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How can we peer closer to the beginning of the universe?

TEMPE—The first annual Origins Symposium at Arizona State University here began yesterday with a bang—a big bang, that is—as a panel outlined the theoretical and technical challenges of peering still closer to that signal event in the history of the cosmos for clues about the nature and evolution of the universe we know today.

The weekend meeting pulls together experts, including several Nobel laureates, in origins studies across all disciplines, from those concerned with outer space to the inner space of human consciousness; public presentations will follow on Monday.

“There’s only so far back we can see, and that’s about 380,000 years” after the big bang, when detection of light particles, or photons, becomes impossible because of the high energies at that time, said physicist Michael S. Turner of the University of Chicago, who moderated the panel. “Within Einstein’s theory of general relativity, the big bang is a singularity—we can’t go beyond that singularity.” He outlined five key problems to getting closer to that instant:

Walls. In principle, neutrino measurements could get to within one second of the big bang, but that hasn’t yet been demonstrated.

Horizons. The observable universe is 14 billion light-years across, and our view is limited.

Redshift. Older electromagnetic radiation traveling from the early universe is redder—it has longer wavelengths—and is harder to detect.

Particle properties. Many of the particles researchers would like to measure interact only weakly, and have short lifetimes or large masses—making them difficult to detect or to produce in experiments.

Measurement limitations. Noise and quantum limits make perfect measurements impossible.

“I got into this area a half century ago with great unease,” said physicist P. James E. Peebles of Princeton University in New Jersey. “I had no idea we’d have such success.” At the same time, there’s more work to do, he said. Theories of inflation—an early period dominated by rapid expansion of the universe—explain the characteristics of today’s observable universe. “The good news is that the theory of inflation adequately accounts for the structure that we see,” said Nobel laureate Steven Weinberg of the University of Texas at Austin. “That’s also the bad news.” Various inflation theories fit the data, showing that we do not have a complete understanding of the phenomenon. “I don’t see how we’re going to go beyond it in any reasonable time,” he said.

Some look to the potential of string theory. “Can we experimentally test what’s beyond the wall? Probably not,” said string theorist Brian Greene of Columbia University in New York. “But can we learn what’s beyond the wall [with string theory]? Probably so.”

“Inflation is remarkably consistent with every measure we can make. It just smells good. But is consistency enough?” asked Lawrence M. Krauss, the director of the Origins Initiative. “What we want is something that could falsify it [a particular model]. Gravitational waves are the greatest hope.” LIGO, the Large Interferometer Gravitational Wave Observatory, for one, will search for gravity waves, which are disturbances in the curvature of spacetime caused by the motion of matter, as will the upcoming Planck satellite. But the waves may be at problematically tiny scales. “In fact, anything that happens in the early universe that will produce a spectrum of gravitational waves that looks like inflation. It’s going to be difficult [to separate out the data]. I’m not saying impossible.” He added: “Are we at a point where certain things are empirically unknowable?”

Not to worry, countered Weinberg. Uncertainties are “the natural state of science,” he said. “There are lots of things we’re never going to be able to calculate or predict. What is important is that a theory has enough of a success that we believe it could calculate more” beyond what is possible today. “The important thing is to learn the principles.”

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