Mather, Smoot share 2006 Nobel Prize in physics

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.”

John C. Mather George Smoot

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 1978 Nobel Prize in Physics.

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 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 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.

Emitted radiation by the early universe is distributed between the various wavelengths of the electromagnetic spectrum, the shape of  which depends entirely on temperature. So if scientists know the  temperature of a given thing–in this case, the entire universe–they can precisely predict what the resulting spectrum should look like. NASA launched COBE on November 18, 1989, and got the first results after a mere nine minutes of observations. The accumulated data points formed a perfect spectrum. It was such a perfect match with theory that, when the resulting curve was first shown at the 1990 American Astronomical Society meeting, there were audible gasps in the assembled scientists, followed by a standing ovation. From this, the team was able to measure the minute temperature  fluctuations in the CMB, and therefore where matter in the universe began to aggregate.

Mather and Smoot, together with other members of the COBE project collaboration, first announced their results in 1992. 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.”