Cocktail Party Physics

freeze frame

I've been known to poke fun occasionally at the high technical level of the supposedly "general" press conferences organized at APS meetings -- and because the folks who organize them have been my colleagues for more than 10 years, they're very good-natured about enduring my teasing comments. Alternatively, when a press conference hits the ball out of the park, it's only fair that I give credit where credit is due. The three physicists who showed up in the press room at the APS April meeting in Jacksonville on Monday afternoon to talk about the experimental results from MiniBooNE -- officially announced the week before -- hit an unqualified home run. That press conference has become my new gold standard for just how good scientific communication with the press can be.

For those who find the vast array of clever acronyms for esoteric physics experiments confusing, MiniBooNE is short for Mini Booster Neutrino Experiment -- mini because they reduced the number of detectors originally planned from two to one. It's housed at Fermilab, and the centerpiece of the equipment is a stunning array of photodetectors just crying out for a closeup (hence the photo). As high-energy experiments go, it's pretty much just like every other particle collision, barring a few tweaks here and there. A bunch of protons smash into a fixed target, thereby creating a horde of scattered mesons, which last for fractions of a second before decaying into a bunch of neutrinos (of the muon variety; more on this below). The detector, about 500 meters away, picks up the telltale "signatures" of these decay patterns and records them. The subsequent analysis is all-important, because it's easy to confuse the signatures of the events of interest with background noise or an entirely different kind of event altogether.

The above is a pretty straightforward description of the nature of the experiment itself, provided one has a bit of scientific background. It's less informative for someone who hasn't been following the epic Tale of the Neutrino over the years it's been unfolding. I think one of the reasons why MiniBooNE's results have been (to date) mostly discussed among scientists and what one might call the "science trade press" -- which these days includes the scientific blogosphere -- is that it's really tough to sum up exactly what the project was testing and why, in a short and snappy sound bite. And mainstream media, like it or not, is all about the snappy sound bite.

For starters, you've got to define neutrinos, and establish where they fit in the Standard Model of particle physics -- which, depending on how savvy your audience is, might involve defining the Standard Model, too. Then you've got to describe the experiment, how it was set up, and what it found. Finally, you've got to drive home the implications of those results in clear, concise, and relatively jargon-free language. It's easier said than done, especially when you're dealing with a fairly arcane topic like neutrinos, but Janet Conrad, Eric Zimmerman, and Heather Ray (who also wrote an excellent guest post over at Cosmic Variance last week outlining the more technical details from the MiniBooNE experiment) pulled off that nifty hat trick with ease.

First, that all-important definition: Neutrinos are tiny subatomic particles that travel very near the speed of light. Because it's still technically Poetry Month (or Week, or Nanosecond), we feel obliged to mention that John Updike’s 1959 poem, “Cosmic Gall,” pays tribute to the two most defining features of neutrinos: they have no charge and, until quite recently, physicists believed they had no mass. They are extremely difficult to detect, because they very rarely interact with any type of matter, even though they're the most abundant type of particle in the known universe. (They react solely through gravity or via the weak nuclear force, and the latter only kicks in at very short range distances at the atomic level.) Only one out of every 1,000 billion solar neutrinos would collide with an atom on its journey through the earth. Isaac Asimov dubbed them “ghost particles.”

There's a long, rich history filled with fascinating personalities and pivotal experiments concerning these tiny ghost particles, but to fully grasp the significance of what MiniBooNE found, you mostly need to know about neutrino oscillations. See, the current Standard Model posits three different kinds of neutrinos (electron, muon and tau); the most common are the solar (tau? I can never remember which is which) neutrinos that come from our own Sun -- specifically, the nuclear processes taking place at its core. When a neutron inside an atom decays, it produces a proton, an electron, and a neutrino. This occurs hundreds of billions of times every second in the core of stars like our sun, as hydrogen is converted into heavier elements like helium, releasing huge amounts of energy in the process (i.e., sunshine). Trillions of neutrinos are produced by the sun every day.

But for decades, experiment after experiment showed far fewer solar neutrinos than predicted by theory, and it wasn't until the Sudbury Neutrino Observatory announced its results a few years ago that physicists realized those neutrinos weren't really "missing," but were merely in disguise. Solar neutrinos are sneaky little particles: they can actually change into another kind of neutrino as they shoot through space on their way to Earth -- a phenomenon called “neutrino oscillation.” In the past I've employed the analogy of piano strings, which are tuned to specific notes: let’s say G, E and C (notes that comprise the C Major chord). Scientists previously assumed that if a neutrino was born as a G, it would always be a G. But neutrinos can “de-tune” over time, just like the strings on a piano. So a G can gradually become a E, or a C.

It's an admittedly overly broad, imperfect analogy that misses some of the more intriguing subtleties of neutrino oscillations, namely, that the oscillations happen precisely because neutrinos have the tiniest bit of mass. So I was pleased when, at the APS press conference, Janet Conrad came up with a nifty device to illustrate how a small amount of mass can affect neutrinos. She brought in a couple of tuning forks, tuned to the same frequency, except one had a tiny bit of mass added to one of its tines. Then she struck one, then the other, producing a "wah-wah-wah" kind of sound. (The reporter from German Public Radio was thrilled, because that's the kind of thing that's just made for radio.)

It was an excellent demonstration. Like most elementary particles, neutrinos also have a wavelike nature, and waves oscillate back and forth. Add two waves together and you get a new composite wave. And when two very similar notes are played together, there's an interference effect that causes the sound to wobble between loud and soft, producing "beats." Similarly, oscillating neutrinos are comprised of three different waves that combine in different ways as they travel through space. The "beats" are caused by small physical differences in mass that lead to those telltale interference effects. Except neutrinos aren't supposed to have mass. If, indeed, neutrinos oscillate -- as seems to be the case, per experimental results from Japan's  Super-Kamiokande collaboration announced in 1998 -- then they are not the massless particles assumed by the Standard Model. (This doesn't mean the entire Standard Model is wrong, mind you, just that it's imperfect and incomplete -- which we already knew.)

So okay, we've defined neutrinos and their place in particle physics theory, and we've described one of their key properties, this ability to oscillate back and forth between three different species. About 10 years ago, an experiment at Los Alamos threw another unexpected wrinkle into the mix: the possibility of a fourth kind of neutrino, a "sterile" neutrino that would only interact through gravity (apparently the weak nuclear force just isn't good enough for a sterile neutrino, which has a very high opinion of itself). This totally throws off the neat symmetry of the Standard Model, so it was a Very Big Deal (VBD) in particle physics, especially since the level of observed oscillations suggested very different values for neutrino masses than those inferred from prior studies of solar neutrinos and other accelerator-based experiments. MiniBooNE was conceived to test the results of that earlier Liquid Scintillator Neutrino Detector (LSND) experiment. Replicate the same findings, and you'd have solid, experimental confirmation of a fourth kind of neutrino, ergo, potentially exciting new physics beyond the Standard Model.

Of course, once you collect the data, you've got to be able to interpret it correctly, and also ensure that the resulting analysis is free from bias. Now, I'm one of those people who can quickly become catatonic in the face of detailed discussions of data analysis methods, particularly when it comes to the complexities of accelerator data. It doesn't help that said data is usually conveyed in grainy, hard-to-read charts with blurred data points . MiniBooNE's official data chart seems to be a model of clarity in that respect (or maybe it's my new glasses); it's pretty straightforward.

And it's to Heather Ray's considerable credit that not only did I stay awake during her entire presentation, but I was genuinely interested in the unusual approach they used to guard against bias when analyzing MiniBooNE's data. They took a "blind box" approach, meaning that as they were collecting the neutrino data, they didn't even look at any of the data in the "region of interest" (they had a pretty good idea where those telltale oscillation signatures were likely to be from the recorded LSND results). They didn't "unblind" the data and open the box until three weeks before the official announcement. Talk about pressure! But it does ensure against involuntarily tweaking the data points to fit one's expectations.

And what did they find at the great unveiling? There was no telltale oscillation signature, contradicting the LSND findings from 1995. So MiniBooNE's results pretty much rule out that fourth sterile neutrino, thereby verifying the current Standard Model with its three low-mass neutrino species. But it wasn't quite a slam-dunk; a new anomaly presented itself. There were some electron neutrino events detected at low neutrino energies, which means more experiments are needed, this time using a beam of anti-neutrinos. It's a tiny subset of the overall data, but physicists are very detail-oriented, and that tiny bit of data must be explained and accounted for.

This post turned out to be much longer and technically detailed than I'd intended. If you're not feeling a bit mentally muddled right about now, you're probably a physicist. Neutrinos are a tough topic to cover in the general public arena. That's why it's so important to present these kinds of results in the appropriate context, or -- dare I say it? -- framework. I've stayed out of the ongoing "Framing War" in the science blogosphere -- framing is the new "F" word; use it today! -- mostly because there's very little I could add to what's already been said. I'm pretty "pro-framing," though. I've been doing it instinctively for much of my science writing career, without even realizing there was a bona fide term for it. So I know that framing is not the equivalent of "spin", does not require a squelching of "truth," and that, when done properly, it is a powerful tool for communicating scientific research to the general public, and (one hopes) fostering more appreciation for the fact that science is as much a central part of our culture as art, music, or literature.

What is an effective press conference, after all, if not a successful framing of the research result du jour? A month ago, at the APS March Meeting in Denver, I attended a press conference on the latest research on metamaterials, a.k.a., "left-handed materials," because they have a negative index of refraction. It's a cool topic, especially the "superlensing" achieved by Purdue University's Vladimir Shalaev. But the reporters struggled mightily to make sense of the jargon-laded technical presentation; the speaker pretty much showed the same material as he did during his session talk -- an entirely different audience, comprised of his peers. Only during the Q&A did he strike gold, when asked for an analogy that might explain why left-handed materials are so special. He said (and I paraphrase): "Imagine if you dropped a pebble in a pond and the ripples traveled inward instead of outward.... it's just not something that happens in nature."

Bingo! Metaphorical light bulbs lit up in the brains of the assembled reporters. He should have opened with that analogy, thereby providing a solid context for the elaborate technical detail that followed. Compare that rather muddled approach to the simple, well-ordered clarity of the MiniBooNE press conference, with its nifty live demonstration of oscillating effects and carefully structured framework to make sense of a complicated scientific topic. If you were a frazzled journalist on a tight deadline, which press conference would you rather attend? That's the real power of framing.

cosmic convergence

I'm going to indulge my inner Fangrrl for a moment and wax nostalgic over one of my favorite scenes in the now-canceled TV series Angel (for those not in the know, it was a spin-off of the also tragically canceled Buffy the Vampire Slayer). Every Reformed-Vampire-Seeks-Redemption-By-Saving-the-World series should have a resident physicist, and in the case of Angel, it's Winifred Burkle, known simply as "Fred." In an episode entitled "Supersymmetry," Fred gets a paper on string compactification published in a scientific journal and is asked to speak at a symposium on string theory at a fictional southern California university. There are two other speakers on the program: real-life physicists Edward Witten and Brian Greene, whom she excitedly describes to her clueless cohorts as the "Sammy Sosa and Nomar Garciaparra" of theoretical physics.

It's always gratifying to see physics seep into the broader culture-at-large, but I admit, I was a wee bit disappointed that the episode didn't feature actual cameo appearances by Witten and Greene. 'S'okay, I rebounded; it's a hard truth that no self-respecting physicist would deliberately appear on a show about soulful vampires and a pending Apocalypse, however intelligently written. (Sniffs Jen-Luc, "Really, what would the other physicists think?") I'm a grown-up (most of the time). I can handle the occasional puncture in my great big balloon of wishful thinking.

But sometimes the universe throws you a bone. I moseyed on down to Capitol Hill this afternoon to hear Brian Greene give a talk on string theory to Congressional staffers, representatives, and the random policy wonk. Who else should be in the audience? Ed Witten! Talk about a cosmic convergence!

Of course, this is hardly the first time Witten and Greene have been in the same room together, but it was the first time they'd inhabited the same room in our presence. We basked in the self-referential, pop-culture, "Life Imitates Art", sheer fabulousness of the moment, even if we were the only ones who deemed the convergence significant. Jen-Luc Piquant even dug out her tiara to mark the occasion, especially since we were also rubbing elbows with the likes of Neal Lane, Michael Turner, Ray Orbach, and the only two physicists currently serving in Congress, Rush Holt and Vern Ehlers. (This being Washington, Ehlers got more applause than Witten; no disrespect to Ehlers, but the situation would almost certainly have been reversed at a scientific meeting.) Had Buffyverse creator Joss Whedon been on hand as well, our joy would have been complete, but it seems his invitation got lost in the mail. (We console ourselves with the newly acquired knowledge that The Physics of the Buffyverse, my forthcoming book, has hit the radar of the fine folks at Whedonesque.com -- another kind of cosmic convergence.)

Any time I attend an organized event on the Hill, the first question that pops into my brain is, "Okay, what are they selling?" Because there is almost always an Ulterior Motive, and therefore a corresponding need to Stay On Message. If one is lucky, lunch is provided, or at least a tasty snack, to help take the edge off the propaganda. Washington is a city devoid of pure, unadulterated altruism, although pockets of genuinely good intentions can be found here and there. If we were being 100% honest, we'd admit that there is no such thing as a purely unselfish motive in human nature, period. (We are reminded in particular of an episode of Friends, in which Phoebe sets out to do something truly unselfish, but her acts of generosity make her feel good about herself, thereby reducing it to a selfish act.)

There was ostensibly no ulterior motive to having Greene speak, other than for general outreach purposes to Congress; in fact, the event had been delayed from earlier in the year due to scheduling conflicts. But the timing couldn't have been more fortuitous, coming as it did on the heels of the recently released report of the National Academies' Committee on Elementary Particle Physics in the 21st Century (a.k.a., EPP2010).  So much has been written about this, both in the mainstream media and in the blogosphere, that I won't even attempt an accurate synopsis. Far more educated minds than mine have already done so, such as Joanne Hewett and Clifford Johnson over at Cosmic Variance. Suffice to say that Greene's comments were right in line with making the case for funding the next generation of particle accelerators, at a time when that support is desperately needed. Brookhaven and Jefferson Laboratory, for instance, barely dodged a bullet this past year before Congress restored planned funding cuts that would have shuttered one or both facilities -- at least temporarily.

Greene is always a delightful speaker, even when covering well-worn ground, and this afternoon was no exception. He deftly outlined the basics of Newtonian gravity, general relativity, quantum mechanics, and string theory, and -- more importantly, from my perspective -- provided that all-important contextual framework to illuminate how they all link together. And he wasn't above teasing his audience: he asked how many of us had heard of the Uncertainty Principle, and when nearly everyone raised their hands, he shot back, "And how many of you can honestly say you understand it?" The number of raised hands decreased by an order of magnitude.

Greene also provided an excellent answer to the inevitable question: why spend billions of taxpayer dollars to construct a gigantic facility to detect exotic things we can't even observe directly (e.g., the Higgs boson, sparticles, extra dimensions...), that have no immediate bearing on, say, rising gas prices, or how many downloaded episodes of Buffy we can fit on our 60 Gb iPods. And he did so via a story, namely, Einstein's persistence in developing general relativity over the course of 10 long years.

Newton's Principia may well be the most significant physics treatise that hardly anyone has read in full, certainly not in the original Latin. (Copernicus' De Revolutionibus runs a close second.) Newton's genius lay in mapping out the law of universal gravity so precisely, that we can use his fundamental equations to predict where a ball tossed in the air will land. But when it came to explaining how gravity actually works, the underlying mechanism, Newton copped out, declaring that he would leave this question to the consideration of the reader. Most of his readers didn't bother giving it much consideration, being content to just assume this was how the world worked, and leave it at that. Einstein was different. Einstein kept asking why, pushing the envelope further, and in the process, he revolutionized physics. Newton believed gravity was a force, one object exerting a pull on another by virtue of their respective masses. Einstein figured out how it worked: an object's mass warps the fabric of spacetime, and this makes us feel the effects of gravity. ("Some of us feel it more than others," Greene quipped.)

Most importantly, Einstein laid out a testable prediction that light would follow the curvature of spacetime, and this was borne out in 1919 by observations made during an eclipse. String theory is all about finding testable predictions these days, having suffered a bit of a backlash in the physics community. Those heady initial days of infatuation over the potential of string theory to unify the conflicting theories of general relativity and quantum mechanics inevitably gave way to a period of disillusionment as the initial promise began to fade. The big issue: how can you experimentally verify strings that are much too small to observe directly? Technological capability has not kept pace with theory, in that respect. Yet Greene and his fellow string theorists have nonetheless persevered, and judging by his comments this afternoon, Greene remains optimistic about the potential to test certain key aspects of string theory indirectly, via the nearly completed Large Hadron Collider in Switzerland and the proposed next-generation International Linear Collider (which many in the high energy physics community are lobbying to have built in the United States).

Of course, even if we manage to find the Higgs boson and uncover evidence for both sparticles and extra dimensions, it's almost a given that the answers will give rise to an entirely new crop of questions. And that's actually a good thing, if you're a physicist. Like Einstein 100 years ago, Greene hopes the scientific community won't be content to sit back on its laurels, but will keep asking those fundamental questions to push the envelope of scientific knowledge to the next "final frontier." It's a journey without a penultimate end; all the fun comes in the discoveries one makes along the way.

Just in case anyone missed the message, free preprint copies of the EPP2010 report were available to those in attendance, but while the fine folks at Cosmic Variance gamely slogged through all 100+ pages, I found a more broadly targeted brochure far more to my liking. It's called Discovering the Quantum Universe: The Role of Particle Colliders, and it is -- almost unbelievably, given the light creative touches sprinkled throughout, and the crystal-clear descriptions -- the product of a committee.

We love the whole notion of particle accelerators serving as "Einstein's telescope," looking so far back in time as to witness the very earliest moments of our universe. We love the dashes of humor, such as this line about the explosion of subatomic particles discovered in the 20th century: "Physicists were running out of Greek letters to name them all." And we love the "Postcards from the Terascale" motif  -- "Very warm here. Plan to explore for Higgs tomorrow." -- and the amusing marginalia. Jen-Luc was especially tickled by the fact that when physicists "suspect that the underlying theory for something is complex, they call it a 'moose.'" (If anyone can explain the origin of that particular jargon, we'd be delighted to hear about it.) And it still manages to make a strong, clear case for what the LHC and ILC can each bring to the particle physics table. Our compliments to the committee.