Astronomers announced today the first direct evidence of cosmic inflation – a theory that the Universe we inhabit burst into existence almost 14 billion years ago in an extraordinary event that initiated the Big Bang. In the first fleeting fraction of a second, the Universe expanded exponentially – by 100 trillion trillion times – stretching far beyond the view of our best telescopes.
Researchers from the BICEP2 collaboration reported that 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.
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 polarisation. On Earth, sunlight is scattered by the atmosphere and becomes polarised, which is why polarised sunglasses help reduce glare. In space, the cosmic microwave background was scattered by atoms and electrons and became polarised too.
“Our team hunted for a special type of polarisation called ‘B-modes’, which represents a twisting or ‘curl’ pattern in the polarised orientations of the ancient light,” said Jamie Bock (Caltech/JPL), co-leader of the BICEP2 collaboration.
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 polarisations.
“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 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 John Kovac (Harvard-Smithsonian Center for Astrophysics), leader of the BICEP2 collaboration. “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 polarisation 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.
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.”