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-T_c 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-T_c 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

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.

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

Waves appear early in most university physics courses. Richard Feynman introduced them halfway through the first volume of his Lectures on Physics. And if I remember correctly, my first term at Imperial College, London, included a course on waves given by a plasma physicist named H. J. Pain.

The ubiquity and importance of wave phenomena account for their early pedagogical debut. Diffraction, interference, and other wave concepts help us understand the propagation not only of light and sound, but also of electrons in metals and plasma in the Sun’s corona.

But even though I’ve written many times about different kinds of waves, big and small, in solids, liquids, and gases, I was surprised to receive a press release from CERN linking neutrino oscillations and whale songs.

Neutrinos come in three flavors, which, in order of increasing mass, are electron, muon, and tau. In 1957 Bruno Pontecorvo predicted that neutrinos could spontaneously swap back and forth from one flavor to another. Neutrino oscillations were presumed to account for an apparent deficit of neutrinos from the Sun. In 2001 detectors housed deep in an old Canadian nickel mine confirmed that neutrinos do indeed oscillate.

It turns out that the wavelength of neutrino oscillations is about the same as the wavelength of whale songs. That fortunate cosmic coincidence has led to a collaboration between particle physicists and biophysicists. To quote the CERN press release:

European astroparticle physicists are developing together KM3NeT, a large undersea neutrino telescope in the Mediterranean, dedicated to tracking neutrinos from astronomical sources. The deployment of deep sea neutrino detection lines for current experiments such as AntarËs in France, Nemo in Italy and Nestor in Greece has opened up the possibility of also installing monitoring devices for the permanent study of the deep sea environment: studies of ocean currents, of bioluminescence, of fauna and of seismic activity.

The accompanying cartoon shows what the KM3NeT detectors look like.

I couldn’t find any pictures of hydrophones, seismographs, and other instruments that will be deployed alongside the KM3NeT detectors, but hydrophones at a different undersea neutrino experiment have already made an interesting and unexpected discovery: That sperm whales currently live in the Mediterranean.

Wave phenomena are sufficiently rich and varied that professors who teach them don’t lack interesting, realworld examples. Still, it’s my recollection that Pain and most other lecturers relied on examples that were tried and true, rather than new and exciting. Now, 29 years after my freshman year, I know enough to find the connection between neutrinos and whales to be surprising. Then, back in Pain’s class, I’d have found it inspiring.

Charles Day

Juliet answered her famous rhetorical question with: “That which we call a rose by any other name would smell as sweet.” Romeo, her besotted interlocutor, promptly agreed.

But the recent kerfuffle over who might be honored with a Nobel Prize if the Large Hadron Collider discovers the Higgs boson shows that particle physicists care about names and the provenance they imply. The Higgs boson was proposed more or less simultaneously in three papers that came out in 1964. How the particle acquired the name of only one of the papers’ six authors, Peter Higgs, was recounted last month in a letter to Nature.

The letter’s author was Ian Sample, a science reporter at the Guardian. According to Sample, it was the particle theorist Benjamin Lee who coined the name Higgs boson. Lee was asked to provide the closing summary at an international conference held at Fermilab in 1972. For Lee, “Higgs” was just a convenient shorthand to refer to the mechanism that the six original authors had described in 1964 and its later elaborations. “From there,” wrote Sample, “the name stuck and the Higgs boson was born.”

The single-parent name of the Higgs boson is somewhat awkward. In the more equitable case of the J/ψ meson, both groups that simultaneously discovered the particle are represented: Sam Ting’s, which bestowed the name J, and Burton Richter’s, which bestowed the name ψ.

As far as I know, the Higgs boson and the J/ψ meson are exceptions. Most particles bear uncontentious names. Indeed, my favorite particle name is perhaps the least contentious of all because it’s the most literal: the gluon.

Charles Day

On 10 November 1937 during the Great Purge, Joseph Stalin’s secret police executed Lev Shubnikov on trumped-up charges of treason. Although he was only 36 at the time, Shubnikov had already made pioneering discoveries in magnetism and low-temperature physics. As a wanton waste of scientific talent, his killing ranks with those of Archimedes in 212 BC and Antoine Lavoisier in 1794.

Stalin’s carelessness with the lives of physicists soon changed. By 1942, the Soviet leader had been tipped off about the Manhattan Project. To forestall a US nuclear monopoly, the Soviet Union had to develop its own weapon. And to attain that goal, Stalin provided physicists with resources, comfort, and a modicum of academic freedom. By 1949, he had his atomic bomb.

Igor Kurchatov, Vitaly Ginzburg, Andrei Sakharov, and the other physicists who developed the Soviet Union’s fission and fusion bombs lived in the closed town of Arzamas-16 under congenial conditions. They could hardly have been unaware of Shubnikov’s fate, or those of Stalin’s other, countless victims. Perhaps the physicists consoled themselves that their work would protect their country and their compatriots. That the cold war never became a world war is arguably the result of the dreadful balance of power that Kurchatov and colleagues helped to create and maintain.

Sakharov famously and courageously became a dissident in the 1960s, but how did he feel during the 1940s and 1950s when he was, in effect, arming a tyrant with weapons that could obliterate entire cities? The moral dilemmas that physicists faced under Stalin would be hard for me to imagine, but for a remarkable novel: Life and Fate by Vasily Grossman.

The photo shows Grossman in 1945 in the German city of Schwerin. For almost the entire duration of what Russians call the Great Patriotic War, Grossman was a war reporter for Red Star, the Soviet army’s newspaper. Drawing from his experience at the front and elsewhere, he wrote Life and Fate in 1959.

The novel, which runs to 896 pages in its English translation, provides a broad and detailed view of Soviet society during the battle for Stalingrad. Its main character, Victor Shtrum, is not a reporter like its author or a soldier, but a nuclear physicist based on Lev Landau.

I could summarize the novel’s plot and how Shtrum fares in it, but I won’t, lest I spoil your experience of one of the most moving, engaging, and enlightening novels I’ve ever read.

Charles Day

Last Friday I received an e-mail entitled “LHC video by Bob Dylan’s son.” When I clicked on the link inside, I thought the link was out of date. What appeared on my screen was not the Large Hadron Collider, its mammoth detectors, nor anything obviously to do with particle physics.

Instead, the five-minute video opens with shots of a little boy wandering about in a forest, as an unknown narrator talks about the names of birds in different languages. So far, so New Agey, I thought, but the video soon shifts its attention scienceward to the 19th-century naturalist Alfred Russel Wallace, whose dogged study of Earth’s animals and plants led him to propose a theory of evolution independent of Charles Darwin’s.

Next comes Brian Cox, a member of the collider’s ATLAS team, who discusses links between art and science. Pictures by William Blake, Leonardo da Vinci, and other artists flash by.

Collider for CERN from MadeByFreeForm on Vimeo.

The images of the LHC that fill most of the remainder of the piece are eye-catching, even beautiful. Aesthetically, they hold their own against the photos and drawings of nature and the works of art that precede them. The instruments of particle physics, if not perhaps the science itself, are beautiful, the video seemed to say.

But the video offers another, possibly contradictory point of view—that of Richard Feynman, who appears in extracts from archival interviews. Feynman says that nature is what it is. We might want to find a single ultimate theory but, he warns us, reality could consist of millions of onionlike layers.

That nature at its most fundamental level should be as beautiful as nature at its highest level is a prejudice, a hope, and possibly a mistake.

Charles Day