Mather, Smoot Share 2006 Nobel Prize in Physics

Researchers honored for their work on advancing scientific understanding of the cosmic background radiation.

John C. Mather George Smoot

APS fellow John C. Mather (NASA Goddard Space Flight Center) shared the 2006 Nobel Prize in physics with George Smoot (Lawrence Berkeley National Laboratory) for “their discovery of the blackbody form and anisotropy of the cosmic microwave background radiation.” Mather and Smoot will split a 10M Swedish Kroner (~$1.4M) prize.

The Nobel Prize Committee cited the physicists for their work on the Cosmic Background Explorer (COBE) project. This orbiting spacecraft was the first to detect faint temperature variations in the cosmic microwave background (CMB) radiation–the faint microwave signals from space that are remnants of the Big Bang. The CMB was first observed experimentally in the 1960s by Arno Penzias and Robert Wilson at Bell Labs, for which they later received the Nobel Prize.

Prior to the COBE map of the universe, it was unclear why the universe contained stars and galaxies rather than an evenly distributed dust cloud. Theorists had predicted that a sensitive measurement of microwaves from the sky would reveal minute temperature fluctuations, which represent variations in the density of matter in the early universe. It was proposed that denser portions served as seeds for galaxies that formed later.

COBE was the first experiment sensitive enough to confirm the predicted temperature variations encoded in the map of the microwave background. COBE found variations at the level of parts per hundred thousand against an overall average temperature of 2.7 K. COBE was also the first to provide a very precise average temperature of the universe: 2.726 K.

Credit: COBE/DMR Science Team. Different contributions to the Cosmic Microwave Background Radiation based on two years of COBE Observation

It was not an easy experiment to perform. The faint variations in the CMB temperature had to be measured against a foreground cloud of microwave radiation coming from our solar system, our galaxy and other celestial objects. Furthermore, the motion of Earth around the sun, the sun around the Milky Way, and the Milky Way within our local cluster of galaxies also had to be taken into account.

Mather and Smoot, together with other members of the COBE project collaboration, first announced the discovery. The 1992 APS April meeting in Washington, DC. (See the 1992 press release announcing the COBE mapping breakthrough at www.aip.org/pnu/1992/split/pnu077-1.htm)

APS Executive Officer Judy Franz was at the APS meeting fourteen years ago.“I remember attending the COBE talk in ‘92,” says Franz. “We all knew it was exciting at the time. In recent years, people tended to ask not whether it was worthy of a Nobel Prize, but when the Nobel Committee would get around to presenting them with the award. I'm glad they finally ended the suspense.”

“The COBE project was a very difficult and speculative experiment,” APS President John Hopfield added upon learning of the prize. “It was extraordinary to carry out the measurement so well. Mather and Smoot are richly deserving of the Nobel Prize. In these political times I add my fervent hope that our level of investment in US physical science research and education once again becomes adequate, and that American science may still be strong enough to receive such awards twenty years hence.”

Since then, other CMB detectors–notably Boomerang and DASI–added more and more detail to the microwave background. The most recent and best microwave measurements have been presented by the WMAP detector, which supplies the best values for important cosmological parameters. These include the age of the universe, the overall curvature of spacetime, and the time when the first atoms formed, as well as the first star.