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Crystallizing the Early Cosmos
25 October 2007 (All day)
A new analysis of the afterglow of the big bang supports a novel theory of how the universe took shape, theoretical physicists say. The existence of a curious cold spot in the sky suggests that the cosmos quickly sported flaws that resulted in the formation of the first stars and galaxies.
Studies of the big bang afterglow, also known as the cosmic microwave background (CMB), have already revealed plenty about how the universe came to be. The continuing expansion of the universe has stretched the light blasting out of the big bang into microwaves and cooled it to just 2.7° above absolute zero. In 2003, researchers working with NASA's orbiting Wilkinson Microwave Anisotropy Probe (WMAP) mapped fluctuations in the temperature of the CMB, which varies by only a few parts in 100,000 across the sky. Comparing the data with theoretical models confirmed that the universe sprang into existence precisely 13.7 billion years ago (ScienceNOW, 11 February 2003). The variations in the CMB's temperature also trace out slight fluctuations in the density of the nascent universe, which eventually seeded the galaxies.
The WMAP data generally support theorists' understanding of the origins of the universe, but they also show some quirks that could point to new and more exotic physics. For example, researchers have known that the CMB sports a large cold spot. Now a team says the cold spot is too large to be explained by standard models and is evidence that, like a giant patchwork quilt, the universe might have something like texture. "This is surprising," says physicist and lead author Marcos Cruz of the Instituto de Física de Cantabria in Spain.
The cold spot may be evidence that the early universe underwent a change somewhat akin to the formation of ice from water, Cruz's team argues online today in Science. Ice contains structural defects wherever water molecules do not align perfectly within the crystal. When the four forces--gravity, electromagnetism, the weak nuclear force, and the strong nuclear force--split off from an ur-force not long after the big bang, the universe might have been threaded with defects that gave it a texture. And the CMB may reflect that texture with its temperature variations, including the cold spot, the researchers argue.
Here's how it might have happened: The separation of the forces involves a process called symmetry breaking, which is a bit like arbitrarily choosing a direction on a compass to call north. If different directions are chosen in different regions of space, then defects would arise between them. Containing energy, these defects would then exert a gravitational pull that would mottle the CMB and accumulate matter that would eventually become stars and galaxies. A statistical analysis of the CMB shows that the cold spot is consistent with this scenario, the researchers say.
Others are skeptical. "Further tests and stronger evidence are needed," says physicist Robert Caldwell of Dartmouth College. He agrees that if confirmed, the conclusions would give detailed clues to how nature's forces separated after the big bang. Still, he says, they're not entirely compatible with other observations. There's also a chance, the authors concede, that the cold spot might be just a fluke--"an unusually large and rare fluctuation in the density of matter in that region of the sky."