Interesting--but probably wrong. That sums up the reaction of most physicists and radio astronomers to an extraordinary claim appearing in today's Physical Review Letters that space itself might have a favored direction--in effect, an up and a down.
Aired amid a barrage of publicity last week in The New York Times and elsewhere, the claim was based on unaccountable differences in the way radio waves seem to propagate to Earth from galaxies at different spots in the sky. But other researchers say that Borge Nodland of the University of Rochester in New York and John Ralston of the University of Kansas have not made a convincing case. "Extraordinary claims demand extraordinary evidence," says Michael Turner, a physicist at the University of Chicago. "The evidence presented does not yet meet this standard."
Ralston says he's not surprised by the criticism. "It's always going to be there as long as somebody tries something new," he says. He and Nodland analyzed published observations of 160 radio-emitting galaxies scattered around the sky. The electric field in radiation from such galaxies often arrives at Earth with a distinct polarization, or orientation. The duo tried to estimate the original orientation by assuming that each galaxy emits radio waves polarized at a specific angle relative to its observed structure. After accounting for warping from charged particles and magnetic fields in space, they found a residual twist in the radio waves. The twist varied with the distance of the galaxy, and it was least for galaxies lying in a particular direction, toward the constellation Sextans.
The effect, if real, would have momentous consequences. For starters, it could overturn Einstein's theory of relativity, which holds that physical laws are the same everywhere in the universe. But radio astronomers point out that Nodland and Ralston rely mainly on data from before about 1980, when the Very Large Array in Socorro, New Mexico, came on line and began making far better observations of radio galaxies. And some experts say the assumption that each galaxy emits radio signals at a single, predictable polarization is decades out of date. "Of course, there are newer data on radio galaxies in general," responds Ralston, but he says he didn't find any other observations that had all the features needed for his analysis.
Most researchers think the effect would simply vanish in a larger, more modern data set. "I wouldn't look at this and say there's no chance it could be right," says Ruth Daly, a physicist at Princeton University. "But it's not clear whether [the analysis is] telling us something interesting about the universe or about problems in the data."