Françoise Barré-Sinoussi (left), Luc Montagnier (centre) and Harald zur Hausen share the medicine Nobel for their work on viruses. Credit: INSTITUT PASTEUR; U. ANDERSEN/GETTY IMAGES; REUTERS

Two French virologists who discovered HIV share this year's Nobel Prize in Physiology or Medicine with a German oncovirologist who showed that human papilloma virus (HPV) causes cervical cancer. The Nobel Prize in Physics went to two Japanese researchers and a Japanese-born American for their work on symmetry breaking in subatomic physics.

Françoise Barré-Sinoussi and Luc Montagnier identified the human immunodeficiency virus (HIV) that causes AIDS in 1983, while working at the Pasteur Institute in Paris. They originally called it lymphadenopathy associated virus (LAV).

By awarding the prize to the French duo, the Nobel committee effectively ends years of bitter controversy arising from a counter claim for HIV's discovery by virologist Robert Gallo of the US National Institutes of Health in Bethesda, Maryland. In 1987 the French and US heads of state brokered an agreement to share the benefits of the discovery.

Many believed that the Nobel prize could not be awarded for this field of research, despite its importance, while tempers ran high. Now, the Nobel committee has made its position clear, saying the discovery of Barré-Sinoussi and Montagnier "was accepted by the research community and resulted in an explosion of scientific breakthroughs". It then refers to Gallo's "detection of a novel … virus from a vast number of patients with AIDS or pre-AIDS in 1984 … [which] showed considerable similarities with LAV-1". Gallo says he is "gratified" that he was considered "equally deserving", adding that he is proud of his colleagues.

The work of the French scientists has led to the development of diagnostic tools, blood screening agents and drugs that have helped to fight spread of the disease and dramatically increased life expectancy.

Harald zur Hausen, former director of the German Cancer Research Center (DKFZ) in Heidelberg, Germany, was honoured for going against the prevailing dogma to discover that it was not a herpes simplex virus that causes cervical cancer, but in fact HPV.

"Virologists and gynaecologists thought his idea about the papilloma virus was very strange," says Herbert Pfister, a former colleague, now at the University of Cologne in Germany. "But he carried through his theory in a determinedly logical way, not caring about the controversy he was raising."

During the 1980s, zur Hausen described first HPV-16, which occurs in around half of human cervical cancers as well as other anogenital cancers, and then HPV-18, which accounts for a further 25% of cases. His work led to the development of vaccines against HPV, which are now in widespread use and expected to slash the rates of cervical cancer, which affects nearly 500,000 people a year and is the fifth most deadly cancer in women.

The physics prize went to Japan's Makoto Kobayashi of the High Energy Accelerator Research Organization (KEK) in Tsukuba and Toshihide Maskawa of Yukawa Institute for Theoretical Physics at Kyoto University for discovering the origin of the 'broken symmetry' that contributed to a preponderance of matter over antimatter in the Universe. They share the prize with Yoichiro Nambu of the Enrico Fermi Institute at the University of Chicago in Illinois, who discovered the mechanism by which spontaneous broken symmetry occurs in particle physics.

Symmetry breaking describes how symmetrical systems can suddenly show a preference for one direction over another. As a simple example, imagine balancing a pencil on its tip. Viewed from the top, the balanced pencil appears symmetrical, but after a time it will fall and point in a single direction.

This concept applies to many physical systems, including superconductors, but it was Nambu who extended the theory to fundamental particles, according to John Ellis, a theorist at CERN, Europe's particle-physics laboratory near Geneva, Switzerland. Physicists now think that symmetry breaking is responsible for the creation of the Higgs boson, the particle that is believed to endow all other particles with mass, and which is a target of CERN's Large Hadron Collider.

Kobayashi and Maskawa showed how violation of symmetry could create more matter than antimatter in the Universe — a long-standing problem in particle physics. In the early 1970s, the pair showed that the interactions of quarks via a fundamental force, called 'the weak force', could cause 'CP-violation', a phenomenon by which some particles decay in a different way from their anti-matter counterparts.

"They wrote down this huge expression whose physical interpretation is the violation of symmetry between matter and antimatter," says Ken Peach, a physicist at the University of Oxford, UK. The equations also predicted a third family of quarks (the particles that make up protons and neutrons in an atom's nucleus).

The idea of a thirds family seemed "far-fetched" at the time, says Ellis, but Kobayashi and Maskawa's work has since been verified by two high-energy experiments. The Belle experiment at KEK and the BaBar experiment at the Stanford Linear Accelerator Center in California both measured the decay of particles made of bottom quarks. The physicists' predictions were borne out to a high degree of accuracy.