TIME: Almanac 1990/1990 Time Magazine Compact Almanac, The (1991)(Time).iso/time/102389/10238900.018

Text File | 1990-09-22 | 3KB | 58 lines

NATURE, Page 116

A Trinity of Families

Scientists reduce all matter to three fundamental types


    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.