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Dark energy may rip apart Universe

Crab Nebula

The Crab Nebula: some distant supernovae are used to study dark energy which some scientists say is ripping our Universe apart

Some say the Universe will end in a "Big Crunch," others expect a "Big Chill," and now some U.S. physicists are saying the end could be something more like a "Big Rip".

Assistant Professor Robert Caldwell of Dartmouth College in New Hampshire and colleagues publish their unusual hypothesis in the current issue of Physical Review Letters.

According to the theory, which is actually called the "Big Rip", the continuous growth of the Universe's "dark energy" pushes things apart and may account for much of the Universe's expansion since the "Big Bang."

If dark energy increases fast enough, in about 20 billion years the repulsive force could become so strong that it pushes apart galaxies, stars, solar systems and eventually even atoms will fly to pieces: "It's a runaway process," said Caldwell.

The dark energy called on by Caldwell is different from the more famous dark matter in that it has no mass or gravity. In fact it's a sort of anti-gravity called on to explain why stars and galaxies are flying away from each other so quickly.

Based on detailed observations of exploding stars, astrophysicists have been able to estimate that dark energy makes up about 70 % of "stuff" in the universe. The rest is made of dark matter (25 %) and regular matter that makes up stars, planets and us (5 %).

In Caldwell's scenario, the universe will last about 20 billion more years. Sixty million years before the end, dark energy will cause the Milky Way galaxy to fly apart. Three months before the end solar systems will break down, flinging planets helter-skelter. Finally, at a tiny fraction of a second before the end of everything, dark energy will be so great that it will overcome the powerful forces that hold matter together, throwing apart atoms.

"It's as plausible as the other [scenarios]," said astrophysicist Professor Abraham Loeb of Harvard University. "And it's good to know what the possibilities are".

The other scenarios, the "Big Crunch" and "Big Chill" call on too much or too little gravity in the universe, respectively. If there is too much gravity, all matter will come back together in a tremendous "crunch." Too little gravity and the present expansion of the universe will continue forever - until every star burns out and the universe becomes a very cold and dead. In this scenario, entropy wins.

Only improved measurements of cosmic forces by astronomers will tell which scenario is likely to prevail, Caldwell said.

Tags: astronomy-space