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In the Stars: The (big) question of time

By PHIL BERARDELLI, Science & Technology Editor

WASHINGTON, Nov. 18 (UPI) -- How simple it was, many moons ago, when humans sat smug and comfortable at the center of the universe. Earth represented absolute solidity and permanence, as the sun crossed the sky during the day, the stars and strange objects the Greeks called "planetes" or wanderers moved during the night, and the moon chose alternatively to inhabit both settings.

Only in the 16th and 17th centuries A.D., when four scientists -- an Italian, a Dane, an Austrian and an Englishman named, respectively, Galileo, Brahe, Kepler and Newton -- began announcing disturbing theories and discoveries about celestial bodies did humanity's sense of superiority start to ebb. Suddenly the sun, not Earth, was central.

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The slide continued as astronomers discovered our local star was just a member of a neighborhood of millions of other stars in the Milky Way. Then in the 20th century, Edwin Hubble looked through his telescope and saw the strange clouds in the night sky called nebulae were composed of millions of stars -- the Milky Way became a galaxy, not the one and only galaxy.

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Hubble also observed for the first time the nebulae in every direction seemed to be moving away from Earth.

Today, using imaging power undreamed of by Hubble, his namesake telescope has helped to confirm the universe is populated by hundreds of billions of galaxies, each containing hundreds of billions of stars and all being carried toward dark oblivion by a recently discovered force of immense power called dark energy.

Hubble's powerful ultra deep field observation, for example -- which entailed a combined exposure of more than 1 million seconds -- yielded an image of a tiny portion of the sky containing about 10,000 galaxies, some of them so distant their light has taken nearly 13 billion years to reach Earth.

Even that immensity may not comprise all of existence, however -- far from it. Researchers over the past couple of decades have determined that visible matter comprises only a small fraction of the universe -- about 4 percent. The remainder is divided between dark matter (23 percent) -- an as-yet-unobserved component that holds galaxies together yet does not seem to interact with ordinary atoms -- and the even-more-mysterious dark energy (73 percent).

Now, a new theory suggests the Big Bang -- the sudden expansion of space and time that brought everything we know into existence some 13.7 billion years ago -- could be simply a periodic event in the natural evolution of the cosmos.

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Two University of Chicago physicists predict there may be many big bangs -- perhaps even an infinite number -- that will repeat over incredibly vast time scales as the universe expands, empties out and cools off.

"We like to say that the Big Bang is nothing special in the history of our universe," said Sean Carroll, assistant professor of physics. Carroll and graduate student Jennifer Chen have composed a theory that attempts to address two ambitious questions:

-- Why does time move only forward?

-- How could the Big Bang have appeared in empty space according to the known laws of physics?

The unilateral direction of time has befuddled scientists since the days of Einstein because "for the most part the fundamental laws of physics don't distinguish between past and future -- they're time-symmetric," Carroll said.

The second question relates to the concept of entropy, which says any state of organization will naturally deteriorate into increasing states of disorganization.

"You can turn an egg into an omelet, but not an omelet into an egg," Carroll explained.

Previous researchers have studied the Big Bang using the assumption that entropy is finite, but Carroll and Chen have taken the opposite approach.

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"We're postulating that the entropy of the universe is infinite," Chen said. "It could always increase."

Their theory relies on a concept called inflation, which is related to the Big Bang. According to inflation, the universe underwent a period of massive expansion during its earliest period. That expansion -- of space itself -- occurred much faster than the current cosmic speed limit, 186,000 miles per second or the speed of light.

The concept has a problem, however, Carroll said. For inflation to begin, the universe would have had to encompass a minuscule patch of space-time in an extremely unlikely configuration, something that would not be a favorable starting point. Also, in a universe of finite entropy, matter would have to transition from a high-entropy state into low entropy -- something Carroll and Chen call a statistical long shot.

"The conditions necessary for inflation are not that easy to start," Carroll said. "There's an argument that it's easier just to have our universe appear from a random fluctuation than to have inflation begin from a random fluctuation."

In other words, it would be more likely for the universe to spring, full-bloom, from nothingness than for a Big Bang to occur spontaneously and transition into inflation.

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Carroll and Chen's solution: something called infinite entropy, which is related to the 1998 discovery of dark energy, a force that seems likely to propel the universe's expansion forever.

"In our current universe, the entropy is growing and the universe is expanding and becoming emptier," Carroll said.

The problem is that even empty space contains faint traces of energy that fluctuate on the sub-atomic scale. Previous research by Jaume Garriga of Universitat Autonoma de Barcelona, Spain, and Alexander Vilenkin of Tufts University in Boston has shown these fluctuations can generate their own big bangs in tiny areas of the universe that are widely separated in time and space.

Based on their calculations, Carroll and Chen think inflation could have started in reverse sometime in the universe's distant past. If so, during that period time would have appeared to run backwards.

Regardless of the temporal direction they run in, any new universes created by the ancillary big bangs would continue to increase entropy. In this never-ending cycle, the universe never achieves equilibrium. If it did achieve equilibrium, nothing would ever happen -- there would be no time passage at all.

"There's no state you can go to that is maximal entropy," Carroll said. "You can always increase the entropy more by creating a new universe and allowing it to expand and cool off."

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The only question, then, is what comes next?

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In the Stars is a weekly series by UPI that reports on new discoveries and theories about the cosmos. E-mail [email protected]

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Editors: Images of the Hubble Ultra Deep Field are available as UPI photos WAS2004030901, WAS2004030902, WAS2004030903, WAS2004030905 and WAS2004030911

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