Theorists Tackle Universe's 'Coincidence Problem'

Oct. 22, 2008 -- Australian scientists have come up with a simple solution to one of the deepest puzzles in our understanding of the cosmos -- why life on Earth coincides with a momentous shift in the makeup of the universe.

Ph.D. student Chas Egan and Charley Lineweaver from Australian National University publish their solution to the so-called "coincidence problem" this week in the journal Physical Review D.

The conundrum has its roots in the way the universe changes as it expands, explained Egan.

Soon after the Big Bang, some 14 billion years ago, most of the energy in the universe was in the form of heat. Later, as the universe cooled and expanded, matter, such as stars and planets, became dominant.

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As the expansion continues, it is expected that "dark energy" -- a mysterious force that causes the expansion of the universe to accelerate -- will become most important.

Over the past 10 years, observations of the universe have shown that the expansion is accelerating, suggesting that the gradual transition from the current matter-dominated phase to the dark-energy era is underway.

"We're right on the cusp between the matter-dominated and dark energy-dominated epochs," said Egan.

Astronomers have been puzzled why this shift is happening right now, just when humans are here to observe it.