Afterglow of the Big Bang

"We had the sky, up there, all speckled with stars, and we used to lay on our backs and look up at them, and discuss about whether they was real, or only just happened."
-- Mark Twain, Huckleberry Finn
One of Bertschinger's two approaches involves modeling the "glow" of the early universe. The cosmic microwave background, discovered in 1965 by Arno Penzias and Robert Wilson, who subsequently received a Nobel prize, is thermal radiation from the big bang, still traveling through space 15 or so billion years later. "Imagine that our eyes could detect microwave radiation," explains Bertschinger, "like that produced by microwave ovens. The night sky would be luminous." For cosmologists, this afterglow is a fossil of the universe in its infancy.

This microwave radiation is almost perfectly uniform from all directions, as predicted by the big bang theory. In 1992, however, using NASA's Cosmic Background Explorer satellite, scientists found minute fluctuations. This was the first direct evidence of irregularities in early stages of the universe that could account for how matter clumped into planets, stars, galaxies and the clustered chains of galaxies found in the past decade.

With the CRAY C90 and, more recently, the CRAY T3D, Bertschinger has carried out what he believes are the most accurate calculations yet that track the consequences of these microwave fluctuations. Using code he developed, called LINGER (for linear general relativity), his basic approach is to apply a random fluctuation to the first second of the big bang and evolve forward in time. The results are then compared with observed data.

Because the microwave fluctuations are so minute, they are extremely difficult to measure accurately, and observations from different experiments haven't yet settled into agreement. Bertschinger's modeling suggests that fluctuations should show up at smaller scales than have been measured so far, results that will help guide design of new measurement techniques.

The numerical approach Bertschinger uses in this modeling is analogous to an electronic synthesizer sampling music from the universe. "Basically, what we're doing is decomposing acoustic waves into their different frequency components." Each harmonic can then be computed independently, an approach that fits extremely well with parallel processing. The speedup from T3D scalability, going from 32 to 64 or 128 processors, says Bertschinger, is nearly linear, better than 99.9 percent. "The T3D has been a wonderful machine for this project. We get turnaround in a couple of days that would take months on a single Alpha chip workstation."

No, they're not Easter Eggs. They're the infant universe hatching from its structureless shell. The COBE science working group produced the blue and pink all-sky map from data collected by the Cosmic Background Explorer (COBE) satellite. It depicts minute temperature fluctuations, ranging from 0.00015 degrees Kelvin colder (blue) than the background to 0.00015 degrees K. warmer (pink). The second map represents Edmund Bertschinger's simulations on the CRAY T3D at Pittsburgh. This map, at higher angular resolution (0.5 degrees) than COBE could detect (7 degrees), shows negative (blue) and positive (red) fluctuations of 0.0002 degrees K. The simulation assumed a mixed hot and cold dark matter model with 5 eV neutrino mass.

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