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18 March 2014
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. Cardiff physicists are part of an international team that have turned this scientific theory into scientific fact.
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.
"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.
Professor Peter Ade of Cardiff University's School of Physics and Astronomy said "Having worked on many ground breaking CMB experiments for the last 30 years it is pleasing to finally confirm the inflationary hypothesis with this detection of B-modes." Dr Rashmi Sudiwala, a senior member of the Cardiff team, contributed to the experiment build and deployment in Antarctica, whilst Dr Carole Tucker contributed to the development an provision of key optical components.
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 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 have a "handedness," much like light waves, and can have left- and right-handed polarizations. It was predicted in the 1970s, by Cardiff University's Leonid Grishchuk, that this squeezing would produce a distinct pattern in the cosmic microwave background.
"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).
Professor Bangalore Sathyaprakash, a theoretical physicist at Cardiff University, commented that "This result is key to answering some of the biggest questions in cosmology. It provides insights into processes that took place in the early Universe, and just how violent the birth of the Universe was. It's wonderful to see the realisation of the prediction that our esteemed colleague Leonid Grishchuk made back in 1975."
"The next step in the story is to confirm this discovery with the Planck Satellite. The full analysis of the Planck data is currently ongoing, and we hope will be ready for release later this year", concluded Professor Ade.
More information is available on the Harvard CfA website: http://www.cfa.harvard.edu/news/2014-05
BICEP2 is the second stage of a coordinated program, the BICEP and Keck Array experiments, which has a co-PI structure. The four PIs are John Kovac (Harvard), Clem Pryke (UMN), Jamie Bock (Caltech/JPL), and Chao-Lin Kuo (Stanford/SLAC). All have worked together on the present result, along with talented teams of students and scientists. Other major collaborating institutions for BICEP2 include the University of California at San Diego, the University of British Columbia, the National Institute of Standards and Technology, the University of Toronto, Cardiff University, and Commissariat à l’Energie Atomique.
BICEP2 is funded by the National Science Foundation (NSF). NSF also runs the South Pole Station where BICEP2 and the other telescopes used in this work are located. The Keck Foundation also contributed major funding for the construction of the team’s telescopes. NASA, JPL, and the Moore Foundation generously supported the development of the ultra-sensitive detector arrays that made these measurements possible.
The search for direct detection of gravitational waves is ongoing, and is expected to be made in the next few years by the LIGO-Virgo laser interferometric detectors, of which Cardiff is a key member. LIGO and Virgo target gravitational waves from astrophysical systems such as colliding neutron stars and black holes. They are not likely to detect primordial gravitational waves reported here, except if the amplitude of the primordial waves fall off as a function of frequency more slowly than what theorists currently believe.
Technical details and journal papers can be found on the BICEP2 release website:
Professor Peter Ade
School of Physics and Astronomy Cardiff University
Tel: +44 (0)2920 874643
Dr Rashmi Sudiwala
Tel: +44 (0)2920 875469
Dr Carole Tucker
Tel: +44 (0)2920 874144
Prof Bangalore Sathyaprakash
Tel: +44 (0)2920 876962
Dr Chris North
Tel: +44 (0)2920 870537
Dr Enzo Pascale
Tel: +44 (0) 2920 870531
Emma DarlingPublic RelationsCommunications and International Relations Division Cardiff UniversityT: 029 2087 4499E: DarlingEL@cardiff.ac.uk
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