Blogs / Cosmic Variance

I had that somewhat rare experience two days ago, getting the message from Physical Review Letters that our paper had finally been published online. In our field it can take quite a long time to get a paper all the way to publication; this one took longer than usual…

The paper describes the results of our search for Higgs bosons predicted in supersymmetric theories, in the CDF experiment at Fermilab. Alas, we didn’t see any evidence for Higgs boson production, despite earlier hints that something might lurk in our sample, and so we were able to rule out some regions of supersymmetric parameter space. We first obtained a preliminary result from this analysis in late 2007. A group of us from Rutgers University, University of Valencia, and UC Davis all worked directly on it, within our several-hundred-member collaboration, using Tevatron data recorded up through mid-2007. Since then we’ve more than tripled our data sample, but this result stuck with the data sample on which it was based and has finally reached publication.

The analysis was the topic of the Ph.D. thesis of my student Cris Cuenca, who was formally a student of my former postdoc Juan Valls at University of Valencia. Cris was a visitor in our group at UC Davis, and I was effectively his thesis advisor. After we got the preliminary results, Cris focused on writing his thesis, eventually defending it in Valencia in April 2008. One nice effect of that was that I got to visit Valencia for the first time: what a fantastic city!

Once the thesis was done, it was clear we needed to publish the result formally. In fact, we should have been already writing the paper but as usual it’s hard to find time to get started on writing projects. Here is a place we could have saved some time, though…

Anyway, I wrote a draft after the birth of our son Ian in June 2008, while helping with baby care at home. In our collaboration there is a very formal review process before submitting a paper for publication. The spokespeople of the collaboration “godparents” who perform a full internal review of the analysis and the draft of the paper. Without naming names, we got some very knowledgeable godparents who asked us hard questions. Some of these questions took weeks to answer, because more data analysis had to be performed. And some of them led to even more questions. This review process is a good thing — it ensures that the quality of the final paper is very high, and that the result is correct to the best of our ability. In fact, in the course of the review process we found that there was a minor software bug, and we repeated the full end stage of the analysis. As it turned out, the bug had very little effect on the final result but we needed to be sure. (At present there are only unknown bugs in the analysis software!)

Whenever there is a change to an analysis like this, it needs to be re-approved in our physics analysis group meetings, with two presentations: a “pre-blessing”, and then a “blessing” two weeks later. (Hey, I’m not responsible for the pseudo-religious jargon used in this process…) This eventually happened in March 2008.

With the result final and the godparents happy with the paper draft, it was time for the general collaboration review. The collaboration gets two weeks to comment on each draft. Then the authors go through comment by comment and reply to the commenters, modifying the draft as needed. The godparents reviewed our replies and then we arrive at the next draft. This part of the process can take many weeks depending on how much time the authors have two devote to the paper. Once the final draft stage is reached, a “paper reading” is scheduled at the weekly general collaboration meeting. Following the presentation of the result, the collaboration has 48 hours before the paper is submitted to the journal. For us this happened, finally, in June of this year.

We heard back from PRL in late July, with blind referee comments to address. There then ensued a back-and-forth between us and the referees, answering questions, making changes to our submission, and eventually reaching agreement that the paper would be published in PRL. This happened a few weeks ago, and our paper has now appeared in what I think is still considered to be the most prestigious journal in our field, though Nature possibly tops it. (That might inspire a comment flame war but I hope not…)

Maybe this is an extreme example, and I certainly will endeavor to bring results to publication much more quickly in the future. (I always say that.) Certain results, if they are “hot”, can be published on a fast track in CDF, within weeks, but that is quite rare.

Many will, no doubt, argue that print media of almost every form is on the way out. Will this happen to print science journals? I do think there is a strong need for blindly refereed publication of scientific results, even though many scientists have reviewed these papers by the time they are submitted.

And clearly once the LHC experiments have physics results to publish, we will need a very rapid means of getting them into print. For any striking new discovery we’ll want to have a paper submitted for publication when we announce the result…this is in contrast to the case of not-very-striking results, where we announce the results at conferences first and publish later. The reason is that the experiments will try to establish scientific priority by publishing striking results before the other one does, but I have to wonder, in the modern age of electronic media and collaborations with thousands of members, whether simply announcing or presenting the the result in public doesn’t accomplish that anyway. If ATLAS says they see a resonance in muon pairs at 1.5 TeV mass and so does CMS, the same week, will we really say “ATLAS found it first” or “ATLAS was the one to discover it and CDF confirmed it?” I hope the science mainstream media don’t present such a thing that way…but more than that I just hope this is a problem we will actually face!

Lead paragraph from the Times Online UK about the latest LHC snafu:

The rehabilitation of the beleaguered Large Hadron Collider was on hold tonight after the failure of one of its powerful cooling units caused by an errant chunk of baguette.

This month’s issue of WIRED features a great story by Amy Wallace: “An Epidemic of Fear: How Panicked Parents Skipping Shots Endangers Us All.” It’s an overview of the anti-vaccination movement in the United States, a topic that should be very familiar to anyone who reads Discover’s baddest astronomer. At ScienceBlogs, Orac and Abel Pharmboy gives big thumbs-up to the article.

The anti-vaccination movement is a little weird — they claim that vaccines, which are universally credited with wiping out smallpox and polio and other bad things, are responsible for causing autism and diabetes and other also-bad things, all just to make a buck for pharmaceutical companies. The underlying motivation seems to be a combination of the conviction that things must happen for a reason — if a child develops autism, there must be an enemy to blame — and a general distrust of science and technology. Certainly the pro-science point of view is fairly unequivocal; like any medicine, vaccines should be used properly, but they have done great good for the world and there are very real dangers of increased risk for epidemics if enough children stop receiving them. Good for WIRED for taking on the issue and publishing an uncompromisingly pro-science piece on it.

But the anti-vax movement is more than just committed; they’re pretty darn virulent. And since the article came out, author Amy Wallace has been subject to all sorts of attacks. She’s been documenting them on her Twitter feed, which I encourage you to check out. Some lowlights:

It’s pretty horrifying stuff. But there is good news: Wallace also reports that the large majority of emails she has received were actually in favor of the piece, and expressed gratitude that she had written it. There are strong forces arrayed against science, but the truth is on our side, and a lot of people recognize it. It gives one a bit of hope.

Recent years have seen a notable increase in the number of successful TV shows with some sort of scientific component — Numbers, CSI, House, Bones, Lie to Me, Fringe, and so on. But there’s no doubt which network show has the most accurate science on TV; that would be the CBS comedy The Big Bang Theory.

And it’s not because the writers are all physics Ph.D.’s who have traded in equations and laboratories for a glamorous life in Hollywood. It’s because the Big Bang Theory is one of the very few shows to have a full-time science advisor: David Saltzberg, a particle physicist at UCLA. David confers with the writers, reads every script, provides complicated-looking equations for the white boards in Sheldon and Leonard’s apartment, and suggests the occasional physics joke.

And now David, encouraged by some of his well-meaning friends, is going to be explaining the science behind the show in his new blog:

• The Big Blog Theory

The show is a comedy, but the science here is completely serious — read about dark matter, quantum mechanics, monopoles, and all sorts of good stuff. I’m sure much of this was explained carefully in the original scripts, but landed on the cutting-room floor in interests of time.

The Big Bang Theory, of course, raises strong feelings among scientists. Right here at Discover, you can read both pro and anti feelings about the show. The complaints are mostly about the cheerful reliance on various stereotypes that we would just as soon see stamped out. All four of the main scientist characters are socially maladjusted guys; the one main non-scientist is a blonde woman with severe science-phobia.

I think the critique of sexism is mostly fair. In the real world, plenty of brilliant socially-maladjusted scientists are female! (To be fair, Penny represents the everyperson character to which the audience is supposed to relate; in almost every activity not related to science or technology, she is much more competent than the boys.) The critique that all these nerdy scientist characters somehow damage the image of science I find much less compelling — even though, in the real world, plenty of brilliant scientists aren’t socially maladjusted at all. It is, after all, a sitcom, not a public-service announcement; sitcoms get a lot of their mileage out of stereotypes. And as socially awkward as the scientist characters are, they are also portrayed as lovable and warm people at heart. Shows like this humanize science, and who knows what ten-year-old kid will see an episode and start thinking that physics is a career to which real people can actually aspire.

Now if we could just get across the idea that even young girls can aspire to these careers, we’d be getting someplace.

A recent essay in the New York Times by Dennis Overbye has managed to attract quite a bit of attention around the internets — most of it not very positive. It concerns a recent paper by Holger Nielsen and Masao Ninomiya (and some earlier work) discussing a seemingly crazy-sounding proposal — that we should randomly choose a card from a million-card deck and, on the basis of which card we get, decide whether to go forward with the Large Hadron Collider. Responses have ranged from eye-rolling and heavy sighs to cries of outrage, clutching at pearls, and grim warnings that the postmodernists have finally infiltrated the scientific/journalistic establishment, this could be the straw that breaks the back of the Enlightenment camel, and worse.

Since I am quoted (in a rather non-committal way) in the essay, it’s my responsibility to dig into the papers and report back. And my message is: relax! Western civilization will survive. The theory is undeniably crazy — but not crackpot, which is a distinction worth drawing. And an occasional fun essay about speculative science in the Times is not going to send us back to the Dark Ages, or even rank among the top ten thousand dangers along those lines.

The standard Newtonian way of thinking about the laws of physics is in terms of an initial-value problem. You specify the state of the system (positions and velocities) at one moment, then the laws of physics tell you how it will evolve into the future. But there is a completely equivalent alternative, which casts the laws of physics in terms of an action principle. In this formulation, we assign a number — the action — to every possible history of the system throughout time. (The choice of what action to assign is simply the choice of what laws of physics are operative.) Then the allowed histories, the ones that “obey the laws of physics,” are those for which the action is the smallest. That’s the “principle of least action,” and it’s a standard undergraduate exercise to show that it’s utterly equivalent to the initial-value formulation of dynamics.

In quantum mechanics, as you may have heard, things change a tiny bit. Instead of only allowing histories that minimize the action, quantum mechanics (as reformulated by Feynman) tells us to add up the contributions from every possible history, but give larger weight to those with smaller actions. In effect, we blur out the allowed trajectories around the one with absolutely smallest action.

Nielsen and Ninomiya (NN) pull an absolutely speculative idea out of their hats: they ask us to consider what would happen if the action were a complex number, rather than just a real number. Then there would be an imaginary part of the action, in addition to the real part. (This is the square-root-of-minus-one sense of “imaginary,” not the LSD-hallucination sense of “imaginary.”) No real justification — or if there is, it’s sufficiently lost in the mists that I can’t discern it from the recent papers. That’s okay; it’s just the traditional hypothesis-testing that has served science well for a few centuries now. Propose an idea, see where it leads, toss it out if it conflicts with the data, build on it if it seems promising. We don’t know all the laws of physics, so there’s no reason to stand pat.

NN argue that the effect of the imaginary action is to highly suppress the probabilities associated with certain trajectories, even if those trajectories minimize the real action. But it does so in a way that appears nonlocal in spacetime — it’s really the entire trajectory through time that seems to matter, not just what is happening in our local neighborhood. That’s a crucial difference between their version of quantum mechanics and the conventional formulation. But it’s not completely bizarre or unprecedented. Plenty of hints we have about quantum gravity indicate that it really is nonlocal. More prosaically, in everyday statistical mechanics we don’t assign equal weight to every possible trajectory consistent with our current knowledge of the universe; by hypothesis, we only allow those trajectories that have a low entropy in the past. (As readers of this blog should well know by now; and if you don’t, I have a book you should definitely read.)

To make progress with this idea, you have to make a choice for what the imaginary part of the action is supposed to be. Here, in the eyes of this not-quite-expert, NN seem to cheat a little bit. They basically want the imaginary action to look very similar to the real action, but it turns out that this choice is naively ruled out. So they jump through some hoops until they get a more palatable choice of model, with the property that it is basically impotent except where the Higgs boson is concerned. (The Higgs, as a fundamental scalar, interacts differently than other particles, so this isn’t completely ad hoc — just a little bit.) Because they are not actually crackpots, they even admit what they’re doing — in their own words, “Our model with an imaginary part of the action begins with a series of not completely convincing, but still suggestive, assumptions.”

Having invoked the tooth fairy twice — contemplating an imaginary part of the action, then choosing its form so as to only be relevant where the Higgs is concerned — they consider consequences. Remember that the effect of the imaginary action is non-local in time — it depends on what happens throughout the history of the universe, not just here and now. In particular, given their assumptions, it provides a large suppression to any history in which large numbers of Higgs bosons are produced, even if they won’t be produced until some time in the future.

(more…)

Oddly addicting…a million views and rising!

The Sloan Digital Sky Survey is one of the most ambitious and successful astronomical surveys ever performed. It has left an impact far and wide, ranging from asteroids to cosmology. As Sean has mentioned, the SDSS would have been impossible without optical fibers and CCDs, and this year’s Nobel Prize in Physics acknowledges the development of these technologies. The SDSS would also have been impossible without Jim Gunn.

President Obama yesterday conferred The National Medal of Science to Jim Gunn, as well as 8 other scientists. This is our nation’s highest scientific honor. It is a clear demonstration that our society values science, and acknowledges its contributions; even though this may not always be apparent in the squabbling on Capitol Hill, or on school boards “debating” evolution. Once a year scientists take pride of place, and are officially thanked by a grateful Nation. As usual, Obama unleashes his eloquence:

So this nation owes all of you an enormous debt of gratitude far greater than any medal can bestow. And we recognize your contributions, but we also celebrate the incredible contributions of the scientific endeavor itself. We see the promise — not just for our economy but for our health and well-being — in the human capacity for creativity and ingenuity. And we are reminded of the power of free and open inquiry, which is not only at the heart of all of your work, but at the heart of this experiment we call America.
…
there are those who say we can’t afford to invest in science, that it’s a luxury at a moment defined by necessities. I could not disagree more. Science is more essential for our prosperity, our security, and our health, and our way of life than it has ever been. And the winners we are recognizing only underscore that point, with achievements in physics and medicine, computer science and cognitive science, energy technology and biotechnology. We need to ensure that we are encouraging the next generation of discoveries — and the next generation of discoverers.

Full transcript here. Jim Gunn was honored “for his brilliant design of many of the most influential telescopes and instruments in astronomy, and in particular for the crucial role those technological marvels played in the creation of the Sloan Digital Sky Survey, which has cataloged 200 million stars, galaxies, and quasars; discovered the most distant known quasars; and probed the epoch of formation of the first stars and galaxies.”

Sitting in the audience were members of the administration, including Steve Chu (Secretary of Energy) and John Holdren (Science Advisor), widely respected scientists in their own right. Seeing them gathered with Obama, celebrating science, is a hopeful image. There is a perception that scientists are losing the goodwill amassed in the last Century, and are now thought of as just another interest group. But we need science to address many of the world’s most pressing challenges. We need young people to be inspired, and to want to become scientists. Occasions like this remind us that science, and scientists, will play a crucial role in our future.

The Institute for Complex Adaptive Matter has released a new online museum, The Emergent Universe. This is, I think a truly novel approach to communicating the central ideas of the new field of emergent phenomena and complexity, combining the underlying physical basis of a wide array of examples with art and music. The site itself presents an animated, non-directed interface to branching sets of topics and what I guess one would call exhibits (since it’s a museum after all). A lot of these are quite fun, and instructive. A visitor is left with the feeling that there is lots more to explore. The interface itself, I have to say, is very cool and a glimpse of what is to come on the internet. Today’s text- and photo-heavy web pages are bound to give way to sleek sophisticated designs like this one…

Have fun!

It is a truth universally acknowledged that a provocative scientific idea will, before too long, end up in the hands of villains that must be fought by superheroes. Witness Boltzmann brains. Sure, they’ve already made a cameo in Dilbert, but the stakes were pretty low. Now Jim Kakalios (author of the excellent The Physics of Superheroes) sends along sends along a couple of snippets from The Incredible Hercules #133 — in which our intrepid protagonists are attacked by freak observers fluctuated out of thermal equilibrium!

Actually here they are described as “freaky observers,” rather than the more conventional “freak observers.” That description brings to mind Smoove B rather than Ludwig Boltzmann, but who knows? Maybe unlikely thermal fluctuations tend to be pretty kinky.

And yes, before you all start in: we know that Boltzmann Brains don’t really make for a credible alien menace, if you insist on being persnickety about what they supposedly really represent. It’s not that they “perceive” a universe more chaotic than ours — it’s that they would dominate the total number of observers if the universe really were more chaotic than ours. (Which it isn’t!) Also, they would tend to dissolve back into the chaos from which they came, rather than staging a coordinated attack on our homeland. Still! What a novel challenge for the Allies’ greatest hero.

Over the last couple of months I’ve been working on a new project with an undergraduate student and a postdoc. I’m not really ready to talk about the details yet, but one thing that became clear during our work was that we would understand the results of our numerical solutions much better if we had a movie of them. This is pretty standard these days and (particularly when you have a smart, motivated and fast student) one can obtain quite sophisticated animated solutions that allow one to develop a feeling for rather unintuitive results.

Having said this, I must confess that my own research isn’t one of the areas of science that typically lends itself to spectacular and artistic visualization. And I’m always therefore a little jealous of those people whose results allow dramatic representations.

A number of these are being featured in Wired’s Best Science Visualization Videos of 2009. These are drawn from across all of science and what they all have in common, aside from their usefulness in their respective fields, is their great beauty.

The closest one of these to my own area is the quite stunning movie of the simulation of a type Ia supernova explosion, credited to Brad Gallagher, George Jordan, Dean Townsley, Robert Fisher, Nathan Hearn, Jim Truan and Don Lamb.

A good theoretical description of these objects is certainly fascinating astrophysics in its own right. However, as we’ve discussed many times on this blog, it is also an important step in understanding how, and the extent to which, type Ia supernovae can serve as standardizable candles, with which we may track the expansion history of the universe. The current understanding of this has been enough to discover the fact that the universe is accelerating, but our future plans are to exploit it further, to help provide insight into the origin of cosmic acceleration. A detailed understanding of how supernova explosions occur would be a valuable contribution to this quest.

And they’re just lovely to watch.