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Possible cosmic defect may be a window into the early universe

October 26, 2007

An unusual cold spot in the oldest radiation in the universe, the cosmic microwave background, may be caused by a cosmic defect created just after the Big Bang, a Spanish and U.K. research team has found.

Although these findings need confirmation with further research, the suggestion may provide cosmologists with a long-sought clue about how the infant universe evolved.

This study will be published online by the journal Science, at the Science Express website, on 25 October, 2007. Science is published by AAAS, the nonprofit science society.

"These findings open up the possibility of looking for cosmic defects, similar to crystal defects, in the fabric of the universe. Although their existence has been proposed by theorists for decades, no defects have been seen. The jury is still out on the cold spot's origin, but this surprising finding will be testable and may lead to new views of the cosmos in its infancy in years to come," said Joanne Baker, associate editor at Science.

"Science is honored to be publishing this important research, and it seems fitting that an international collaboration between Spanish and British scientists be presented the same week that Spain is celebrating the importance of scientific achievement, through the Prince of Asturias Awards," she said.

The research team, led by Marcos Cruz of the Instituto de Fisica de Cantabria, in Santander, Spain, was careful to say that they have not definitively discovered a defect. Rather, they have found evidence in the cosmic microwave background -- the frozen map of the early universe from the time when the first atoms formed and became separate from photons, hundreds of thousands of years after the Big Bang -- that could be explained by the presence of a defect.

Because defects would have formed at extremely high temperatures, at particle energies far in excess of those achievable at laboratory accelerators, their properties would provide physicists with powerful clues as to the fundamental nature of elementary particles and forces.

"It will be very interesting to see whether this tentative observation firms up in coming years. If it does, the implications will be extraordinary. The properties of the defect will provide an absolutely unique window onto the unification of particles and forces," said Neil Turok of the University of Cambridge in Cambridge, United Kingdom, who is a coauthor of the Science study.

Shortly after the Big Bang, the universe began to cool and expand, undergoing a variety of phase transitions -- more exotic versions of the gas-liquid-solid transitions that matter experiences on Earth.

In both the early universe and the average kitchen freezer, when matter changes phase, it does so irregularly. In an ice cube, for example cloudy spots mark defects that formed as the water crystallized.

In the mid-1970's, particle physicists realized that different sorts of defects should also have developed as various particles separated from the infant universe's hot plasma.

One such defect, known as a texture, is "a three-dimensional object like a blob of energy. But within the blob the energy fields making up the texture are twisted up," according to Turok.

Textures and other defects should be detectable as temperature variations in the cosmic microwave background.

"The cosmic microwave background is the most ancient image we have of the universe and therefore it's one of the most valuable tools to understand the universe's origins. If this spot is a texture, it would allow us to discriminate among different theories that have been proposed for how the universe evolved," said Cruz.

When Turok and his colleagues first described cosmic texture and showed how it might be detected, the cosmic microwave background hadn't been mapped accurately enough to detect them. But since 2001, the Microwave Anisotropy Probe, also known as WMAP, has provided a detailed survey of the temperature changes across the cosmic microwave background.

The Science study began with Cruz and his colleagues at the Instituto de Física de Cantabria puzzling over an unusual cold spot in the WMAP data and trying to figure out what could have caused it. When the problem defied all explanations other than a defect, they brought their problem to Turok.

The research team then analyzed WMAP data and determined that the cold spot had the properties that would be expected if it had been caused by a cosmic texture.

"Now, here is an example where this exotic theory trumps more mundane ones," said Baker.

"We're not certain this is a texture by any means. The probability that it's just a random fluctuation is about 1 percent. But what makes this so interesting is that there are a number of follow-up checks which can now be done. So the texture hypothesis is actually very testable," said Turok.

American Association for the Advancement of Science