If cosmologist Will Percival of the University of Portsmouth in England is right, the universe will end about 60 billion years from now, when every molecule and atom will be torn asunder by a mysterious entity that opposes gravity's pull and turns it into a cosmic push.

The cosmic killer is a runaway version of what astronomers call dark energy, an unidentified substance that pervades all of space. Dark energy appears to cause the universe to expand at an accelerated rate. Many studies have found hints that the density of dark energy is constant over time and that it therefore exerts a constant repulsive force.

But Percival and his collaborators, studying cosmic expansion by measuring sound waves generated in the early universe, have found the first sign that dark energy could be growing stronger over time. It's as if someone had floored the cosmic gas pedal. And that would lead to a universe that ends in the Big Rip.

Percival's team examined the echo of sound waves created soon after the Big Bang, when photons and baryons — ordinary subatomic particles like electrons — were bound together. The primordial cosmic sound-wave oscillations arose because of the tug of war between gravity, which acted to compress each photon-baryon clump, and the radiation pressure exerted by the photons, which resisted that clumping. Although the sound waves ceased some 400,000 years after the Big Bang, when the universe became cool enough for photons and baryons to go their separate ways, the echoes of this cosmic symphony left their imprint as ripples in the distribution of galaxies in the modern-day universe. The characteristic wavelength of these ripples provides a standard ruler for gauging cosmic expansion.

(Science News)