Has Dark Matter Finally Been Detected?

Posted on December 17, 2009 by woit

No.

The CDMS experiment today reported the observation of two events, with an expected background of .8 events (I gather this is a 1.5 sigma result, but there is no arXiv preprint yet). Based on this, the Guardian reports that “Hunt may well be over for mysterious and invisible substance that accounts for three-quarters of mass of universe” and Science News has Experiment Detects Particles of Dark Matter, Maybe. Science News quotes Craig Hogan as saying the results are “potentially very exciting”, and the Guardian has “If they have a real signal, it’s a seriously big deal.” Unfortunately they don’t have a real signal, so it’s not a seriously big deal.

I just noticed that the New York Times is also covering this, but more soberly, describing the results as “faint hints”. They do quote Gordy Kane, who describes the mood at the KITP in Santa Barbara as “a high level of serious hysteria”, which he then embodies by claiming “It seems likely it is dark matter detection, but no proof.”

For those unfamiliar with the terminology experimentalists use to characterize signals of various statistical significance, here’s a summary:

5 sigma: discovery

3 sigma: observation

1.5 sigma: noise

Update: Scientific American gets it right here.

Update: The paper is here. It includes the information that “Reducing the revised expected surface-event background to 0.4 events would remove both candidates.” There really literally is no signal here.

Update: Ethan Siegel’s blog posting about this explains the appropriate scientific response to the news that two events were observed when .8 were expected:

Well, La-dee Frickin’ Dah!

Adrian Cho at Science has an excellent piece about the story: Wimpy Evidence for Dark Matter Particles. He quotes two experimentalists who explain the significance of this (Richard Gaitskell: “Nobody should be attempting to say that this is evidence” for dark matter, and Edward Thorndike: “Absolutely not” an observation of dark matter). There’s also this comment from theorist Joseph Lykken:

Even so, Joseph Lykken, a theorist at Fermilab, says he’s relieved that CDMS has finally seen something. WIMPs are predicted to exist by theories involving a principle called supersymmetry, which posits a heavy partner for every particle currently known. Had CDMS continued to see nothing, the results would have undermined those theories. So seeing something is better than seeing nothing, Lykken says.

Lykken seems to be ignoring the fact that the new CDMS results, two events and all, rule out yet more of the supersymmetry parameter space. For an explanation of this, written when the last CDMS results came out, already causing problems for supersymmetry, see Tommaso Dorigo’s posting SUSY more unlikely by the new CDMS II results.

Posted in Experimental HEP News | 44 Comments

2010 LHC Schedule

Posted on December 17, 2009 by woit

The LHC shut down yesterday for an end-of-year break after a very successful initial period of beam commissioning at beam energies of 450 GeV and 1.18 TeV. Tomorrow at CERN there will be public reports about the state of the LHC and the initial results from the experiments. I gather that by now all sorts of particles have been rediscovered, including kaons and lambdas, here are some details from Jim Pivarski.

There’s now a tentative schedule 2010 out. Hardware commissioning of the new quench protection system, allowing beam energies up to 3.5 TeV, will begin on January 4, and be completed by February 15. A new checkout to prepare for beam commissioning will take place Feb. 17-19, and next injection of a beam into the LHC should be around February 20. Commissioning of 3.5 TeV beams and some pilot physics runs at that energy should take a month or so, with the first regular physics runs at 3.5 TeV/beam beginning around March 25. A tentative month-long shutdown to reconfigure the machine to run at higher energy (up to 5 TeV/beam) is scheduled for May 3-June 2.

From January 25-29 machine experts will meet in Chamonix to discuss whether to try and run at 5 TeV/beam in 2010, and how to implement this if it seems feasible. Plans will also be made for the late 2010-2011 shutdown. This will require deciding what to do about all the problematic splices in the machine in order to allow operation at the design energy of 7 TeV/beam, as well as understanding how much retraining of the dipoles will be needed in order to get to that energy. Current plans call for a “long shutdown” in 2013-4 to begin some upgrades of the LHC, and this is another topic that will be discussed.

While news coverage of the LHC in science magazines like Science News has been a mixed bag, often focussing on extra-dimensional speculation irrelevant to the actual science that will get done there, there’s a quite good new article here, in a surprising location: Vanity Fair. The LHC has become a real celebrity…

Posted in Experimental HEP News | 6 Comments

Life in the Multiverse

Posted on December 17, 2009 by woit

The latest Scientific American features a cover story on Life in the Multiverse: Could the strange physics of other worlds breed life? The magazine earlier this year fired a third of its staff and replaced its editor (the new editor has a column this month about the Multiverse and Star Trek).

I don’t think one can blame the new editor for this though. Over the last few years, Scientific American has made multiverse pseudo-science stories a staple of its coverage of science. See for instance Parallel Universes, The String Theory Landscape, The Great Cosmic Roller-Coaster Ride and Does Time Run Backwards in Other Universes?

Update: Alejandro Jenkins and Gilad Perez, the authors of the Scientific American piece, pointed out to me something that I really should have made clear in this posting, that their arguments about the possible implications of a multiverse are of a different nature than those in previous Sci Am articles. They are arguing not for or against a multiverse, but against some popular anthropic arguments that try and explain the values of fundamental constants as being necessary for life. Anyway, my apologies to them for not making this clear, and here’s something they sent me explaining in more detail their point of view:

The title of our article in the current issue of Scientific American –as well the first bullet for the “Key Concepts” — might give the impression that our work argues for the reality of the multiverse, but this isn’t really the case.

Our research suggests skepticism about the usefulness of anthropic selection arguments when applied to particle physics (see the references below). The anthropic argument seems reasonably convincing when applied exclusively to the cosmological constant, as Weinberg did in 1987. But our own work shows that the parameters of the strong and weak interactions could be significantly different from what they are, without there being any obvious obstruction to the evolution of organic life. This means that the anthropic principle might not be enough to explain the microscopic laws of particle physics. In this sense, then, our story counter-balances the claims made previously by other experts about many of the parameters of the Standard Model being obviously “fine-tuned for life” (and therefore admitting an anthropic explanation).

Our work is simply based on varying the parameters of the Standard Model and trying to understand how things would change from what we see in our world. It is true, though, that this intellectual exercise is motivated in part by the expectation from inflationary models (and from certain speculative proposals for the physics at the Planck scale) that the fundamental physics might produce many distinct universes besides our own.

Posted in Multiverse Mania | 4 Comments

String Theory and Heaven

Posted on December 16, 2009 by woit

I hadn’t heard much about Dinesh D’Souza since the Reagan era when for some mysterious reason his views were widely promoted in the media. He has continued since then to play the role (supposedly according to the New York Times Magazine) of “one of America’s most influential conservative thinkers.” His last book was The Enemy at Home: The Cultural Left and its Responsibility for 9/11, and he has a new one out called Life After Death: The Evidence. In a recent magazine interview he explains the main thesis of the book, that string theory has vindicated Christian theology by proving the existence of heaven and hell (they’re out there in the multiverse somewhere).

How might science explain heaven and hell as places that could exist?

Scientists now posit through string theory the presence of multiple realms, multiple dimensions. One of the implications of the big bang is that space and time had a beginning, and that space and time are properties of our universe. If that’s true, then outside our universe or beyond our universe, there would be different laws of space and time, or no space and no time.

The idea that our universe may not be the only one and that there may be other universes operating according to different laws is now coming into the mainstream of modern physics. So the Christian concept of eternity, which is God outside of space and time, is rendered completely intelligible. It opens up possibilities that would have seemed far-fetched even for science fiction a century ago.

Update: Here’s the link to the interview: String Theory and Heaven.

Posted in Uncategorized | 30 Comments

Various and Sundry

Posted on December 13, 2009 by woit
  • The proof of the fundamental lemma by Ngo has made it onto Time magazine’s list of the top ten scientific discoveries of 2009. Ngo will be visiting Columbia in the near future, and I might even end up understanding what this is about. He’s giving the Ritt lectures here later this week, and will be Eilenberg visiting professor for the Spring 2010 term, giving a series of weekly lectures.
  • The collaborative work on the Density Hales-Jewett theorem initiated by Timothy Gowers on his blog has made it into today’s New York Times magazine’s survey of the “Annual Year in Ideas”.
  • Tony Zee’s book Quantum Field Theory in a Nutshell will be coming out in a second edition next year, featuring some new material covering recent advances in computing scattering amplitudes in gauge theory. The new preface is available here and has some interesting comments from Zee about the book and about QFT books in general. It also contains a response to those Amazon reviewers described as “nuts who do not appreciate the Nutshell“. I suggest that Zee get a blog, it gives one an excellent way to respond to nuts who misunderstand and don’t appreciate one’s book…
  • Last weekend there was a meeting held at Rutgers in memory of I. M. Gelfand, with some materials available here.
  • A couple weeks ago there was a very good article in Science magazine by Adrian Cho about recent discussions of the possibility of a muon collider. Since muons are much heavier than electrons, one can in principle use a storage ring to collide them without the problem of synchrotron radiation loss that limits the energy of electron-positron rings to the LEP energy scale. The fact that muons are unstable and decay fairly quickly is a huge problem. Besides making it difficult to use the “cooling” techniques needed to produce a usable beam intensity, the decay products create a very challenging environment for a detector to operate in, as well as producing neutrino intensities so high they are capable of causing problematic levels of radiation wherever they emerge from the earth.
  • C. J. Mozzochi has a page here with links to many of his wonderful photographs of mathematicians, mostly in action at various conferences or lecture series.

    • Update: One more. Last night I watched a spectacularly bad Sci-Fi movie, Annihilation Earth, brought to the world by the Syfy channel. I don’t think it’s a movie that really can be spoiled for you, so here’s a plot synopsis: three supercolliders in Geneva, Orleans and Barcelona are providing power for Western Europe. Scientists who designed them realized that in a certain configuration the critics were right, and the Higgs field would get out of control and form a black hole that would destroy the earth. Evil Arab terrorists hack into one of them and reconfigure it to self-destruct. The remaining two are all that is keeping the Higgs field from expanding exponentially and causing the black hole that will annihilate everything. One of the scientists refuses to believe the other when he explains this to him, because of the color of his skin and the fact that he’s an Arab too (although he doesn’t look it). So, in the final scene he shuts down one of the remaining super-colliders and the Earth is annihilated. I guess the film-makers should be congratulated on this innovation in sci-fi film-making, ending the film with the scientists not saving the Earth but destroying it.

    Posted in Uncategorized | 20 Comments

    News From the LHC

    Posted on December 8, 2009 by woit

    Just saw this from Tommaso Dorigo, which made me realize that I should get to work and write a blog posting before the CERN press office people wake up. The big news today is that the first collisions at a record energy higher than that of the Tevatron have occurred, marking a first step into new territory past what has been the energy frontier in HEP for a very long time. Two beams of two bunches each were successfully ramped up to 1.18 TeV, and although one of the beams was lost after a while, before that point some collisions at a total energy of 2.36 TeV were observed. An event display from ATLAS is here.

    Over the next few days, the main objective of the beam commissioning team is to try and increase the intensity per bunch and provide a large number of collisions at 450 GeV/beam to the experiments. They’ll also continue tests in which they ramp up the energy to 1.18 TeV/beam, and if all goes well should be able to provide the experiments with an equally large number of collisions at that energy. The experimenters are gleeful about finally having real data to play with. CMS has publicly announced the re-discovery of the pi-zero, and I assume that by now they’re working their way through the 1950s, already rediscovering kaons and other particles with strange quarks. If they manage to get a significant amount of data at 2.36 TeV, there must be some sort of cross-section they can measure at an energy that just beats out the Tevatron, although with this size of a collision sample, it won’t be one that anyone cares much about…

    Beam commissioning work for 2009 should end on December 16, and the accelerator complex will be shut down over the holidays, re-starting January 4. During January the LHC will go back into hardware commissioning mode, with a month-long plan to commission the new quench protection system in all sectors, allowing operation at 3.5 TeV/beam. The injectors are supposed to restart on February 5, LHC beam commissioning restarting on February 8. The way things have been going, they may have at least some 7 TeV collisions happening quite quickly after that.

    Update: This morning again a pair of 1.18 TeV beams were stored and brought into collision at the LHC. This time CMS as well as ATLAS is publicly saying that collisions were seen, with event displays here. CERN’s twitter feed is saying over a million collisions at 900 GeV, 50,000 at 2.36 TeV. Still no press release from CERN gloating about how they now are doing physics at higher energy than Fermilab.

    Posted in Experimental HEP News | 9 Comments

    Spreading Wild Rumors

    Posted on December 7, 2009 by woit

    One effect of Nature’s embargo policy is to encourage the spread of wild rumors. It’s almost part of the mission statement of this blog to participate in this, so I feel I must link to this.

    Update: Nature unequivocally denies that they will be publishing a CDMS paper on the 18th. The collaboration does plan to reveal the results of their latest run on that date. The wild rumor that they have seen WIMPS and will reveal all on the 18th remains in force…

    Update: There’s now a statement on the CDMS web-site, saying that there will be two talks on December 17, and plans to submit a paper to the arXiv before the talks.

    Posted in Uncategorized | 7 Comments

    A Black Future

    Posted on December 5, 2009 by woit

    Tom Siegfried, the editor of Science News, seems to have decided to join with Michio Kaku in the science-fiction as science business. He marks the startup of collisions at the LHC with A Black Future, an article about how “the Large Hadron Collider might help humans explore the cosmos”. Here “exploring the cosmos” doesn’t mean understanding how the cosmos works, it means building an interstellar spaceship to travel across it.

    The argument seems to be that the LHC will produce black holes, and a recent paper by Crane and Westmoreland suggests that black holes can be used to power a space-ship. Siegfried somehow manages to drag Steven Weinberg and supersymmetry into this, with a claim I don’t understand that the Crane-Westmoreland idea “may be realistic only if cosmic physics incorporates a mathematical framework known as supersymmetry.”

    Posted in This Week's Hype | 19 Comments

    50 Years of Nobel Memories in High Energy Physics

    Posted on December 4, 2009 by woit

    Over the past two days, CERN has been hosting a program consisting mostly of talks by Nobel prize winners in high energy physics, under the title 50 Years of Nobel Memories in High Energy Physics. It has been a while since anything Nobel Prize worthy has been discovered in HEP, so the speakers of necessity are all getting on a bit in years. The talks pretty much all seem worth paying attention to. Many of them are now on-line, and of the few I’ve had a chance to look at, the comments by Burt Richter about the ILC/CLIC issue were notable, as well as Veltman’s explanation of the possible significance of not finding a Higgs.

    I started watching the webcast towards the end of David Gross’s talk, in time to hear him give his usual praiseworthy defense of physics against anthropic pseudo-science. Weinberg’s talk by video-conference was unfortunately cut short, since he thought it would be an hour long, but it was just scheduled for half an hour.

    CERN DG Heuer ended the program by thanking everyone, and looking forward to the first run of LHC collisions at reasonable intensity with the detector magnets on (although only at 450 GeV), which is now scheduled for Saturday.

    Update: Videos of the talks are now available here and I’ve watched a few of them. One interesting thing I noticed was Frank Wilczek’s talk about QCD, where his response to a question about AdS/CFT was “I’m not as impressed as I should be.”

    Posted in Uncategorized | 19 Comments

    Sci-Fi Science

    Posted on December 2, 2009 by woit

    I watched the first two episodes of Michio Kaku’s Sci-Fi Science show last night (for a review, see here). The format of the show is that Kaku uses supposedly real physics to design on his laptop a revolutionary new device, then unveils it at the end of the show to a group of sci-fi fans for what I guess is supposed to be a form of peer review. The adoring fans are suitably impressed. In the first episode the device was a warp drive, in the second a portal to other universes, based on a big accelerator and “negative matter”. In both cases “negative energy” played a big part.

    Neither episode involved a non-negligible amount of legitimate science, instead treating the physics in a completely misleading way. The second episode included participation by Max Tegmark, Alan Guth and Neil Turok. I wonder if they’ve seen the final product and what they think of it.

    Posted in Uncategorized | 49 Comments