The apparent detection of primordial gravitational waves from the big bang 14 billion years ago sent ripples of cautious excitement through Perimeter Institute today.
Perimeter researchers gathered to watch a webcast press conference from the Harvard-Smithsonian Center for Astrophysics, at which it was revealed that a sophisticated telescope at the South Pole had captured a signature of the universe expanding with unbelievable acceleration when it was a tiny fraction of a second old.
Perimeter Director Neil Turok, a cosmologist whose work centres on our understanding of the early universe, said, “If confirmed — and it is a big if — then this result is spectacular and will have opened an entirely new window on the big bang.” He noted that, if it is confirmed, it would refute a model of the early universe he proposed with Princeton’s Paul Steinhardt.
“It would conclusively refute the ekpyrotic and cyclic models we proposed a decade ago. However, more recent bouncing universe models based on the Higgs field might still be viable.”
Other Perimeter researchers responded with varying degrees of caution and optimism. “If this is confirmed, it is really amazing,” said Perimeter Faculty member Kendrick Smith, who explained the newly released data to a lecture hall packed with researchers and students. “If it’s true, it’s the most exciting result in cosmology in the past 30 years.”
Smith, an observational cosmologist, has developed key numerical methods for analyzing astrophysical data. He is a member of the Planck satellite collaboration, which is expected to release its own findings on the early universe later this year.
Today’s result was obtained by a multi-institution collaboration of researchers at an Antarctic telescope called BICEP2 (Background Imaging of Cosmic Extragalactic Polarization), which scanned a relatively uncluttered patch of sky for remnant energy from the big bang at microwave frequencies.
Whereas the cosmic microwave background (CMB) has previously revealed a snapshot of the earliest known light, which emerged when the universe was about 300,000 years old, gravitational waves provide unprecedented insight into the much earlier universe.
Detecting gravitational waves represents the final frontier in testing Einstein’s theory of general relativity. Analogous to how a seismic wave from an earthquake propagates through the earth’s crust, causing land to buckle and contort in its wake, a gravitational wave is an oscillation in the gravitational field, propagating through empty space at the speed of light, expanding and compressing spacetime. Just as the earthquake leaves a pattern of toppled trees and shifted rocks behind it on the face of the earth, a gravitational wave would subtly distort everything it passed through.
The waves BICEP2 claims to have detected are primordial gravitational waves, thought to have originated from events in the infant universe, well before light broke free and created something we could later see. Many physicists are greeting the current work as the first direct evidence for the theory of cosmic inflation, which posits that the universe underwent a period of hyper-rapid expansion in its first trillionth of a trillionth of a trillionth of a second.
It was by examining patterns in the cosmic microwave background that the team found the signature of gravitational waves – areas where space had been squeezed and expanded in just the way that the theory of cosmic inflation would predict. The results from the BICEP2 team seem to show, with a higher-than-expected degree of accuracy, the presence of so-called B-mode polarization created by gravitational waves.
“The experiment is a real hardware tour-de-force,” said Smith. “It’s amazing to see such a tiny signal teased out of these incredibly sensitive experiments.”
Will Kinney, a University of Buffalo faculty member visiting Perimeter to deliver a talk about early-universe inflation, said the “blockbuster” result has “changed everything,” requiring him to scrap his planned talk and write a new one from scratch.
“Isn’t it wonderful how science works like that?” he said. “If these data are correct and corroborated by other experiments, it will open a whole new window to the early universe.”
Turok, however, sounded a note of caution. “As far as inflation goes, there is a real tension, which the BICEP2 authors admit, between the BICEP2 result and the previous WMAP and Planck results. If all these experiments are correct, then inflationary models would be in trouble because fitting all the data requires tweaking inflationary models in very artificial ways: such models would be contrived and unconvincing.” He went on to say that this conclusion is the opposite of that reached by the BICEP2 authors.
These surprising results could be the result of some unaccounted-for variable or error, but Perimeter Faculty member Latham Boyle is optimistic the results may well prove accurate.
“From the outside, it does look as if they’ve detected primordial gravitational waves, and that is just staggering,” Boyle said. “I don’t recall being this floored by another experiment in my career.”
For Perimeter Emmy Noether Fellow Claudia de Rham, the experimental result is exciting not only for the answers it seems to provide, but for the new questions it poses.
“Each time you discover something, you realize there is so much more to do,” she said. “If this is confirmed, there will be a lot more work to be done, and I’m looking forward to seeing what’s next.”
For Smith, whose research with the WMAP team mapping the cosmic microwave background was awarded the prestigious 2012 Gruber Prize, the newly released work on gravitational waves promises exciting times ahead for cosmology.
“If this result is correct, it’s a true historic event,” he said. “It’s a very exciting time to be a practicing scientist when results like this come out.”
Turok ended on a measured note. “As Carl Sagan said, ‘extraordinary claims require extraordinary evidence.’ I am not sure BICEP2 has provided that yet.”