1. Bose condensates make waves - again

Bose condensates and atom lasers were in the news throughout 1999. The year started with four groups reporting evidence for an atom laser - a highly directional and coherent beam of atoms in which all the atoms have the same wavelength - and ended with Wolfgang Ketterle and colleagues at MIT in the US and a collaboration between the Tokyo and NIST Gaithersburg groups both reporting evidence for the successful amplification of an atom laser beam. All these experiments relied on Bose condensates - a state of matter in which all the atoms occupy the same quantum state - to supply the atom laser beam.

Other condensate-related highlights included the observation of vortices and critical velocities - which could lead to an improvement in our knowledge of superfluidity - and an experiment in which a condensate was used to slow light down to a velocity of 17 kilometres per second. Finally, Brian DeMarco and Deborah Jin of the JILA laboratory in Boulder, Colorado, produced a quantum degenerate gas of fermions in which all the atoms occupied the lowest-energy quantum states available to them.

2. Superheavy elements

January saw the creation of an element with 114 protons and the first evidence for a new family of stable "superheavy" elements. At the time element-114 was the heaviest element known, but it was joined later in the year by elements 116 and 118, and a second isotope of 114. The two isotopes of element-114 were created by a Russian-American collaboration working at the Dubna Laboratory of Heavy Ion Nuclear Reactions in Russia, while elements 116 and 118 were created by a German-American team working at the Lawrence Berkeley National Laboratory (LBNL) in the US. The discoveries confirmed the existence of the so-called island of stability.

NB: The paper reporting the discovery of element 118 was retracted by its authors in 2002. The retraction followed an investigation into alleged scientific misconduct by one of the authors, Victor Ninov. More details about the investigation can be found at Report on the Formal Investigation of Alleged Scientific Misconduct by LBNL Staff Scientist, Dr Victor Ninov (6M pdf file).

3. Supersymmetry in nuclei

Another breakthrough in nuclear physicists was the first firm experimental evidence for supersymmetry in nuclei. In supersymmetry fermions - particles with an intrinsic angular momentum or "spin" of ½, 3/2 and so - can be related to bosons - which have spins of 0, 1, 2 and so forth - by a series of space-time transformations. The supersymmetry manifests itself through relationships between the energy levels in quartets of so-called even-even, even-odd, odd-even and odd-odd nuclei (where an even-even nucleus has an even number of both neutrons and protons and so on). The technique cannot, however, be extended to tests of supersymmetric theories in particle physics.

4. Quantum precision

1999 was a good year for precision experiments in quantum mechanics. Two of the highlights were the repeated measurement of a single photon in a superconducting cavity and the observation of quantum interference effects in a beam of carbon-60 molecules. The single-photon experiment at the Ecole Normale Supérieure in Paris was an example of a quantum non-demolition measurement: the team was able to repeatedly observe the photon without destroying it. The carbon-60 experiment at the University of Vienna in Austria observed wave-like behaviour in a beam of carbon-60 molecules - the largest particle for which quantum interference effects have been observed.

5. Extra-solar planets

Although more than 30 planets have been observed outside our solar system since 1995, this year saw three new highlights in this field. In April Paul Butler of the Anglo-Australian Observatory and co-workers discovered three Jupiter-sized planets orbiting the star Upsilon Andromedae. It was the first time that more than one planet had been found orbiting around a star other than the Sun. These planets, like all of those discovered before them, were observed indirectly as a result of the 'wobble' in the star's motion. More direct evidence arrived in November when Greg Henry of Tennessee State University and co-workers observed a star become slightly dimmer as a planet passed in front of it. And this month Andrew Cameron from St Andrews University and co- workers reported the observation of light that had been reflected from the planet orbiting around the star tau Bootis.

6. Nanotubes

Carbon nanotubes - tiny tubes of carbon that are just a few nanometres across and several microns long - continued to surprise in 1999. In February researchers at Michigan State University in the US and NEC in Japan came up with a scheme for using nanotubes to make superfast computer memory. Other potential applications included artificial 'muscle' and a nanotube-based storage system for liquid hydrogen that could help make hydrogen-fuelled cars a common sight on our roads. Fundamental physics with nanotubes included a demonstration of the Aharonov-Bohm effect and Luttinger-liquid type behaviour.

7. Spintronics

Traditional electronic devices exploit the charge on an electron but not its magnetic moment or "spin". Over the years various spin-based devices - such as spin transistors, spin memory storage devices and spin quantum computers - have been proposed. Many of these devices rely on being able to inject a spin-polarized current into a device: in other words, all the electron spins must point in the same direction. 1999 saw several advances in 'spintronics'. A team at the University of Würzburg in Germany found a way to inject spin-polarized electrons into a light-emitting diode (LED), while a team at the University of California at Santa Barbara (UCSB) was able to inject spin-polarized holes into an LED, causing it to emit polarized light. Earlier in the year the UCSB team showed how to transport electrons over a distance of 0.1 millimetre while preserving their quantum properties.

8. Cosmology and astrophysics

There are major advances in astrophysics and cosmology in most years and 1999 was no exception. For the first time, astrophysicists managed to record an entire gamma-ray burst over a wide range of wavelengths, including the visible region. Astronomers now know that there are two different types of gamma-ray bursts, one of which is connected with supernovae explosions. Meanwhile, despite problems with its gyroscopes (which are currently being repaired), the Hubble Space Telescope allowed astronomers to converge on a value of 12 billion years, plus or minus 10 per cent, for the age of the universe. There was also further evidence for both a "flat" universe and an accelerating universe, although the latter continued to be a subject of debate within the astrophysical community.

9. Extra dimensions you can see?

How many dimensions exist in the universe? Many theories predict that the universe contains 10 or more spatial dimensions. The problem is that all but three of these extra dimensions are rolled up or "compactified" so small that experiments cannot even begin to observe them. However, recent developments in theory suggest that these extra compact dimensions might have scales of 10-10 and 10-13 metres. If the theory is correct, the extra dimensions might show up at the Tevatron accelerator at Fermilab in the US or at the Large Hadron Collider being built at CERN in Europe.

10. Physics get fashionable

Physics sometimes makes it to the front page of newspapers but until this year it had never, to PhysicsWeb's knowledge, made it to the fashion pages. In March Thomas Fink and Yong Mao, physicists at Cambridge University, announced that they had discovered six new "aesthetically pleasing" tie knots. Fink and Mao used a triangular lattice and methods from statistical physics to study the problem of knotting a tie, and have since written a book about the physics of ties.