While deeply held feelings about string theory (”Genius!” “Total Bunk!”) may sometimes drive us apart, all of us can certainly get behind the theory that chocolate is a net good. However, in spite of its appeal as a tasty eatable (with or without bacon), it’s actually a bit of a pain to work with. If you’ve ever tried to use chocolate in its melted form, you’ve probably discovered that chocolate has a number of peculiarities that frequently thwart your best culinary efforts. For example, if your melted chocolate becomes contaminated with an errant drop of water, the chocolate siezes up. If you try to reharden chocolate that’s been melted (say, in making chocolate covered strawberries), you’re frequently left with a matte finish and crumbly texture that in no way resembles the dark glossy chocolate you began with.

The reasons for this should be familiar to any solid state physicist (or at least, they were to the one who made my wedding cake and first clued me in). Cocoa butter, one of the dominant ingredients in chocolate, contains several triglycerides that lock into a crystal form when cooled. However, there is not just one form that the triglycerides can lock into, but six of them (β(I) through β(VI)). Each successive form is more stable and has a higher melting point. Almost all commercial chocolate is in the β(V) form — from what I can tell, you only get to sample β(VI) in the afterlife, if you’ve been very, very good. When chocolate goes all wrong, it is usually a failure of the melted and cooled chocolate to recrystallize into the β(V) state. Similar problems can affect commercial chocolate suppliers as well, leading to chocolate that develops that unsightly chalky film we associate with old chocolate. Even previously stable β(V) chocolate can wind up with the same unsightly film after temperature fluctuations break down the crystal structure, or melt and reharden a thin layer on the surface. Given the commercial implications, there’s been some solid technical work on the structure of the magical β(V) form, which has been studied with x-ray diffraction using synchrotron radiation (more technical data here).

Given the above, when cooking with chocolate, one’s goal is to coax the cooled chocolate back into the β(V) form if one wants the end product to look glossy, be solid at room temperature, and have a nice crisp snap when bitten. The traditional mechanism for this is known as tempering (video here). Traditional tempering involves carefully controlling the temperature of the chocolate as it cools, so that the chocolate favors the preferred crystalline state. However, there is a vastly simpler mechanism, namely, seeding the crystal. If you take a lump of unmelted commercial chocolate, toss it into your bowl of melted chocolate, and stir for a bit, you’ll melt the new lump while cooling the melted chocolate. The cooling chocolate will then prefer the same crystal structure as the melting lump, such that when it hardens completely, you’ll find it in the luscious β(V) state.

PS. I can verify that the above works exactly as advertised. Last weekend I made the wedding cake above for the same solid state physicist who made mine a decade ago. (The cake was alternately described as looking like the Heatmiser’s hair, Mordor, and Garrett Lisi’s E₈ symmetry group, so you can imagine it was a pretty techie crowd). Making the thin chocolate sheets from which I cut the decorations, I got huge swaths of perfectly glossy chocolate. Occasionally, though, there’d be a small section with a matte surface, that was clearly a different crystalline form. Science. It works, bitches.

I’m going to take a vacation from blogging for a little while. Partly a mental-health break, partly a need to get other stuff done. But there are many things I would love to blog about! So here is a list of recent stuff I’ve saved — you can fill in for yourself all the illuminating and entertaining words that would undoubtedly accompany a full-blown discussion.

• Algae! The Editors chide me for carelessly conflating ethanol and biofuels. Fair enough. If algae are a clean and efficient way to capture and store energy from the Sun, I’d be all for it.
• Meanwhile, we continue to heavily subsidize corn for ethanol, and as a result people are dying.
• Don’t like your government? Take to sea and create your own!
• At some point I will say more about Ben Rosen’s great blog, and especially Harold Rosen’s great entry for the Google Lunar X-Prize, about which Deborah Castleman blogs here. Private ingenuity will be crucial to the future of human spaceflight, especially when NASA can’t remember how to replicate its heat shields from the 1960’s.
• I was going to score some non-partisanship points by criticizing Barack Obama for peddling nonsense about autism and vaccinations, just as John McCain does. (Hint: there is no connection!) Then I noticed that Hillary Clinton does the same thing, sadly. And, worse, Clinton has bought into John McCain’s panderiffic notion of declaring a summer holiday on gas taxes — at least Obama has come out squarely against that. (Encouragement to burn more fossil fuels is probably not sound policy.)
• You might also be interested in Michael Berube’s rundown of the candidates stances on disability issues. McCain’s, you’ll be unsurprised to hear, consists of exhortations along the lines of “Hey, disabled folks! Suck it up!”
• John McCain doesn’t want you to forget that Barack Obama is the preferred candidate of Hamas. He’s also the preferred candidate of nearly everyone outside the U.S., but whatever.
• At The Corner, Michael Novak continues Jonah Goldberg’s project of portraying Fascism as left-wing. His evidence is that a friend of Albert Camus’s joined the Nazi Party because everything in the world had lost its meaning. Novak seems to miss the fact that this anecdote proves the opposite of his point — Camus’s friend became a Nazi because the Nazis provided “a meaning in the destiny of our nation,” not because they denied the existence of objective meaning. But keep trying!
• Gerard ‘t Hooft proposes a locally finite model for gravity. A related discussion of whether the universe is continuous or discrete appears in an article from FQXi, which is annoyingly only available in pdf. I actually think the universe really is continuous, not discrete, for reasons that might become clear if I can just get this paper finished.
• Tomorrow, April 29, is Duke Ellington’s birthday. He was the master.

  And here is the orchestra, with Paul Gonsalves on tenor.

• Oops, almost forgot this one: Cosmo Girl! suggests you should design your own religion, just like you design your favorite Starbucks coffee beverage. (Simile theirs.)

Be excellent to each other.

Vladimir Nabokov had requested that his last work, fragments of an unfinished novel The Original of Laura, be destroyed after his death. But it won’t be, as his son Dmitri has (after tortuous deliberation) decided to go against his father’s wishes and publish the work. Via Marginal Revolution, which has several previous discussions.

Tom Stoppard, whose opinion is worth listening to, thinks it should be destroyed:

It’s perfectly straightforward: Nabokov wanted it burnt, so burn it. There is no superior imperative. The argument about saving it for the “greater good” of the literary world is null, as far as I’m concerned. There are parallel universes, might-have-been worlds, full of lost works, and no doubt some of them would have been masterpieces. But our desire to possess them all is just a neurosis, a completeness complex, as though we must have everything that’s going and it’s a tragedy if we don’t. It’s nonsense, an impossible desire for absoluteness. At best, it’s natural curiosity – personally, I’d love to read Nabokov’s last work, but since he didn’t want me to read it, I won’t – and it’s hardly modest to make one’s own desire more important than his.

Stoppard is right about the neurosis, and ultimately I agree with his conclusion, but I can’t quite buy his reasoning. Hard-nosed, unsentimental materialist that I am, I don’t think that the wishes of dead people should carry much weight in and of themselves. They’re dead, they don’t care any more.

However, live people do count, and they are faced with subtle and competing interests (as various MR commenters have pointed out). On the one hand, sure, we might be curious about Nabokov’s last work. However, there is some degree to which the moral control over the disposition of a manuscript accrues to the family or whoever survives the author. If they felt strongly that they would be happier knowing that the author’s wishes had been respected, that would be a perfectly valid reason for carrying them out. But that doesn’t seem to be the case here; after thinking through the issues very carefully, Dmitri Nabokov came down on the side of letting it become public, even concocting a little story to excuse the apparent contravenance of his father’s instructions:

From his winter home in Palm Beach, Dmitri justified his decision by saying, “I’m a loyal son and thought long and seriously about it, then my father appeared before me and said, with an ironic grin, ‘You’re stuck in a right old mess - just go ahead and publish!’”

But there is one more set of interests to be accounted for: those of authors and creators who are not yet dead, but someday will be. (Most of us, I imagine.) If I create something right now, I certainly have the right to destroy it. But I might also want to have the confidence that, if I leave instructions that it should be destroyed, they will be carried out. Otherwise I might be tempted to destroy it ahead of time, and regret it later. More generally, if we treat the stated wishes of the deceased as strictly irrelevant in the calculation of social goods, wills and other sorts of legacies will become relatively meaningless. It’s not just about respecting the wishes of the dead; it’s about letting living people live with some confidence that their reasonable requests will be carried out once they’re gone.

Via Eric Rauchway (of The Edge of the American West, but guest-blogging at Crooked Timber), here is a list of the Top 100 Public Intellectuals, as put together by Foreign Policy and Prospect magazines. (You can vote for your top five.) Here are the natural scientists they’ve chosen to include:

• Richard Dawkins, biologist, author
• Jared Diamond, biologist, historian
• Neil Gershenfeld, physicist, computer scientist
• James Lovelock, environmental scientist
• Lee Smolin, physicist
• Harold Varmus, medical scientist
• J. Craig Venter, biologist, entrepreneur
• E.O. Wilson, biologist

Bjørn Lomborg is also on the list, but I don’t count him as a natural scientist — Sunita Narain is also a close call, but seems to fall more on the activism side than pure environmental science. Noam Chomsky and Steven Pinker would also be there if you classified linguistics as a natural science. I also didn’t include economists, who are certainly social scientists in my classification. And V.S. Ramachandran I counted as more of a psychologist. This is a thankless task.

Note that the list is concerned with public intellectuals — people who have influenced the wide-ranging public discussion in some substantial way — so there’s no point in wondering why Lee Smolin is there but not Ed Witten. You are, however, allowed to wonder why there aren’t more physicists over all, and whether physicists should be blaming themselves or shaking impotent fists of rage at the selection committee. Either way, those biologists are kicking our butts.

Remember E = mc²? It’s the one equation that you are allowed to include in your popular-physics book (unless you’re George Gamow, who couldn’t be stopped). Mark gave a nice explanation of why it is true some time back, and I babbled about it some time before that. For a famous equation, it tends to be a bit misunderstood. A profitable way to think about it is to divide both sides by the speed of light squared, giving us m = E/c², and take this as the definition of what we mean by mass. The mass of some object is just the energy it has in its rest frame — according to special relativity, the energy (not the mass!) will be larger if the object is moving with respect to us, so the mass of an object is essentially the energy intrinsic to its state, rather than that imparted by its motion. Energy is the primary concept, and mass is derived from it. Interestingly, the dark energy that makes up 70% of the energy of the universe doesn’t really have “mass” at all, since it’s not made up of objects (such as particles) that can have a rest frame — it’s a smooth field filling space.

All of which is to say that the mainstream media have let us down again. C. Clairborne Ray, writing in the New York Times, attempts to explain whether a spinning gyroscope weighs more than a stationary one, and answers “The weight stays the same; there is no known physical reason for any change.” Actually, there is! The spinning gyroscope has more energy than the non-spinning one. As a test, we can imagine extracting work from the spinning gyroscope — for example, by hooking it up to a generator — in ways that we couldn’t extract work from the stationary gyroscope. And since it has more energy, it has more mass. And the weight is just the acceleration due to gravity times the mass — so, as long as we weigh our spinning and non-spinning gyroscopes in the same gravitational field, the spinning one will indeed weigh more.

Admittedly, it’s a very tiny difference — the energy will increase by an amount proportional to the speed of the spinning gyroscope, divided by the speed of light, that quantity squared, which is really tiny. Nothing you’re going to measure at home. (I’m guessing it’s never even been measured in any laboratory, but I don’t know for sure.) And the article is correct to emphasize that there is no difference in mass that depends on the direction of spin of the gyroscope — that would violate Lorentz invariance, which is something worth looking for in its own right, but would be a Nobel-worthy discovery for anyone who found it.

You may have heard some of the buzz about a new result concerning the direct detection of dark matter particles in an underground laboratory. The buzz originates from a new paper by the DAMA/LIBRA collaboration; David Harris links to powerpoint slides from Rita Bernabei, leader of the experiment, from her talk at a meeting in Venice.

The new experiment is an upgrade from a previous version of DAMA, which had already been on record as having recorded a statistically significant signal of the form you would expect from the collision of weakly interacting massive particles (WIMP’s) with the detector. The experiment uses a challenging technique, in which their focus is not on eliminating all possible backgrounds so as to isolate the dark-matter signal, but to look at the annual modulation in that signal that would presumably be caused by the Earth’s orbital motion through the cloud of dark matter in the Solar System: you expect more events when we are moving with a high velocity into the dark-matter wind. Other workers in the field have not been shy about expressing skepticism, but the DAMA team has stood their ground; as Jennifer notes in her report from the recent APS Meeting, the DAMA collaboration home page currently features a quote from Kipling: “If you can bear to hear the truth you’ve spoken/ twisted by knaves to make a trap for fools,/ ……………you’ll be a Man my son!”

To help provide some insight and context, we’ve solicited the help of a true expert in the field — Juan Collar of the University of Chicago. I got to know Juan back in my days as a Midwesterner, and a trip to his bustling underground experimental empire was always a highlight of anyone’s visit to the UofC physics department. You can hear him talk about his own work in this colloquium at Fermilab; he’s agreed to post for us about his views on the new DAMA result, and more general thoughts on what it takes to search for 25% of the universe. I promise you won’t be bored.

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My dear friend Sean has me blogging: hey, I’ll try anything once. On the subject of the recent DAMA results no less, as per his request. I am normally a bit of a curmudgeon but… Sean, you really want the worst of me out there permanently on the internets, don’t you?

I’ll try to keep this to the point. A bard I am not, nor the subject invites any poetry. I have therefore chosen brief eruptions of flatulence as the metric and style for this piece. The result of indigestion, you see. I’ll start with the most negative, so as to end up on a brighter note:

• The modulation is undeniable by now. I don’t know of any colleagues who doubted these data were blatantly modulated already back in 2003, when “the lady” (DAMA) decided to keep mum for a while. However, to conclude from something this mundane that the experiment “confirms evidence of Dark Matter particles in the galactic halo with high confidence level” or that there is “an evidence for the presence of dark matter particles in the galactic halo at 8.2 sigma confidence level” is simply delusional. There is evidence for a modulation in the data at 8.2 sigma, stop. Compatible with what would be expected from some dark matter particles in some galactic halo models, full stop. Anything beyond this is wanting to believe, and it smears on the rest of us in the field. Of course, of course… there is no other observed process in nature that peaks in the summer and goes through a low in winter, so this must be dark matter, right? (Occam is turning in his grave, rusty razor still in hand. He is thinking a remake of that opening scene in “Un chien andalou”, with help from this little lady. I am channeling him loud and clear).
• Someone should take the DAMA folks aside for a beer, make them see the following. If one day soon we are all convinced that this effect was DM-induced (see below for what that will really take), they will be recognized for one of the greatest discoveries in the history of science, without them having to look desperate or foolish today. Or making the rest of us in the field do, by association: thanks DAMA, for cheapening the level of our discourse to truly imbecilic levels. (Sean, if you edit this I will scratch the paint off your car. I may not write blogs, but I do read them: I know how to hurt you).
• Deep breath. Having cleared the air some (or just made it toxic, whatever), it is not DAMA’s fault that there is a penury of signatures in this field of ours, laboratory searches for particle dark matter. The one possible exception to this is a detector with good recoil directionality and sufficient target mass to be truly competitive, but we don’t know of a good enough way to do this as of today (“good enough” folds in the price tag). People are still trying. The diurnal modulation in the DM signal that would be sensed by such a device is wickedly rich in features, extremely hard for nature to imitate with anything else. The annual modulation resides on the other side of this spectrum of complexity. It is the poor man’s smoking-gun to DM “evidence”. Inspected carefully, it is disappointingly feeble: different models of the halo can shift the phase of this modulation completely, turning expected maxima into minima and vice-versa, changing the expected amplitude as well. Add to this the fact that essentially every possible systematic effect able to pass for a “signal” can be yearly-modulated, for one reason or another. That’s the ones we can presently think of, and the ones yet to be proposed. To grow convinced that we have observed dark matter in the lab we’ll require a number of entirely different techniques, using a variety of targets, all pointing at the same WIMP (mass, cross sections), with additional back-up information from accelerator experiments and from gamma-ray satellite observations (so-called indirect searches). All of those lines crossing at one point, so to speak. This I (for one) will call “evidence”. I know of no single existing or planned DM experiment, including those I participate in, that would be able to make anything close to a bulletproof claim on its own. My advice to any overambitious individuals looking for a quick kill is to look elsewhere in physics. WIMP hunting is not it, no matter how important the discovery of these particles might be.

Continue reading ‘Guest Post: Juan Collar on Dark Matter Detection’

My beloved Philadelphia Seventy-Sixers, under the coaching tutelage of local hero Maurice Cheeks, have returned to the playoffs after a two-year absence. It wasn’t easy; they started the season with an ugly 5-13 record, but turned it around late to slip into the seventh seed in the tepid Eastern Conference. Their efforts earned them a series with the Detroit Pistons, a perennial power who finished with the league’s second-best record. Pistons center Rasheed Wallace has played in more playoff games than all 15 members of the 76ers roster combined.

But this afternoon, the plucky Sixers came back from a 15-point third-quarter deficit to beat the Pistons in their first game. That’s why they play the games. In their honor, here is my favorite video of Mo Cheeks, back from when he was coaching Portland a few years ago: chokes me up every time I watch it.

Much of the April 15th angst that Sean described comes from student’s questioning “Will I be a success if I go to this particular graduate school?”. They place a tremendous weight on this decision (and rightly so, given the 5+ year duration of a typical PhD). The decision of where to go to school presents a clean well-defined juncture, where you can imagine two clear paths before you, one that leads to a happy land filled with unicorns and flowers and all night coffee shops and independent record stores, and another that leads to a sad grey land where you spend your time shuffling piles of paper for The Man. However, having been in the game from the faculty side for nearly a decade, I can say that much of what determines whether one is a “success” is largely independent from this decision. (An aside: for this discussion I’m going to assume “success” equals working as a research scientist, which is the typical goal of an entering grad student. I don’t mean this as a value judgement, since “success” is really “whatever career path you find fulfilling”, and I’m just as happy to train phenomenal future high school science teachers as future faculty at Harvard.)

I think the essence of what determines your long-term success as a scientist is your ability to influence the scientific discussion. When you’re at a point in your career when people pay attention to your work, and want to know “What does <your name > think about this?”, you are on a near certain path to a stable position as a research scientist. Instead, if no one is reading your papers (to the extent that you’ve published them at all), or wants to hear what you say at conferences, or calls you up to ask you about your area of expertise, then you’re in danger of drifting out of the field.

Now, the factors that lead to having scientific influence are many. Among the most important are:

• Writing lots of papers
• Writing interesting papers
• Writing papers using novel or superior data sets
• Writing papers on a timely topic
• Being recognized as leading the above papers, rather than being directed by others
• Communicating your ideas with clarity
• Being socially well-connected in your field
• Being really, really, really, unusually smart and/or creative
• Having influential mentors promoting you

To be scientifically successful, you don’t need to have all of these factors, or even most of these factors. You just need to have enough of them, or a long enough suit in one or two of them, that people can’t ignore what you’re doing.

Of this list, there are at least half that are almost entirely under a student’s own control, no matter where they go to graduate school. You can pick inspiring mentors, write lots of papers on interesting, timely topics, and give riveting talks about them, no matter where you are. You can fail to write any papers (on topics boring or not) and give lousy talks, under the negative guidance of ineffective advisors, even if you go to a top-ranked school. Some of the other factors do probably have some correlation with top-ranked programs, in that such programs are more likely to have the luxury to admit only students with early evidence of brains and creativity, and they tend to have more of the resources that lead to superior data access, or a larger pool of productive theorists (postdocs & faculty). [However, in astronomy at least, there is sufficiently rich access to public resources (SDSS, NASA's Great Observatories, 2MASS, etc) that one can usually have sufficient access to create "novel or superior data sets" no matter where you are. For lab-based physics, this is likely less true.] In this list, the relative “prestige” of one’s graduate program has little direct impact on your eventual scientific impact. When I hire postdocs, or evaluate fellowship applications, I am drastically more impressed by what someone actually did, than where they went to school.

Besides the import for deciding where to attend school, the above elucidates why “climate” issues can have such a large impact on your eventual career success. If you’re at an institution that places obstacles in your path that make it difficult for you to write papers, to find good mentors, and to make scientific connections in your field, then you’ve got a problem. You’re going to be struggling uphill.

However, the same list also provides the recipe for climbing that hill, if you find that you’re on it. The number one thing you can do is to write papers (and preferably interesting and timely ones). People cannot ignore a large body of high quality work for long. Sometimes it takes a while before they notice, it’s true. But the more you publish, the more likely it is that people will begin to notice your work, and be influenced by it. As that happens, they will start noticing you as well, and will tend to deem you “someone worth having around”, whether as a postdoc, or at their conference, or as their next faculty colleague. This process is vastly easier with a good mentor behind you, but if you wound up without one (or gawd forbid with an anti-mentor), it’s going to be your only route out.

I think the clearest evidence of this is a relatively jaw-dropping preprint that was recently posted to the arXiv (h/t to Zuska). A former particle-physics postdoc (and current grad student in statistics) carried out a very detailed analysis of the productivity of postdocs on the Run II Dzero experiment, and how that translated into giving conference presentations, and being hired into faculty positions. The paper found that the postdocs’ success in eventually landing faculty jobs were highly correlated to productivity (as measured by internal papers), to conference presentations (which were awarded by the leadership of the project), and to the degree of “physics socialization”. These correlations are all what you would expect, and reinforce the above list of what leads to being scientifically influential.

The jaw-dropping aspect of the paper is that the awarding of conference presentations was grossly gender biased (as was the fraction of service work assigned to the women). The female postdocs had drastically higher levels of productivity (indeed, half the men were less productive than the least productive woman), but were allocated far fewer conference presentations than men with comparable productivity. (Note: this is a paper you actually have to read, rather than just flipping to the table at the end. It’s a very well-done piece of statistical analysis, and can’t be fully appreciated from just comparing two means in a table.)

In this exercise, we see the influence game writ large. You need to be productive and visible. If some sort of bias (against women, or shy people, or people from state schools, or whomever) is present that conspires to make you less visible, you’re going to have to be even more productive. It’s not fair, and people in positions to fight against the bias in their institution should do so. But, at least it’s something that you have a chance of controlling.

April is Poetry Month, just like it was last year. We’re celebrating with Shakespeare’s Sonnet 64, about the Second Law of Thermodynamics.

When I have seen by Time’s fell hand defaced
The rich proud cost of outworn buried age;
When sometime lofty towers I see down-razed
And brass eternal slave to mortal rage;
When I have seen the hungry ocean gain
Advantage on the kingdom of the shore,
And the firm soil win of the watery main,
Increasing store with loss and loss with store;
When I have seen such interchange of state,
Or state itself confounded to decay;
Ruin hath taught me thus to ruminate,
That Time will come and take my love away.
This thought is as a death, which cannot choose
But weep to have that which it fears to lose.

Anyone watching this evening’s episode of Comedy Central’s new Lewis Black vehicle, The Root of All Evil (10:30, 9:30 Central), might just see some familiar scientists and/or bloggers. Maybe.

Elsewhere, stars of the CBS sitcom The Big Bang Theory (about which more anon) seem to have been reading up on their Spacetime and Geometry.

No appreciable bump in my Amazon ranking, though.