Detecting Ripples from the Birth of our Universe

Detecting Ripples from the Birth of our Universe

By Claudia Geib, Journalism & Environmental Science, 2015

It’s not often that physicists make headlines. Thursday, March 27 was the exception. At a seemingly out-of-the-blue press conference at the Harvard-Smithsonian Center for Astrophysics, researchers from the Background Imaging of Cosmic Extragalactic Polarization (BICEP) experiment set the media abuzz with the announcement that they had recorded an “echo” of our primordial universe: evidence that, in the nanoseconds after the Big Bang, the young universe underwent a period of exponential expansion called inflation.

Despite headlines that might suggest otherwise, the concept of inflation is not new to the astrophysical community; Alan Guth and Andrei Linde of MIT developed the theory of inflation in the 1980s. Inflation describes the period of growth beginning some 10^-36 seconds after the Big Bang, during which the universe went from a quantum-sized, white-hot, infinitely dense point to a region the size of a melon. That melon-sized universe has been expanding ever since. Yet while the continued growth of the universe has been supported by conclusive evidence, inflation has never had anything but theoretical physics to back it up.

That’s where BICEP stepped in. The BICEP team set about hunting for the evidence of the gravitational waves that inflation left behind. The enormous gravity produced by such an exponential growth, the researchers reasoned, must have left an imprint on the universe it created — specifically, an imprint on the cosmic microwave background, or CMB, the omnipresent haze of light that permeates the universe in the aftermath of the Big Bang. The BICEP researchers hypothesized that the photons in the CMB would be bent by the gravitational waves produced by inflation, causing a twist or swirl to be observed in the polarization of these photons. This pattern is called B-mode polarization.

The hunt for these whorls of light led the BICEP team to the dark and cold of the South Pole, a place forbidding for humans but ideal for examination of our universe. With an average temperature of about -72 degrees Farenheit (-58 Celcius), Antarctica’s super-dry air ensures that valuable incoming microwaves are not absorbed by atmospheric water vapor. “The South Pole is the closest you can get to space and still be on the ground,” said John Kovac, an astronomer from the Harvard-Smithsonian Center for Astrophysics and leader of the BICEP collaboration.

It was in this bleak environment that the BICEP team spotted the first conclusive signs of inflation. Using highly-sensitive, small-aperture refractor telescopes, the researchers produced images such as the one shown above, in which the black lines represent polarization of light from the CMB. After three years of research, two different BICEP telescopes, and many months of analysis — kept carefully under wraps by the team — these results were announced simultaneously in a briefing at the Center for Astrophysics and a set of papers submitted to The Astrophysical Journal. The secrecy of the research, nearly unheard of in the “gossipy” world of physics, made the reaction to the news even more enthusiastic. (Click here to see Andrei Linde’s emotional reaction to hearing that his 30-year-old theory had finally been lent credence.)

The findings of the experiment have already been hailed as one of the most significant recent discoveries about the birth of our universe. They rule out a number of other plausible inflationary models and support the concept of a grand unified energy scale during inflation — the idea that the electromagnetic, strong and weak forces in the universe might have been combined into one single force at the time. The discovery has also inspired a swarm of speculation about new particles, black holes, dark matter and multiverses.

Yet BICEP researchers and much of the scientific community have been much more cautious about the discovery’s significance. Five cooperating telescopes dubbed the Keck Array have replaced BICEP2, the most recent project telescope, and BICEP3 will deploy to the South Pole later this year to continue gathering data. Meanwhile, competing experiments are attempting to duplicate the results of BICEP from land, space and sea, seeking to corroborate — or discredit — these extraordinary findings.