A Challenge to Evolution of Universe
'Dark Energy' Finding Casts Doubt
on Einstein's 'Cosmological Constant'
By Guy Gugliotta Washington Post Staff Writer
Thursday, January 12, 2006; Page A02
In the quest to decipher
the evolution of the cosmos,
no topic generates greater
interest among scientists than
"dark energy," the mysterious
force that appears to be
causing the universe to expand
at an ever-accelerating rate.

Yesterday, Louisiana State
University astronomer Bradley
E. Schaefer tossed a grenade
into this debate, presenting
new research to suggest that
the force dark energy exerts
may have varied over time.
That casts new doubt on the
validity of Albert Einstein's
"cosmological constant" only
a few years after astronomers
rescued the concept from
scientific oblivion.
"I'm not pushing this as a proof,"
Schaefer said in an
interview at this week's
meeting of the American
Astronomical Society in
the District, where he presented
his research. "It's pointing
against the cosmological
constant, but it's a first result
describing how dark energy
changes with time. We need
more people to test the
results and get more information."

Schaefer based his findings
on analysis of ultra-bright
cosmic explosions called
gamma-ray bursts, detected as
far as 12.8 billion light-years
away. He found that the
most distant explosions
appeared brighter than they
should have been if the universe
were accelerating at
a constant rate.
"As you go back in time, the
universe is pushing [outward]
less and less," he said. "At
some point, the pressure of dark
energy is zero and is exerting
no force on the universe.
There is no explanation for it."

Schaefer's findings, the first
attempt to use gamma-ray
bursts to study dark energy,
produced a result that
disagreed with accumulating
evidence gleaned from
observing a different kind of
blast -- the exploding stars
called supernovae. That work
suggested that the expansion
of the universe is accelerating
in accordance with Einstein's
cosmological constant.
"The idea of using a gamma-ray
burst as a distance
indicator is a very exciting one,"
said California Institute
of Technology astronomer
Richard Ellis, a supernova
cosmologist. "The trouble is
there are no ways to check
the techniques. I'm not saying
it's no good, but I can't
believe it's as precise as supernovae."
The concept of dark energy
emerged in 1999 as a way to
explain the fact that the
expansion of the universe, once
thought to be slowing ever
since the big bang about 13.7
billion years ago, was accelerating.
That resurrected the
idea of a cosmological constant,
introduced by Einstein
more than 80 years ago as a
"fudge factor" to explain why
the universe then appeared to
be in equilibrium, rather
than being pulled together
by gravity.
A few years later, however,
astronomer Edwin Hubble
discovered that the universe
was not in stasis, after all,
but was expanding. There
was no "constant." Einstein
condemned his own idea
as "my greatest blunder."

But in the 1990s, astronomers
found ways to use
supernovae as cosmic "standard
candles" whose luminosity
could be analyzed to track
the history of the universe's
expansion as far back as
9.8 billion light-years.
That led to the 1999 discovery
that the expansion of the
universe was accelerating
rather than slowing. There had
to be some "repulsive force"

overcoming the gravity that
should have been causing
the universe to come together.
Astronomers called the force
dark energy, and "it mimics
the cosmological constant,"
said Michigan Technological
University astronomer Robert
J. Nemiroff. Einstein may
have been right after all.

Astronomers estimate that
dark energy makes up 70 percent
of the universe, but they do not
know what it is.

Solving the
mystery is as all-consuming
as any passion in physics. "It's
so spooky," said Astronomical
Society President Robert B.
Kirshner, a cosmology expert
at the Harvard-Smithsonian
Center for Astrophysics.
"Everybody is looking for ways to
get at it."

Schaefer said he had been
interested for several years in
using gamma-ray bursts -- the
brightest explosions in a
violent universe -- to look
far deeper into the past than
astronomers could reach
with supernovae.
The key were the launches of
the Massachusetts Institute
of Technology's HETE-2 satellite
in 2000, and NASA's Swift
satellite in 2004. Both were
designed to locate and observe
gamma-ray bursts, which last
milliseconds to several minutes.
Schaefer analyzed 52 of the
bursts and found that the most
distant of them were brighter
than the cosmological constant
would have predicted --
indicating that the universe's
expansion was accelerating
at a slower rate than it is today.
Schaefer "gets full marks for
coming up with a new technique,"
Ellis said in a telephone interview,
but "we still really don't
have a clue" what dark energy is.
"It's mayhem at the
moment" in cosmology, he added.
"The theorists are having
a field day, because there's no data."

New Doubts Are Cast on Einstein's Cosmological Constant
By DENNIS OVERBYE Published: January 12, 2006

Einstein was wrong.
Einstein was right.
He was wrong about being wrong.

An astronomer from Louisiana State University
said yesterday that a new
analysis of cosmic history cast doubts
on Einstein's cosmological
constant, the leading explanation for
the mysterious force that appears
to be pushing apart the universe.

But other astronomers said that conclusion
itself was in doubt.

The astronomer, Bradley E. Schaefer,
said his analysis showed that the
force, known as dark energy, was
not constant, as Einstein would have
predicted, but was growing more
violent as cosmic time went on.

"The cosmological constant does not
look good," said Dr. Schaefer, who
used the violent flashes called gamma
ray bursts as cosmic mileage
markers to describe the history of
the expansion of the universe.

In an interview Dr. Schaefer cautioned
that it was just a preliminary
result with years before a final answer
came in. He presented his report
at a meeting of the American
Astronomical Society in Washington.

Several astronomers said it was
Dr. Schaefer, not Einstein, who was
wrong.

His conclusion, they said, was
undermined by mathematical and
statistical flaws.

Moreover, some
astronomers questioned whether the
properties of gamma ray bursts were
known precisely enough to serve as
cosmological beacons.
"I flat out don't believe this result,"
said Adam Riess, an astronomer
at the Space Telescope Science Institute
in Baltimore who was a
discoverer of dark energy eight years ago.

Einstein first proposed the constant in 1917,
as a way of explaining how
the universe could be static despite
the force of gravity. It was a sort
of universal antigravity embedded in
space. He abandoned that theory as
a blunder when the universe proved
to be expanding.

But in 1998, the cosmological constant gained
new life. It was then that
competing teams of astronomers, using
exploding stars known as Type 1a
supernovas as cosmic mileage markers,
discovered that the expansion of
the universe appeared to be accelerating,
as if a dark antigravitational
force were indeed at work.

As Steven Weinberg of the University of
Texas said, Einstein's biggest
blunder was believing the cosmological
constant was a blunder.

Since the 1998 discovery, astronomers
have been racing to chart the
history of the expansion of the universe
more precisely to pin down the
properties of dark energy. Observations
by Dr. Riess and his colleagues
with the Hubble Space Telescope two
years ago have determined that the
universe hit the gas pedal about five
billion years ago.

Dr. Schaefer used as his mileage markers
52 gamma ray bursts, which are
100 to 1,000 times as powerful as Type 1a
supernovas, and can thus be
seen much farther away, or back in time.
The bursts, which can be seen
only from space, have been studied by
satellites like the High Energy
Transient Explorer, or HETE.

The most distant burst, at 12.8 billion
light-years, occurred when the
universe was 6 percent of its present
age, Dr. Schaefer said.

His measurements put the dark energy
in a controversial category named
phantom energy, which if it continued
unabated would rip apart the
cosmos in a few billion years.

But Donald Lamb, an astronomer at the
University of Chicago, and others
who were interviewed before Dr. Schaefer's
talk but were made familiar
with its conclusions, disagreed.

They said Dr. Schaefer had been forced
to his finding about the Einstein
constant by his use of a mathematical
parameter called w-prime, a
measure of how fast the violence of
the dark energy appears to be
changing with distance in the universe.

At large distances, Dr. Lamb said, the
parameter becomes mathematically
meaningless, and theorists have dropped it.

Moreover, he said, if Dr. Schaefer's
analysis is valid, his results
agree with Einstein's constant, within
the measurements' uncertainties.

"It's not a meaningful discrepancy,"
Dr. Lamb said, adding that a
statement like Dr. Schaefer's required
stronger evidence. "The bottom
line is the result doesn't show Einstein
was right. And it doesn't show
he was wrong."

That was echoed by Robert R, Caldwell,
a dark-energy theorist at
Dartmouth, who added that if dark
energy evolved as swiftly as Dr.
Schaefer said, it would have interfered
with the formation of galaxies.

Another criticism is that most of
Dr. Schaefer's data points are from
the early universe, more than five billion
years ago, before dark energy
became a dominant force in the universe.
The action, they say, is all at
later times, when dark energy's effects
are more easily seen, but his
data is sparse there.

In his presentation, Dr. Schaefer said
it was too early to make claims
about the usefulness and ultimate
meaning of his proposal.

"The first results are pointing to the
cosmological constant not being
constant, a point I don't want to push
too much," he said. "This is the
first demonstration of cosmologically
useful results from a new method.
We can't be too confident in the results
right now."

The dispute shines an awkward light on
what some astronomers regard as a
promising and powerful tool for
cosmology, gamma ray bursts. Dr.
Schaefer called his work a "proof of
purchase" for the use of the
bursts, which can emit as much light
in a second as our Sun does in a
billion years, to investigate dark
energy and other puzzles of the long
night.

George Ricker, a gamma ray astronomer
at M.I.T., said of Dr. Schaefer's
work: "It's great that he's doing this.
He's drawing attention to fact
that this is possible."

Other astronomers said the use of gamma
ray bursts for cosmology was in
its infancy at best.

Until recently, astronomers did not even
know what they were. Lately,
the bursts have been traced to the titanic
implosions of very massive
stars into black holes, and astronomers
have begun to learn how to
calibrate the flashes.

Lorenzo Amati of the Institute of Space
Astrophysics and Cosmic Physics
in Bologna, Italy, and his colleagues
discovered a correlation between
the total luminosity of a gamma ray burst
and the wavelength at which it
appears brightest.

Using such techniques, astronomers can
estimate the intrinsic luminosity
of a gamma ray burst within 25 percent,
Dr. Lamb said. That is only two
or three times the uncertainty associated
with the Type 1a supernova
explosions, considered the gold
standard for cosmological work.

Dr. Lamb was the lead author of a report
last summer outlining how a
gamma ray burst mission could be
used to investigate dark energy.

Such a mission is unlikely soon, however,
because NASA's science budget
suffers overruns from the James Webb
Space Telescope, and scientists are
trying to find money to maintain the HETE
satellite, which is scheduled
to be turned off.

Optical astronomers point out that it will
take many more gamma ray
bursts than supernovas to reach the
same precision. Lacking a sound
theoretical reason to believe that gamma
ray bursts should be standard
candles, they are reluctant to give them
much credence.

Dr. Riess said, "The news is that we are
really stumped about this dark
energy puzzle and are being forced to be
very creative to probe it."

Warren E. Leary contributed reporting
from Washington for this article.