A DISCOVERY WITH PROFOUND GRAVITY

The 10-meter South Pole Telescope and the BICEP (Background Imaging of Cosmic Extragalactic Polarisation) Telescope are shown against the Milky Way. BICEP2 recently detected gravitational waves in the cosmic microwave background, a discovery that supports the cosmic inflation theory of how the universe began. (Image credit: Keith Vanderlinde, National Science Foundation)

Approximately fourteen billion years ago, our universe burst into existence in an extraordinary event that initiated the Big Bang. In an infinitesimally small fraction of a second, the universe expanded exponentially to a truly gargantuan size, inflating far in excess of the views of our most powerful telescopes. All this, of course, was just a theory.

Astronomers from the Background Imaging of Cosmic Extragalactic Polarisation (BICEP2) radio telescope at the South Pole have announced the first direct evidence for this cosmic inflation. Their data also represent the first images of gravitational waves, or ripples in space-time, a major prediction of Einstein’s 1915 Theory of General Relativity, in effect his theory of gravity. They have been described as the "first tremors of the Big Bang." Finally, the data confirm a deep connection between the (until now) irreconcilable pillars of modern physics: quantum mechanics and general relativity itself.

"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 John Kovac (Harvard-Smithsonian Centre for Astrophysics), leader of the BICEP2 collaboration.

These ground-breaking results came from observations by the BICEP2 telescope of the cosmic microwave background - a faint glow left over from the Big Bang. Tiny fluctuations in this afterglow provide clues to conditions in the early universe. For example, small differences in temperature across the sky show where parts of the universe were denser, eventually condensing into became polarized too.

Wilkinson Microwave Anisotropy Probe all-sky Cosmic Microwave Background Radiation (CMBR) image.

"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," said co-leader Jamie Bock of Caltech and NASA’s Jet Propulsion Laboratory (JPL).

Gravitational waves trigger ripples in space, seen in this illustration.
Image courtesy of NASA

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.

"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," said co-leader Chao-Lin Kuo at Stanford University and the SLAC National Accelerator Laboratory.

The team examined spatial scales on the sky spanning about one to five degrees (two to ten times the width of the full Moon). To do this, they travelled 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 signature of primordial gravitational waves, as seen in the cosmic microwave background in the image, are twisting patterns known as B-mode polarization. Graphic courtesy of the BICEP Project.

They were surprised to detect a B-mode polarization signal considerably stronger than many cosmologists expected. The team analysed 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-leader Clem Pryke of the University of Minnesota.

When asked to comment on the implications of this discovery, Harvard University theorist Avi Loeb said, "This work offers new insights into some of our most basic questions: Why do we exist? How did the universe begin? These results are not only a smoking gun for inflation, they also tell us when inflation took place and how powerful the process was."

Technical details and journal papers can be found on the BICEP2 release website:

http://bicepkeck.org

Original source: Harvard-Smithsonian Centre for Astrophysics

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