Highlights of the Year
Dec 20, 2002
2002 has been an exciting year for physicists. From the production of large numbers of anti-atoms at CERN to the first measurement of the polarization of the cosmic background radiation, there has been no shortage of important developments. PhysicsWeb selects its top ten stories of 2002 -- a year that will also be remembered for two high-profile cases of scientific misconduct.
1. Anti-atoms at CERN
2. Cosmic microwaves reveal polarization
3. New results confirm neutrino oscillation
4. Defying the second law
5. Advances in Superconductivity
6. Ultra-cold atoms research continues to make advances
7. Magnets in nanoscale logic devices
8. Neutrons used to measure quantum gravitational effects
9. First evidence for ‘tetra-neutrons’
10. Bright times in optics
11. Low points of the year
12. Hope for the future
Large numbers of cold anti-atoms were produced this year for the first time. In September the ATHENA experiment at CERN made 50 000 cold antihydrogen atoms by combining antiprotons and positrons in a series of magnetic and electrostatic traps.
Two months later the ATRAP experiment, which is also based at CERN, produced an estimated 170 000 antihydrogen atoms. This group was also able to study the internal states of antihydrogen for the first time. Both groups used similar techniques to make the anti-atoms, but different detection methods.
The ultimate goal of both experiments is to compare the energy levels of hydrogen and antihydrogen atoms in detail and perform the most accurate ever tests of CPT (charge-parity-time) symmetry. Any violation of CPT symmetry -- which would require new physics beyond the Standard Model of particle physics -- would appear as a slight difference in the frequency of electronic transitions between the ground state and the first excited state in hydrogen and the corresponding transition in antihydrogen.
Astronomers in the US detected the polarization of the cosmic microwave background -- the microwave ‘echo’ of the Big Bang -- for the first time. The researchers used the Degree Angular Scale Interferometer (DASI) at the South Pole to make the measurements, which agree with predictions and provide further support for the standard Big Bang plus ‘inflation’ model of cosmology. The results also confirm that ordinary matter accounts for less than 5% of the total mass and energy of the universe.
Earlier in the year, the Cosmic Background Imager produced the sharpest ever images of the cosmic background. These images allowed astrophysicists to see for the first time the tiny density fluctuations that became our present-day galaxy clusters.
Ultimately polarization experiments may be able to investigate the Universe in the very first fractions of a second after the Big Bang -- when it underwent a period of extremely rapid expansion known as ‘inflation’. If the inflation model is correct, then gravitational waves emitted during this period will leave a signature on the polarization of the cosmic background.
In April, physicists at the Sudbury Neutrino Observatory (SNO) in Canada presented conclusive new evidence that electron neutrinos oscillate -- or change ‘flavour’ -- on their way from the Sun to the Earth.
Previous results from SNO and the Superkamiokande experiment in Japan had strongly suggested that neutrinos can oscillate. Oscillation can only occur if neutrinos have mass -- a finding that requires new physics beyond the Standard Model.
Later in the year, the KamLAND experiment confirmed that electron anti-neutrinos also oscillate.
This year’s Nobel Prize for Physics recognized two astrophysicists who pioneered the fields of neutrino astrophysics. Ray Davis of the University of Pennsylvania and Masatoshi Koshiba of the University of Tokyo shared half the prize. Riccardo Giacconi received the other half for his contribution to X-ray astronomy.
The second law of thermodynamics says that the entropy or disorder of an isolated system undergoing a cyclic process will increase or remain the same. In July, however, Australian researchers showed that entropy can decrease over short time periods for small systems. This is the first time that a deviation from the second law has been demonstrated experimentally.
The researchers state that the discovery could be important in the design of micromachines, and argue that the probability of thermodynamic systems running ‘in reverse’ will increase as they become smaller. This could have important consequences for nanotechnology and could even give researchers an insight into how life itself functions.
Two more elements joined the ranks of the superconductors this year. Physicists in Japan and the US found that lithium becomes superconducting when subjected to extremely high pressures. Superconductivity was also observed in a plutonium-based material for the first time. Researchers in the US and Germany discovered that an alloy of plutonium, cobalt and gallium exhibited superconductivtiy at temperatures below 18.5 Kelvin. The material also has a large critical current, which would be of technological importance if it were not for the hazardous radioactive properties of plutonium.
The properties of magnesium diboride -- which made its debut as a superconductor in January 2001 -- were also investigated further this year. Theorists in the US proposed that its relatively high transition temperature could be explained by the presence of two superconducting energy gaps rather than one.
Research on ultra-cold atoms has been strong this year, with advances being made in the study of both Bose-Einstein and degenerate Fermi gases.
A Bose-Einstein condensate is a novel state of matter in which all the atoms collapse into the same quantum state. A degenerate Fermi gas is the equivalent condensation for atoms that obey Fermi-Dirac statistics.
The year began with the first ever observation of a quantum phase transition in a condensate. This occurs when the atoms go from all having the same quantum phase and being able to move about without friction to one where the atoms are no longer able to move freely.
Physicists also showed that the presence of a Bose-Einstein condensate could trigger the collapse of a Fermi gas -- raising hopes that superfluidity could be observed in Fermi gases. Researchers also reported on the unusual expansion characteristics in an ultra-cold Fermi gas this month.
Caesium joined the condensates in October when researchers made a Bose-Einstein condensate with this element for the first time.
Physicists in the UK built a nano-metre scale logic gate made entirely from metal that works at room temperature. In existing electronic circuits, logic operations are carried out by semiconductor devices. However, the density of electrons flowing through a semiconductor is limited and this restricts how small these devices can be made. Metals have higher electron densities than semiconductors so a metallic logic gate could be made smaller than a semiconductor one.
If such devices could be built, they would be ideal for mobile applications such as phones and smart cards because the data could be stored without a power source.
The quantum properties of the electromagnetic force are seen in many phenomena, such as the electronic orbits in atoms and the structure of nuclei. However, it is extremely difficult to make analogous observations in gravitational fields because the effect of gravity is negligible at the atomic scale.
However, physicists at the Institute Laue-Langevin (ILL) observed quantized states of motion under the influence of gravity for the first time in 2002. The ILL team used ultra-cold neutrons to make their measurements, and the findings could be used to study the ‘equivalence principle’ and other fundamental aspects of physics.
It is important to understand the interactions between nucleons to understand the nucleus. Physicists already know that pairs of neutrons can exist in an ‘almost bound’ state, and they have spent many years trying to find evidence of these and higher numbers of neutron clusters. However, these experiments are difficult because neutrons or clusters of neutrons have no charge.
In May researchers working at the GANIL accelerator in France reported the first evidence for ‘tetra-neutrons’ -- nuclear clusters containing four neutrons and no protons. They found six possible candidates for the four-neutron clusters among fragments of neutron-rich beryllium nuclei. If confirmed, the findings could greatly help in our understanding of nuclear forces.
Optical physicists made progress in many directions in 2002. Researchers in Göttingen used conventional optics to image clumps of bacteria just 33 nanometres across -- equivalent to a mere 1/23 of the wavelength of light used to illuminate them. The achievement shows that 'far-field' optical microscopes can operate well beyond the so-called diffraction limit. Meanwhile physicists in Bielefeld and Vienna continued last year’s revolution in the generation of attosecond laser pulses by using such pulses to investigate the dynamics of the electrons in krypton atoms.
There was also a series of firsts in the realm of quantum optics: the first quantum NOT gates, the storage of two bits of information on a single photon, and the near-perfect cloning of a photon (perfect cloning is forbidden by the laws of quantum mechanics). Physicists in the UK and Germany also set a new distance record for the transmission of a “quantum key” in free space. Such keys are essential components of secure communication systems.
Microscopes move to smaller scales
First light for attophysics
Quantum logic: to be, or NOT to be?
Single photons to soak up data
Photons get the quantum cloning treatment
Quantum key travels record distance
Two physicists were fired from prestigious labs in 2002 for scientific misconduct. Victor Ninov was dismissed by the Lawrence Berkeley National Laboratory in June after a committee found that he had fabricated data concerning the discovery of element 118 -- which would have been the heaviest element ever made. Jan Hendrik Schön was sacked by Bell Labs in September after a different committee found him guilty on 16 out of 24 charges of scientific misconduct. Schön had published over 100 papers over a five-year period, most of them on the properties of organic semiconductors.
More than 300 physicists from around the world -- most of them women -- met in Paris in March for the first International Conference on Women in Physics. The meeting, which was organized by the International Union of Pure and Applied Physics, unanimously approved eight recommendations to enable women to contribute more effectively to physics. The recommendations were aimed at schools, universities, industry, government and funding councils. The delegates have now returned to their home countries, where they hope to turn words into action.
About the author
Belle Dumé is Science Writer at PhysicsWeb