Now another observation of atomic and planetary systems behaving in surprisingly similar fashion has been reported by Robert Birtcher and Sandrine Schlutig at Argonne National Laboratory, US, and Stephen Donnelly of Salford University, UK (Phys. Rev. Lett. 2000 85 4968). In the March issue of Physics World, Kai Nordlund of the University of Helsinki in Finland describes how the pair used xenon ions to produce huge craters in a gold film – and how their work might shed light on planetary-impact phenomena.
Revenge of the science writer
I once interviewed a well known European physicist whom I had arranged to meet at a table in the noisy lunchroom at the Brookhaven National Laboratory. I pulled out a tape recorder and asked him about one of his experiments. The scientist could barely disguise his impatience. After five minutes we had a slight misunderstanding about where a certain event took place. I corrected him; he thought I hadn’t been listening.
“That’s it!” he fairly roared as he abruptly stood up, his chair shooting backwards. The background hubbub in the lunchroom suddenly plummeted and everyone turned to stare. He strode away, shouting, “This is a total waste of time! You’re an imbecile!” Or at least I think that’s what he shouted. I can’t be sure, because I destroyed the tape. I was too embarrassed to consider replaying it, or risk having others know my humiliation.
Many who write about physics from the outside – historians, sociologists, anthropologists, or journalists – have had experiences like this. At conferences we regale each other with stories. Most of us destroy our tapes, swallow our pride, regard the episodes as occupational hazards and never write about them. The scientists involved count on that, I think, and would be annoyed if we did use the material.
I’m not talking about cases of writers trying to reap publicity, prestige and money by seeking to glean nuggets from prominent, busy people who are struggling with a full schedule. No, I’m talking about scholars and writers who are trying to carry out research into the history, nature or place of science in society. They contact a physicist, describe their purpose, confirm arrangements and then get treated like a cold-call solicitor. It happens rarely, but often enough to arouse speculation that physicists have a special contempt for outsiders.
Writing the Sistine Chapel
One man who does not destroy his tapes is John Horgan, a former editor on Scientific American. Horgan once flew to Chicago for a prearranged interview with the late astrophysicist Subrahmanyan Chandrasekhar, who shared the 1983 Nobel Prize for Physics for his theoretical work on the structure and evolution of stars.
Chandrasekhar, who was then writing a book on Newton’s Principia, demanded to know Horgan’s purpose. Horgan replied that he was writing a two-page profile about Chandrasekhar and his project.
“What!” the Nobel laureate hollered, ordering Horgan out. “You think that you can summarize Homer’s Odyssey in two pages? You think that you can write about the Sistine Chapel in two pages?” Horgan laughed nervously, wondering if this was a joke. It was not. Chandrasekhar again demanded he leave.
A University of Chicago public-relations aide eventually coaxed Chandrasekhar to stop the bullying and go through with the interview – but afterwards Chandrasekhar insisted that Horgan should not print anything about their meeting. Horgan, within his rights, did so anyway, penning a delicate, toned-down description of the encounter.
Horgan’s book, The End of Science, is full of such stories. I think the outraged reaction of many scientists to his book stemmed from the fact that Horgan seemed to pay less attention to what the scientists said than to the way they said it. But his point, in part, was to display the personal involvement of scientists in their work. Uncharitably, one might say that they revelled in the purity and majesty of their knowledge and resented having to debase it by using terms that outsiders can handle – like doing a two-page Odyssey or a dot-to-dot Sistine Chapel.
More charitably, one might say that scientists, ultimately, traffic in words to a lesser extent than others and can get distracted or frustrated by using only that medium. In Horgan’s portrait of the paleontologist Stephen Jay Gould, he notes that the latter can be careless with words not because he doesn’t care about his thoughts but because he cares too much. “Mere speech,” writes Horgan, “is not enough to engage him fully.”
And Richard Feynman, according to one story, was once thrown uncharacteristically on the defensive in a discussion. Losing his temper, he said: “Damn it, don’t listen to what I say, listen to what I mean!”
Hard on colleagues, Feynman was rougher on outsiders who were not up to speed. He was once so rude and rebuffing to an Omni editor that she hung up in disgust. He then called her back to apologize and invited her to fly to Los Angeles to speak to him. She did, produced a tape recorder and asked the first question – whereupon he became enraged because he had been asked precisely that question before in a published interview, screamed at her for her supposed ignorance, ended the interview before it began, and left her to fly back to New York empty-handed.
The critical point
In my own encounter with Feynman – which, incidentally, is recounted in the epilogue to James Gleick’s biography Genius – I asked him questions about episodes of his intellectual development. Feynman’s replies were direct, but accompanied by intense curiosity about why I was asking; he sought to learn. Then I asked him about progress in science. This did not interest him. A physiological change in his face told me that I had abruptly gone from scholar to scribbler.
All at once he grew angry, stood up, and began shouting. “It’s a dumb question,” he yelled, “I don’t know how to answer it. Cancel everything I said!” He slammed his fist into the mountains of papers on his desk, then strode to the door. “It’s all so stupid. All of these interviews are always so damned useless.” He walked down the corridor, shouting: “It’s goddamned useless to talk about these things! It’s a complete waste of time! The history of these things is nonsense! You’re trying to make something difficult and complicated out of something that’s simple and beautiful!”
In that instant, witnessing his curiosity evaporate, I realized this had nothing to do with me, nor with contempt for outsiders, nor with scorn for history. Rather, it had everything to do with Feynman’s absorption in his own work – the same kind of absorption that made him a great physicist.
That was one tape I kept.
The flood-plains of Ganymede
Schenk’s team blended images collected by the Voyager expedition and the recent Galileo probe to construct a three-dimensional map of a region known as Sippar Sulcus, which covers thousands of square kilometres. The technique combines two-dimensional photographs taken from different angles to create a ‘digital elevation map’. The map revealed that the smooth areas lie at an altitude around 800 metres below that of the rugged regions. The depths of the grooves in the rough terrain contrast starkly with the flatness of the low-lying areas, and this strongly suggests that these areas are not original features but have been ‘resurfaced’ – or flooded. “These features directly support the idea that the smooth strips were created by volcanic activity”, says William B McKinnon, a member of the team. Moreover, the gentle gradient in the smooth areas implies that they were filled with a runny liquid, such as a mixture of ice and water. “The liquid is not like solid glacial ice, which would have rounded edges,” says McKinnon.
Schenk and co-workers speculate that Jupiter’s enormous tidal forces may have partially melted Ganymede’s frozen mantle to form the icy lava, which then weakened the surface and erupted through it, but they cannot be sure. It is also possible that liquid water existed on Ganymede – which is the largest moon in the solar system and bigger than Mercury – billions of years ago.
Exciting times for superconductors
The Bardeen-Cooper-Schrieffer (BCS) theory describes how the thermal vibrations of a superconductor’s crystal lattice – known as phonons – enable pairs of electrons to travel through the superconductor without meeting electrical resistance. It also relates the mass of the atoms in the lattice to the superconducting transition temperature – the temperature below which material conducts electricity without resistance. Sergei Bud’ko and co-workers at the Ames Laboratory of Iowa State University, US, found that they could modify – and even raise – the transition temperature of the compound by using different isotopes of boron. This strongly suggests that superconductivity in magnesium diboride is governed by BCS theory, although it is still possible that an unknown coupling effect between the pairs of electrons may be obscuring the result.
New research is appearing in the Los Alamos archive every day as physicists around the world clamour to establish the properties of the newly discovered superconductor. The investigations into magnesium diboride range from the theoretical – including its critical current density and quantum characteristics – to the applied, for example, its ability to form wires and tapes. Future studies may focus on the hunt for superconductivity in similar compounds. Paul Canfield and his team from Ames Laboratory have also found that magnesium diboride superconducts in wire form, raising hopes that the material is the key to the superconducting devices of the future.
Busquin calls for EU Framework increase
Busquin has identified seven key emerging technologies and research priorities: genomics and biotechnology for health; information society technologies; nanotechnologies, intelligent materials and new production methods; aeronautics and space; food safety and health risks; sustainable development and global change; and citizens and governance.
Busquin is also proposing special measures for innovation, the mobility of researchers, and the networking of national research programmes. It is also hoped that the participation of small- and medium-sized companies (SMEs) will increase from 10% in the current Framework to 15% in the sixth programme.
The European fusion programme is also funded through the Framework programme. At an informal meeting last month European research ministers recommended that the EU maintain its current spending on fusion research throughout the sixth Framework, thereby giving the green light to the International Thermonuclear Experimental Reactor (ITER). France, Japan and Canada are currently vying to host ITER.
Turbulent times for fluids
Bodenschatz and co-workers had studied turbulence for several years using conventional methods based on tracking ‘tracer particles’ in the fluid. But it was impossible to accurately track particle motion in highly turbulent conditions because the method only revealed changes in acceleration over relatively long periods. “We were about to call it quits”, Bodenschatz told PhysicsWeb, “when I spoke to Jim Alexander at the Cornell Electron-Positron Collider”. The collider at Cornell uses arrays of light-sensitive silicon strips capable of gathering up to 70 000 images every second. Bodenschatz and co-workers adapted the system for their experiment and were delighted to find that it could image particle motion with vastly improved time resolution.
Bodenschatz’s team studied highly turbulent flows with Reynolds numbers – a measure of turbulence – of up to 63 000. The Reynolds number is related to the density and velocity of the fluid, and a value of 2000 marks the transition from streamline or ‘laminar’ flow to turbulence. In the new set-up, three arrays of silicon detectors image the motion of tracer particles in each dimension, and a computer program calculates the three-dimensional acceleration measurements. The team was surprised by the enormous range of accelerations they found, from zero to 12 000 m s-2. Statistically, this is an increase from zero to 30 times greater than the root mean square velocity and back again – all within fractions of a millisecond and hundreds of micrometres.
Studies of turbulence underpin our understanding of cloud formation, atmosphere and pollution transport as well as numerous industrial processes involving chemical mixing and combustion. “On the academic side, however, we still have no understanding of the universal properties of turbulence”, says Bodenschatz, “but such accurate particle tracking opens up a whole new avenue”.
Bodenschatz adds that these extremely chaotic conditions may already be well understood – by mosquitoes, which are known to cling perilously to blades of grass when the wind exceeds a certain speed, presumably to avoid being swept up in the turbulent atmosphere.
Leonard Mandel and Ugo Fano die
Leonard Mandel performed a string of ground-breaking experiments during his career to convincingly demonstrate that the various counter-intuitive predictions of quantum theory can be observed in the laboratory. Mandel’s group was the first to observe both photon ‘anti-bunching’ and the interference of single photons with themselves. Mandel also made many other contributions, both experimental and theoretical, to quantum optics.
After obtaining a PhD in nuclear physics from the University of London, Mandel lectured at Imperial College for nine years. In 1964 he moved to the University of Rochester in the US, where he spent the rest of his career. He published more than 300 papers, and with his colleague, Emil Wolf, jointly organized the influential Rochester conferences on coherence and quantum optics and co-wrote a 1166-page book Optical Coherence and Quantum Optics.
Ugo Fano dedicated his career to the study of atoms and molecules and their interactions with electrons and light. In particular, Fano is known for his contribution to the basic physics underpinning the gas laser, the ubiquitous tool of the physical and biological sciences. His work also paved the way for the use of radiation in medicine.
Fano began his career in 1934 working with Enrico Fermi at the University of Rome, and later worked with the Nobel prize-winning physicist Werner Heisenberg at the University of Leipzig. Fano later joined the University of Chicago in 1966 after spells at the Washington Biophysical Institute, the Carnegie Institution of Washington, the US Army Ballistic Research Laboratory and the National Bureau of Standards. He received a raft of awards and two honorary degrees for his exceptional contribution to the field of atomic physics.
The hunt for new dimensions
Theorists believe that gravity may seem weak because it is spread out among up to eleven dimensions, unlike the other fundamental forces, which are thought to be confined to the familiar three spatial dimensions. If this is the case, the gravitational attraction between two objects may deviate from the well-known ‘inverse square law’ when they are close together. ‘String theory’ suggests that extra dimensions may be curled up or ‘compactified’ on short length scales – not least because there is no evidence that they exist on the larger scale of our everyday experience. If there are extra dimensions in which only gravity exists, we can only probe them using the interactions of gravity. “No one has ever detected gravity at distances less than a millimetre”, says team member Blayne Heckel.
Adelberger and colleagues set up a ‘torsion pendulum’ consisting of a horizontal aluminium ring 2 mm thick and 55 mm in diameter, suspended on a fine wire and free to spin. Beneath it – separated by 0.2 mm – is a slowly turning horizontal copper disk called the ‘attractor’. The pendulum and the attractor each have a ring of ten equally spaced holes bored through them. As the attractor slowly turns, it twists the pendulum ten times – corresponding to the ten copper ‘bridges’ between the holes – for each complete revolution. A laser reflected off the pendulum measures the degree of twist, from which the attraction between the two components is calculated. The experiment was also shielded from spurious electrical and gravitational effects.
The Washington team found that gravity between the just-separated objects does indeed exist – and that it acts exactly as it does at larger separations. This implies that any dimensions that might be revealed by the strange behaviour of gravity must be tucked away in smaller regions of space. “This doesn’t mean the idea of extra dimensions is crazy”, says Adelberger. “It’s just not as straightforward as the simplest picture”. The team is currently designing a more sensitive experiment to measure gravity at even smaller scales.
Beating the femtosecond limit
They used a technique known as ‘high-harmonic’ generation to convert a 7 femtosecond infrared pulse into a 1.8 femtosecond X-ray pulse. In harmonic generation a large number of photons are combined in a noble gas – the Vienna team used neon – to create a single photon with a correspondingly reduced wavelength. By filtering the harmonics, it is possible to control the duration and wavelength of the X-ray pulse. Krausz and co-workers used such a pulse to study an laser-induced energy shift in krypton atoms with a time resolution that was shorter than a single cycle of their laser source (which lasts 2.6 fs).
Physicists may be able to use the new technique to study processes that occur on sub-femtosecond timescales such as inner-shell phenomena in atoms and ionization via ‘optical tunnelling’. Drescher and colleagues are optimistic that their discovery will pave the way for ultrafast spectroscopy – the study of processes that take place on timescales of just attoseconds – 10-18 seconds.
Over the last four years, other groups have produced laser pulses with durations of around 10 femtoseconds using the high-harmonic method. However, the light in these pulses had longer wavelengths – in the visible and near-infrared regions of the spectrum. These pulses could not be shortened further because they were already approaching the fundamental lower limit for light of these wavelengths.
Heat leaves atom clusters cold
Haberland’s team used a laser technique known as photofragmentation to measure the internal energy of the clusters at different temperatures. Photons deliver energy to the clusters – each containing 147 sodium atoms – prompting atoms to evaporate. The researchers determined how much energy the clusters absorbed from the number of atoms ejected. This yields the energy-temperature profile of the clusters from which the researchers calculated their heat capacity. They found that, around the melting point of the clusters, the temperature fell as the energy increased – in other words, the heat capacity was negative. This phenomenon is expected to exist in many small clusters of atoms. Haberland’s team chose sodium atoms because their electronic structure is simple and well understood.
We are familiar with how large quantities of solids melt. When we warm an ice cube, for example, the kinetic energy or heat is converted continuously into the potential energy needed to break down the crystalline structure. This is the latent heat that increases the entropy of the system without raising the temperature. The amount of solid in the ice cube decreases evenly as it melts. In bulk quantities of ice, only a minuscule fraction – around 10-7 – of the atoms are at the interface between solid and liquid. This ratio makes the increase in entropy energetically favourable.
In contrast, a large fraction – around 20% – of the atoms in tiny clusters are at the interface between the liquid and solid phases. This makes a partially melted state energetically unfavourable. Consequently, the atoms convert some of their kinetic energy into potential energy to help the melting process. The temperature therefore falls – even though the total energy has increased.
Haberland told PhysicsWeb that although an application for the discovery may be some way off, it is nevertheless a significant contribution to our understanding of atomic systems, which is crucial in the rapidly expanding field of nanotechnology.
Physicists have observed similar phenomena in fragmenting nuclei and astronomical objects, suggesting that they share a certain characteristic. Haberland notes that none of these systems can be treated as simple aggregates of their parts. Local effects – for example, gravity between different parts of a binary star system – must be taken into account. A star system sounds enormous compared atom clusters, but is actually very small in terms of the long-range action of gravity. “When Donald Lynden-Bell first applied the concept of negative heat capacity to astrophysical systems, the physics community thought it was nonsense”, said Haberland, “but we have proved that the phenomenon is real”.
Copyright © 2026 by IOP Publishing Ltd and individual contributors