CAMBRIDGE, U.K.--When light from the big bang cooled, it left microwave radiation spread throughout space. This fiery glow holds clues to the characteristics of the early universe and the secrets of its formation. Now, a team of researchers has announced that temperature fluctuations in the glow clash with one well-accepted theory of how the universe formed. The findings--presented here at a cosmology conference this week--are still preliminary, but if confirmed, they could change cosmologists' understanding of the moments immediately after the big bang.
In 2003, NASA's Wilkinson Microwave Anisotropy Probe (WMAP) satellite mapped small temperature variations in the cosmic microwave background radiation across the sky (ScienceNOW, 11 February 2003). The average temperature is 2.7 K, but it differs by a few millionths of a degree from one spot to another. By studying such subtleties, cosmologists have determined the age and makeup of the universe and confirmed predictions of inflation (ScienceNOW, 16 March 2006), the reigning description of the ballooning universe.
Inflation predicts that the universe expanded exponentially for a fraction of a second, making it mostly smooth and flat. Small primordial ripples in the structure of spacetime, which can be seen in the cosmic microwave background, grew to colossal scale and led to the formation of stars, galaxies, and other structures. Several models invoke inflation, but the simplest and most accepted, "single-field slow-roll inflation," predicts a particular distribution of the temperature fluctuations.
To test the theory, cosmologist Benjamin Wandelt of the University of Illinois, Urbana-Champaign, and his colleague Amit Yadav compared that predicted distribution with WMAP's measurements. The patterns did not match. Although the findings don't rule out traditional inflation theories, they do open the door for other theories about how the universe began, including the idea that the universe began with a splat rather than a bang (ScienceNOW, 9 April 2001). "This is telling you something about the physics acting in the first instant of time," Wandelt says.
Not everyone is convinced. To accurately measure the fluctuations in the cosmic microwave background, Wandelt and Yadav had to filter the Milky Way's spiral arms and interstellar dust from the WMAP picture. At the conference, cosmologists questioned the accuracy of these filters. In addition, David Spergel, a theoretical astrophysicist at Princeton University, says there is so much data--and so many ways of looking at it--that researchers are bound to find anomalies. "If you know what you are looking for, you can sometimes find it," he says.
Still, the community was buzzing and most were intrigued. Charles Bennett, a cosmologist at Johns Hopkins University in Baltimore, Maryland, says this work is an important first stab: "We are right in the ballpark of detecting things about our early universe."
More-detailed analysis could come from additional WMAP data as well as from the Planck satellite, set to launch in 2008. Princeton cosmologist Paul Steinhardt says now is the time for theorists to decide what their theories predict. Although Wandelt and Yadav's finding, if confirmed, would not kill inflation, Steinhardt says it would represent a setback. "It emphasizes that some things are still quite open, and there are key issues yet to be decided," he says.