http://www.msnbc.msn.com/id/4327735/
Dark energy confirmed as constant presence
Universe has at least 30 billion years left, scientists say
By Robert Roy Britt
Senior science writer
Updated: 4:35 p.m. ET Feb. 20, 2004
Recent Hubble Space Telescope images of distant exploding stars add
further confirmation to the permanence of a mysterious, repulsive force
called dark energy that appears to dominate the universe.
While scientists are not ready to close the case, they said today that
dark energy, which is thought to permeate the cosmos and work in
opposition to gravity, does appear to be a constant presence as
predicted.
The results bolster a theory that the universe won't end soon. But they
leave researchers no more informed about the actual nature of dark
energy.
"We still have almost no clue what it is," said study leader Adam Riess
of the Space Telescope Science Institute (STScI) in Baltimore.
Dark energy was conjured to explain a phenomenal discovery in 1998:
Nearly all galaxies in the universe are receding from each other at an
ever-faster pace.
Gravity is losing some unknown battle, cosmologists admit. They theorize
that about 70 percent of the universe is made up of dark energy, while
most of the rest is another mysterious thing called dark matter and only
a small fraction is real matter like stars, planets and living entities.
Albert Einstein was the first to consider something similar, which he
called a cosmological constant. He said even the emptiest space would
have some of this strange stuff in it.
But when Edwin Hubble discovered the expansion of the universe in the
1920s, Einstein called his cosmological constant his greatest blunder.
Einstein is back
With the more recent finding that the expansion is accelerating,
Einstein's idea was revived.
The new findings support Einstein's cosmological constant, which modern
cosmologists say implies that dark energy should not characteristically
change over time. If that's right, the universe will continue to expand
at an accelerating forever.
The new results suggest that even if Einstein and modern dark energy
theory are both wrong, dark energy will not destroy the universe for at
least 30 billion years, Riess and his colleagues say.
"Right now we're about twice as confident than before that Einstein's
cosmological constant is real, or at least dark energy does not appear
to be changing fast enough, if at all, to cause an end to the universe
anytime soon," Riess said.
The universe is presently 13.7 billion years old.
Riess' team uses Hubble to find stars that exploded when the universe
was about half its present age. A certain type of these supernovas, as
they are called, shine with a known brightness. So examining the light
that reaches Hubble tells astronomers how far away each one is and the
rate at which the universe was expanding when that star exploded.
That rate of expansion has changed over time, other studies have shown.
The initial expansion, after a theoretical Big Bang, was the most rapid
and was called inflation. Then things leveled off before another round
of acceleration, which is apparently underway now.
Riess' team has now observed 42 of the very distant supernovas --
including 16 in the new work -- in its Great Observatories Origins Deep
Survey (GOODS) program.
The data was first presented last fall but has only now been fully
analyzed. The results were discussed in a teleconference with reporters
Friday and will be published in the Astrophysical Journal.
What's going on
There are two main ideas for the source of dark energy. It might
percolate from empty space, as Einstein theorized, and is unchanging and
of a fixed strength. The other holds that dark energy is associated with
a changing energy field called "quintessence," something akin to a
magnetic field. In that scenario, the field causes the current
acceleration of the universe.
Another research team recently theorized that if the repulsion from dark
energy gets stronger than Einstein's prediction, the universe could
expand so incredibly that it would end in a Big Rip. All matter —
galaxies, then stars, then planets, and everything right down to the
atomic level — would be torn apart.
If dark energy can change, it might also one day reverse course and pull
the universe back together in a Big Crunch. "This looks like the least
likely scenario at present," Riess said.
There are two initial questions scientists are trying to answer: What is
the strength of dark energy today, and does it grow or decay with time?
The new data show that if the repulsive force is changing, "it is not
changing very rapidly," Riess said.
There is a lot of work ahead.
"Determining these two properties still leaves us very, very far from
understanding what dark energy is," said Mario Livio, a theorist who
heads the science division at the STScI. But until these first two
parameters are determined, a fundamental understanding of the cosmos
will remain elusive. It remains possible, for example, that our
understanding of gravity "is completely lacking," Livio said.
There are other methods for probing dark energy, but none are as
developed as the supernova observations. So in the near term, progress
toward understanding dark energy will rely heavily on more observations
of exploded stars that are even farther away and deeper in time.
Astronomers worry, however, that if Hubble stops working by around 2007,
which would be the case under NASA's current plan, they would lose their
primary tool in the hunt for distant supernovas.
And with NASA's new human spaceflight plans, other useful projects are
in jeopardy. Many missions under NASA's Beyond Einstein initiative,
including proposed missions to study dark energy, have taken a budgetary
back seat to programs that will help get humans back on the Moon and on
to Mars.
Whatever methods are applied, Anne Kinney, director of NASA's Astronomy
and Physics Division, cautioned that final answers on the nature of dark
energy will not likely come for a very long time. Science can sometimes
be much like art, she said: "You approach, you don't arrive."
© 2004 Space.com.
Stoney
"Designated Rascal and Rapscallion
and
SCAMPERMEISTER!"
When in doubt, SCAMPER about!
When things are fair, SCAMPER everywhere!
When things are rough, can't SCAMPER enough!
/end humour alert
alt.atheism military veteran #11
{so much for the 'no atheists in foxholes' rubbish}
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