March 17, 2014 | 6
Few people were as thrilled with the big physics news today as physicist Andrei Linde. One of the main authors of inflation theory—the idea that the universe expanded incredibly rapidly just after it was born in the big bang—Linde has reason to be excited. Physicists announced this morning that they have discovered imprints of gravitational waves in the cosmic microwave background light pervading the sky—a finding that many are calling “direct evidence” of inflation theory.
Chao-Lin Kuo, an assistant professor of physics at Stanford University and a co-leader of the Background Imaging of Cosmic Extragalactic Polarization 2 (BICEP2) team behind the finding, knocked on Linde’s door to deliver the news personally. Kuo tells an accompanying cameraperson, “He has no idea that I’m coming.”
Linde and his wife Renata Kallosh, both professors of physics at Stanford, look flummoxed when they answer the door. “I have a surprise for you,” Kuo says. “It’s 5 sigma, at .2.” Linde and Kallosh are taken aback; she comes forward to hug Kuo as Linde says, “What?” The ensuing reactions of both as they process the news are completely endearing—all the more so because Kuo’s arcane pronouncement could elicit such joy only from the few people in the world who would immediately know what he meant.
“5 sigma” refers to the statistical significance of BICEP2’s discovery. Kuo was telling Linde and Kallosh that his experiment had seen a very strong signal. “Sigma” denotes standard deviations, and a discovery with a statistical significance of 5 sigma has only about a one-in-3.5-million chance of being a fluke.
The second part of Kuo’s message, “.2,” refers to the value BICEP2 had measured for a parameter called r, which indicates the ratio of the fluctuations in the CMB caused by gravitational waves to the fluctuations caused by perturbations in the density of matter. Previous experiments such as the European Planck satellite had suggested r might have a value of less than 0.11, so the measurement of 0.20 is noteworthy.
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.
The findings announced today validate many of Linde’s ideas and make a pretty solid case for inflation being the true history of our universe. As Linde says, “Let’s just hope that it is not a trick.”