Cost Force May Be Acting Against Gravity; Findings May Upset
Theories of the Universe
(Doug: I jokingly renamed this article "Lets see what John Baez
does with this")
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 ones as they
reverberate through studies of the largest-scale structures in
the cosmos and 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 an 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 today'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 Albert 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, 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 are needed
to ensure there is no other explanation for the data.
Alan Guth, a leading cosmologist from the Massachusetts Institute
of Technology, said the recent spurt of findings could pose a
challenge to particle physicists like himself, who will have to
explain this antigravity mechanism. They know that empty space
is "enormously complex," he noted, with theories of "virtual"
particles winking in and out of existence. But, he added, "The
field is in a primitive state. . . . There certainly will be some thrashing
about" as researchers try to explain the unexpected data.
Physicists have theorized about "a whole Pandora's box of
`repulsive stuff' " with names like "quintessence" and "X-matter,"
Kirshner said.
Whatever the antigravity mechanism is, said team member Adam
Riess, of the University of California at Berkeley, "We're seeing
the universe take off."
The High-z team (like the other team that reported similar results
last month, led by Saul Perlmutter of Lawrence Berkeley National
Laboratory in California) studied variations in the brightness of
very distant exploding stars, or supernovae, up to 7 billion light-years
away to gauge how the rate of cosmic expansion has changed over
time. They used the Hubble Space Telescope and ground-based
telescopes in Hawaii, Australia and Chile to analyze the gradual
brightening and fading of the light arriving from each of more than
a dozen supernovae.
The astronomers found that "the dimness of the supernovae --
pointing to unexpectedly great distances -- implies that cosmic
expansion has actually sped up in the billions of years since the
stars exploded," team member Alex Filippenko, of the University
of California at Berkeley, told colleagues at a Los Angeles meeting
last week.
The High-z team, sometimes in tandem with the Perlmutter team,
made what it called intense efforts to account for the dimness in
other, less exotic ways, such as the effects of intervening dust in
the cosmos or some intrinsic dimness in the most remote stellar
explosions that make them unreliable yardsticks.
They found no other explanation. Schmidt said the team concluded
with a statistical confidence of between 98.7 percent and 99.99
percent that cosmic expansion is getting an antigravity boost.
"The thing that keeps you awake at night is worrying that you've
done some stupid thing -- like forget about pi," Kirshner said.