17 March 2014

First direct evidence supporting cosmic inflation

by Will Parker

Scientists announced today that they have successfully measured a B-mode polarization signal in the Universe's cosmic microwave background (CMB). The signal, detected using a telescope at the South Pole, represents an important confirmation of the theory of cosmic inflation and provides insights into how the Universe may have behaved in the first fractions of a second of its existence.

B-mode describes a specific type of CMB polarization that's associated with gravitational waves. The Background Imaging of Cosmic Extragalactic Polarization (BICEP2) research team said their findings also provided the first images of these gravitational waves. These waves have been described as the "first tremors of the Big Bang" and confirm a deep connection between quantum mechanics and general relativity.

"Detecting this signal is one of the most important goals in cosmology today. A lot of work by a lot of people has led up to this point," said Harvard's John Kovac, a member of the BICEP2 collaboration.

The groundbreaking findings came from observations by the BICEP2 telescope of tiny fluctuations in the CMB. Small differences in temperature across the sky show where parts of the Universe were denser, eventually condensing into galaxies and galactic clusters.

Since the cosmic microwave background is a form of light, it exhibits all the properties of light, including polarization. On Earth, sunlight is scattered by the atmosphere and becomes polarized, which is why polarized sunglasses help reduce glare. In space, the cosmic microwave background was scattered by atoms and electrons and became polarized too.

"Our team hunted for a special type of polarization called 'B-modes,' which represents a twisting or 'curl' pattern in the polarized orientations of the ancient light," explained BICEP2 co-researcher Jamie Bock, from Caltech.

"Gravitational waves squeeze space as they travel, and this squeezing produces a distinct pattern in the cosmic microwave background. Gravitational waves have a 'handedness,' much like light waves, and can have left- and right-handed polarizations," added co-researcher Chao-Lin Kuo, from Stanford. "The swirly B-mode pattern is a unique signature of gravitational waves because of their handedness. This is the first direct image of gravitational waves across the primordial sky."

The team examined spatial scales on the sky spanning about one to five degrees. To do this, they traveled to the South Pole to take advantage of its cold, dry, stable air. "The South Pole is the closest you can get to space and still be on the ground," said Kovac. "It's one of the driest and clearest locations on Earth, perfect for observing the faint microwaves from the Big Bang."

The team was surprised to detect a B-mode polarization signal considerably stronger than many cosmologists expected. The team analyzed their data for more than three years in an effort to rule out any errors. They also considered whether dust in our galaxy could produce the observed pattern, but the data suggest this is highly unlikely. "This has been like looking for a needle in a haystack, but instead we found a crowbar," said co-researcher Clem Pryke, from the University of Minnesota.

The results, he adds; "are not only a smoking gun for inflation, they also tell us when inflation took place and how powerful the process was." It's also possible that the gravity waves detected in the CMB may be the direct result of quantum gravity. And although there may be other sources of primordial gravitational waves, this signal could help scientists put real boundaries on theories of quantum gravity.

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Source: Harvard-Smithsonian Center for Astrophysics