Physicists propose tests for dark energy

by MIKE MARTIN, UPI Science Correspondent

PASADENA, Calif. June 7 (UPI) -- A major announcement that may solve one of science's greatest lingering mysteries -- tests that should be able to detect the effects of elusive "dark energy" that supposedly pervades the cosmos -- surprised researchers today at the national meeting of the American Astronomical Society.

Physicists Kevork Abazajian and Neal Dalal of the University of California, San Diego said observations of distant supernovae, quasars (very distant galaxies), and galaxy clusters can be used to determine whether current models for dark energy need radical revision or minor fine tuning. The researchers said some of these observations are possible with today's technology, while others may require specially-designed space observatories.

Current observations, Abazajian explained, point to the existence of large quantities of dark energy -- and its counterpart, dark matter -- in the universe. This dark energy is accelerating the expanding universe, he said.

An odd twist, Abazajian said, is the acceleration seems to be kicking in just now -- in recent times -- creating a nasty dilemma for scientists generally loathe to think we are specially positioned -- in space or time. If scientists fine tune the theoretical amount of dark energy to fit observations, dark energy has been negligible right up until now. In the future -- our future -- it will become even more important, accelerating the universe at an ever-increasing pace.

"The good news is that simple models of dark energy can provide an excellent fit to many observations," Abazajian told the conference. "The bad news is these models give no explanation of the implied cosmic coincidence that we are apparently living in a very special time in the history of the universe."

Abazajian and Dalal claim dark energy's effects on the evolving universe can be assessed by measuring the dimming of supernovae with distance; the apparent angular separation of intergalactic clouds in front of quasars; the bright cores of galaxies visible from great distances; and the rate at which giant galaxy clusters form over vast epochs.

Present supernova surveys, data from the Sloan Digital Sky Survey, and deep-space x-ray surveys by NASA's Chandra X-ray observatory may provide enough information to confirm the simplest dark energy models, Abazajian said. The proposed Supernova Acceleration Probe, an optical infrared space telescope, would provide more definitive results.

"It is possible to get around this giant coincidence by modifying the theory of gravity or invoking extra dimensions," Neal Dalal explained. "The tests we have proposed can give us insight into whether these far-out ideas are worth pursuing."