Reflecting on BICEP2
On Monday, March 17, 2014, collaborators working with the BICEP2 telescope at the South Pole presented the world with its first direct evidence of primordial gravitational waves and thus of cosmic inflation. Caltech professor of physics Jamie Bock, co–principal investigator for BICEP2 and the chief architect of the telescope's detectors, described the finding as "mind-boggling."
Cosmologists were thrilled by the news that BICEP2 had observed B-mode polarization in the cosmic microwave background at a level twice the intensity they had expected. This faint swirling polarization is thought to be a relic of the rapid inflation of the universe, faster than the speed of light, that took place in the first "trillionth of a trillionth of a trillionth of a second after the Big Bang," according to Caltech senior research associate Sean Carroll, who along with John Preskill, the Richard P. Feynman Professor of Theoretical Physics at Caltech, has been blogging about both the specifics of the BICEP2 finding and its implications.
A massively energetic event like inflation would have produced gravitational waves, ripples in the fabric of spacetime predicted by Einstein's general theory of relativity but never directly detected. As they traveled through the early universe, these gravitational waves should have left their signature on the cosmic microwave background, which is the oldest visible radiation in our universe, dating to 300,000 years after the Big Bang.
This prediction about the behavior of primordial gravitational waves and its polarizing effect on the cosmic microwave background was made in the late 1990s by, among others, Marc Kamionkowski, a professor of theoretical astrophysics at Caltech from 1999 to 2011 who is now at Johns Hopkins University. Kamionkowski describes the BICEP2 finding as "not just a home run," but "a grand slam," while Max Tegmark, a cosmologist at MIT says, "If this stays true, it will go down as one of the greatest discoveries in the history of science."
But it wasn't just cosmologists who took notice. In the days since the announcement, headlines around the world have announced the cosmological finding from BICEP2, and journalists from The New York Times to Al Jazeera have proclaimed this a "landmark in science" and an "epic discovery."
The BICEP experiments that have caught the world's attention began at Caltech in 2001 with discussions between Bock, then a research associate at JPL, and Brian Keating, a postdoctoral scholar at Caltech, about how to design a telescope that could observe the cosmic microwave background across a relatively large area of the sky. When Bock and Keating brought the idea to the late Andrew Lange, then Marvin L. Goldberger Professor of Physics at Caltech, Lange declared it a wild goose chase . . . and then happily plunged in.
As the BICEP project developed, Lange and Bock brought talented graduate students and postdoctoral scholars to join the BICEP team at Caltech and JPL. Former Caltech graduate student Randol Aikin (PhD '13), a BICEP2 collaborator now on staff at MIT's Lincoln Laboratory, says, "In addition to being superb scientists, Andrew and Jamie had an extraordinary capacity to empower students and give them room to take ownership of their work."
Among the postdoctoral scholars nurtured at Caltech are John Kovac, now a professor at the Harvard-Smithsonian Center for Astrophysics, who was the first Kilroy Fellow in Astrophysics at Caltech, and Chao-Lin Kuo, now a professor at Stanford University and an associate at the SLAC National Accelerator Laboratory; both are principal investigators on the BICEP2 project along with Bock and Clem Pryke of the University of Minnesota. (The project has a co-PI structure. At each stage of the BICEP experiments, one PI takes the lead. Lange was the leader for BICEP1; Kovac is the leader for BICEP2, and Kuo is the leader for BICEP3, already in progress.)
By the standards of other major experiments in physics, such as the Planck space telescope or the Large Hadron Collider, the BICEP2 team is quite small; there are just 47 coauthors on the paper that has disseminated the experiment's results, and only around 20 team members working closely on the core analysis. The BICEP2 team credits its success to the team members' focus, dedication, and close collaboration, and, says Keating, to the skill and determination of Bock, "one of the hardest working scientists I've ever met." Adds Hien Nguyen, a BICEP2 collaborator from JPL, says, "It's always a pleasure to sit back and see Jamie in action. There are a lot of details in the telescope that never would have been there if Jamie didn't pay attention at the beginning. He actually foresaw the intricacy of the experiment way ahead of time."
A strong public/private partnership has sustained this project throughout its 12-year history. The BICEP2 finding was made possible through grants from the National Science Foundation and the gifts of generous donors, including the W. M. Keck Foundation and the Gordon and Betty Moore Foundation. The Moore Foundation, along with Caltech and JPL internal funds provided the support to invent the unique detectors that were essential to achieving these results. A grant from the Keck Foundation funded the building of the Keck Array telescopes that have helped to provide preliminary confirmation of the BICEP2 results. The John M. Robinson estate granted additional funding to BICEP2 at a critical time, while the Jim and Nellie Kilroy Foundation provided resources to support members of the team at Caltech.
At a celebration for the Caltech/JPL BICEP2 team, Cyndi Atherton, previously of the Moore Foundation, said, "When I first took over supervision of the foundation's grant to Caltech for the BICEP2 project, my colleagues told me, 'We don't quite know what they're going to do, but there's this group of really smart people at Caltech and JPL. We're going to give them money and we're going to let them work.' I think you have made Gordon and Betty Moore and the Keck family proud to be associated with this project. I know my colleagues and I are walking taller this week, saying 'This is what science does for us.'"
Written by Allison Benter