Sean Carroll

Author: Sean Carroll

  • Science! It Marches On

    The news from Geneva this morning is in. Essentials: what we’re seeing is pretty consistent with the existence of a Higgs boson around 123-126 GeV. The data aren’t nearly conclusive enough to say that it’s definitely there. But the LHC is purring along, and a year from now we’ll know a lot more.

    It’s like rushing to the tree on Christmas morning, ripping open a giant box, and finding a small note that says “Santa is on his way! Hang in there!” The LHC is real and Santa is not, but you know what I mean.

    Here are the technical write-ups from ATLAS and CMS. For stories and some live-blogs, check out Philip Gibbs, Matt Strassler, Aidan Randle-Conde, Ken Bloom, or Jester. Or if you just want the bottom line sigmas, Jim Rohlf provides them. ATLAS gives 3.6 sigma local significance, 2.3 sigma global significance; CMS gives 2.6 sigma local significance, 1.9 sigma global significance (although CMS points to about 124 GeV, while ATLAS points to about 126, which might be important). The difference between “local” and “global” is that the first asks “if I were only looking at this one point in parameter space, how surprising would the result be?”, while the latter asks “what is the chance I would find this kind of deviation somewhere in parameter space?” Nominally the global significance is obviously more relevant, although one could argue that we have good reasons to expect that the Higgs is actually lurking right there, so the local significance isn’t completely cheating.

    Let’s put it this way: if we were testing a theory that everyone thought was wrong, rather than one that everyone thinks is right, nobody would take these results as strong indications that the idea was correct. We have a strong theoretical bias that the Higgs exists and is somewhere close to this mass range, so it’s completely reasonable to think that we are seeing hints (tantalizing ones!) that it’s there, but wait-and-see is still the right attitude.

    Here are the simplest plots I could find. First the full analysis from ATLAS (zoomed in on the interesting region), via Philip Gibbs’s blog.:

    Then from CMS, via Ken Bloom:

    These plots are complicated because they’re trying to tell you two things at once. The black curve is the data, the green/yellow bands are the expected ranges of the data at 1 sigma and 2 sigma. If all you want to do is ask whether we can exclude the Higgs in a certain range, just check whether the black band is below the value 1. But if you want to say you have evidence for the Higgs, you need the black line to wander above the yellow band (or higher, if you want more than 2 sigma [and you do]). So ATLAS sees something at 126 GeV, CMS is at least consistent with 123-124 GeV (although it doesn’t see much at 126).

    As Sarah Kavassalis puts it, the real message today is that the LHC is working great. 2012 will bring another year of data, hopefully at even higher luminosity (so many more total events). The Higgs has been around for 13.7 billion years, it will still be there tomorrow.

  • Not Being Announced Tomorrow: Discovery of the Higgs Boson

    Tomorrow, Tuesday 13 December, there will be a couple of seminars at CERN presented by Fabiola Gianotti and Guido Tonelli, speaking respectively for the ATLAS and CMS collaborations at the LHC. They will be updating us on the current status of the search for the Higgs boson. The seminars will be webcast from CERN, and there should be a liveblog on Twitter that you can follow by searching for the #higgsliveblog hashtag (no Twitter account required). The seminars start at 14:00 Geneva time, so that’s 5:00 a.m. Pacific time if I do my calculations correctly. Of course there will be plenty of news coverage immediately thereafter, so don’t feel too bad if you sleep through it. Many places with LHC physicists (including Caltech) are also having their own local seminars. Should be exciting!

    If you want to know why it’s exciting, after you’ve read John’s description of life in the trenches and Matt Strassler’s post about the multiple stages of hunting the Higgs and mine about why we need something like it, see even more recent posts by Matt, Jester, and Pauline Gagnon. Reader’s Digest version: not only are we being updated on the status of the search, there are believable rumors that the searches are actually seeing something — hints of a Higgs near 125 GeV, with better than 3-sigma significance from ATLAS and better than 2-sigma significance from CMS. But obviously rumors are no match for what actually happens.

    All I’m here to tell you is: you should not expect to hear anyone announcing that we have discovered the Higgs boson. This will, at best, be a hint — “evidence for” something, not “discovery of” that thing. The collaborations realistically can’t claim to have actually discovered the Higgs, even if it’s there — they don’t have enough data. (CERN even issued a press release to drive home the point.) And in the real world, hints are sometimes misleading. That is: the experimenters will give us their absolute best judgment about what they are seeing, but at this stage of the game that judgment is necessarily extremely preliminary. If they say “we have 3.5-sigma evidence, which is quite suggestive,” do not think that they are just being coy and what they really mean is “oh, we know it’s there, we just have to follow the protocols.” The protocols are there for a reason! Mostly, that many 3-sigma findings eventually go away. This is one step on a journey, not the culmination of anything. (For Americans out there: it’s like a bill has been passed by the House, but not yet passed by the Senate, and certainly not signed by the President. Much can go wrong along the way.)

    The journey of a thousand miles begins with a single step. It’s possible that tomorrow’s announcement means that we’re nearing the end of the journey, say at the mile-990 marker. But we can’t be sure, and there are no royal roads to particle physics. Patience! The excitement of not knowing for sure is what makes science one of the most compelling human stories.

  • A Salon of Ideas

    Matt Strassler’s post prodded me to look back and notice something: we really have had quite an amazing collection of guest bloggers over the years. There is a page on the site dedicated to keeping track (as well as a category), but nobody every clicks there, so I thought I would just reproduce the list here. We have a few more in the pipeline, keep your eyes peeled!

  • Guest Post: Matt Strassler on Hunting for the Higgs

    Perhaps you’ve heard of the Higgs boson. Perhaps you’ve heard the phrase “desperately seeking” in this context. We need it, but so far we can’t find it. This all might change soon — there are seminars scheduled at CERN by both of the big LHC collaborations, to update us on their progress in looking for the Higgs, and there are rumors they might even bring us good news. You know what they say about rumors: sometimes they’re true, and sometimes they’re false.

    So we’re very happy to welcome a guest post by Matt Strassler, who is an expert particle theorist, to help explain what’s at stake and where the search for the Higgs might lead. Matt has made numerous important contributions, from phenomenology to string theory, and has recently launched the website Of Particular Significance, aimed at making modern particle physics accessible to a wide audience. Go there for a treasure trove of explanatory articles, growing at an impressive pace.

    ———————–

    After this year’s very successful run of the Large Hadron Collider (LHC), the world’s most powerful particle accelerator, a sense of great excitement is beginning to pervade the high-energy particle physics community. The search for the Higgs particle… or particles… or whatever appears in its place… has entered a crucial stage.

    We’re now deep into Phase 1 of this search, in which the LHC experiments ATLAS and CMS are looking for the simplest possible Higgs particle. This unadorned version of the Higgs particle is usually called the Standard Model Higgs, or “SM Higgs” for short. The end of Phase 1 looks to be at most a year away, and possibly much sooner. Within that time, either the SM Higgs will show up, or it will be ruled out once and for all, forcing an experimental search for more exotic types of Higgs particles. Either way, it’s a turning point in the history of our efforts to understand nature’s elementary laws.

    This moment has been a long time coming. I’ve been working as a scientist for over twenty years, and for a third decade before that I was reading layperson’s articles about particle physics, and attending public lectures by my predecessors. Even then, the Higgs particle was a profound mystery. Within the Standard Model (the equations that used at the LHC to describe all the particles and forces of nature we know about so far, along with the SM Higgs field and particle) it stood out as a bit different, a bit ad hoc, something not quite like the others. It has always been widely suspected that the full story might be more complicated. Already in the 1970s and 1980s there were speculative variants of the Standard Model’s equations containing several types of Higgs particles, and other versions with a more complicated Higgs field and no Higgs particle — with a key role of the Higgs particle being played by other new particles and forces.

    But everyone also knew this: you could not simply take the equations of the Standard Model, strip the Higgs particle out, and put nothing back in its place. The resulting equations would not form a complete theory; they would be self-inconsistent. (more…)

  • On Determinism

    Back in 1814, Pierre-Simon Laplace was mulling over the implications of Newtonian mechanics, and realized something profound. If there were a vast intelligence — since dubbed Laplace’s Demon — that knew the exact state of the universe at any one moment, and knew all the laws of physics, and had arbitrarily large computational capacity, it could both predict the future and reconstruct the past with perfect accuracy. While this is a straightforward consequence of Newton’s theory, it seems to conflict with our intuitive notion of free will. Even if there is no such demon, presumably there is some particular state of the universe, which implies that the future is fixed by the present. What room, then, for free choice? What’s surprising is that we still don’t have a consensus answer to this question. Subsequent developments, most relevantly in the probabilistic nature of predictions in quantum mechanics, have muddied the waters more than clarifying them.

    Massimo Pigliucci has written a primer for skeptics of determinism, in part spurred by reading (and taking issue with) Alex Rosenberg’s new book The Atheist’s Guide to Reality, which I mentioned here. And Jerry Coyne responds, mostly to say that none of this amounts to “free will” over and above the laws of physics. (Which is true, even if, as I’ll mention below, quantum indeterminacy can propagate upward to classical behavior.) I wanted to give my own two cents, partly as a physicist and partly as a guy who just can’t resist giving his two cents.

    Echoing Massimo’s structure, here are some talking points:

    * There are probably many notions of what determinism means, but let’s distinguish two. The crucial thing is that the universe can be divided up into different moments of time. (The division will generally be highly non-unique, but that’s okay.) Then we can call “global determinism” the claim that, if we know the exact state of the whole universe at one time, the future and past are completely determined. But we can also define “local determinism” to be the claim that, if we know the exact state of some part of the universe at one time, the future and past of a certain region of the universe (the “domain of dependence”) is completely determined. Both are reasonable and relevant.

    * It makes sense to be interested, as Massimo seems to be, in whether or not the one true correct ultimate set of laws of physics are deterministic or not. (more…)

  • Horological Concept Video of the Day

    Mechanical watches have a complicated history. The first pocketwatch appeared in the early 1500’s, and they became popular fashion accessories long before they were very good at telling time. The idea of putting a watch on a strap and wrapping it around your wrist was very slow to catch on, and it wasn’t until the idea became popular among pilots and military personnel (for whom functionality trumped fashion preference) that wristwatches really took off. The course of the 20th century witnessed the rise of finely crafted mechanical wristwatches (especially Swiss) as both indicators of status and genuine works of technological art.

    This all came crashing down with the quartz crisis of the 1970’s, when Seiko and other companies started to produce electronic timepieces that were both much cheaper and more reliable than mechanicals. For the kids today, of course, with their smartphones and iThings, wristwatches are seemingly going the way of the cassette tape. The Swiss watchmaking industry nearly collapsed, before the surviving companies were able to re-position themselves by appealing to horological connoisseurs and elitist yuppies who would like to think they are.

    As someone who thinks about time as a full-time occupation (as well as a bit of an elitist yuppie myself), it was inevitable that I would become fascinated by watches. I don’t have nearly the financial wherewithal to splurge on the latest masterpieces out of Geneva, and my watch-snob credentials are ruined by the fact that I don’t mind wearing a well-designed quartz. But there’s a fascinating little sub-culture there, which you can experience at the WatchUSeek or TimeZone watch forums.

    A reasonable argument could be made that we the Golden Age of mechanical watches is right now. As a luxury niche market, watchmakers at the high end have some freedom to experiment and innovate. There are some hits and some misses, of course. At some point I may find the time and energy to post something substantive about watchmaking, but right now I’ll just offer up this cool video for the Urwerk UR-110. (If you can find one for under $80,000, consider it a bargain.) It features a clever design in which a series of rotating barrels display the hour, and move by a dial on the side to indicate the minutes. There’s no attempt to explain what’s going on — this is pure glitz. Still — pretty compelling glitz.

  • Interdisciplinarity

    Zachary Ernst, a philosopher at the University of Missouri, has written up an aggravating tale of sexism in academia. (Via New APPS. I initially mistakenly said Ernst was at the University of Wisconsin, which is where he went to grad school — fixed by commenters.) A woman philosopher in his department — who happened to be his wife — was denied tenure. It’s always hard to discern the influence of sexism in individual cases, but he was able to directly compare what his wife was forced to go through to his own experience in the same process. I have no way of judging the merits of the tenure case (and the opportunity for bias in this kind of report is clear, and clearly acknowledged), but the differences in standards seem to be pretty clear.

    But I wanted to highlight this bit, because it makes a different point that I have touched on before. [Update: in the comments, Andrew Melnyk (who I gather was the department chair being quoted) offers a different recollection of this conversation.]

    While I was still an assistant professor, I had published in several different areas – I had papers in ethics, action theory, game theory, logic, and philosophy of science. The chair of my department was unhappy about this, and he told me so. He said, quite explicitly, that it would be very difficult for me to get tenure with such research breadth. This may sound unbelievable to someone outside of academia, but his reasoning was quite sound. Tenure decisions were made largely based on whether the faculty member had developed a reputation in the field. And it is easier to do that if you repeatedly publish in the same narrow subset of the academic literature. Spreading myself around too much, I was told, might result in my having failed to achieve a reputation. At the time I had this conversation, I had two distinct feelings. On the one hand, I felt that this was totally absurd – how can the ability to publish in several distinct areas be considered a liability? But on the other hand, I had to admit that he was right, and that this was good advice.

    The reality is that everyone likes breadth and interdisciplinarity in theory, but the resistance in practice is considerable. A university is a bureaucracy, and a bureaucracy is made of slots, into which people are fit. We know what slots we like, and are suspicious when people or ideas don’t fit into the slots. Note that Ernst wasn’t exactly straying way off the reservation, dabbling in aeronautical engineering or Medieval prosody; he was doing technical work in philosophy, just in more than one different area. To an outsider it might be hard to discern any difference at all, but within a department this is taken as a lack of seriousness.

    One could certainly imagine an unapologetic defense of narrow interdisciplinary categories for their own sake; research proceeds fastest when attention is focused on depth rather than breadth, something like that. But this defense is very rarely explicitly articulated; the department chair in the above quote was just more candid than usual. (And he wasn’t trying to defend the state of affairs, just making sure it was understood.)

    For those of us who do think interdisciplinary work is useful, it’s hard to know exactly how to change things. The problem is structural; universities are divided into departments, each with their own carefully-guarded boundaries, and strict sub-categorizations within the department itself. (Everyone loves biophysics, but people who actually try to do biophysics within either biology departments or physics departments inevitably encounter stumbling blocks.) Some specific institutions can be populated by individuals who respect boundary-crossing and even encourage it, and of course there will always be ornery researchers who do it despite any obstacles that are thrown their way. But it would be nice to have more reliable and institutional ways of encouraging good work for its own sake, rather than only because it fulfills a narrow ideal of what work counts as valuable. From the comments at New APPS, here’s news of an interesting attempt along these lines at USC. It would be good to see other universities consider similar strategies.

  • The Amorphous Menace Creeps Forward

    We here at Cosmic Variance have long been warning of the coming robot menace. Not only are they gaining consciousness, they keep developing new and creepy ways to move. Along those lines, here’s a new robot from Harvard that looks like an innocent piece of plastic, but is actually a silent ninja with a variety of interesting gaits. (Via Mariette DiChristina’s Twitter.)

    Soft Robot Walking and Crawling

    Researchers at George Whiteside’s lab explain that the idea came from observing squid and worms. Well, that’s comforting.

  • Thanksgiving

    This year we give thanks for a concept that has been particularly useful in recent times: the error bar. (We’ve previously given thanks for the Standard Model Lagrangian, Hubble’s Law, the Spin-Statistics Theorem, conservation of momentum, and effective field theory.)

    Error bars are a simple and convenient way to characterize the expected uncertainty in a measurement, or for that matter the expected accuracy of a prediction. In a wide variety of circumstances (though certainly not always), we can characterize uncertainties by a normal distribution — the bell curve made famous by Gauss. Sometimes the measurements are a little bigger than the true value, sometimes they’re a little smaller. The nice thing about a normal distribution is that it is fully specified by just two numbers — the central value, which tells you where it peaks, and the standard deviation, which tells you how wide it is. The simplest way of thinking about an error bar is as our best guess at the standard deviation of what the underlying distribution of our measurement would be if everything were going right. Things might go wrong, of course, and your neutrinos might arrive early; but that’s not the error bar’s fault.

    Now, there’s much more going on beneath the hood, as any scientist (or statistician!) worth their salt would be happy to explain. Sometimes the underlying distribution is not expected to be normal. Sometimes there are systematic errors. Are you sure you want the standard deviation, or perhaps the standard error? What are the error bars on your error bars?

    While these are important issues, we’re in a holiday mood and aren’t trying to be so picky. What we’re celebrating is not the concept of statistical uncertainty, but the elegant shortcut provided by the concept of the error bar. Sure, many things can be going on, and ultimately we want to be more careful; nevertheless, there’s no question that the ability to sum up our rough degree of precision in a single number is enormously useful. That’s the genius of the error bar: it lets you decide at a glance whether a result is possibly worth believing or not. The power spectrum of the cosmic microwave background is a pretty plot, but it only becomes convincing when we see the error bars. Then you have a right to go, “Aha, I see three peaks there!”

    And the error bar isn’t just pretty, it provides some quantitative oomph. An error bar is basically the standard deviation — “sigma,” as the scientists like to call it. So if your distribution really is normal you know that an individual measurement should be within one sigma of the expected value about 68% of the time; within two sigma 95% of the time, and within three sigma 99.7% of the time. So if you’re not within three sigma, you begin to think your expectation was wrong — something fishy is going on. (Like maybe a Nobel-prize-worthy discovery?) Once you’re out at five sigma, you’re outside the 99.9999% range — in normal human experience, that’s pretty unlikely.

    Error bars aren’t the last word on statistical significance, they’re the first word. But we can all be thankful that so much meaning can be compressed into one little quantity.

  • Brutality

    You’ve probably heard that protestors at Occupy UC Davis were pepper-sprayed by police during a non-violent protest. (It’s very likely that you have heard but it hasn’t registered, as there have been many similar events nationwide and it’s hard to keep track.)

    After the incident, UC Davis police chief, Annette Spicuzza, had this to say:

    “There was no way out of that circle. They were cutting the officers off from their support. It’s a very volatile situation.”

    Imagine in your mind the kind of “volatile situation” to which this description might apply. Now here’s the picture:

    Having never been pepper-sprayed, I have no idea what it’s like, although it doesn’t seem pleasant. But these protestors can take some solace in the idea that this kind of display will bring more support to their movement than a million chanted slogans. The police were obviously badly trained, but the ultimate responsibility lies with UC Davis Chancellor Linda Kaheti, who ordered them in. It’s a horrifying demonstration of what happens when authority is unchecked and out of touch. I’m not sure where the propensity of local authorities to call in police dressed like Storm Troopers started, but it has to end. This isn’t what our country is supposed to be about.

    Here’s the video:

    Police pepper spraying and arresting students at UC Davis

    Update: On the question of since when are all protests met with police in riot gear freely dispensing pepper spray, Alexis Madrigal has researched the answer, which is: since the 1999 WTO/anti-globalization protests. Apparently police training is not flexible enough to accommodate the fact that different situations call for different responses.