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NEW YORK -- In the beginning there was certainty, soon followed by blatant bewilderment.
Since its humble beginning nearly 70 years ago, the big-bang theory has remained the most successful idea ever offered for cosmic origins. It has been widely used to make sense of the visible universe.
Still, some aspects of the big-bang model remain puzzling. Dark matter and dark energy, for instance, test the limits of the theory -- everyone agrees they exist, but no one really understands what they are or how they behave.
And what caused the big bang? Was the bang followed by the considerable crunch? Do MACHOs make up much of the universe, or are WIMPs really the ruling class?
Do discoverable, static rules govern the actions of the universe, or is everything forever in flux?
Figuring all this out could be the work of a lifetime. Or we could have the answer next Tuesday. Right now, the only thing scientists know for sure about the beginning of the universe is how much they don't know.
Five of the finest scientific minds gathered at New York City's American Museum of Natural History Tuesday night to debate pressing questions on the origins, life cycle and possible future of the universe.
The annual Isaac Asimov Memorial Panel Debate was moderated by Hayden Planetarium Director Neil Tyson, who didn't have a particularly difficult job. As debates go, this was a civilized occasion.
The panelists generally agreed that the now-classic big-bang theory is just the thing to explain how the universe was created. But their theories on what caused the bang and what followed it diverged.
Paul Steinhardt, a physics professor at Princeton University, expounded on what he called the "one major surprise of recent astronomical research" -- a model that he refers to as the cyclic universe.
"This is not a new theory but a very old one," Steinhardt explained. "The big bang was not the beginning; it was a bridge between now and an earlier time."
Steinhardt believes that the universe cycles through a series of expansion periods, each followed by a contracting "big crunch" collapse, and then yet another expanding big bang. In between are trillions of relatively peaceful years.
We are now in the cosmic acceleration phase, he said, in which the universe will purge itself of all the entropy and black holes it produced during the last big bang.
Panelist Alan Guth, a professor of physics at MIT, explained his theory of inflationary cosmology, which proposes that "in the billion-trillion-trillionth" second before the big bang there was a period of hyper-rapid "inflation."
The universe experienced a rapid, exponential growth in size, and the stresses of that propelled the bang. Guth didn't buy Steinhardt's crunch theory, arguing instead that the universe continues to expand, sans any deflationary activity. Wall Street should be so lucky.
Guth conjured up his inflationary universe theory in 1979. It was widely doubted until 1992, when the space probe COBE seemingly confirmed the theory of the expanding universe.
"The big-bang theory as proposed by Hubble is essentially correct; inflation simply fills out the theory and expands our understanding of it," Guth said.
James Peebles, a professor of physics at Princeton University and a proponent of the classical big-bang theory, noted that scientists' confidence in their theories is sometimes greater than the confirmable data supporting those theories.
Peebles pointed to dark energy as an issue that no one quite understands, but almost everyone agrees exists in the universe.
The universe, he said, was idling along until about 6.3 billion years ago, when something caused it to speed up dramatically. That growth continues to this day.
Panelists said the growth is spurred by dark energy, a repulsive gravitational force caused by a response to dark matter, the invisible substance that composes nearly a quarter of the universe.
Some of that dark matter energy could be contained in MACHOs, clusters of massive compact halo objects, which include exploded stars, rogue planets and black holes created by the big bang.
The MACHO Project recently published the results of a decade-long study that seems to indicate that MACHOs account for at least half of the invisible universe.
Others believe dark matter is produced by WIMPs, or weakly interacting massive particles.
Some physicists think that WIMPs could make up as much as 99 percent of the total mass of the universe. No one can see them, but they can see WIMPs' gravitational effects by observing the way the stars and other components of galaxies rotate.
The panelists also discussed recent data returned by the Hubble Space Telescope, now one of the major tools being used to investigate dark energy.
"Within 10 years we should know whether the universe will go on growing, begin to contract or will reach a static point," said panelist David Spergel, professor of astrophysics at Princeton University.
Lee Smolin, researcher at the Perimeter Institute for Theoretical Physics, author of Life of the Cosmos and co-inventor of loop quantum gravity, said that these are exciting times for physicists.
"We have a flood of data now, instead of a flood of untestable theories."
Smolin originated the theory of cosmological natural selection, which proposes that black holes recreate the universe, and as the universe changes, so do the laws of physics.
Smolin's theory is that the universe is a sometimes unpredictable process of events that can be best explained by Charles Darwin's theory of natural selection. The universe evolves, and as it evolves it recreates the rules that govern its behavior.
The panelists disagreed on whether the universe was recreating itself according to its own needs or proceeding according to not-yet-understood rules, but they did agree wholeheartedly on one issue -- plenty of surprises lie ahead.
