By Marc Kaufman
Washington Post Staff Writer
Friday, November 17, 2006
Dark energy -- the mysterious force that makes up 70 percent of the energy in the universe and is pushing it to expand ever faster -- was present in early days of the universe, NASA researchers reported yesterday.
The finding that dark energy was present 9 billion years ago moves back substantially the time when this force, which is thought to act as an opposite to gravity, existed in the universe. It also lends support to one of the most debated theories put forward by Albert Einstein, what the renowned physicist called a "cosmological constant" in the universe that includes a force that works against gravity, creating equilibrium.
The energy that makes up that force, which researchers say is present in every cubic inch of space, is probably the most studied field in physics today.
Although scientists know virtually nothing about it -- neither its form nor its nature, or even whether it is permanent or fleeting -- they have concluded that it is theoretically necessary to make sense of other information they have about the cosmos. Yesterday's results were presented as a significant scientific advance.
"Although dark energy accounts for more than 70 percent of the energy of the universe, we know very little about it, so each clue is precious," said Adam Riess of the Space Telescope Science Institute and Johns Hopkins University in Baltimore. In 1998, Riess led one of the first studies to find the presence of dark energy, and he is the leader of the current study.
"Our latest clue is that the stuff we call dark energy was relatively weak but starting to make its presence felt 9 billion years ago," he said. Astrophysicists believe the universe began with the big bang about 13.8 billion years ago.
The new information about dark energy came from four years of observations by the Hubble Space Telescope, which orbits about 350 miles above Earth and has allowed scientists to look deeply into distant galaxies. In particular, the Hubble discovered 23 supernovas, exploding stars whose brightness or faintness can tell astronomers how far away they are.
Based on information from those ancient explosions, scientists were able to determine that the universe at that time was expanding in a way consistent with the presence of dark energy.
Einstein had initially proposed his cosmological constant a century ago as a way to explain how and why the universe does not implode because of gravity. Subsequent observations by other scientists determined that the universe was in fact expanding, prompting Einstein to call the theory his "biggest blunder."
But in the late 1990s, Riess and his team used Hubble and ground-based telescopes to detect an acceleration in the expansion of space -- a discovery that gave weight again to Einstein's theory about the presence of a "repulsive" form of gravity in space.
Riess called dark energy "this strange feature that Einstein first predicted" and said it appears to be speeding up the expansion of the universe today as it did 9 billion years ago -- when the universe was half the current size.
While the new finding tends to support the cosmological constant theory, researchers said yesterday that it did not confirm it and that several competing theories remain plausible, including one that contends our understanding of the nature of gravity is flawed.
Sean Carroll of the California Institute of Technology, who participated in yesterday's teleconference as an expert although he did not work on the report, said that dark energy may have played a central role in the initial expansion of the universe after the big bang.
"Something like dark energy was driving" the expansion of the universe early on, he said. "Something like dark energy is around now. It is natural to wonder if it is the same thing."