Two US politicians introduced a bill to the US Congress last month that attempts to prohibit the energy secretary, Federico Peña, from re-opening the troubled High Flux Beam Reactor at the Brookhaven National Laboratory. Reacting to the bill, Allan Bromley of Yale University, president of the American Physical Society, fired off an open letter stating, “from a scientific standpoint, I believe that such action is unwise and unwarranted.”
Jobs for the boys
Just under half of all UK undergraduate physics students who graduated in 1995/96 had found jobs by the end of last year, according to the UK’s Higher Education Statistics Agency. In comparison, two-thirds of all students were by then working. One reason for the difference is that 39% of physicists went on to do other study or training, compared to just 20% of all undergraduates.
The most popular employment sector for physicists was a broad category that included business and research activities, property development and renting. Manufacturing was also popular, followed by the wholesale and retail trade, public administration, defence and social security, and finance.
The figures also highlighted the gender imbalance in physics. While women made up 53% of the total student population, just 20% of the physicists who replied to the survey were female.
Axis row rolls on
The axis of the universe debate sparked into life again last month with three papers in the 8 September issue of Physical Review Letters. The story began in April when Borge Nodland from the University of Rochester and John Ralston from the University of Kansas in the US claimed that there is a preferred direction in space, pointing from the constellation Sextans in one direction to Aquila in another. They based their claim on evidence that the plane of polarization of radiation travelling through the cosmos appeared to undergo a systematic rotation.
But Daniel Eisentstein from Princeton University and Emory Bunn from Bates College in the US now say that Nodland and Ralston’s claim is based on a flawed statistical analysis – and that even if the effect existed, it would be impossible to measure. Nodland and Ralston, meanwhile, are standing their ground. “[Their comment] inaccurately reported what we did, is incorrect in several assertions and does not alter our conclusions, ” they insist.
However, three other US scientists, led by John Wardle at Brandeis University, used Nodland and Ralston’s method to analyse recent high-resolution radio and optical signals from various galaxies and quasars. They say that the effect claimed by Nodland and Ralston is “statistically indistinguishable from zero”.
Chile retains role
The country had been threatened with expulsion unless it paid the money it owed to the collaboration by 1 September and also met other conditions on the status of the project. Then on 29 August, Chile came up with the necessary $2.2m.
The news came as a blow for Australian astronomers, who were poised to take over Chile’s 5% share in Gemini. Nevertheless, they may still be able to take part. Informal discussions were held last month during a meeting of the Anglo-Australian Observatory (AAO) board in Durham, UK. Although the AAO cannot make a bid on behalf of Australia, “we are very hopeful that a solution can be found, ” says Ian Corbett, director of science at the UK’s Particle Physics and Astronomy Research Council and a UK representative to both the AAO and Gemini. “We all recognize the benefits to Gemini if Australia were to join and contribute its expertise and additional funds, ” he says. “We are therefore now working together to see if we can establish a basis on which Australia could be invited to join the collaboration.”
Fractional charge carriers discovered
Electric charge normally comes in an indivisible unit: the charge of an electron. Indeed, quarks were thought to be the only particles with fractional charge – and today they only exist in particles that have a integer charge. But last month, two groups of physicists revealed the first direct evidence that an electric current can be carried by quasiparticles with fractional charge."All the interacting electrons are there but they behave as if they are non-interacting quasiparticles with charges of one-third, " says Moty Heiblum of the Weizmann Institute of Science in Rehovot, Israel, who heads one of the groups.
The Israeli group, published its results in Nature, while a French group based at the CEA laboratory near Paris, published its results in Physical Review Letters.
Both groups measured a small electrical current in a two-dimensional electron gas sandwiched between two semiconductor layers. Fluctuations in the current – shot noise – were used to measure the electrical charge of the carrier particles. The sample was chilled to less than 1 K and a strong magnetic field applied at right angles to the layers. By analysing the shot noise in this regime, both groups reported evidence that the electric current is carried by quanta with charge one-third that of the electron. "Up until now, there was no evidence that current could be carried by a fractionally charged quasiparticle, " says Christian Glattli, who heads the French group.
The results agree with a theory which was formulated by Robert Laughlin in 1982 to explain the fractional quantum Hall effect. According to Laughlin, electrons in strong magnetic fields form an exotic new collective state, similar to the way in which collective states form in superfluid helium. A quantum of magnetic flux and an electron exist as a quasiparticle that carries the electric current.
So why did the researchers observe quasiparticles with charges of a third, rather than any other fraction? In Laughlin’s theory, the denominator is always odd, so quasiparticles can carry one-third, one-fifth, one-seventh – or indeed, two-thirds, two-fifths or three-fifths – of the charge on an electron. "It is very difficult to explain intuitively – it is just how nature works, " says Heiblum.
"It is a beautiful result, " says Mark Fromhold of Nottingham University. "It is remarkable that electrical signals from individual quasi-particles can be detected and used directly to measure their fractional charge."
Mission to Saturn back on track
The Cassini/Huygens mission was set to lift off from Cape Canaveral in Florida on 13 October. The flight was delayed, not because of protests by environmentalists, who are concerned that the craft is carrying plutonium, but because of strong winds and technical problems. NASA officials tried a second successful attempt on the 15 October.
A joint mission between NASA and the European Space Agency (ESA), the Cassini spacecraft is designed to orbit Saturn – exploring the planet, its satellites and rings – while the Huygens probe will examine Titan and its atmosphere. The £2.2 bn mission is due to arrive at Saturn on 1 July 2004.
Cassini/Huygens will carry 24 experiments – 18 on the orbiter and six on the probe. The Cassini spacecraft will try to discover more about Saturn’s interior structure, the chemical composition of its rings and how many satellites it has. Its instruments will gather optical and microwave images of Saturn, its satellites and rings, and will also analyze the planet’s magnetosphere and the particles trapped in it.
Some of the Cassini instruments will also gather data en route to Saturn. A cosmic dust analyzer, for example, will examine interplanetary and interstellar dust on the way to Saturn and on arrival will study the planet’s rings. “We know that interstellar dust is passing through the solar system and could even be reaching the Earth, ” says Eberhard Grün of the Max Planck Institute for Particle Physics in Heidelberg, Germany, who is principal investigator on the experiment. “Interstellar dust is extremely interesting stuff. It is very important as it is what the planets are made of, ” he says.
Four months after arriving at Saturn, the Huygens probe will separate from Cassini and make the 22-day journey to Titan. Researchers are particularly interested in Titan because it is thought to resemble the Earth as it was before life began – its nitrogen atmosphere is thick with carbon compounds.
The Huygens probe will parachute through Titan’s atmosphere, making measurements of its physical and chemical properties as it descends. After its journey of more than seven years, the probe will take data for just two hours and 15 minutes – and researchers do not even know whether it will then hit a solid surface or a molten one. “It is due to arrive on 27 November 2004 – that’s a Saturday if I remember right, ” says Michael Bird of Bonn University, who is principal investigator on an experiment to measure Titan’s wind speeds.
To reach Saturn, Cassini/Huygens will make a series of slingshot manoeuvres, using the gravitational pull of Venus, the Earth and Jupiter. Even if the launch passes off without any problems, environmental protesters are concerned that the spacecraft could crash back to Earth as it swings by in August 1999. Electrical power for Cassini and its instruments will be provided by three radioisotope thermoelectric generators containing about 33 kg of plutonium. Protesters are concerned by the consequences of any accident. However, NASA says that the chances of any accident are minimal. A similar campaign failed to halt the 1989 launch of the Galileo mission to Jupiter.
Proliferation worries grow at US reactor
For the last half-century, the US government has taken care to maintain a strict separation between civilian and military nuclear reactors and related technologies. Then last month, the Department of Energy (DOE) started manufacturing tritium for nuclear weapons at the Watts Bar civilian nuclear plant, owned by the Tennessee Valley Authority.
During a scheduled refueling at Watts Bar last month, four lithium-filled rods were loaded into the reactor to produce tritium. The Nuclear Regulatory Commission approved the plan on 16 September, despite protests that civilian nuclear programmes should be separate from military ones and that the move would have a negative effect on efforts to prevent the spread of nuclear weapons.
The DOE started using civilian reactors for tritium production because its own reactors have broken down and its current supplies are decaying. An order signed by the US president, Bill Clinton, specifies that the country has to be able to make more tritium by the year 2005.
Superconductivity: New model goes on the block
Colin Humphreys, head of materials science at Cambridge University, disclosed his ideas at a symposium on the centenary of the discovery of the electron at Cambridge. He has submitted a paper based on his ideas to Nature.
Superconducting materials lose all electrical resistance below a critical temperature; but for many years, this temperature was below 23 K for all known superconducting substances. High-temperature superconductivity was discovered in 1986 when materials with critical temperatures as high as 35 K were found. Since then one of the holy grails of modern physics has been to develop room-temperature superconductors. Such materials could, for example, replace conventional electrical cables and carry current without any loss of power. The present upper limit for superconductivity is 164 K; Humphreys believes his model could be used to design room-temperature superconductors.
All high-temperature superconductors consist of parallel planes of copper-oxide. The atoms lie on a square lattice and the charge is carried by “holes” sitting on oxygen sites. However, no clear theory has emerged that adequately explains high-temperature superconductivity – and very few theories have even been ruled out. Some theorists, such as Phillip Anderson from Princeton University in the US, believe that fundamentally new physics is needed to construct a proper theory, while others argue that an essential piece of existing physics is missing. “I think my model will be very controversial because it’s saying that fundamental assumptions of a lot of theories are wrong. People have put a lot of effort into their pet theories, ” says Humphreys.
Humphreys believes that existing theories fail because they do not take into account the distribution of the holes. He argues that each copper-oxide plane consists of square “nanodomains”, separated by channels that are one unit-cell wide – rather like a grid of streets surrounding blocks of houses. Holes at the edges of adjacent blocks are magnetically paired, he says, and superconductivity occurs because these hole-pairs march collectively along the channels, like trams on pairs of tramlines running between the blocks of houses. There is one hole on each tramline, according to the model, and the pairs of holes move down the channels, hopping from oxygen to oxygen via adjacent copper sites.
Reaction to Humphreys’ model was cautious. “I want to know why the holes pair up in the tramlines and – as with any potential theory of superconductivity – whether it can properly explain why normal materials do not superconduct, ” said Mike Gunn, a theorist from Birmingham University, when told about the model by Physics World. He added that the test of the model will be if it can make concrete predictions that can be experimentally verified.
However, Gunn does see some similarity between Humphreys’ model and recent experimental and theoretical evidence for “stripe phases” in some copper-oxide superconductors, which was obtained by John Tranquada at the Brookhaven National Laboratory and Steve Kivelson of the University of California at Los Angeles. The stripes, containing a high density of holes, lie between insulating regions with low hole-density.
But others are sceptical about any new theories. “There have been many claims to understand high-temperature superconductors, but there is no consensus yet so I am naturally very cautious, ” says Andy Schofield, a Cambridge theorist.
About 100 000 papers have been published on high-temperature superconductivity in the last ten years, which makes it hard for anyone to claim to have a definitive answer. And although Humphreys admits that the model will need to be developed into a full-blown theory before predictions can be made, he believes that in the meantime his model should be used to re-analyse existing data.
US Star Wars test fails
Last month, the US Army Space and Strategic Defense Command received permission to shoot down an orbiting satellite using its mid-infrared advanced chemical laser, Miracl. In the Pentagon’s view, the test would represent a major step towards developing weapons to destroy reconnaissance satellites and other spacecraft in wartime.
Miracl’s six-foot-wide beam was fired at a miniature sensor technology integration satellite (MSTI-3), launched last year by the US Air Force as part of a project to improve the tracking of missiles from space. During the test, engineers plan to increase Miracl’s power slowly, to determine the brightnesses at which various components of its optics start to malfunction. Miracl is based at the White Sands Missile Range in New Mexico.
“We think [the test] is a rather bad idea, ” says Steven Aftergood, a senior research analyst at the Federation of American Scientists. “It tends to violate the status quo of a moratorium on anti-satellite weapons in a way that would jeopardize the security of orbiting satellites.” In addition, adds Aftergood, the test is unnecessary. “If you needed to curtail the reconnaissance capacity of an unfriendly power, you could do it by disabling its ground receivers, ” he says.
It is not even sure whether shooting down satellites would provide a overwhelming military advantage. This years U.S. Army After Next summer war games held at Carlisle Barracks, Pa, looked at the effect of shooting down satellites in the 21st Century. Their results imply that there would be a rapid replacement of knocked out enemy satellites because of the large numbers of orbiting equivalent commercial craft, suggesting limited disruption to the battlefield using such tactics.
So far, the first two attempts at firing the laser have failed. On October 4 a software breakdown caused the experiment to be scrubbed, and a second attempt on the 6 October was canceled due to poor weather. Time might soon be running out for further experiments. On the 23 October MSTI-3 has to be placed into a new decay orbit to reenter the atmosphere. Presently, Defense Secretary Cohen has not authorized further attempts to be made.
Heavy ions split US and Europe
The dispute centres around European contributions to the relativistic heavy-ion collider (RHIC) at the Brookhaven National Laboratory in the US and American contributions to a large ion collider experiment (ALICE) at CERN, the European particle physics laboratory in Geneva. Each side wants the other to participate more fully in its experimental programme – but there are problems with funding and timing.
Both experiments seek to recreate the primordial “soup” of particles than existed immediately after the big bang and from which everyday matter condensed out. Today quarks only exist inside strongly interacting particles, called hadrons, where they are held together by gluons. By colliding two beams of relativistic heavy ions, the physicists hope to create matter with an energy density so high that the quarks and gluons will co-exist as a plasma.
To study this, US physicists have built RHIC. When completed in 1999, it will collide gold ions at energies of 100 GeV per nucleon in each beam. The European ALICE experiment is one of the four detectors planned for the large hadron collider, which will be ready in 2005. Although both sides recognize the advantages in collaboration, obstacles remain.
Europe has contributed to the RHIC experiments at the 10-15% level through various national funding agencies. However, it was originally anticipated that Europe would contribute much more than this. “Historically, the European relativistic heavy-ion community played a leading role in the development of the field. Thus it was natural for the Americans to assume that RHIC would be the world centre and that the community – including the Europeans – would converge on it, ” says Peter Braun-Munzinger of the GSI laboratory in Darmstadt, Germany.
Meanwhile, R&D for the ALICE detector is due to finish at the end of 1998. At this stage, the major groups responsible for building the detector must be identified. However, this coincides with the start of experiments on RHIC and there are concerns that the US will not be able to commit at this stage. “RHIC has taken all of our resources to complete; we do not expect to be able to afford a significant contribution to ALICE until 2002-03, ” says Tom Ludlam of Brookhaven. “We have a very clear timetable for experiments but we do not have a timetable for collaboration, ” says Jürgen Schukraft, who is the ALICE spokesperson at CERN. Nevertheless, there may be a solution that satisfies both sides. Two more European projects on RHIC are under serious consideration, according to Schukraft. And if later funding for ALICE could be found by the US, he adds, the collaboration could get started with intellectual co-operation and perhaps a few $100 000 for R&D.
“I feel that there will be significant US and Japanese contributions to ALICE, ” says Braun-Munzinger. “I also believe strongly that we should leave the door open for a mechanism in which the US can jump into ALICE in 2000-01.”
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