'Dark energy' backs Einstein, Hubble suggests

Published: 02.21.2004
By James Glanz
THE NEW YORK TIMES

MARINA DEL REY, Calif. - A dark, unseen energy is steadily pushing the universe apart just as Einstein once predicted, suggesting the universe may have a more peaceful end than more recent theories envisioned, according to new measurements of distant exploding stars by the Hubble Space Telescope.

The energy, whose source remains unknown, was named the cosmological constant by Einstein. In a 1917 prediction he later called "my greatest blunder," Einstein posited a kind of antigravity force pushing galaxies apart with a strength that did not change over billions of years of cosmic history.

Theorists seeking to explain the mysterious force have suggested that it could, in fact, become stronger or weaker over time - either finally tearing the universe apart in a violent event called "the big rip" or shutting down in the distant future - tens of billions of years from now.

If the force somehow shut down, gravity would again predominate in the cosmos and the universe would collapse on itself. That version of oblivion is sometimes called "the big crunch."

On Friday, Adam Riess of the Space Telescope Science Institute in Baltimore presented the first broad set of observational data that gauges the strength of the antigravity force over time. The data, he says, suggest the cosmos will gradually expand, cool and darken, more akin to a slide into senescence rather than a violent apocalypse.

Riess and his team, which included Louis Strolger of the science institute and Alexei Filippenko of the University of California-Berkeley, used the Hubble to search for exploding stars, or supernovas, which are swept up in the dark energy's cosmic push. They discovered 42 supernovas in their survey area, including six of the seven most distant known.

But rather than seeing the changes in the push that many theorists had predicted, Einstein's steady, unchanging cosmological constant fits the data better than any of the alternatives.

"What we've found is that it looks like a semipermanent kind of dark energy," Riess said. "It appears like it's been with us for a long time; if it is changing it's doing so slowly."

"Einstein's theory," Riess said, "is looking a lot better than before this data."