1. Cosmology
2. Particle physics
3. Condensates
4. Optics and electromagnetism
5. Quantum information
6. Quantum optics
7. Electricity from water
8. Magnetism
9. New superconductors
10. Laser-based nuclear transmutation

1. Cosmology

This year, NASA unveiled the first detailed full-sky map of the cosmic microwave background - the microwave "echo" of the Big Bang. Scientists created the map using data collected by the Wilkinson Microwave Anisotropy Probe satellite (WMAP) over a period of 12 months. The results provide further support for the inflationary Big Bang model of the universe and reveal when the first generation of stars was created.

The data indicate that the Universe is now about 13.7 billion years old and that the earliest stars in the universe were created just 200 million years after the Big Bang. The results also support the idea of an infinite, flat universe that is made up of 4% ordinary matter, 23% dark matter and 73% dark energy. The WMAP results were important enough to be featured as Science magazine’s top breakthrough of 2003. They also appeared on the cover of the April issue of Physics World.

However, in October cosmologists in France and the US suggested that space could be finite and shaped like a dodecahedron instead. They argued that this shape could account for the disagreement between theory and the WMAP data for regions of space separated by large angles.

Ancient radiation sheds new light on the universe
Is the universe a dodecahedron?

First quasars shed light on the early universe
A new spin on black holes
Gravity and light move at the same speed

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2. Particle physics

Finding the Higgs boson and various supersymmetric particles may be the top priority of most high-energy physicists, but that has not stopped several new particles turning up out of the blue at experiments in Japan, the US, Russia and Germany. The new particles, which could have implications for the Standard Model, came as a stunning surprise to the global particle-physics community.

The first new particle was announced in April, when physicists at the BaBar experiment at Stanford, California, reported evidence for a new D-meson that might contain four quarks - although this interpretation has not been confirmed.

Two months later the first evidence ever for a pentaquark – a particle with 5 quarks – was published by Japanese researchers. This new particle was found to have two up quarks, two down quarks and a strange antiquark. Most other particles, in contrast, are either mesons - with a quark and an antiquark - or baryons, which comprise three quarks or three antiquarks.

Finally in November, the Belle collaboration at the KEK laboratory in Japan discovered a new sub-atomic particle which it called the "X(3872)". This particle does not fit into any known particle scheme and researchers believe it could be a hitherto unseen type of meson that contains four quarks.

Babar detects new particle
Physicists discover particle with five quarks
New particle turns up in Japan

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3. Condensates

Condensate physics has featured on PhysicsWeb’s top ten list for the last three years in a row and research in this field continues to be strong - in 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.

In July, physicists at Kyoto University in Japan said that they had observed Bose-Einstein condensation in a gas of ytterbium atoms for the first time. Ytterbium differs from most elements that have been condensed because it has two valence electrons rather than one and can be prepared in a non-magnetic state. Such novel condensates could be used in tests of fundamental symmetries.

A few weeks ago, Austrian and American researchers created a Bose-Einstein condensate of bosonic molecules from a gas of fermionic atoms. This breakthrough brings physicists closer than ever to the holy grail of ultracold atomic gas research - to observe superfluidity in a Fermi gas.

Ytterbium joins the condensates
Condensates enter new era

Bose-Einstein condensates break temperature record
Fermi gas atoms form supercool molecules
Cold molecules come of age

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4. Optics and electromagnetism

After three years of fierce debate, physicists finally confirmed that "negative-index" materials do not violate the laws of physics. These materials bend light in the opposite direction to conventional materials. Some physicists, however, argued that although the phase velocity of the light was negatively refracted, the group velocity was not. Others claimed that negative refraction violated causality by permitting velocities greater than the speed of light.

Other optical physics breakthroughs include the first observation of the "inverse Doppler effect" – in a transmission line - and the focusing of light down to the smallest spot size ever. German researchers managed to focus a laser beam to an area of just 0.06 square microns. This is almost half the size of the previous record.

Good news for negative-index materials
New look for the Doppler effect
Scientists bring light to sharpest focus

Optical vortices show their true colours

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5. Quantum information

Researchers made much progress in 2003 towards creating a real quantum computer. "Qubits" - the quantum equivalents of ordinary bits - have been made with trapped photons, atoms and ions, but physicists would prefer to build real working devices with solid-state systems. This still remains a challenge.

In February, however, one group of physicists reported on "entangling" two qubits in a solid-state device for the first time, while a second team demonstrated a new type of superconducting qubit.

In August, a third group described how they created a logic gate using two electron-hole pairs - also known as "excitons" - in a quantum dot. Most importantly, the researchers showed that the quantum-dot system could behave like a controlled-NOT gate under certain conditions.

Qubits are on solid ground
Quantum logic gate lights up

Teleportation moves on
Entanglement reaches new lengths
Cryptography breaks 100 km barrier
Entanglement goes macroscopic
Bad news for code breakers

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6. Quantum optics

2003 saw the first demonstration of a single atom laser when researchers at Caltech trapped a caesium atom in an optical cavity. The light emitted by the device exhibits "photon antibunching", which makes it "quieter" or more ordered than light from ordinary lasers. The laser could find applications in quantum information technology.

Another breakthrough came in December when US and Russian physicists showed how they could "stop" light in a gas of hot atoms. Their technique could offer greater control over light itself and have applications in optical communications and quantum information. Earlier experiments on stopped light only stored the "signature" of light pulses – rather like creating a hologram - but the new approach now traps actual signal photons.

First light for one-atom laser
Switching light on and off

Fast and slow light made easy
Squeezed light breaks quantum barrier
Quantum effect improves tomography

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7. Electricity from water

Engineers in Canada triggered a media frenzy in October when they claimed to have discovered the first new way of producing electricity in 160 years.

Their idea consists of pumping water through tiny microchannels in a glass disk to generate an electrical current. This allows them to directly convert the energy of a moving liquid into electricity without any moving parts or unwanted pollution. The concept still needs some fine tuning, but such a power source could be used in batteries for small electronic devices like mobile phones.

Extracting electricity from water

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8. Magnetism

This year saw cobalt enter the record books when a team of European physicists found that it has a magnetic anisotropy energy (MAE) of about 9.3 meV per atom - the largest ever recorded to date. MAE controls the alignment of the atomic spins that give rise to magnetism in a material. In contrast, samarium cobalt, which is a widely used permanent magnet, has a MAE of just 1.8 meV per cobalt atom.

Physicists also observed magnetic domain walls moving on subatomic length scales for the first time. This surprising feat opens up new avenues of fundamental research in condensed matter physics and could even lead to the development of new magnetic materials.

Cobalt breaks magnetism record
Magnetism on the move

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9. New superconductors

Recent years have seen tremendous progress in superconducting physics – and this year has been no exception.

Hot off the press is the news that physicists at the University of Tokyo have discovered a new superconductor made of potassium, osmium and oxygen. The work, which is yet to be published, describes a "pyrochlore" material – KOs2O6 – which has a superconducting transition temperature of 9.6 K and remains a superconductor in high magnetic fields.

Earlier in the year, another group of Japanese physicists found that cobalt oxide could be transformed into a superconductor simply by adding water to it. Researchers suspect that the fundamental physics in both the high-temperature cuprate superconductors and cobalt oxide materials might be the same.

Water helps cobalt oxide to become a superconductor
Another superconductor shows up

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10. Laser-based nuclear transmutation

And finally, physicists made history this year by showing that they can transmute radioisotopes with lasers. This breakthrough could prove vital for the safe storage and disposal of radioactive waste in the future. Teams based in Germany and the UK showed that iodine-129 (which has a half-life of 15.7 million years) could be converted into shorter-lived iodine-128 using a laser-based source of gamma rays. Iodine-128 only has a half-life of 25 minutes.

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