Monthly Archives: April 2011

What do you want to be when you are older? A physicist!

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John Eger teaches journalism and media studies at San Diego State University. He also blogs about creativity, innovation, education, and economic development for the Huffington Post—which is where I found a heartening quote from 12- or 13-year-old girl.

In a recent blog post, Eger describes the Lux Art Institute, a museum in the Southern California beach town of Encinitas. The Lux’s current artist in residence is Rick Stich, who paints the patterns he sees or imagines he sees reflected in water. Here’s an example.

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The Lux, to quote from its website, “is redefining the museum experience to make art more accessible and personally meaningful. At Lux, you don’t just see finished works of art; you see the artistic process firsthand, engaging with internationally recognized artists in a working studio environment.”

It was one of those engagements, with Stich, that provided the opening for Eger’s blog post and the inspiration for this one. As Eger tells it:

Recently one sixth grader asked: “You paint the water, but water moves so how do you do that . . . the water keeps changing, moving.” Curious, Rick commented that this was a very thoughtful question and asked “What do you want to be when you are older?” “A physicist,” she said.

Besides being delighted that a sixth grader from San Diego County wants to become a physicist, I was struck by the parallels between what the Lux Art Institute does for art and what the Exploratorium in San Francisco does for science.

Founded in 1969 by the physicist Frank Oppenheimer, the Exploratorium lets its visitors experience, through hands-on exhibits, the joy of scientific discovery unlike traditional museums that display, in glass cabinets, the fruits of scientific discovery.

Although the Lux is younger than the Exploratorium—planning for the institute began in 1998—I wonder if it has a thing or two to teach its older cousin. From Eger’s blog post I learned about a novel program called the Valise Project, which the Lux describes

as a way to reintroduce art into the classroom. Inspired by Marcel Duchamp, who carried miniatures of his work inside a suitcase, Lux commissions portable works of art that double as powerful interdisciplinary teaching tools. The valises travel to hundreds of classrooms around San Diego County each year, giving students a rare up-close and hands-on experience with museum-quality art.

Wouldn’t it be great if the Exploratorium or other science institutions created their own valise projects? The objects in each suitcase wouldn’t be works of art; they’d be intriguing objects about which a teacher or other volunteer could tell a story, a story that’s interesting enough to inspire a sixth grader to become a physicist.

Charles Day

Fashionable physics

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One of my favorite physicist bloggers, Doug Natelson of Rice University, once observed with mock exasperation:

I used to think that I was the only condensed matter physicist not working on graphene. Now I realize I’m the only condensed matter physicist not working on graphene, iron pnictide superconductors, or topological insulators.

Doug was writing in 2009. A year later—as I’ve only just found out—a team led by Takashi Takahashi of the WPI Advanced Institute for Materials Research at Tohoku University created an iron pnictide material, barium iron arsenide (BaFe2As2), whose electronic properties resemble those of graphene and topological insulators. If Doug or anyone else wants to start research programs in the three hottest areas of condensed-matter physics, it can be done with just one material.

To burst on the physics scene and spawn scores of preprints, a new discovery must be interesting and potentially important. But it must also be somewhat accessible to researchers. Adding super-heavy elements to the periodic table on the way to discovering the island of stability may be interesting and important, but only three groups—at the GSI Helmholtz Center for Heavy Ion Research in Garching, Germany; the Joint Institute for Nuclear Research in Dubna, Russia; and Lawrence Berkeley National Laboratory in California—have the expensive specialized equipment needed to participate in the quest.

Graphene is far more accessible. Indeed, the material became hot in part because Andre Geim and Kostya Novoselov discovered a simple, cheap way to make it. If you opt to work on the arsenide members of the iron pnictide family, you’ll need to follow your institution’s rules about working with poisonous materials. Still, as attested by the explosion of papers that followed Hideo Hosono’s 2008 discovery paper, making the materials doesn’t appear to be especially challenging.

As for topological insulators, the first material to exhibit the phenomenon, mercury telluride, is difficult to work with because of mercury’s low melting point. I don’t know about the other materials, but the theorists who rushed to work on topological insulators—graphene and iron pnictides, too—faced no experimental impediments to their creativity.

QPOs and cuprates

I was an astronomy graduate student in 1986 when Georg Bednorz and Alex Müller discovered high-Tc cuprates. Although the explosion of research ignited by their discovery soon reached me at Cambridge University, I barely felt its shock wave.

I did, however, experience the (albeit more modest) frenzy that accompanied Michiel van der Klis and Fred Jansen’s 1985 discovery of quasi-periodic oscillations in the light curves of x-ray-emitting binary stars. In retrospect, QPOs manifested their hotness in the same way that graphene, iron pnictides, and topological insulators do—in a burst of theoretical explanations and further observations or experiments.

Being part of a global race to elucidate and understand a new phenomenon is thrilling. I don’t think the powers that be in science—that is, funding agencies—should put too many restrictions on what curiosity-driven scientists want to work on, even if giving scientists a free hand entails diverting resources.

That said, in so far as following physics fashion prevents you from doing other things, hot fields have their drawbacks. In October 2008, the Institute of Physics of the Chinese Academy of Sciences held a workshop on the recently discovered iron pnictides. Speaking the workshop, Koichi Kitazawa, a veteran of the high-Tc cuprate boom, admitted that, in retrospect, he wished he’d followed the advice of his junior colleagues and not focused so narrowly on cuprate materials. “If I’d listened to them,” he said, “maybe we’d have discovered the iron pnictides.”

Charles Day

Striking the right balance between basic and applied research

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The transistor, the LED, and the medical isotope technetium-99m are important applications of science, yet as far as I know none of them was invented as the result of a government initiative to fund industrially relevant research.

The transistor was invented at Bell Labs. The LED was invented at the University of Illinois at Urbana-Champaign, and technetium-99m was discovered—and its usefulness to medicine recognized—at Brookhaven National Laboratory.

My short list is not meant to buttress an argument that governments shouldn’t fund applied, goal-directed research. They should. The challenge lies is striking the right balance between basic and applied research. If a government overemphasizes applied research, it risks depriving basic researchers of the funds they need to make discoveries and inventions that could prove industrially important.

The question of basic versus applied research has been in the news this year. In February, Nature‘s Jane Qiu reported that

China is betting that an ambitious programme of applied research will help to secure its future as an economic superpower. Innovation 2020, unveiled last week by the Chinese Academy of Sciences (CAS), maintains support for basic research. But the plan will place a new emphasis on translating the research into technologies that can power economic growth and address pressing national needs such as clean energy, said Bai Chunli, vice-president of the CAS, at the academy’s annual conference in Beijing, where the plan was announced.

Earlier this week, another report in Nature outlined a controversial plan to refocus Canada’s National Research Council toward applied research.

Whether China and Canada will benefit from their newfound fondness for applied research is hard to predict. I can say, having visited several industrially focused research labs in Singapore, that success appears to entail working closely with industry—very closely, as exemplified by Singapore’s Institute of Microelectronics.

If you visit the Industry section of IME’s website, you discover that

IME has collaborations with every sector of the electronics industry in Singapore from IC design, wafer fabrication and packaging to niche technology industries such as MEMS and leading edge photonics.

IME aims to provide advanced technology support for a competitive electronics industry through advanced services, technology transfer and R&D manpower development. These collaborations provide the essential inputs to guide IME’s R&D programmes, thereby ensuring that IME stays relevant to the industry.

Canada’s new direction for its National Research Council does not appear to envision such close cooperation with industry. Rather, the plan calls for research in four strategic areas and includes projects—to quote the Nature story—that are aimed at “developing a strain of wheat resilient to environmental stress; improving the manufacture of printable electronics; increasing domestic production of bio≠composite materials; and using algae to soak up carbon dioxide emissions from industry.”

One of the first feature articles I edited for Physics Today was “Amorphous Semiconductors Usher in Digital X-Ray Imaging” by John Rowlands of the University of Toronto and Safa Kasap of the University of Saskatchewan.

Back in 1997 when the article appeared, flat-panel detectors based on amorphous selenium were in their infancy. Now you can buy them from a company called ANRAD, which is based in Saint-Laurent, Quebec.

Out of curiosity, I looked up the 1995 paper in Medical Physics in which Rowlands and Wei Zhao first described the detectors. Funding for the research came from the National Cancer Institute of Canada, whose aim, I presume, was not the promotion of Canadian industry. But that’s what its money ended up doing.

Charles Day

Can a tiger mother raise a Nobel-Prize-winning physicist?

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Amy Chua is a professor at Yale Law School. In January she published Battle Hymn of the Tiger Mother, a book that recounts how she raised her two children Sophia and Louisa. To publicize the book, she wrote an article for the Wall Street Journal under the title “Why Chinese Mothers are Superior.”

Even without the provocative title, the article proved controversial. Chua argues that to become accomplished at anything worthwhile requires diligent, prolonged practice. And by anything worthwhile, she means academic subjects, music, but little else. When they were growing up, Sophia and Louisa were forbidden to

  • attend a sleepover
  • have a playdate
  • be in a school play
  • complain about not being in a school play
  • watch TV or play computer games
  • choose their own extracurricular activities
  • get any grade less than an A
  • not be the No. 1 student in every subject except gym and drama
  • play any instrument other than the piano or violin
  • not play the piano or violin

The apparently harsh, joyless regimen paid off. The elder daughter Sophia was accepted by both Harvard and Yale—but not, I presume with confidence, to major in physics.

Since the mid-1990s, the Nobel Foundation’s website has published laureates’ autobiographies. Not every laureate has provided details of his or her childhood, but enough of them have to identify common features.

As you might expect, several laureates thanked their parents for encouraging and supporting their interest in science. Talented and dedicated teachers were also cited. But what the laureates also tended to have in common was the freedom their parents gave them to pursue their own interests, whether scientific or not.

Three of the most detailed and, as it happens, most engaging autobiographies are those of the physicists Steven Chu, Robert Laughlin (shown here), and John Mather. As youngsters, Chu taught himself to pole vault, Laughlin disassembled TV sets to discover how they worked, and Mather kept eight baby rats under the kitchen table and fed them different diets for a science fair project.

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Granted, some laureates faced parental pressure. George Smoot, who shared the 2006 Nobel Prize in Physics with Mather, wrote in his autobiography, “My mother tutored me in additional science and history, while my father drilled me in the basement, force-feeding trigonometry and introductory calculus courses that were not given at my high school.” Laughlin recalled:

At dinnertime one of my parents, usually my father, would lead a discussion about some controversial matter, such as racial integration of schools, whether John Lennon should have compared himself with Jesus Christ, support of Israel, or the morality of the Vietnam war, and all of us were expected to air and defend our views on these things, even if we did not want to.

But I’ve yet to find an autobiography that describes a household regime like Chua’s. Can a tiger mother raise a Nobel Prize–winning physicist? I don’t know for sure, but the evidence suggests the answer is no.

Charles Day

The ingenuity of experimenters

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The forerunner of the steam engine was the pressure cooker—or steam digester, as its inventor Denis Papin (1647–1712) called it. By keeping water in its liquid state at temperatures higher than its boiling point, the device could extract fats from bones. The periodic venting of the digester’s safety valve gave Papin and his collaborator Robert Boyle the idea for a steam engine.

As James Watt and others began developing the steam engine, scientists began investigating the thermodynamics of liquids and gases. Among them was Charles Cagniard de la Tour, shown here.

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In 1822 Cagniard discovered the existence of water’s critical point—that is, the temperature and pressure at which the distinction between water’s liquid and gaseous states disappears. His experiment was simple and ingenious.

Cagniard partially filled a steam digester with water and then added a flint ball. By rolling the digester like a log, he sent the ball in and out of the liquid, creating a splashing sound that he could hear. When the digester reached 362°C, not far from the true value of 374°C, the liquid–gas interface disappeared and the splashing stopped. The fluid in the digester had become supercritical.

Neutrons and gravity

Cagniard’s experiment came to mind yesterday when I heard of another ingenious confinement experiment: the use of ultracold neutrons to measure gravity on short length scales by Hartmut Abele of the Technical University of Vienna and his colleagues.

The team’s new paper appeared recently in Nature Physics and continues the line of research proposed in a paper published in Nature in 2002.

If cold enough—that is, slow enough—a freely falling neutron that bounces off a polished surface will find itself confined in a quantized gravitational potential. No one can pick up and drop a neutron, but you can launch neutrons on trajectories that are the quantum equivalent of a cannonball’s parabolic path.

In the 2002 experiment, the team, which included researchers from France, Germany, and Russia, sent neutrons on near horizontal paths through a 10-cm-long cavity, whose height ranged from 0 through 160 μm. If the neutrons had behaved classically, some of them would have made it through the cavity even when its height was barely greater than zero. But the neutrons didn’t behave classically. Only when the cavity was at least as high as the first quantized level did any neutrons make it through.

The latest experiment turned the cavity into what Abele calls a gravity resonance spectrometer. By connecting the polished floor of the cavity to a piezoelectric actuator, Abele and his team set up resonance conditions in which ground-state neutrons were given just enough energy to reach one of the higher levels in the gravitational potential.

Because the interlevel spacing depends on g, the cavity serves as a gravitometer. If Abele and his team succeed in increasing the sensitivity of their technique, they’ll have a means to test fundamental theories whose extra dimensions on large length scales are manifested as departures from Newtonian gravity on small length scales.

France’s King Louis XVIII made Cagniard a baron for his contributions to science. The first successful detection of non-Newtonian gravity would likely earn its discover a different sort of prize.

Charles Day

Thoughts on this year’s Templeton Prize

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Earlier this month the John Templeton Foundation announced the recipient of its annual $1.6 million prize: astrophysicist and cosmologist Martin Rees. The news surprised me at first. Rees’s views on science and its role in society are profound, wide-ranging, and humane—qualities that I presume the Templeton Foundation upholds—but Rees, I knew, does not believe in God.

Why did the prize, whose avowed aim is to honor “a living person who has made an exceptional contribution to affirming life’s spiritual dimension,” go to an atheist?

I can’t answer for the Templeton Foundation, but I suspect that the members of its prize committee found Rees’s quiet atheism palatable. Unlike Richard Dawkins and Christopher Hitchens, Rees is not an anti-God polemicist.

Rees is, however, actively engaged in explaining science and its value to the general public. Since 1995, he has occupied the ceremonial but prominent position of Britain’s Astronomer Royal. From 2005 to 2010, he served as the president of the Royal Society.

Most physicists and astronomers of Rees’s eminence are either atheists or agnostics. In 1998, Edward Larson and Larry Witham published the results of a survey of the religious beliefs of the members of the US National Academy of Sciences. Only 7.5% of NAS physicists and astronomers believe in God.

As an atheist myself, I admire the forthright stance on religion of Steven Weinberg, whose quoted remarks include “I’m in favor of a dialog between science and religion—just not a constructive one.” But I also admire atheists who recognize, either implicitly or explicitly, that engaging the public about science entails accepting and respecting religious beliefs.

Charles Day

Nitrogen in your car tires

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My wife and I bought a new car on Saturday, a 2011 Honda Fit. Given that my previous car, a 1993 Honda Civic, was equipped with Spartan disdain for distracting comfort, I expected the new car to abound in features that my old car lacked, such as electric windows, a radio, and air conditioning.

But when Peter the Honda salesman was touting the Fit’s features, I didn’t expect him to say that the car we ended up buying had nitrogen in its tires (indicated by the green tire stem cap in the photo).

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“But air is 80% nitrogen,” I pointed out, “What’s the advantage of using pure nitrogen?” Peter explained that nitrogen is used in aircraft tires to reduce the effect of temperature fluctuations on pressure.

I didn’t press him on the issue, but I remained puzzled. Under everyday conditions, the gas in a tire should behave like an ideal gas—that is, its pressure should be proportional to its temperature regardless of its molecular composition. Curious, I looked into the matter.

Aircraft tires indeed are filled with nitrogen to mitigate temperature fluctuations, but not because nitrogen has any special heat-absorbing qualities. Rather, it’s the presence of water that makes standard, commercially available compressed air a poor, even dangerous choice for aircraft tires.

At low temperatures, such as a plane might encounter at Chicago’s O’Hare airport in midwinter, the water in an air-filled tire exists as liquid droplets. But if that plane had to land and brake suddenly, heat from the screeching tires would vaporize the droplets, adding an extra pressure-exerting component to the gas in the tires.

The sudden increase in pressure from the water vapor can be fatal. On 31 March 1986, a tire on Mexicana Flight 940 was mistakenly filled with air, not nitrogen. Fifteen minutes after takeoff from Mexico City, an overheated landing gear brake caused the tire to explode. The resulting crash killed all 167 passengers and crew.

Pure nitrogen has other advantages over air besides its dryness. When tires get very hot, oxygen, the second most abundant component of air, can react with volatile chemicals in the rubber and cause an explosion. Even at lower, everyday temperatures, oxygen reacts with rubber, weakening it.

So will I refill my tires with nitrogen? Not if it costs more than a few dollars. Having owned the same car for 18 years, I know that worn treads will prompt me to replace the tires long before oxidation sets in.

Charles Day

Analogies and metaphors

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I’ll be the ticket if you’re my collector
I’ve got the fare if you’re my inspector
I’ll be the luggage if you’ll be the porter
I’ll be the parcel if you’ll be the sorter

—”Love Song” by Dave Vanian, Captain Sensible, Rat Scabies, and Algy Ward

“Love Song” is the opening track of the Damned’s album Machine Gun Etiquette, which I bought in 1979 when it was first released as a vinyl LP. The punk band’s deft use of metaphor in the opening verse has always reminded me that analogy, metaphor, and other tropes are not just for poets and orators. Indeed, physicists and the people who write about physics deploy them freely.

Perhaps the most straightforward use of metaphor in physics is for descriptive labels. In 1937 John Slater approximated the atomic potentials in a crystal as a lattice of nonoverlapping wells. By 1961—at least according to the earliest reference I could find—Slater’s approximation had acquired the apt, delightful, and easy-to-recall name “muffin tin.”

In 1997 observations made by the SOHO spacecraft cleared up a mystery having to do with the inactive, “quiet” regions of the Sun’s corona. Thanks to its then-unprecedented resolution and sensitivity, the SOHO‘s Michaelson Doppler Imager revealed that the quiet corona’s magnetic field arises not from plasma that diffuses from active regions, but from the magnetic activity of the quiet corona itself. To Alan Title the newly discovered field lines that sprout from the quiet corona resembled the looped tufts of a carpet—hence the name he devised, “magnetic carpet.”

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Some concepts in physics can be hard to convey, especially to nonphysicists. As an explanatory tool, my fellow science writers and I sometimes use analogy and metaphor to relate an unfamiliar concept to a familiar one.

For example, in a 2004 news story for Physics Today I compared molecular dynamics (MD) simulations, which seek to track the motion of every particle, with a new variant of the Monte Carlo algorithm that Nicholas Metropolis and his collaborators devised in 1953:

So, if MD is like a movie, the Metropolis algorithm is like a sparse set of shuffled snapshots. If you simulated a cocktail party with the Metropolis algorithm, you wouldn’t see dynamical events, such as guests arriving and departing, or rare events, such as a waiter refilling a punchbowl. But, taken together, the Metropolis snapshots would fairly represent the party in full swing. From them, you could deduce whether, on average, people had enjoyed themselves.

However, sometimes analogies and metaphors are not used for literary effect, but for literal comparison. Earlier this year my colleague Richard Fitzgerald wrote about a tabletop experiment that sought to mimic the radiation that leaks out of a black hole via a mechanism proposed in 1974 by Steven Hawking.

Remarkably—at least at first glance—the experiment involved water flowing at high speed over and around obstacles. Because of the similarity of the equations that underlie both Hawking radiation and the waves shed by the obstacles, the two systems are analogous to each other. But whereas one system, the waves, is easily observed in the lab, the other, Hawking radiation, isn’t.

Whether studying one member of an analogous pair brings true physical insight into the behavior of the other member is not obvious. To justify evoking the analogy, you have to be sure that both systems are governed by the same mathematics. Yet to make that justification, you have to understand both systems well—which would seem to vitiate the need to evoke the analogy in the first place.

That said, knowing the equations that govern a system isn’t the same as understanding its behavior. Superconductivity, ferromagnetism, and other electronic phenomena could emerge from quite simple Hamiltonians, but the long-range many-body interactions embodied in the Hamiltonians are too complex to calculate or even to simulate.

But in principle, a cold-atom analogue of an electronic system could be engineered to test whether, say, the Hubbard model is sufficient to capture the onset of superconductivity in a high-Tc cuprate. Indeed, several research groups around the world are working toward that end—which, if achieved, would be a literal, not metaphorical, triumph.

Charles Day

Thanks to Maire Evans for suggesting the topic of analogies.

Crumple zones

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The bespectacled man in the photo below is the automobile engineer BÈla BarÈnyi. In 1937, when he was 30, BarÈnyi came up with the idea of crumple zones for cars. To protect occupants in the event of head-on or rear-end collisions, BarÈnyi proposed that cars should consist of three cells: a strong, rigid, central cell that would house the driver and passengers, and weaker cells front and back that would absorb the energy of a crash by deforming plastically.

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The first production cars to incorporate crumple zones belonged to the W111 series made in 1958–59 by BarÈnyi’s employer, Mercedes-Benz.

Another car that incorporated crumple zones was my 1993 Honda Civic hatchback. I use the past tense because yesterday my wife and I were involved in a four-car pile-up on US Route 1 just outside the Capital Beltway. The car’s front end was indeed crumpled, but none of the four cars’ six occupants was seriously injured.

The accident was caused by a driver of a Ford Taurus, who apparently went into diabetic shock and failed to stop or even apply the brakes when the traffic light ahead of him turned red. The Taurus hit a Toyota Camry, which hit my car, pushing it into a Nissan Xterra.

Because the Toyota driver and I were still braking, the first two collisions, Ford–Toyota and Toyota–Honda, were mostly elastic. The Nissan ahead of us had come to a complete stop. The last collision, Honda–Nissan, was therefore inelastic, as you can see from the photo.

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When a car that doesn’t have a crumple zone smashes into something at high speed, its entire frame, including the passenger compartment, can buckle and its front end, including the engine if it’s in the front of the car, can be pushed into the passenger compartment. As BarÈnyi recognized 74 years ago, either consequence imperils passengers.

The collision my wife and I were involved in was at low speed. If the car didn’t have crumple zones and had instead a rigid frame, I doubt we’d have been crushed by a buckled frame or pushed-in engine.

But the crumple zone spared us from injury in another way. Thanks to its crumple zone, my car took longer to decelerate when it was slammed into the Nissan than a rigid car would have done. That extra time meant that our heads required less force from the objects that brought them to rest: our necks.

Charles Day