Physicists Debate Claims of Evidence for Cosmic Inflation
This artist's conception depicts the creation of gravitational waves from two orbiting black holes as ripples in space-time. In March, astronomers announced the detection of primordial gravitational waves and said it supported the view that the universe began with a burst of inflation. Now some critics say the detection may actually be nothing more than the signature of dust in the Milky Way.NASA
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NEW YORK — The physics world was agog in March over the announcement that astronomers had possibly found ripples in space-time from the earliest moments of the universe. But some scientists now question whether the findings may be nothing more than galactic dust.
If the finding of these ripples, or primordial gravitational waves, is confirmed, it would represent the best evidence yet for inflation, the idea that the universe underwent an explosive burst in size in the earliest fractions of a second after the Big Bang. If the findings are discounted, inflation could still be correct, but scientists must provide other evidence.
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One of the panelists, cosmologist Alan Guth of MIT, developed the hypothesis of inflation in 1980 to explain the large-scale structure of the universe. The Big Bang left behind remnant heat, known as the cosmic microwave background, or CMB. Although the CMB contains tiny temperature variations, it's still remarkably uniform, which might be expected if the universe expanded from a very small region.
If inflation occurred, scientists suspect it might have left an imprint on the CMB, produced by gravitational waves, which would appear as a swirly pattern in the CMB. Harvard astronomer John Kovac and his colleagues claimed to have detected this pattern in March using the BICEP2 instrument at the South Pole.
Since then, the results have come under fire from scientists who question whether the team had ruled out other possible sources that would produce the same swirly signature, such as dust in the Milky Way. Princeton cosmologist Paul Steinhardt, who supports an alternative model of the universe that suggests the existence of higher dimensions, said Kovac and his colleagues were too confident in their initial claims.
During the panel discussion, Kovac admitted some uncertainty but defended the findings. His team has further analyzed their data and feels "very confident" the results were not spurious, he said.
Other groups are also looking for these ripples from the Big Bang. The European Space Agency's Planck satellite is expected to release its own data soon, and should offer strong evidence one way or the other.