By Philip Elmer-DeWitt

Mid-October is the season for naming Nobel laureates, but it is also a propitious time for scientists to reveal discoveries that may win future Nobels. Last week, even as this year's Nobel winners were reacting to their awards, two teams of physicists made just such a landmark announcement. In rival statements -- one from the Stanford Linear Accelerator Center in California, the other from the European Organization for Nuclear Research (CERN) in Geneva -- scientists disclosed findings they say establishes beyond a reasonable doubt that the universe contains precisely three fundamental types, or families, of matter. No more, no less.

No, they are not animal, vegetable and mineral. In fact, all the matter most people are familiar with can be subsumed within one family of particles. This family includes the common electron, which hovers around the nucleus of the atom; the "up" and "down" varieties of quarks, now known to be the constituents of protons and neutrons; and an obscure particle known as the electron neutrino. Neutrinos have no charge and no measured mass, yet are thought to be among the most abundant particles in the universe.

The members of the other two families are even more elusive. Some have never been directly observed, and the others have only been spotted fleetingly in cosmic rays or high-energy particle accelerators. The second family consists of so-called "charmed" and "strange" quarks, muons and muon neutrinos. The third is made up of "top" and "bottom" quarks, tau particles and tau neutrinos. Last week's announcements do not preclude the possibility that other types of particles could be discovered, but they raise the odds against that happening, by Stanford's estimate, to better than 25 to 1.

These odds were calculated by observing the behavior of the Z particle, the heaviest known unit of matter. Zs are produced in the collision of smaller particles that have been accelerated to nearly the speed of light. By creating large numbers of Z particles, physicists were able to establish the energy range required to form a Z. Working backward from that energy range, they then calculated whether the laws of nature could accommodate more than the three known types of matter. Last week's results made it more than likely that the answer is no.

Why is this important? Because gnawing uncertainty about the number of particle families had plagued two theories that are the foundation of modern physics: the Big Bang theory of the creation of the universe and the Standard Model of the building blocks of matter.

The significance of the new findings was underscored by the haste with which they were revealed. The Stanford team, led by Burton Richter (a 1976 Nobel laureate), went public first, issuing a press release only one day before a European symposium at which CERN's findings were to have been presented. That led to charges of bad sportsmanship from some of the CERN team, led by Carlo Rubbia (1984 Nobel), whose results are said to be more accurate and even more definitive.

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CREDIT: TIME Chart by Joe Lertola

CAPTION: PASSEL OF PARTICLES