Mason Inman - science journalist

22 November 2004, for the CERN Bulletin

A recent analysis, in part by theorists working at CERN, suggests a new view of the cosmic microwave background radiation. It seems the solar system, rather than the universe, causes the radiation's large-scale fluctuations, similar to the bass in a song.

There's a loose end in the data on the microwave radiation leftover from the early universe, say a group of theoretical physicists. But their new analysis may have found the culprit: our solar system.

Across the sky, maps of the cosmic microwave background radiation show fluctuations large and small, like the high and low harmonics in a beat of a drum. Most sizes of fluctuations match expectations. But at the largest scales, akin to the rumbling bass of a song, they're weaker than predicted. At face value, this cosmic bass contradicts prevailing theories of the early universe.

The theorists' new mathematical analysis picks out the large-scale fluctuations from the tumult of the background radiation in maps from the Wilkinson Microwave Anisotropy Probe (WMAP). Their reanalysis suggests, surprisingly, that the observed microwave radiation has a foreground superimposed on it from the motion and orientation of our solar system. If so, the researchers say, cosmologists may need to revise their views of the early universe. Using WMAP to estimate the date the first stars formed, for example, depends heavily on the cosmic bass.

In a paper accepted by Physical Review Letters, the theorists—Dominik Schwarz, then a fellow at CERN; Glenn Starkman of Case Western Reserve University, who worked on the analysis during a sabbatical at CERN; and Dragan Hunterer and Craig Copi, both of Case Western—describe their mathematical analysis. They found that these cosmic bass notes group together in the sky in curious ways.

Of the fluctuations in the microwave radiation generally assumed to be of cosmic origin, the largest is the so-called quadrupole with two maxima and two minima in the sky. The quadrupole aligns perpendicular to the plane of the solar system, as does the octopole, with three maxima and three minima. And both are also at right angles to the direction the solar system is moving. These correlations suggest the cosmic bass is in part local "foreground" superimposed on the cosmic background radiation.

If these large-scale fluctuations are not of cosmic origin-if the true background radiation is mostly treble and little bass-then cosmologists need to revise their interpretations of the WMAP data, the authors say. Conservative estimates put the date of the first stars around a billion years after the big bang, but initial interpretations of the WMAP data slashed that figure by one fifth, to about 200 million years. The new reanalysis would loosen this interpretation, however, allowing for theories of the universe's development in which stars form later. With the reanalysis, the authors say, a first date for stars as late as 800 million years would be consistent with WMAP and spectra from the most distant quasars observed so far.

Theory and measurements of large-scale fluctuations in the background radiation have long been in conflict. Data from the COBE satellite, a predecessor to WMAP, shows a similar discrepancy. But this problem was largely forgotten, the authors of the reanalysis say. Attention focused on how well WMAP pinned down the age of the universe and supported the theory of inflation, which holds that the universe expanded enormously in its early moments. Nonetheless, this loose end in the data remained, in conflict with the predictions of inflation.