posted 03-17-2014 10:04 AM               

First Direct Evidence of Cosmic Inflation

Almost 14 billion years ago, the universe we inhabit burst into existence in an extraordinary event that initiated the Big Bang. In the first fleeting fraction of a second, the universe expanded exponentially, stretching far beyond the view of our best telescopes. All this, of course, was just theory.

Researchers from the BICEP2 collaboration today announced the first direct evidence for this cosmic inflation. Their data also represent the first images of gravitational waves, or ripples in space-time. These waves have been described as the "first tremors of the Big Bang." Finally, the data confirm a deep connection between quantum mechanics and general relativity.

Above: Gravitational waves from inflation generate a faint but distinctive twisting pattern in the polarization of the CMB, known as a "curl" or B-mode pattern. For the density fluctuations that generate most of the polarization of the CMB, this part of the primordial pattern is exactly zero. Shown here is the actual B-mode pattern observed with the BICEP2 telescope, with the line segments showing the polarization from different spots on the sky. The red and blue shading shows the degree of clockwise and anti-clockwise twisting of this B-mode pattern.

"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 Center for Astrophysics), leader of the BICEP2 collaboration.

These groundbreaking 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 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," said co-leader Jamie Bock (Caltech/JPL).

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 (Stanford/SLAC).

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 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."

They were 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-leader Clem Pryke (University of Minnesota).

When asked to comment on the implications of this discovery, Harvard 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."

posted 03-17-2014 10:12 AM               

Frequently Asked Questions

Have you detected B-modes from inflation?

We have detected B-mode polarization at precisely the angular scales where the inflationary signal is expected to peak with very high significance (> 5 sigma). We have extensively studied possible contamination from instrumental effects and feel confident we can limit them to much smaller than the observed signal. Inflationary gravitational waves appear to be by far the most likely explanation for the signal we see.

Couldn't it just be galactic emission or polarized dust?

The data disfavor this. The best current models of polarized galactic emission in our observing region show it to be much fainter than the signal we see. Also, there is little evidence for correlation between our B-mode maps and the predicted pattern from the galaxy. Finally, within our own data, the "color" of the B-modes found by comparing different frequencies is consistent with CMB but disfavors galactic contamination.

Have you detected a gravitational wave?

The frequency of the cosmic gravitational waves is very low, so we are not able to follow the temporal modulation. However, we are indeed directly observing a snapshot of gravitational waves through their imprints on matter and radiation over space. Ordinary density perturbations cannot create the pattern we observe. The presence of a water wave can be detected by feeling its up-and-down motion or by taking a picture of it. We are doing the latter.

posted 03-17-2014 07:31 PM               

Stanford Professor Andrei Linde celebrates physics breakthrough

Assistant Professor Chao-Lin Kuo surprises Professor Andrei Linde with evidence that supports cosmic inflation theory. The discovery, made by Kuo and his colleagues at the BICEP2 experiment, represents the first images of gravitational waves, or ripples in space-time. These waves have been described as the "first tremors of the Big Bang."

As Scientific American notes:

The idea of inflation first came from physicist Alan Guth in 1980. Linde was one of the early theorists who helped refine the theory and has proposed versions of inflation in which our universe is one of many inflationary universes in a vast multiverse.