Mysterious 'Dark Energy' Not as Ominous as Thought

All manner of theories, some involving hidden dimensions and exotic particles, have been tossed around to account for dark energy. One possible solution would be to revise, or even toss out, Einstein's general theory of relativity. The theory holds that gravity is a function of the geometry of four-dimensional "space-time." Matter, as physicists like to say, tells space-time how to curve, and space-time tells matter how to move. The theory is so well established that GPS navigation devices have to account for the curvature of space-time to remain accurate.

But although general relativity is used all the time in modern cosmology, there have been suggestions that it breaks down at the cosmic scale.

"It's never been proved right on the scale of the observable universe," Spergel said.

The most famous confirmation of the theory came in 1919 when, during an eclipse, astronomers measured the way the sun bent the light from a star behind it. If the classical laws of physics developed by Sir Isaac Newton were correct, the sun's gravity should have deflected the starlight to a small but predictable degree. Einstein, with his tale of curved space, predicted twice as much deflection. When astronomers showed that Einstein was right, he became an instant global icon.

The new findings, by bolstering general relativity once again, suggest it will be a while before Einstein's universe is revised the way he revised the Newtonian universe.

Hovering over the new research is the minor matter of the fate of the universe. If the universe continues to expand at an accelerating rate, Krauss has estimated, in about 100 billion to 1 trillion years, almost all the galaxies we see will be so far away they will vanish from sight. It will be a much darker universe.

But what will not happen, apparently, is the cosmic apocalypse that scientists call the big rip. That would occur if dark energy was strong enough to rend asunder all the stars, planets, moons, rocks, dust and even atomic nuclei, as well as any and all innocent bystanders. The new measurement shows dark energy at a level that will permit our immediate surroundings and galactic environment to survive.

"The accelerated expansion will proceed forever," Vikhlinin said, "but will probably not result in a big rip."