[Oe List ...] Dark Energy 9,000,000,000 years old

[LAURELCG at aol.com]

November 17, 2006
  9 Billion-Year-Old 'Dark Energy' Reported    By DENNIS OVERBYE

  A strange thing happened to the universe five billion years ago. As
  if God had turned on an antigravity machine, the expansion of the
cosmos speeded up, and galaxies began moving away from one another
  at an ever faster pace.

  Now a group of astronomers using the Hubble Space Telescope have
  discovered that billions of years before this mysterious
  antigravity overcame cosmic gravity and sent the galaxies scooting
apart like muscle cars departing a tollbooth, it was already
  present in space, affecting the evolution of the cosmos.

"We see it doing its thing, starting to fight against ordinary
gravity," Adam Riess of the Space Telescope Science Institute said
  about the antigravity force, known as dark energy. He is the leader
  of a team of "dark energy prospectors," as he calls them, who
peered back nine billion years with the Hubble and were able to
discern the nascent effects of antigravity. The group reported
their observations at a news conference yesterday and in a paper to
  be published in The Astrophysical Journal.

The results, Dr. Riess and others said, provide clues and place new
  limits on the nature of dark energy, a mystery that has thrown
  physics and cosmology into turmoil over the last decade.

  "It gives us the ability to look at changes in dark energy," he
said in an interview. "Previously, we knew nothing about that.
  That's really exciting."

The data suggest that, in fact, dark energy has changed little, if
  at all, over the course of cosmic history. Though hardly
conclusive, that finding lends more support to what has become the
conventional theory, that the source of cosmic antigravity is the
cosmological constant, a sort of fudge factor that Einstein
  inserted into his cosmological equations in 1917 to represent a
cosmic repulsion embedded in space.

Although Einstein later abandoned the cosmological constant,
calling it a blunder, it would not go away. It is the one theorized
form of dark energy that does not change with time.

Sean Carroll, a cosmologist at the California Institute of
  Technology who was not on the team, said: "Had they found the
  evolution was not constant, that would have been an incredibly
  earthshaking discovery. They looked where no one had been able to   
look before."

  The paper by Dr. Riess and his colleagues represents a sort of
  progress report from the dark side, where astrophysicists have
  found themselves more and more as they try to understand what is
happening to the universe.

This encounter with the invisible began eight years ago, when two
competing teams of astronomers were using exploding stars known as
  Type 1a supernovas as cosmic distance markers to determine the  
fate  of the universe.

  Ever since the Big Bang 14 billion years ago, the galaxies and the
rest of the universe have been flying apart like a handful of
  pebbles tossed in the air. Astronomers reasoned that gravity would
  be slowing the expansion, and the teams were trying to find out by
  how much and, thus, determine whether all would collapse one day
into a "big crunch" or expand forever.

Instead, to their surprise, the two teams, one led by Saul
Perlmutter of the University of California, Berkeley, and the other
  by Brian Schmidt of the Mount Stromlo and Siding Spring
  Observatories in Australia, found that the universe was speeding up
  instead of slowing down.

  But the ground-based telescopes that the two teams used could track
  supernovas to distances of just seven billion light-years,
corresponding to half the age of the universe, and the effect could
  have been mimicked by dust or a slight change in the nature of the
supernova explosions.


  Since then, Dr. Riess, who was a member of Dr. Schmidt's team, and
  his colleagues have used the Hubble telescope to prospect for
supernovas and dark energy farther out in space or back in time.


  The new results are based on observations of 23 supernovas that are
more than eight billion years in the past, before dark energy came
to dominate the cosmos. The spectra of those distant supernovas,
Dr. Riess reported, appear to be identical to those closer and more
recent examples. By combining the supernova results with data from
  other experiments like the NASA Wilkinson Microwave Anisotropy
Probe, Dr. Riess and his colleagues could begin to address the
  evolution of dark energy.

  "That's one of the $64,000 questions," he said. "Is dark energy   
changing?"

So far, he said, the results are consistent with the cosmological
  constant, but other answers are also possible. The possibility that
  it is the cosmological constant is a mixed blessing. Physicists
concede that they do not understand it.

  Dr. Carroll of Caltech said, "Dark energy makes us nervous."

Einstein invented his constant to explain why the universe does not
  collapse. After he abandoned it, the theory was resuscitated by
quantum mechanics, which showed that empty space should be bubbling
with staggering amounts of repulsive energy. The possibility that
it really exists in the tiny amounts measured by the astronomers
  has flummoxed physicists and string theorists.

  Because it is a property of empty space, the overall force of
Einstein's constant grows in proportion as the universe expands,
  until it overwhelms everything. Other theories of dark energy like
strange force fields called quintessence or modifications to
Einstein's theory of gravity can change in more complicated ways,
  rising, falling or reversing effects.

Astronomers characterize the versions of dark energy by their so-
called equation of state, the ratio of pressure to density, denoted
by the letter w. For the cosmological constant, w is minus one.


Dr. Riess and his group used their data to make the first crude
 > measurement of this quantity as it stood nine billion years ago.
 > The answer, he said, was minus one - the magic number - plus or
 > minus about 50 percent. By comparison for more recent times, with
 > many more supernovas observable and thus more data, the value is
 > minus one with an uncertainty of about 10 percent.

  "If at one point in history it's not minus one," Dr. Riess said,
  "then we have killed the very best explanation."

Getting to the precision needed to kill or confirm Einstein's
  constant, however, will be very difficult, he conceded. One of the
biggest sources of uncertainty is the fact that the Type 1a
explosions are not completely uniform, introducing scatter into the
  observations.

  The Hubble is the sole telescope that can pursue supernova
  explosions deeply enough to chart the early days of dark energy.
  The recent announcement that the National Aeronautics and Space
Administration will send astronauts to maintain and refurbish the
Hubble once again, enabling it to keep performing well into the
  next decade, is a lift for Dr. Riess's project. A new camera could
  extend observations to 11 billion or 12 billion years back.

http://www.nytimes.com/2006/11/17/science/space/17dark.html?
  ex=1164517200&en=2cf5dc81cde144a4&ei=5070&emc=eta1