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Physicists find further evidence for inflationary universe
30 April 2001

Deane Morrison, University of Minnesota
and Robert Sanders, UC Berkeley

WASHINGTON, D.C. - Astrophysicists at the University of Minnesota and the University of California, Berkeley, have just developed a "snapshot" of the infant Universe taken in 1998. New data on the cosmic microwave background radiation indicate that the inflationary model of the Universe, which claims that the clumps of stars and galaxies we see today resulted from a spatial pattern of energy in the primordial "soup," is essentially correct. The data disfavor theories known as "defect models," which attribute the modern pattern of stars and galaxies to changes in phase, or properties, of energy early in the life of the Universe. The work has been submitted to the Astrophysical Journal Letters and will be presented at 12:57 p.m. Saturday, April 28, at a meeting of the American Physical Society in Washington, D.C.

The data represent a closer examination of the pattern of microwave background radiation that was reported last year by researchers on the MAXIMA project, in which a high-altitude balloon experiment measured infinitesimal temperature fluctuations resulting from the microwave radiation that permeates the Universe. The first analysis found strong fluctuations on a scale of about one degree (two full moon widths) on the sky. In the current study, patterns of fluctuations were picked up on finer scales--about one-tenth of a degree on the sky. The temperature variations on this fine scale are approximately 50 millionths of a degree Kelvin; those that occur on the degree scale are about twice as big.

The microwave radiation is being emitted by a wall of hot charged particles, or plasma, that surrounds us. This plasma is receding from Earth at nearly the speed of light, so the radiation from it is redshifted down to microwave frequencies. This radiation dates from the very early Universe and is called an "echo of the Big Bang."

The fact that the microwave radiation is "splotchy" on these finer scales is predicted by the inflationary model of the Universe, said Shaul Hanany, an assistant professor of physics at the University of Minnesota and a leader of the MAXIMA project. "We're very excited about this because the results give us a strong indication of the magnitude of temperature fluctuations on this scale," Hanany said. "The observed magnitude is consistent with what inflation predicts."

If such fine-scale temperature variations had not been detected, physicists would have to revise some basic theories about the early history of the Universe.

The theory of inflation predicts a period of rapid expansion of the early Universe and a "flat," or ordinary, geometry for the Universe, in addition to the fine scale variation in temperature. Results announced last year from MAXIMA and BOOMERANG, another balloon-borne experiment, showed that the Universe is flat.

The current data were collected on an August 1998 balloon flight launched from NASA's Balloon Facility in Palestine, Tex. Hanany said the observed microwave temperature fluctuations are the seeds of the stars, galaxies and clusters of galaxies we see today. Inflation theory predicts that these fluctuations come from clumpiness in the energy that permeated the very early Universe. Inflation also predicts a particular harmonic pattern for the fluctuations of temperature in the microwave radiation. The current data may be the first glimpse of that pattern.

"This study provides strong confirmation that overall we're using the right model to describe the Universe," said Paul Richards, professor of physics at Berkeley and principal investigator for the MAXIMA project. "Our results last year implied just the right density of matter and energy for light to travel in straight lines across the observable Universe. This is what cosmologists mean by a flat Universe. The new results give support for an additional feature of the inflationary theory."

"The most amazing thing is that all our experiments are broadly consistent," said Adrian Lee, assistant professor of physics at Berkeley. Lee is first author of the current paper and a leader of the MAXIMA project. He is also on the staff of Lawrence Berkeley National Laboratory. "Our earlier measurements, on a scale of one degree of sky, taken together with observations of supernovae, imply that there's a 'dark energy' accelerating the expansion of the Universe."

The data were analyzed at the Lawrence Berkeley Laboratory's National Energy Research Scientific Computing Center, which is supported by the U.S. Department of Energy, and at the Minnesota Supercomputing Institute at the University of Minnesota. Radek Stompor of the Berkeley Space Sciences Laboratory was the principal data analyst for the project. The MAXIMA project began in the NSF Center for Particle Astrophysics at Berkeley and has been supported by the NSF and NASA.

The MAXIMA team is now analyzing data from a second balloon flight, in June 1999. The researchers hope the new data will strengthen the findings from the earlier flight. They also plan to launch an experiment to study the polarization of the microwave radiation. Polarization can be visualized as a vibration of photons as they travel through space, and patterns of variations in polarization--that is, vibrations in different planes--will be useful in sorting out variants of the inflation model, said the researchers.