, as long as it does not turn out to be necessary to warm up more sectors, late October is the time-frame for trying again to circulate a beam and begin beam commissioning.

Update: There’s a video of Wenninger’s talk last week available here, where he gave some more details in the question session afterwards. Sector 45 will be warm and ready for measurements next Monday (June 22). If the results show good correlation with what was measured at 80K, at the end of the month the temperature of the three remaining sectors will be stabilized at 80K and measurements will be made on those.

About the current schedule for when to try and circulate a beam, he says “I know that officially it’s still September [last week] but I have problems to sell that…” with a better guess of sometime in October (assuming the three sectors at issue don’t need to be warmed up). He also remarks that it will be a while (2012?) if ever before the machine operates at 7 TeV. 5 TeV is the likely energy at the beginning, with a possibility of going up to 6 TeV.

Posted in Experimental HEP News | 17 Comments

String Universality

Posted on June 7, 2009 by woit

There’s a new paper out on the arXiv this evening, advertising a new concept called “string universality”. The authors argue that in six dimensions, by use of appropriate compactifications, any consistent 6d supergravity theory has a string theory realization. They go on to conjecture that the same might be true in four dimensions. As for the implications of “string universality”, they write:

If it is correct, or even close to correct, that string universality holds in six dimensions, then in this case we seem in some sense to be in the worst possible situation vis a vis low-energy predictions. If every possible consistent theory can be identified from low-energy considerations, and all of these theories can be realized in string theory, then string theory would seem to have no predictive power for low-energy physics…

Not being able to predict anything sounds bad for string theory. But wait, they go on to explain why not only is this not a deadly problem, it’s actually a “strength of the theory”. You see, there’s “symmetry and elegance” to a principle that is consistent with absolutely everything and constrains nothing. Some worrywarts might have problems with such a principle since it can’t be tested, but, just because something can’t be tested doesn’t mean it’s not right, no?

This may seem like a very awkward situation for string theory. It should be emphasized, however, that there is no reason a priori why a theory of quantum gravity relevant at the Planck scale of 1019 GeV should make any prediction for physics at the scale of 1 TeV, 16 orders of magnitude below the quantum gravity scale. String theory is valuable as a framework for describing quantum gravity. If in fact, string theory can be used to provide a UV completion of essentially any low-energy theory whose coupling to quantum gravity does not violate some basic principle like unitary via anomalies, this can be seen as a strength of the theory. There is a certain symmetry and elegance about the notion of a quantum gravity theory which provides for the production of essentially all possible low-energy behaviors in some regime of the theory or region of the metaverse.

If indeed, string theory can give rise to such a wide range of low-energy behavior that predictions at the TeV scale cannot be made precisely, it may bother some scientists that this makes the theory difficult to test. But, on the other hand, this does not make the theory any less likely to be correct. It just makes it more difficult to verify.

Posted in Multiverse Mania | 28 Comments

Multiverse News

Posted on June 1, 2009 by woit

Some items from around the multiverse:

  • Srednicki and Hartle have a new preprint on hep-th about Science in a Very Large Universe. Like many other multiverse papers, it doesn’t really have any equations in it, so it’s a bit hard to figure out what their argument is. Maybe readers can figure it out from the conclusion:

    It is no surprise that information about us is required to make predictions for our observations. Our data suggest that we are located some 13.7Gyr from a Big Bang. To make a reliable prediction from that information, we have to assume that it describes our physical situation. If the universe is rife with delusion, we must assume that we are atypical in order to have predictive and testable scientific theories. Indeed, it is only by making such assumptions that we are able to do science in a very large universe. We imagine that even Copernicus would have agreed that it was necessary to assume that Ptolemy was not deluded in his observations of the planets.

    The authors thank about a dozen or so other theorists for their help with this.

  • World Science Festival 2008 here in New York was a huge success, and I suspect that the 2009 version starting June 10 will be too, which is great. Of the many events, one where I might have a difference of opinion with some of the panelists will be a session on Infinite Worlds: A Journey through Parallel Universes, sponsored by the Templeton Foundation.
  • Seed magazine had a story a couple months ago about the theological implications of the multiverse.
  • Astrophysicist Jeffrey Zweerink has a book out called Who’s Afraid of the Multiverse?
  • Over at FQXI there’s a recent blog entry discussing the question of whether God might be “unsure as to whether He is really just a brain floating in a vat?”
  • Somehow I missed this one last year. Wheaton College held a research symposium on String Theory and the Multiverse: Philosophical and Theological Implications.

    • Update: For a more skeptical and philosophical take on the multiverse, there’s The Unique Universe, a piece by Lee Smolin that just came out in the latest Physics World.

    Update: The proceedings of the Wheaton College conference on string theory, the Multiverse and theology are available here. They include audio recordings of the discussions, and inform us that string theory

    implies that physical reality is far vaster and possesses greater grandeur than ever imagined.

    Posted in Multiverse Mania | 37 Comments

    LHC: status and commissioning plans

    Posted on June 1, 2009 by woit

    The LHC’s Mike Lamont has just posted a preprint here based on a recent Moriond talk describing the current status of the LHC commissioning. Here is his discussion of the on-going campaign to identify bad splices and figure out what to do about them. From it, I gather that the big unanswered question is what to do about possible bad splices in sectors that have been cooled down, since warming up the sectors would significantly delay the scheduled startup.

    One additional danger that has recently surfaced is a bad electrical contact between the copper of the busbar and the U-profile of the splice insert on at least one side of the joint. Combined with a bad contact between the cable and the copper this leaves the splice without an alternate route for the current in the case of a busbar quench – in a good splice the current can flow in the copper removing the danger of excessive resistive heating in the quenched superconductor. A good contact between the Rutherford cable joint is assumed (i.e. less that 2 nano-ohm).

    Such situation can be detected by measurements at warm using low current and a nanovoltmeter across short segments of the machine. Under such circumstances the current flows in the copper and the resistance of a good joint is around 12 micro-ohm. Extensive measurements of the four warm sectors (May 2009) have revealed 16 segments with excess resistance of over 30 micro-ohm. The relevant interconnects have been opened. Individual splice measurements have revealed resistances of 30 – 50 micro-ohms. All such splices have been re-done and re-measured.

    Warm quadrupole measurements started in May 2009. Measurements at at 80 K in sector 23 are also ongoing at this time. The measurements at 80 K are more difficult and show a lot more signal variation – the resistivity of copper falls by a factor of 7.5 at this temperature. The question of what to do if suspect splices are found at this stage of re-commissioning is to be addressed.

    Posted in Experimental HEP News | Comments Off on LHC: status and commissioning plans

    The Music of the Superstrings

    Posted on June 1, 2009 by woit

    String theorist Oswaldo Zapata continues (see here for an earlier posting about this) his remarkable series of essays about string theory and how it came to dominate research in theoretical high energy physics. The latest one, entitled The Music of the Superstrings is about the metaphorical use of classical music to promote superstring theory, and it concludes:

    Metaphors are powerful rhetorical tools. But, at the same time, they are much more than that. Indeed, when used astutely, that is, when anchored in deep shared meanings and aspirations, they can create an enthusiastic army of supporters to the discourse displayed. This has been one of the strongest weapons of string theorists in the battle for the control of future research in high energy theoretical physics.

    Zapata examines how and why string theorists have chosen to advertise string theory to the public by claiming a deep connection to music, especially to classical music. He recalls the many ways this analogy has been promoted by many different string theorists, from Brian Greene, who has made it a prominent part of his popular explanations of the theory, to Edward Witten, who told an interviewer in 1988:

    In the case of a violin string, the different harmonics correspond to different sounds. In the case of superstring, the different harmonics correspond to different elementary particles.

    I’ve always found this kind of thing grating, for a reason that Zapata doesn’t address. Statements like Witten’s give people the impression that the known fundamental particles of nature somehow correspond to the harmonics produced by vibration of a string. This is rather misleading, since all known particles correspond to the lowest energy state of the string. The quantum states corresponding to “harmonics” of a string are all supposed to be at unobservably high energy. The way the theory is sold to the public, via the musical metaphor that electrons and muons are different “harmonics” of a string vibrating at different frequencies makes it seem that such particles can be matched to the characteristic behavior of the harmonics of a string-like mechanical system, which is simply not true.

    Zapata also now has a Reactions page, where he has posted links to commentary about his essays, as well as some comments from Bert Schroer in a recent preprint.

    Posted in Uncategorized | 22 Comments

    Interview With Simons and Yang

    Posted on June 1, 2009 by woit

    Steve Miller pointed me to a fascinating interview with Jim Simons and C. N. Yang, available on YouTube here.

    Simons tells the story of how he got kicked out of his job at the IDA in 1968 over his opposition to the Vietnam War, and ended up at Stony Brook as chair of the math department there. He and Yang collaborated on raising money to support anti-war efforts.

    They describe how Yang went to Simons to try and find out about fiber bundles and what they might have to do with gauge theory. Simons started by referring Yang to Steenrod’s The Topology of Fibre Bundles, which Yang couldn’t make any sense of (Simons admits he never made it all the way through the book himself). This did in the end lead Simons and Yang to some real understanding of how vector potentials in gauge theory and connections on bundles were the same thing, with monopoles examples of topologically non-trivial bundles. Simons lectured at Stony Brook in 1975 on this, and a paper later that year by Wu and Yang included what became known as the “Wu-Yang dictionary” relating terminology in gauge theory and geometry. Singer learned about this soon thereafter when he visited Stony Brook, and went on to spread the news to Oxford, MIT and elsewhere.

    Simons also describes what is going on with plans for the new Simons Center for Geometry and Physics, including some of the thinking that led him to decide to support this. The official ground-breaking ceremony for the new building there was held last week, you can follow construction progress here.

    Posted in Uncategorized | 6 Comments

    No Landscape and No Math in Rome

    Posted on May 29, 2009 by woit

    Strings 2009 is about three weeks away, and it will bring 450 or so string theorists to Rome. The topics of the talks at the Strings 200x conferences give a good idea of what the hot topics in the field are, and this year’s talk titles are now available. What’s big this year are scattering amplitudes, as well as the usual AdS5/CFT4 topics, supplemented by the more recently popular AdS4/CFT3. As far as phenomenology goes, the hot topic is definitely local F-theory models, with three separate talks on the subject.

    One topic that is not hot is anything mathematical, with no research talks by mathematicians or Witten, and little about mathematically significant topics such as mirror symmetry. What also seems to no longer be hot is either string cosmology or the landscape. No cosmology, multiverse or Boltzmann Brains are to be found among the research talks, although Brian Greene will give a public lecture about the issue of possible multiple universes.

    Posted in Uncategorized | 5 Comments

    Role Reversal

    Posted on May 29, 2009 by woit

    It used to be that New Scientist had somewhat of a reputation for publishing misleading articles about speculative physics, and Science News was a more stodgy but reliable publication that stuck to serious physics. Recently there has been a role reversal. New Scientist is running a long, relatively sensible article about the use of AdS/CFT methods in condensed matter physics, entitled What string theory is really good for. It avoids the usual “String theory finally makes predictions!” hype that some string theorists have been trying to promote. Science News on the other hand, is now being run by Tom Siegfried, who is quite a fan of string theory hype, the more speculative the better. Last month was Strings Fight Back at Science News, this week it’s multiverse madness, with a cover story on Infinity, which promotes the latest multiverse/Boltzmann Brain pseudo-science. Towards the end of the article, David Gross is allowed a few words as skeptic, arguing that we don’t understand string theory, so can’t be sure it leads to this mess: maybe some missing insight will get string theorists out of it. Siegfried responds with the thought that the “missing insight is merely realizing the need to master the inconveniences of infinity to resolve the cosmic conundrums.”

    Update: The New Scientist article makes it to Slashdot where, as usual, it gets transformed into nonsense:

    His [Maldacena’s] theory states that the known universe is only a 2D construct in anti-de-Sitter space, projected into 3 dimensions.

    Posted in Multiverse Mania, This Week's Hype | 2 Comments

    Singer Birthday Conference

    Posted on May 28, 2009 by woit

    Last weekend I was up in Cambridge attending the conference in honor of Is Singer’s 85th birthday. Singer has had a very long and distinguished career in mathematics, much of it at MIT, where he arrived as one of the first Moore instructors back in 1950. Besides a wide range of purely mathematical contributions, Singer was responsible for bringing together mathematicians (including Atiyah) and physicists starting back in 1976, at first around questions related to instantons. He has run a joint physics and mathematics seminar for about a quarter century, at Berkeley while he was there, then back at MIT. Unfortunately, this past year will have been the last year of the seminar, partly due to Singer’s imminent retirement, partly due to a shift in the interests of Boston area physicists towards phenomenology and away from mathematics.

    Jim Simons, an old friend and student of Singer’s, played an important role at the conference, as master of ceremonies at the dinner, and as a financial backer. Back in 1975 it was his lectures to physicists at Stony Brook that got Yang and ultimately Singer interested in the question of the relation of gauge theory to geometry.

    While in Cambridge, I picked up a copy of a new book, Recountings, which has interviews with many MIT mathematicians (including Singer), and does a good job of portraying the history of the MIT math department over the past 50 years or so.

    Of the conference talks I managed to get to, probably the best was that of Mike Hopkins, who gave a blackboard talk about the Kervaire invariant problem. This one was a lot more accessible than his talk last month at the Atiyah80 conference, where he unveiled his dramatic new results with Hill and Ravenel (more about this story here). In the MIT talk, Hopkins concentrated on explaining the background and significance of the problem, as well as giving some of the philosophy of the proof, which uses what he describes as a “designer” cohomology theory.

    Some quick notes on a few of the other talks that I made it to:

  • Atiyah described some of the history of how Singer got him interested in physics, then went on to promote a very speculative idea about a non-local version of the Dirac equation.
  • I can’t say that I really understood Polyakov’s talk, but it was along the lines of this.
  • Cumrum Vafa talked about his local F-theory models and attempts to understand the hierarchy of particle masses this way.
  • Michael Douglas gave a rather odd blackboard talk: no equations, no math, just pretty much straight promotional material about the philosophy of the landscape.
  • Richard Kadison mostly reminisced about working with Singer, leading into a description of what is known as the Kadison-Singer problem.
  • Greg Moore talked about work with Dan Freed and Jacques Distler. You can see their versions of the talk here and here.
  • Wati Taylor gave another landscape talk, similar to the one discussed here.
  • Orlando Alvarez gave a talk about work with Paul Windey, based on this paper.
    • Posted in Uncategorized | 7 Comments

    Latest on the LHC

    Posted on May 28, 2009 by woit

    The Resonaances blog has a report from Planck 2009 on a talk about the status of the LHC. The slides of the talk explain the problems with training quenches that have necessitated initially running the machine at 5 TeV per beam instead of the 7 TeV design energy. They also explain the analysis of what caused the accident last September: bad soldering of the interconnections between copper bus-bars connecting the magnets.

    There has been an ongoing campaign to check the quality of the interconnections by careful measurements of the resistance, with slide 44 noting:

  • Ongoing race to identify and repair faulty joints.
  • Unfortunately poor quality joints are localized in many places – likely to slow down progress with the machine re-commissioning.

    • It remains unclear exactly how many joints will have to be opened up and repaired, and what impact that will have on the re-commissioning schedule. While this remains to be decided, the latest draft schedule I’ve seen has about 1-2 weeks of slippage from the current official schedule, with powering tests on all sectors not finished until the first week of October, whereas the official schedule now envisages first circulating beam the week of September 21. The Planck 2009 talk just says “Beam commissioning scheduled to resume in September or October 2009”.

    For some misinformation about the LHC schedule, see here.

    Posted in Experimental HEP News | 4 Comments