21 May 2007

'Axis of evil' a cause for cosmic concern

  • 13 April 2007
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  • Zeeya Merali
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Some believe it is just a figment of overactive imaginations. But evidence is growing that the so-called "axis of evil" - a pattern apparently imprinted on the radiation left behind by the big bang - may be real, posing a threat to standard cosmology.

According to the standard model, the universe is isotropic, or much the same everywhere. However, in 2005, Kate Land and Jo�o Magueijo of Imperial College London noticed a curious pattern in the map of the cosmic microwave background (CMB) created by NASA's WMAP satellite. It seemed to show that some hot and cold spots in the CMB are not distributed randomly, as expected, but are aligned along what Magueijo dubbed the axis of evil.

Some astronomers have suggested straightforward explanations for the axis, such as problems with WMAP's instruments or distortions caused by a nearby supercluster (New Scientist, 22 October 2005, p 19).

Others doubt the pattern's very existence. "There's still a fair bit of controversy about whether there's even something there that needs to be explained," says WMAP scientist Gary Hinshaw of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

Now, two independent studies seem to confirm that it does exist. Damien Hutsem�kers of the University of Li�ge in Belgium analysed the polarisation of light from 355 quasars and found that as the quasars get near the axis, the polarisation becomes more ordered than expected. Taken together, the polarisation angles from the quasars seem to corkscrew around the axis.

"This is really promising," says Hinshaw. "Cosmologists should sit up and take notice."

Cosmologist Carlo Contaldi of Imperial College London is intrigued, but thinks more quasars should be analysed before drawing conclusions. "There is a danger that once people know about the axis of evil, they start seeing evil in all sorts of sets of data," he says.

The quasar finding has support from another study, however. Michael Longo of the University of Michigan in Ann Arbor analysed 1660 spiral galaxies from the Sloan Digital Sky Survey and found that the axes of rotation of most galaxies appear to line up with the axis of evil (www.arxiv.org/astro-ph/0703325). According to Longo, the probability of this happening by chance is less than 0.4 per cent. "This suggests the axis is real, and not simply an error in the WMAP data," he says.

Land, now at the University of Oxford, thinks Longo must rule out other reasons for why the spirals are aligned the way they are. For instance, neighbouring galaxies could have formed from the same rotating dust cloud, giving them similar orientations, she says. "But if he is correct, then this is really exciting, not only as independent confirmation of the axis, but because it'll help us understand what may have created it," she says.

One way to create the axis was presented by Contaldi at a conference on outstanding questions in cosmology at Imperial College last month. The universe is thought to be isotropic because the early universe went through a period of exponential expansion known as inflation, smoothing out any unevenness. Contaldi and his colleagues Emir G�mr�k��oğlu and Marco Peloso at the University of Minnesota, in Minneapolis, modified inflation to allow the universe to expand more in one direction. "Provided inflation stops at a relatively early point, this would leave traces of the early [unevenness] in the form of the axis of evil," he says.

A map of the cosmic microwave background seems to show that hot and cold spots are not distributed randomly

Longo favours a more radical theory proposed by Paolo Cea of the University of Bari, in Italy, and Leonardo Campanelli of the University of Ferrara, Italy, which suggests that magnetic fields stretched across the universe could be responsible (New Scientist, 2 September 2006, p 28). "A magnetic field would naturally orient the spiral galaxies," says Longo.

Regardless of the reasons, one thing is clear: the axis of evil won't be written off any time soon. "Interest keeps growing as people find more weirdly connected observations that can't all be put down to coincidence," says Land. "And hey, everybody loves a conspiracy."

From issue 2599 of New Scientist magazine, 13 April 2007, page 10
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