The good news from NASA’s Hubble Space Telescope is that Einstein was
right–maybe.
A strange form of energy called “dark energy” is looking a little more
like the repulsive force that Einstein theorized in an attempt to
balance the universe against its own gravity. Even if Einstein turns out
to be wrong, the universe’s dark energy probably won’t destroy the
universe any sooner than about 30 billion years from now, say Hubble
researchers.
“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,” says Adam Riess of the Space Telescope Science Institute,
Baltimore.
Riess used Hubble to find nature’s own “weapons of mass destruction” —
very distant supernovae that exploded when the universe was less than
half its current age. The apparent brightness of a certain type of
supernova gives cosmologists a way to measure the expansion rate of the
universe at different times in the past.
Riess and his team joined efforts with the Great Observatories Origins
Deep Survey (GOODS) program, the largest deep galaxy survey attempted
by Hubble to date, to turn the Space Telescope into a supernova search
engine on an unprecedented scale. In the process, they discovered 42
new supernovae in the GOODS area, including 6 of the 7 most distant
known.
Cosmologists understand almost nothing about dark energy even though it
appears to comprise about 70 percent of the universe. They are
desperately seeking to uncover its two most fundamental properties: its
strength and its permanence.
In a paper to be published in the Astrophysical Journal, Riess and his
collaborators have made the first meaningful measurement of the second
property, its permanence.
Currently, there are two leading interpretations for the dark energy, as
well as many more exotic possibilities. It could be an energy
percolating from empty space as Einstein’s theorized “cosmological
constant,” an interpretation which predicts that dark energy is
unchanging and of a prescribed strength.
An alternative possibility is that dark energy is associated with a
changing energy field dubbed “quintessence.”
This field would be causing the current acceleration — a milder
version of the inflationary episode from which the early universe emerged.
When astronomers first realized the universe was accelerating, the
conventional wisdom was that it would expand forever. However, until we
better understand the nature of dark energy–its properties–other
scenarios for the fate of the universe are possible.
If the repulsion from dark energy is or becomes stronger than Einstein’s
prediction, the universe may be torn apart by a future “Big Rip,” during
which the universe expands so violently that first the galaxies, then
the stars, then planets, and finally atoms come unglued in a
catastrophic end of time. Currently this idea is very speculative, but
being pursued by theorists.
At the other extreme, a variable dark energy might fade away and then
flip in force such that it pulls the universe together rather then
pushing it apart.
This would lead to a “big crunch” where the universe ultimately
implodes. “This looks like the least likely scenario at present,” says
Riess.
Understanding dark energy and determining the universe’s ultimate fate
will require further observations. Hubble and future space telescopes
capable of looking more than halfway across the universe will be needed
to achieve the necessary precision. The determination of the properties
of dark energy has become the key goal of astronomy and physics today.
Electronic images and additional information are available at:
http://hubblesite.org/news/2004/12
The Space Telescope Science Institute (STScI) is operated by the
Association of Universities for Research in Astronomy, Inc. (AURA), for
NASA, under contract with the Goddard Space Flight Center, Greenbelt,
MD. The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency (ESA).
