The fate of the universe may be to continue expanding forever.
That is the conclusion, reported here today to an international scientific meeting, of new evidence on one of cosmology's most fundamental questions.
Eternal expansion, or what scientists call an open universe, is one of two alternatives that cosmologists have debated for decades.
The other, a closed universe, is that the universe's present expansion will gradually slow and reverse into a contraction. Eventually, the contraction would compress all matter back into a small space. The "big bang" -- the theory that the universe was sent scattering in one massive explosion -- therefore would lead to what has been dubbed a "big crunch."
The deciding factor is whether there is enough matter in the universe to produce enough collective gravitational pull to slow and reverse the expansion.
Many scientists find a big crunch philosophically satisfying because it would be easy to envision a crunched universe rebounding into a new big bang. In this view, the universe repeatedly renews itself.
But if the galaxies simply keep racing apart, a time will come when all the stars die, leaving a universe of lifeless cinders that grows steadily emptier.
Today's report does not settle the question, but it does lend weight to the belief in an open universe.
The evidence was developed by Victor E. Viola, an Indiana University chemist, and reported to the International Chemical Congress of Pacific Basin Societies, a meeting of scientists from the United States, Japan, Canada, and 35 other countries.
Viola's findings are based on theories of how each of the chemical elements was formed. The simplest elements -- hydrogen; helium; and one form, or isotope, of lithium -- are believed to have originated in the first moments of the big bang as the energy of the primordial fireball condensed into protons, neutrons, electrons and other subatomic particles.
None of the other elements could form until more than a million years later, after the formation of stars, whose nuclear reactions rearranged subatomic particles, welding them into heavier elements, including those necessary for life.
"There is one element, however, an isotope of lithium, that we think is too fragile to have been formed in stars or in any other process we can think of except in the big bang," Viola said. This is lithium-7.
Viola said the amount of lithium-7 in the universe would depend on the amount of matter present in the big bang at the stage at which lithium-7 was formed. "We think we have a pretty good handle on the cosmic abundance of lithium-7," Viola said, "and from that we think we can estimate the baryon density of the primordial fireball."
Baryons are the heavy subatomic particles, protons and neutrons. They account for nearly all the universe's known mass.
"Our calculations show that to produce the amount of lithium-7 in the universe there can only have been about 9 percent of the mass -- in the form of baryons -- necessary to close the universe," Viola said. In other words, the universe appears to have less than one-tenth the mass needed to produce enough gravity to halt its expansion.
"Our conclusion is that we have an open universe that will expand forever," he said.
There is, however, one unresolved question that could reverse the conclusion. Whether a particle called the neutrino has mass and, if so, how much.
Neutrinos are unusually tiny particles with no electrical charge that fly through space in all directions. The universe is awash in neutrinos, billions of them penetrating every human body every second. Because they are so small, they almost always pass completely through the Earth without touching any other particle.
For many years it was believed that neutrinos have no mass. Some physicists have reported that neutrinos may have a very small mass. If their mass is large enough, there are so many neutrinos that they could provide enough mass to close the universe.