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Priorities are a priority

Ideally you would consult a list of priorities and decide accordingly, taking into account national strengths, weaknesses and needs. But the chances of finding such a list of priorities are slim. Most governments have never asked for such a list and scientists have certainly never volunteered one. There are signs, however, that this is changing.

As always, we can learn from mistakes. The recent trend towards high-powered government-wide co-ordinating councils, for instance, is not the way forward. Such committees have a poor record on both sides of the Atlantic: the National Science and Technology Council in the US rarely meets, while the Council for Science and Technology in the UK has been all but invisible since it was set up in 1993.

Within the UK, the two research councils most closely involved with physics adopt very different approaches. The Particle Physics and Astronomy Research Council is taking the more strategic approach and has drawn up a “road map” of scientific opportunities that, hopefully, can be reconciled with the available budget. With a broader range of subjects to support, the Engineering and Physical Sciences Research Council has developed an algorithmic approach: two panels, each made up of business executives and senior academics, judge physics, chemistry and six other programmes according to a range of criteria. The council then decides the level of funding for each, guided by the panels’ votes. The system ensures that priorities are set, but the method is anything but transparent.

The National Science Board (NSB) in the US has revisited the subject of priorities in a recent working paper, Government Funding of Scientific Research, that concludes: “We are aware of no examples of the scientific community agreeing on the relative priorities for investment across scientific fields. Although many scientists consider the task both undesirable and undoable, the NSB believes that this difficult task will become increasingly important and must be faced over the next few years.”

The NSB report champions the findings of a little-noticed 1993 study by the National Research Council. That report, National Goals for a New Era, is remarkably clear. It advocates that the US should be among the world leaders in all areas of science and that it should maintain clear leadership in some major areas of science. It calls for field-by-field peer assessments by expert panels and even considers, hypothetically, reducing funds for areas in which the US leads the world but in which world leadership is not important. But no other country is as wealthy as the US, so being among the world leaders in all areas is not an option elsewhere.

In a rare example of explicit priority setting, Austria recently asked the European Science Foundation (ESF) for an assessment of two proposals for a transnational research facility – a pulsed neutron source and a crystal-growth facility. The ESF panel, which did not contain any Austrian representatives, did not mince its words: the crystal-growth facility is a non-starter and the neutron-source proposal will need a lot of work if Austria hopes to attract financial support from neighbouring countries.

But without the advantage of size as in the US, or a straightforward question as in Austria, how can priorities be set across science? There are no easy or obvious answers but somewhere, or somehow, astrophysics is being weighed up against zoology in decision-making processes around the world. These are important questions that need to be addressed in public and in detail in every country that takes science seriously. A panel of wise men and women from all disciplines has obvious flaws – the very make-up of the panel will inevitably colour its outlook – but in the absence of anything better, such a root-and-branch (and atom and molecule) review of all science would be an improvement on what is happening now.

Pulsars, glitches and superfluids

These neutron stars usually rotate with such precision that they are known as the best timekeepers in the universe, but every so often their rotation rate suddenly increases. It is thought that these glitches are related to superfluidity inside the star, which allows the neutrons to flow without friction.

Now, a group of Italian scientists have studied the interactions between quantized vortices in the superfluid and the nuclei in the stars, which are widely thought to be responsible for the glitches (P Pizzochero et al. 1997 Phys. Rev. Lett. 79 3347). The work will have important implications for understanding the dynamics and thermal histories of neutron stars.

Neutrons become superfluid at temperatures equivalent to energies of a few MeV. All systems of interacting fermions (particles with half-integer spin) are expected to form a condensate of Cooper pairs at low enough temperatures – familiar examples are superfluidity in helium-3 and electron superconductivity. Neutron stars cool to below 1 MeV very soon after formation, and are therefore expected to have superfluid interiors.

Superfluids are characterized by a forbidden energy gap, which can be calculated using the Bardeen-Cooper-Schrieffer (BCS) equation. The pairing of protons and neutrons in the nuclei also leads to an ordered phase with an energy gap between paired (even) and odd nuclei. Indeed, the equation for the energy gap in nuclei is just a discrete version of the BCS equation. In nuclear matter, the attractive nuclear interactions lead to neutron superfluidity and proton superconductivity.

At the centre of a neutron star, where the density exceeds 2 ´ 1014 g cm-3, the neutrons form a homogeneous superfluid. But in the crust of the star, where the density is lower, this superfluid coexists with a crystalline lattice containing nuclei with comparable numbers of protons and neutrons. The BCS theory must then combine the discrete version for paired nuclei with the extended version for a superfluid.

Direct observational evidence for superfluidity in neutron stars comes from pulsar glitches. A superfluid can only rotate by forming quantized vortices, where the number of vortices per unit area is proportional to the rotation rate. Lines of vortices move outwards from the centre of the star, reducing the vortex density and hence the rotation rate of the superfluid. The coexistence of superfluid and lattice in the crust leads to very distinct rotational dynamics, since vortex lines become “pinned” to nuclei in the lattice. This means that it can take months or even years for the rotation rate to relax after a glitch. If the interior of the star were made up of normal matter, viscous processes would give rise to much shorter relaxation times.

Pulsar glitches are thought to be caused by a sudden release of pinned vortex lines, an idea proposed by Philip Anderson and Naoki Itoh in 1975. Vortex lines can also move continuously through the crust superfluid, either by thermal activation or by quantum tunnelling against pinning forces, a process known as vortex creep. Models indicate that both the unpinning that leads to glitches and the post-glitch relaxation due to vortex creep depend on the strengths of the pinning forces and the lag in rotation rate between the crust superfluid and the lattice.

In particular, a given pinning force can only sustain a certain amount of lag, beyond which the vortex line will become unpinned. Similarly, there is a steady-state lag, somewhat less than the critical lag, at which vortex lines will creep and allow the crust superfluid to relax with the normal matter in the crust. Angular momentum is therefore transferred from the superfluid to the normal matter, and the rate of energy dissipation is proportional to the difference in rotation speed between the two components. Limits on this rate of energy dissipation, obtained from observations of thermal luminosity from pulsars, constitute the most direct constraint on the pinning forces.

So what is the physical reason for pinning? A vortex line is a singularity in the phase of the wavefunction governing the particles in the superfluid. The velocity of superfluid circulating a quantized vortex line decreases as 1/r, where r is the distance from the vortex axis. The kinetic energy of each particle decreases as 1/r2, while the energy that each particle gains through being in the superfluid phase – the condensation energy – is given by ~D2/EF, where D is the superfluid energy gap and EF is the Fermi energy.

At some critical distance, called the coherence length, V, the loss in kinetic energy exceeds the condensation energy. At distances less than the coherence length, the vortex line consists of a cylindrical core surrounding the singularity, within which some particles are in the normal (non-superfluid) state. If the condensation energy varies on similar length scales to V, the vortex line will become pinned to certain preferred sites.

This is the situation in the crust of a neutron star, where the density and condensation energy of the superfluid have different values inside and outside the nuclei. The size of the nucleus is ~10 fm, comparable with the coherence length, while the lattice spacing is 30-50 fm. Pinning forces thus tend to pin the vortex lines to nuclei in the lattice.

The challenge is to calculate and compare the energies when a vortex line goes through a nucleus and when it does not. I made the first estimate of the pinning force in 1977 by simply comparing the condensation energies in these two cases. To estimate the condensation energy inside a nucleus, I combined the local density of superfluid neutrons and the value of D for a homogeneous neutron superfluid at that density.

In 1988, Richard Epstein and Gordon Baym considered how the superfluid density varied between the nucleus and the surrounding neutrons. They used the Ginzburg-Landau approximation, but this is only valid if the density varies over distances longer than the coherence length. However, the change in superfluid density between the inside and outside of a nucleus takes place over about 1 fm. Epstein and Baym therefore rescaled the coherence length by comparing their model’s results for finite nuclei with known experimental results. With this rescaling, sometimes by as much as a factor of 10, they obtained strong pinning energies of around 15 MeV. However, observations of the thermal luminosity of neutron stars give upper bounds on the critical lag between the lattice and the superfluid, ruling out such strong pinning.

Pizzochero and colleagues have instead used a local density approximation, which had previously been used to calculate the superfluid gap and specific heat in the crust of neutron stars. To calculate the pairing energies, they replaced the discrete bound-state energy levels in the BCS equation for nuclei in the crust with a continuous energy spectrum for a single particle. Since the gap and pinning energies mainly depend on the states near the Fermi level, this should be a good approximation to the pairing. The calculation also includes the kinetic energy contributions from the flow around the vortex line.

The results suggest that the pinning force between a nucleus and a vortex line is about 0.5 MeV fm-1, similar to my first rough estimate and about 10 times less than the results obtained by Epstein and Baym. These pinning forces are not strong enough to dislodge nuclei from their equilibrium sites in the lattice, so the vortex line probably only pins to nuclei that lie within its core. Estimates of the critical lag and rate of energy dissipation, assuming this “weak” pinning, agree with observations of thermal X-rays from neutron stars.

Understanding the pairing mechanism in the exotic setting of the neutron-star crust continues to intrigue theoretical physicists, and the microscopic model developed by Pizzochero and colleagues will be used to study other phenomena in neutron stars. It could help, for example, in studying the innermost crust layers, where the “nuclei” might be elongated into rod- or slab-like shapes. And by improving our knowledge of how pinning forces vary in the crust, the model could also provide clues to where vortices accumulate and how glitches are triggered.

Ultraviolet catastrophe?

Synchrotron radiation is now used routinely in many areas of science. Many research groups, especially in physics, chemistry and biology, base large parts of their research programmes on the use of this type of radiation. There are also increasing numbers of scientists who find that a few days’ work at a synchrotron radiation source can provide crucial information to complement their main laboratory-based research. Some of the best examples of this are in protein structure and materials characterization, in which X-ray diffraction and X-ray absorption fine-structure techniques are commonly used.

This widespread applicability of synchrotron radiation is reflected in the growing number of new sources that have recently been built or are being planned or constructed – in many cases in countries where no such facilities previously existed, such as Brazil, Taiwan, Korea, India and Switzerland. Other countries, including Japan, the US, Italy, Germany and Sweden, have facilities that have just opened or are about to open, while the UK is currently debating whether to build a new source called DIAMOND.

Synchrotron radiation is the name given to the light that is emitted when very high-energy electrons or positrons are bent in magnetic fields. The radiation covers a wide and continuous spectral range, from the infrared region to “hard” X-rays at energies above 20 keV. The light is emitted as a narrow cone, enabling large numbers of photons to be delivered to an experiment.

In the early days of synchrotron radiation research in the 1970s, the light was taken “parasitically” from electron accelerators that were built and used for high-energy physics. These “first-generation” machines used bending magnets to contain the electrons in a circular path while they were being accelerated. The synchrotron radiation emitted as the electrons passed through these magnets could be extracted with no disadvantage to the particle physicists working on the machine.

The “second-generation” sources from the 1980s are purpose-built electron storage rings, in which the electrons, once accelerated, are made to orbit the ring at a fixed kinetic energy. These storage rings have beams with half-lives of up to 48 hours and provide a much more stable source of synchrotron radiation than the earlier machines. However, these are still designed to exploit the radiation emitted at the bending magnets.

Third-generation sources

The newest facilities – the “third-generation” sources – exploit so-called insertion devices. These are special magnetic structures that are inserted into the straight sections between the bending magnets on a storage ring. They allow each beamline to have its own spectral characteristics. The two principal types of insertion device – undulators and multipole wigglers – both consist of a linear array of alternating magnetic dipoles, which cause the electron beam to undulate or wiggle about the nominally straight trajectory. The oscillating electrons emit electromagnetic radiation.

The radiation emitted by a multipole wiggler is similar to that of a conventional bending magnet, but if the device has N pairs of magnetic dipoles, the total amount of light emitted is N times greater than from a single bend. The other advantage of multipole wigglers is that they often have higher magnetic fields than the bending magnets. This forces the electrons to travel round tighter bends, delivering more radiation at higher energies.

In contrast, undulators typically have a lower local field than wigglers. However, the radiation emitted at each equivalent point in the periodic oscillating trajectory is temporally coherent, which leads to constructive interference. The emitted radiation is strongly peaked at one particular photon energy – and higher harmonics of this energy – and is emitted in a cone that is even narrower than the radiation produced by conventional bending magnets.

Undulators, in particular, are very attractive sources of radiation. The narrow cone angle means that the “spectral brilliance” – the number of photons per unit area per unit solid angle – is exceptionally high, while the harmonic character of the radiation means that a large amount of radiation power is concentrated at the wavelength of interest. However, the photon energy at which this peak power is generated is directly related to the spatial period of the magnetic array, and although this energy can be tuned by changing the magnetic-field strength, the range is relatively narrow. Typically, an undulator can deliver high-brilliance radiation over a photon-energy range of a factor of no more than 20-40. This tuning range is much narrower than that available from the bending-magnet synchrotron radiation continuum. In other words, the choice of machine energy is vitally important for third-generation sources, since it is so closely matched to the photon energies of interest.

Missing spectral regions

Since undulators produce only a narrow band of photon energies, the scientific community needs synchrotron radiation sources with a significant range of characteristic machine energies. The problem is that all of the new synchrotron sources are clustered round just two energy values. First there are new sources that are optimized to produce X-rays with energies of 2-50 keV – namely the 6 GeV European Synchrotron Radiation Facility in Grenoble, France, the 7 GeV Advanced Photon Source at the Argonne National Laboratory in the US and the 8 GeV Super Photon Ring in Harima Science Garden City, Japan. Then there are sources that have machine energies between 1.2 GeV and 2 GeV, which produce undulator radiation in the range 50-2000 eV. Two other planned machines (DIAMOND in the UK and SOLEIL in France) will have energies lying between these two extremes, while multipole wigglers offer access to even higher photon energies at all of these facilities.

What is conspicuous is the absence of any plans to build third-generation sources that are optimized for lower energy, vacuum ultraviolet (VUV) radiation, especially in the 5-50 eV range. These sources would have a machine energy of about 0.5 GeV. To make matters worse, several existing second-generation machines, which are used extensively for this photon-energy range, are likely to close down as the new facilities come on-stream, mainly for reasons of running costs.

The problem is particularly acute in Europe, where one might have thought that national science policies in this field could be rationally coordinated. However, four third-generation machines with energies in the 1.2-2.0 GeV range are either already in operation or being built. These are the ELETTRA source in Trieste, Italy, MAX II in Lund, Sweden, BESSY II in Berlin, Germany, and the Swiss Light Source in Villingen. The BESSY lab, meanwhile, has recently announced that its second-generation source, BESSY I, will close in 2000, with the run-down actually starting later this year. It is also rumoured that SUPER-ACO in Orsay, France, will be shut down shortly after construction of SOLIEL is planned to begin.

Beamline closures

It therefore seems likely that in the next five years or so there will be a big increase in both the number and quality of synchrotron radiation facilities that produce photons with energies above about 50 eV, but a major reduction in lower-energy beamlines. It is perhaps ironic that the Birgeneau committee in the US recently concluded – in connection with the Advanced Light Source, a new 1.5-1.9 GeV third-generation facility in Berkeley – that the number of important scientific issues that require “soft X-ray” sources (photons at energies of about 500-2000 eV) has declined in the last few years compared with those issues that need higher-energy hard X-rays (Physics World November 1997).

We feel that the loss of vacuum-ultraviolet facilities and the failure to exploit fully the potential of third-generation sources in this energy range are, at the very least, extremely unwise. There is, after all, important science to be done here. Some of the clearest information on the nature of high-temperature superconductivity has come from angle-resolved photoemission in this energy range, a technique that can enable the occupied electronic bands to be mapped directly. For example, German researchers led by Jörg Fink have recently used the BESSY source to identify two Zhang-Rice singlet states associated with the different cuprate sublattices of Ba2Cu3O4Cl2 (1997 Phys. Rev. Lett . 78 4107). Such experiments need the high flux and spectral resolution that are most easily obtained from undulator sources. VUV radiation also offers a powerful source of photons for molecular photochemistry and for a more complete understanding of atomic physics. Recently, for example, a team of British and German physicists led by Hans Kleinpoppen and Uwe Becker studied the magnetic dichroism in photoemission from atomic oxygen (1996 Phys. Rev. Lett. 77 2642).

A common myth is that synchrotron radiation in this energy range is not necessary because lasers can now – or soon will – provide much better sources for these experiments. It is a myth because the characteristics of synchrotron radiation and lasers are intrinsically different, although complementary. Synchrotron radiation can be tuned over a wide range of energies, and has a high average power and a time structure that is effectively continuous for most experiments. Lasers, on the other hand, offer much higher instantaneous power and spectral resolution, but limited or slow tunability. Very few experiments could sensibly be transferred between these two types of source without major restrictions.

Answers, please

The underlying difficulties in rectifying this problem of a lack of VUV sources are twofold. The first is a mixture of fashion and misunderstandings, while the other is financial. One important technical misunderstanding is the role of “electron-beam emittance”, which is the angular spread of the electrons multiplied by the effective source area. The angular spread of the radiation emitted by the electrons cannot be smaller than the angular spread of the electrons themselves. This has encouraged the designers of third-generation sources to aim for lower and lower electron emittances, which has tended to make these machines more complex and more expensive, with beams that do not last as long.

In the VUV region, in contrast, the intrinsic angular spread of the radiation is larger, and low electron-beam emittances are neither necessary nor desirable. However, there is a common belief that lower-emittance machines are old-fashioned and so are not worth building or maintaining. Moreover, the political trend for some years has been to fund sources in the 1.2-2 GeV range, such as ELETTRA, BESSY II and the Advanced Light Source, which offer more immediate impact in applied research in areas like surface analysis and deep lithography. Financial aspects play a role too. In at least one case (BESSY) a perfectly sound second-generation machine is being shut down to save running costs in order to support a new, higher-energy replacement machine. A similar fate appears to await Super-ACO. BESSY I, for example, could easily be upgraded to near-optimal VUV performance with quite modest expenditure.

It is hard to see a solution to this problem. Somewhat perversely, the fact that optimal VUV sources are significantly cheaper than soft or hard X-ray machines – coupled with the fact that they are smaller and can thus handle fewer users at the same time – means that they are not attractive compared with international projects like the European Synchrotron Radiation Facility. On the other hand, with the possible exception of Denmark, no national funding agency seems prepared to commit itself to the creation of a low-energy VUV facility.

The real solution might be to not have national VUV facilities – nor even a single European facility – but rather several machines shared between a group of nations. Some of these could conceivably be obtained by simply upgrading existing sources, such as Super-ACO or BESSY I. In principle, the European Union could be an ideal source of such an initiative, but it is hard to see this happening – especially as we need rapid action if the existing VUV machines are to be saved.

Nobel Prize winner calls for ethics oath

A number of notable speakers attended the event which was organized by the UK Pugwash group and held at the Royal Society in London.

Sir Michael Atiyah, ex-president of the Royal Society and President of Pugwash Conferences on Science and World Affairs, started the proceedings by arguing that “Scientists have a responsibility greater than that of the average citizen”. His reasoning was that as scientists have the knowledge and skills to interpret complex scientific data, they have a duty to inform others of any dangers in their work. His greatest worry was that “If scientists don’t get involved with the ethical debates, the public will backlash against science.”

During his speech, he pointed out the success of movements such as the Federation of American Scientists and Friends of the Earth in promoting scientific analysis to the public.

Bernadette Modell, professor of genetics at University College Medical School, London, described how medical research has affected her principles. She advocates massive screening of the population for hemoglobin diseases. In the UK 10 percent of the population are carriers, and the figure is much higher in the developing world. “Screening is a controversial idea in the medical community, ” she told the audience. Statisically 98 percent of couples want prenatal screening to find out if they are carriers. The ethical implication of screening is that 70 percent of couple would terminate a child with the disease. Prof Modell pointed out “the closer you are to the patient, the more important the patient needs become.”

Ruth McNally of Brunel University discussed some of aspects of commercial scientific research as organizations rush to patent their work. “There is a unholy alliance between biotechnology and patents” she claimed. Her largest concern is a new law on patents passing through the European Parliament. If passed, the law is expected to form the basis of a global patent law on biotechnology. She called on scientists and the public to campaign against it.

The panel finished with Sir Martin Rees, an astronomer at Cambridge University, suggesting weapon scientists were responsible for increasing tension during the cold war. He pointed out how the lack of public controls in the weapons laboratories had created billion dollar programmes with limited research accountability. Rees also stressed how important whistle blowers have been in providing information on such projects. The failure of the X-ray laser, he said, would never have come to light but for the scientists who told the US Congress about it. Rees was also worried about the lack of independent experts available to review defense research in the UK.

In the question session afterwards, Frank Blackaby asked why the speakers had not discussed the issue of whether an action is right or wrong, whatever the morality? Professor Rotblat called for scientists to sign a hippocratic oath, and pushed for the formation of a international science panel on ethics. Jack Boag of the Institute of Cancer Research, University of London, pointed out there already existed a hippocratic oath for scientists, promoted in the US by Student Pugwash USA.

An member of the audience suggested that limited access and misreporting in the media created mistrust between the public and scientists. Others added that censorship in UK laboratories on the BSE disease was not caused by the media but government policy. Georges Kutukdjian, Director of the Bioethics Unit at UNESCO, said that UNESCO has been encouraging newspapers in the developing world to promote science and technology in local news to help break down barriers between science and the public.

Glass floppy disks?

Aluminium alloys are widely used as a substrate in magnetic disks, but the demand for higher storage and faster access times require better materials. A replacement material would need to offer a thinner substrate, a higher recording density, a very smooth surface, and a high degree of flatness.

Originally platinum alloys were considered to be a solution, but drives built with the alloys suffered from electrolytic corrosion caused by interactions between the magnetic film and the substrate.

Yamamura Glass Company believes that glass can replace aluminium. Glass is known for its excellent chemical durability, mechanical strength, heat resistance, surface flatness and surface smoothness. Patent 5691256 describes a process to improve two types of glass substrate for magnetic disks, a ion exchange glass and a glass-ceramic.

These types of glass generally cause deterioration of the magnetic film due to alkalis in the material. Yamamura’s invention is related to a new set of glass compositions, and the way in which they are heated, polished and chemically treated. The process limits the degradation of the magnetic film, without losing the traditional advantages of the material, thus making it the perfect compound for use as a substrate.

Modelling electron orbits

In 1911 Niels Bohr used quantum theory to explain how negatively charged electrons could remain in certain orbits without radiating energy. Patent 5695344 describes an educational demonstrator that simulates the theoretical orbital motion of electrons around the nucleaus of various elements.

The device works by magnetically deflecting a series of wires. Inside a container is an array of permanent magnets. On one side is an electric motor which is used to generate a rotating magnetic field. A series of thin wires are linked from a base unit to a series of coloured balls. These balls represent the electrons. Smaller permanent magnets are in turn repelled and attracted by the rotating field, causing the wires to perturbate freely. This in turn mimics the multiple orbital paths taken by each electron in its respective shell.

Royal observatory could be split up and sold off

It now seems likely that the RGO will be sold and its staff either transferred to other work or made redundant.

The RGO is run by the Particle Physics and Astronomy Research Council (PPARC) and provides technical support for the UK’s overseas telescopes. But in July, PPARC decided to concentrate this activity at a new Astronomy Technology Centre in Edinburgh. Staf f at the RGO then devised plans for the observatory to become an independent institute but PPARC has now rejected these plans.

Three possible options now exist: the RGO could be run as an independent institute if it can raise enough money; it could be bought by a university; or it could be split up and run by several different organizations. The third option seems the most likely .

Highlights of the year

World’s first atom laser

Physicists at the Massachusetts Institute of Technology made the world’s first atom laser in 1997. The team started by cooling sodium atoms in a magneto-optical trap to form a Bose-Einstein condensate. This is a new state of matter in which all the atoms are in the same quantum state. By applying a short radiofrequency pulse to the trap, a laser-like beam of atoms can be released from the trap.

A crucial feature of any laser is its coherence. The MIT team demonstrated the coherence of the condensate by using an ordinary laser to split it into two, and then recording an interference pattern as the two condensates fell under gravity.

The MIT groups describes its atom laser as rudimentary. An operational atom laser would have applications in atom optics, atom lithography and precision measurements.

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NASA’s Mars mission

1997 has been a great year for planetary science. On Independence Day NASA celebrated its first lander mission in over twenty years with a successful touchdown of the Pathfinder spacecraft on Ares Vallis, the mouth of a suspected outflow channel. The lander contained the “Sojourner” rover which moved across the surface sampling different types of rocks. The mission has special revelance to climatologists as data from the probes indicated that Mars was indeed significantly wetter in its past. The first papers from the mission suggest that rocks visualised by the rover had undergone fluvial erosion, comfirming the belief that Pathfinder had landed on a flood plain. Rocks were also found to be similar to Earth rocks.

The Pathfinder Web site has also entered the record books with more visitors in a single 24 hour period than any other Web site.

Mars Observer, Pathfinder’s sister craft, quietly went into orbit around the red planet with a series of breathtaking aerobraking maneourves. Recently cameras on the spacecraft noticed the start of a dust storm in the southen hemisphere which could provide valuable data on Martian dust storms. Information from both spacecraft have reminded scientists how similar Mars is to Earth, and generated significant public interest about the possibility of life on Mars in the past.

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Carbon nanotubes point towards electronics

1997 was the year in which researchers got serious about applications of carbon nanotubes. Previously these nanometre-sized tubes of carbon were only available as bundles of tubes with different diameters or as concentric multiwall tubes. The breakthrough came when researchers at CNST in the US developed a reliable way of making single-wall nanotubes with well-defined diameters.

Nanotubes are characterized by two numbers – usually m and n – which determine many of their properties, including their diameter and whether a given tube is metallic or semiconducting. Nanotubes are also expected to behave as one-dimensional quantum wires and to exhibit many unusual electronic properties. Measurements on single nanotubes have confirmed many of these properties and researchers at Berkeley are now investigating the possibility of building all-carbon nanometre-sized electronic devices. Other experiments have shown that nanotubes also have useful mechanical properties.

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Get ready for quantum information technology

Recent years have seen exciting progress in a new field of physics that goes by the name of quantum information technology. The field is essentially based on the ability of quantum particles to be in two or more places at the same time. In the mid-1980s it was shown that a quantum computer could, in theory, perform calculations much faster than is possible on a classical computer. Two years ago the first simple quantum logic gates were demonstrated – just one of a series of experimental and theoretical breakthroughs that continued in 1997.

Quantum information technology essentially involves three subjects: quantum computation, quantum cryptography (in which quantum entanglement is exploited to achieve completely secure communication), and quantum communication, in which quantum properties are used to communicate in ways that are not possible classically. The most recent breakthrough in the field is the quantum teleportation of the polarization of a photon at the University of Innsbruck.

In addition to its potential for applications, the techniques being used in quantum information technology are also revolutionizing studies of the fundamentals of quantum theory.

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Galileo’s views of Jupiter

1997 sees the end of the Galileo spacecraft’s primary mission. In the past two years the probe has sent over a gigabyte of data and hundreds of photographs back to Earth. Its most notable achievements were the discovery of a magnetic field around the moon of Ganymede, volcanic ice flows on Europa’s surface (which supports the premise of liquid oceans underneath the icy crust), and the presence of metallic cores inside Europa, Io and Ganymede, but no evidence for one in Callisto.

The spacecraft has sent a probe into the Jovian atmosphere, and discovered volcanic activity on Io is more violent than previously thought, with dramatic changes since the Voyager spacecraft first took pictures. It has also discovered Callisto atmosphere contains hydrogen and cardon dioxide.

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New physics beyond the Standard Model

The Standard Model of particle physics has survived for more than two decades despite regular hints of “cracks in the edifice” from accelerator labs and compelling evidence from theory and astroparticle physics experiments that there is “new physics” beyond the model. Results announced by the DESY Research Centre in Hamburg earlier this year are the strongest evidence to date for such new physics.

In the Standard Model there are two types of matter particles – quarks and leptons – and four forces (gravity, the electromagnetic force and the strong and weak nuclear forces). The matter particles all have half-integer spin (i.e. are fermions) and come in three families. The particles that transmit the forces (photons, gluons and the W and Z particles) all have integer spin (i.e. are bosons).

Collisions between positrons and protons at DESY probe the strong force, which most physicists believe is described by the theory of quantum chromodynamics. However, two multinational experimental teams at DESY – working on the H1 and Zeus detectors – have detected more events under certain conditions than are predicted by the Standard Model. The odds of these results being statistical fluctuations are about one in a thousand. Possible explanations of the results are a new particle called a leptoquark or evidence of substructure in quarks.

The results announced in February were based on data taken between 1994 and 1996. DESY researchers are currently analyzing a run earlier this year which acquired twice as much data.

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Visible gamma-ray burst

In the begining of the year, astronomers made the first visible observations of an object causing a gamma-ray burst. The event was still being witnessed by the Hubble Space Telescope some six months after the burst happened. The continued visibility of the object, and its rate of decline over time, supported the theory that the event is from a “relativistic” fireball expanding near the speed of light. This also suggests that such objects occur far outside our own galaxy. The decline in the visible spectrum is as predicted by present fireball theories.

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US agrees to fund CERN

Experiments don’t come any bigger than the Large Hadron Collider (LHC) at CERN, the European particle physics lab in Geneva. And there is no bigger prize in particle physics than the Higgs boson, the particle (or particles) though to be responsible for the generation of mass – and the main raison d’etre of the LHC. But big experiments cost big money and this December the US agreed to contribute $531 million to the construction of the LHC and its two detectors, ATLAS and CMS.

The US contribution will cover about 10 per cent of the costs of the LHC and will also enable the collider to be built by 2005 – three years earlier than would have been possible otherwise. The deal is notable for other reasons: it is the first time that the US has contributed to the construction of a particle physics experiment outside the US, and it should mark the end of the bad feeling that has existed since the cancellation of the US’s Superconducting Super Collider – an even more ambitious experiment to discover the Higgs – in 1993.

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Fractional charge carriers discovered

Electric charge normally comes in an indivisible unit: the charge of an electron. Indeed, quarks are thought to be the only particles with fractional charge – and they only exist in particles that have a integer charge. But this year, physicists from Weizmann Institute of Science, Israel and the CEA laboratory near Paris revealed the first direct evidence that an electric current can be carried by quasiparticles with fractional charge.

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.

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The world-famous magnetic frog

When a group of physicists decided to perform an experiment which, they hoped, would “lead to a wider appreciation of the importance of magnetism in the world around us”, they can hardly have expected to feature on front pages and television bulletins around the world. But that is what happened to a team from the universities of Nijmegen and Nottingham when they levitated a frog in a 16 tesla magnetic field.

The frog floats in mid-air because, like every material and living creature, its possesses molecular diamagnetism. Although this is typically millions of times weaker than ferromagnetism, it means that a frog can be levitated if it is placed in a magnetic field with a high enough gradient. Animal lovers will be pleased to know that the frog was perfectly safe inside the magnet and that afterwards it “returned to its fellow frogs in the biology department.”

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Holes in a final theory?

Reviewed by Bernard Carr.

There are a some ideas in science – usually those that try to extend it in unorthodox directions, or which trespass too far into the domain of metaphysics – that seem to produce very extreme reactions. Depending on their philosophical propensities, people either passionately embrace or vehemently reject them, but they cannot ignore them. One can confidently predict that the idea explored in this book – that a form of cosmological natural selection could have determined the constants of physics – will fall into this class. When I discussed the author’s proposal in a talk some years ago, a distinguished colleague found the idea so annoying that he left the room in a rage. Doubtless others will react in the same way. On the other hand, judging by the number of papers and meetings it has spawned, many people will find the idea intriguing.

The starting point is the familiar argument that certain features of the universe – in particular the values of various physical constants – seem to be necessary in order for life to arise. This is because life requires chemistry, chemistry requires stars, stars require galaxies, and all of these require special relationships between the constants, which are unlikely to arise by chance. Indeed, although it is unclear where his estimate comes from, Smolin gives the probability of a universe with life-conducive conditions as only 1 in 10229!

One reaction to this situation is to invoke the “anthropic principle”. This proposes that the presence of life explains these coincidences. This idea has been interpreted in two ways – either as evidence for a beneficent creator (God) who made the world for our convenience, or as an indication of the existence of many other universes in which the constants and laws are different. Although the second interpretation is less theological (and may even arise naturally in the context of the inflationary scenario for the early universe), both explanations are untestable and therefore equally liable to be dismissed as metaphysics.

Opponents of the anthropic principle would prefer to argue that the constants will turn out to be determined by some “final theory” that unifies all of physics. The latest developments in superstring theory suggest that we may be tantalizingly close to this holy grail, but the current theories still contain a multitude of coupling constants whose values seem to be arbitrary. Some of these constants may be explained by the final theory, but Smolin argues (and I agree with him) that it is unlikely that this will be the case for all of them. Even if they were explainable, it would be remarkable that the values predicted were precisely those required for life. Therefore there is clearly something to explain, and any world-view that does not come to grips with this must be regarded as incomplete.

Smolin, a physicist renowned for his research in quantum cosmology, offers a radically different approach to the problem. He rejects the explanations offered by the anthropic principle and the final theory, arguing instead that the physical constants (and perhaps even the laws of physics themselves) have evolved to their present form through a process akin to mutation and natural selection. (In other words, the physical constants are contingent rather than fundamental.) He harnesses various physical, biological and philosophical arguments in support of this proposal. The status of each of these three types of argument is very different, so I will discuss them in turn.

The underlying physical assumption is that whenever matter gets sufficiently compressed to undergo gravitational collapse into a black hole, it gives birth to another expanding universe in which the fundamental constants are slightly different. Since our own universe began in a state of great density (i.e. with a big bang), it may itself have been generated in this way (i.e. via gravitational collapse in some parent universe). Cosmological models with constants permitting the formation of black holes will therefore produce progeny – which may each produce further black holes since the constants are nearly the same – whereas those with the wrong constants will be infertile. Through successive generations of universes, the physical constants will then naturally evolve via small random variations to have the values for which black-hole (and hence baby-universe) production is maximized.

Although there is no direct evidence for this startling proposal (and perhaps there never can be), a theory that combines features of the big bang and Darwinian evolution certainly has some appeal. There is no need for the constants to be determined by a final theory (indeed, if they are, the proposal is wrong) and there is no need for the anthropic principle since it is the proliferation of universes and not life that is crucial. In Smolin’s view (although this part of the argument is not altogether convincing) life is just an incidental consequence of a universe having sufficient complexity to give rise to black holes. The proposal also has the attraction of being testable, since it implies that any variation of the constants from their present values should lead to a universe with fewer black holes. The effect of such variations can be calculated: many of the variations would indeed reduce the number of holes, but our knowledge of astrophysics is too incomplete to demonstrate that this would be the case for all of them.

In its own way, of course, this proposal is just as metaphysical as the anthropic one, since it is still necessary to invoke a huge number of other universes whose existence can never be ascertained directly. The idea is therefore equally likely to provoke a hostile reaction in certain quarters. It also depends on highly speculative physics associated with the early universe and black-hole collapse. To analyse the scenario properly, one needs to answer a number of questions. Why are the constants changed at the birth of each baby universe and in what way? How many universes are produced from each black-hole collapse? What happens if the entire universe recollapses, so that all of the black holes it contains merge? Until one has a proper theory of quantum gravity, there can be no consensus on these issues, so it is hard to place much confidence in any speculations based on them. Nevertheless, given that such questions may be resolved eventually, the proposal is an intriguing one. After all, as Smolin emphasizes, natural selection was accepted in biology well before the mechanism of mutation was understood.

The biological aspects of the scenario hinge on the nature of life, and are less controversial. Smolin’s description of life as a self-organizing self-reproducing non-equilibrium process maintained by energy flows from stars and manifested as a hierarchy of ecosystems on different scales is fairly standard. More unusual is his claim that this hierarchy extends all the way up to the galactic scale. This is because non-equilibrium processes in the interstellar medium (involving massive stars and phase transitions associated with molecular cloud formation) play a crucial part in the build up of complexity.

He is anxious to emphasize that this does not mean that galaxies themselves are alive but, within the terms of his own hypothesis, it is not clear why this is the case since most of them probably contain massive black holes in their nuclei (i.e. they can reproduce in the sense that they generate other universes containing more galaxies). Indeed, in view of the reproductive capacity attributed to entire universes, the puzzle is that the author does not extend the hierarchy to the cosmological scale and conclude that the entire universe is alive. The proposal is rather confusing on this point: the distinction between life and complexity is never made very clear, and one senses that something is missing here. Perhaps it is any reference to that other attribute of life – consciousness – a topic that the author studiously avoids.

Smolin’s discussion of the philosophical aspects of his proposal is the least satisfactory part of the book. His overriding philosophical standpoint is that one must reject the “absolute” view of the world espoused by Newton and replace it with the “relational” view of Liebniz. Of course, Newton’s notions of absolute space and time were demolished long ago, but the idea that there may be an absolute reality and even an absolute observer (i.e. God) who stands outside the world still prevails. In the relational view neither of these can exist. There is only a consensual reality created by many different observers, and the laws of physics, such as gauge theories, are a reflection of the fact that different viewpoints must be consistent. He argues that such a view is also implied by quantum theory and is incompatible with what he terms “atomic reductionism” – the notion that the fundamental properties of matter are fixed independent of the rest of the universe. For this reason he also rejects the idea that the fundamental constants can be explained by some final theory.

Discussing these issues certainly serves to put Smolin’s idea in a broader intellectual context, but there are always dangers when physicists stray into the field of philosophy, and I find these arguments unconvincing. One could particularly take issue with his inference that his theory disposes of the necessity for God in that it implies the universe can explain itself. As shown by the deeper discussions of some theologians, this argument is much too simplistic.

It is anyway surprising that he spends so much time arguing this point, since it does not really impinge on the viability of his proposal. Indeed, one criticism of this book is that it is unnecessarily long. Its prime message can be stated very succinctly but, to my mind, too much space is devoted to discussing philosophical and theological issues that are peripheral to the main theme. The book is also rather thin on references: several key figures in the area are uncited and it is disappointing that the closely related scenario of Andre Linde, who has discussed the anthropic principle in the context of the inflationary model, is not mentioned (see “Sizing up the universe” by Andrew Liddle Physics World November pp47-48).

Despite these criticisms, this is a provocative and intriguing book, and at least some readers will be in the “passionately embracing” category. After all, any theory that weaves together three of the most important ideas in the history of science – quantum theory, relativity theory and evolution theory – must have something going for it. Indeed, if it did turn out to be correct, it would surely qualify as one of the most important developments in the history of science. The probability of this will be judged to be small by the “vehement rejecters”, but the idea is still worth investigating and this book makes a valiant first attempt.

Bone breakthrough

One of the holy grails of medicine is the production of a compound that help speeds up the regeneration of bone. Toshiyuki Ohnishi and Nobuhiro Moriyama, have patented a material they claim can do so.

The bone inducing material comprising a piezoelectric porous membrane. It has been known for sometime that bone has piezoelectric properties, and various experimental and clinical attempts to increase bone production by electrically stimulating the bone have been published.

Dentists have developed a technique called guided tissue regeneration (GTR) as a means of artificially regenerating bone destroyed by disease. A semi-permeable membrane is used to promote the activation of cells, and to help new bone form on the existing bone tissue. However, in certain situations the bone takes a number of months to heal.

Patent 5684061 describes the results of intensive studies by the two researchers. They found, to their surprise, that when a porous piezoelectric membrane with pores of a certain size is used, bone can be rapidly regenerated. Indeed, the technique can even lead to increased production of bone beyond the area that was damaged in the first place.

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