Advancing Basic Science for Humanity
Chao-Lin Kuo Heads South
(Originally published by Stanford University, April 1, 2009)
To get to the South Pole, first take a commercial flight to Christchurch, New Zealand, then catch a special military flight to McMurdo Station, a large outpost on the Antarctic coast. From there it's a three-hour flight to Amundsen-Scott South Pole Station. The research complex is home to between 50 and more than 200 inhabitants, depending on the season, as well as several scientific projects and one candy-striped pole.
The dry, rarified air of the South Pole is ideal for the instruments he and his collaborators use to collect ancient photons. This light tells the story of the origin of the universe. It is all around, but invisible to the human eye.
"If you had eyes that were sensitive to all photons, you could see stars and galaxies, but you'd also see this background in the microwaves, coming from everywhere, extremely uniform in all directions," Kuo said. This is the Cosmic Microwave Background, or CMB, microwaves emitted just 300,000 years after the Big Bang, more than 13 billion years ago. This background radiation is almost completely uniform, but not quite.
"There are little fluctuations in temperature—in one direction it's 2.7257 kelvin, in another it's 2.72503 kelvin," Kuo said. Scientists call these fluctuations "perturbations," disturbances in an otherwise 2.725 kelvin bath. "Those early perturbations generated all the structures we see today. Without them, there would be no galaxies or planets, basically just hydrogen gas everywhere. It's the seed of everything."
During his years as a graduate student at UC Berkeley, Kuo was part of the team that designed and built the Arcminute Cosmology Bolometer Array Receiver, or ACBAR, a South Pole-based device for mapping the temperature of the CMB with better precision and resolution than ever before. He journeyed to Antarctica to work on ACBAR twice, during the polar summer.
Chao-Lin Kuo in Antartica. (Photo courtesy of Chao-Lin Kuo.)
Over the course of one year at the South Pole, the sun rises and sets only once, separating six months of daylight from six months of darkness. That daylight, the polar summer, corresponds to winter in the northern hemisphere, "so you spend your holidays at the Pole, working," Kuo said.
Residents at Amundsen-Scott have to pass several physical exams that attempt to predict how well they'll endure the harsh and disorienting conditions. The station sits on almost two miles of sheet ice, more than 9000 feet above sea level. On top of that, the atmosphere is thinner at the poles than at the equator, an advantage for astronomical instruments, but a burden on their caretakers.
"In the first 24 hours you feel the lack of oxygen. It's difficult to breathe, difficult to sleep," Kuo said. Then there's the climate—he remembered feeling particularly warm on a day when the mercury read 0 degrees Fahrenheit. "Even tightening a screw becomes very hard when it's so cold," he said.
It's also challenging to get a proper diet. "You used to mix up this yellow powder with water, and fry that for breakfast," Kuo recalled, half-grinning, half-grimacing. "Now there's a greenhouse with fresh fruit and vegetables. There was a huge difference in the food between my first visit and my last visit.
Kuo took a third trip to Antarctica in 2006, as a post-doctoral researcher with the Background Imaging of Cosmic Extragalactic Polarization project, or BICEP. As its name suggests, BICEP measures the polarization of the cosmic microwaves. A polarization map of the sky can be decomposed into two patterns, E-type and B-type polarization. E-type polarization radiates from a central point, while B-type polarization follows a curled pinwheel. These patterns are signatures of the mechanisms that birthed the universe.
So far only E-type polarization, which is due to fluctuations in quantities such as temperature, has been detected. The presence of B-type polarization would be a tell-tale sign of an initial gravitational wave, supporting the widely-held theory that the universe inflated rapidly a tiny fraction of a second after the Big Bang. "It's extremely interesting to ask what exactly happened in the beginning that created the universe with these observed properties," Kuo said. He and his collaborators are analyzing the data collected by ACBAR and BICEP, and designing the next generation of experiments that will search for B-type polarization from the bottom of the world.