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Expansion of the Universe Is Accelerating, Data Suggests

By Kathy Sawyer
The Washington Post
WASHINGTON

The universe is expanding at an accelerating rate, according to startling new evidence suggesting that a mysterious antigravity force permeates "empty" space and is counteracting the pull of gravity on a cosmic scale.

If the new results hold up, scientists said, they could have enormous ramifications for theories of cosmic evolution, resolving some conflicts and creating new dilemmas as they reverberate through studies of the largest-scale structures in the cosmos, the smallest particles in nature, and the frustrating quest for a "theory of everything" that would unify those fields.

Scientists have reacted to the findings with a mix of shock, amazement, horror, excitement and suspended disbelief.

The question of the fate of the universe - whether it will expand to infinity, contract in a "cosmic crunch," or flatline somewhere in between, is one of the oldest and most controversial in cosmology.

Most astronomers agree that the universe began in a Big Bang up to 15 billion years ago, when all of time and space were contained in a single dense point - a singularity - which abruptly expanded outward in a fireball of particles. The most popular, and the simplest, Big Bang model holds that the resulting universe should contain exactly the "critical density" of matter required to keep it geometrically "flat," with just enough gravity to balance the outward momentum, slowing it down. The result: a cosmos coasting indefinitely on the verge of collapse.

Instead, the new evidence indicates that stars and galaxies are flying apart in all directions at an ever-increasing rate - thanks to an antigravity boost. This means there must be a unexpected mix of ordinary matter and some kind of unseen "dark matter" of an exotic nature. It also means, scientists said, that the far-flung universe of billions of years hence will seem dramatically more empty, dark and lonely.

"This is nutty-sounding," said Robert Kirshner, of the Harvard-Smithsonian Center for Astrophysics, a member of the international observing team. "But it's the simplest explanation for the data we've got."

The findings, reported in Friday's issue of the journal Science, appear to bolster similar results presented last month by another international team using similar methods, all made possible only recently by powerful advances in observing technology. Still other researchers using different methods have reported that their data point in the same direction.

The emerging picture of the universe represented in the spate of recent findings appears to reanimate a controversial concept known as the "cosmological constant", which Einstein first proposed in his theory of general relativity. At the time, he introduced the notion of a repulsive force in space - pushing objects apart - to counterbalance the attractive force of gravity - pulling objects together - to support his theory that the universe is static; that is, neither expanding nor contracting. Observations soon showed that the universe is not static at all but, indeed, expanding. Einstein renounced the cosmological constant as his greatest blunder.

But the concept, has been kept around for use as what some call a "fudge factor" whenever it is needed to make theory and observation conform.

"My own reaction is somewhere between amazement and horror," said Brian Schmidt, of the Mount Stromlo and Siding Spring Observatory in Australia, leader of the group that reported the latest results, known as the High-z Supernova Search Team. It also includes scientists from the United States, Latin America and Europe. "Amazement, because I just did not expect this result," he said, "and horror in knowing that [it] will likely be disbelieved by a majority of astronomers who, like myself, are extremely skeptical of the unexpected."

Both the observing teams themselves and independent researchers emphasized that further observations must be done to make sure that there is no other explanation for the data.

Professor of Physics Alan H. Guth '68, a leading cosmologist, said the recent spurt of findings could pose a challenge to particle physicists like himself, who will have to explain this antigravity mechanism.

Physicists have theorized about "a whole Pandora's box of "repulsive stuff"' with names like "quintessence" and "X-matter," Kirshner said.

Whatever the anti-gravity mechanism is, said team member Adam Riess, of the University of California at Berkeley. "We're seeing the universe take off."