Neutrinos come about as close to nothingness as something can be; they make even the tiny electron, the lightest part of an atom, seem like a heavyweight. Yet a new discovery being announced today in Japan by an international team of physicists shows that these minuscule, nearly-weightless wisps of matter may actually dominate the universe.
Though they are the tiniest units of matter in existence, the new discovery, proving that neutrinos do have some mass, indicates that they may have played a key role in the formation of galaxies and stars, and may also be crucial to determining the universe's ultimate fate.
The finding is the culmination of one of the most hard-fought quests in modern physics, but it raises as many questions as it answers. ''It's very exciting,'' said Leon Lederman, a Nobel laureate in physics and director of the Fermi National Laboratory in Batavia, Ill. ''It also exacerbates and emphasizes our total confusion'' as to why matter has mass at all, he said.
Lederman suggested that the discovery was of a class that could well lead to a Nobel Prize, but only if one or two scientists could be singled out for credit from among the large group that made the discovery.
Physicists have debated for decades over whether neutrinos, the most abundant of all subatomic particles, have some tiny amount of mass. Some thought that, like the photons that carry beams of light or radio waves, they might have none at all. Today, after years of effort in a huge underground water-filled cavern built to study the elusive particles, an international team of physicists will report that the answer has been found.
''It's irrefutable evidence'' that the tiny particles really do have mass, said Boston University physicist Larry Sulak, a member of the discovery team, in describing the several lines of evidence produced by experiments at the huge Super-Kamiokande detector. In a telephone interview from Japan, Sulak said that while earlier experiments had produced inconclusive evidence for neutrino mass, with the new experiments ''all the unknowns that we were concerned about have been laid to rest.''
About 100 scientists from 23 institutions participated in the research that led to today's announcement, being made at a conference called ''Neutrino '98'' in Takayama, Japan.
Neutrinos are among the oddest discoveries of modern physics. They are similar to electrons, the tiny particles that make up the outer shells of atoms. But unlike electrons, they have no electrical charge at all. As a result they have virtually no interaction with other forms of matter. The particles are so tiny and elusive that they could hurtle through a quadrillion-mile thickness of solid lead without ever bumping into anything.
When physicist Wolfgang Pauli first came up with the concept in 1929 to explain a discrepancy in measurements of radioactive decay, he was embarrassed. ''I have done something very bad today,'' he told a friend, ''in proposing a particle that cannot be detected; it is something no theorist should ever do.''
Pauli was proved right about his theory, but wrong about the possibility of detection, when neutrinos were first proved to exist in 1956 at an atomic reactor in Washington state.
But the question of whether neutrinos had mass remained much more difficult to pin down. Several experiments over the last 20 years have shown some signs that they did, but fell short of providing compelling evidence.
The new experiments, while they establish that neutrinos have mass, do not provide a way of actually measuring it. Instead, what they measured was the difference between the masses of two different types, or ''flavors,'' of neutrinos. It turns out, the new experiments show, that some neutrinos ''oscillate'' between the two different flavors, and the oscillation provides a way of measuring the difference in mass.
The new findings suggest that neutrinos may have been crucial in causing matter to form ''clumps'' soon after the Big Bang that created the universe. These clumps became galaxies, which then spawned the billions of stars that permeate space.
Neutrinos may also make up a significant part of the ''missing mass'' that astronomers say must exist in space in order to explain the behavior of galaxies. But it would not be enough mass to cause the universe to stop expanding and collapse upon itself, as many physicists believe it must.
This story ran on page A A3 03 of the Boston Globe on 06/05/98. ) Copyright 1998 Globe Newspaper Company.