By reflecting back to the Big Bang, astronomers have a better understanding how the young universe evolved to the one we see today.

Parents prize baby photos, but only one baby photo has won a Nobel Prize. In 2006 George F. Smoot, an astrophysicist at Lawrence Berkeley National Laboratory (Berkeley Lab) in Berkeley, California and the University of California-Berkeley, won the Nobel Prize in Physics for capturing the infant universe on film. The image provided bulletproof evidence of the “Big Bang” theory and explained why the cosmos is lumpy instead of uniform, with matter clumping into stars, galaxies and galaxy clusters.

Smoot, who shared the prize with John C. Mather of the U.S. National Aeronautics and Space Administration’s (NASA) Goddard Space Flight Center, became the 11th Nobel Prize winner associated with Berkeley. “At the time captured in our images, the current observable universe was smaller than the smallest dot on your TV screen, and less time had passed than it takes for light to cross that dot,” Smoot said in a 2006 Berkeley press release.

Smoot’s experiment flew on the Cosmic Background Explorer (COBE), a NASA probe launched in 1989, and involved an instrument called the Microwave Anisotropy Experiment, composed of differential microwave radiometers. The instrument essentially took the universe’s temperature, which hovered slightly above absolute zero—2.72 kelvin, to be more precise. This remnant heat is all that is left of the incredible temperatures generated at the moment of the Big Bang some 14 billion years ago. Moreover, the temperature is uniform across the sky to better than one part in 100,000. Astronomers call this cosmic “afterglow,” the cosmic microwave background (CMB).

The experiment also found that the CMB’s temperature distribution isn’t quite perfect. Regions etched into the cosmic microwave background fluctuate slightly above and below the median temperature of 2.72 kelvin. These hill-and-valley temperature ranges represent a “froth” of overdense (warmer) and underdense (cooler) regions of matter. As Smoot showed, these density fluctuations reveal that during the Big Bang, quantum forces flung particles outward in a not-quite-uniform pattern. These small irregularities provided the seeds for gravity to do its work and draw matter together into the large-scale structures of the universe seen today. After analyzing hundreds of millions of precision measurements from COBE, Smoot and his team produced maps of the entire sky that clearly showed the distribution of “hot” and “cold” spots, produced when the universe was smaller than a proton.

Theorists had been predicting the existence of the cosmic microwave background since the Big Bang theory was first proposed in the 1940s. It was finally detected, accidentally, in 1965. Not until Smoot and his team announced their discovery in 1992, however, could the temperature variations of the CMB be precisely pinned down. Cosmologists hailed the finding as the strongest evidence yet that the Big Bang theory is correct.

“The tiny temperature variations we discovered are the imprints of tiny ripples in the fabric of spacetime put there by the primeval explosion process,” Smoot explained. “Over billions of years, the smaller of these ripples have grown into galaxies, clusters of galaxies and the great voids in space.”

Smoot was one of the first astrophysicists to devise methods for conducting experiments that produce data and information about the early universe. As such, he helped move cosmology from a purely theoretical science into the realm of hard data.

Adding a twist to the CMB story, in 1998 astronomers with the Supernova Cosmology Project (SCP), also led by a physicist at Berkeley, Saul Perlmutter, announced that, contrary to what had been assumed for years, the universe is not decelerating as would be expected if gravity was doing its job of preventing the cosmos from flying apart. Rather, it was accelerating.

Perlmutter, who still heads the SCP, and his colleagues used brightness measurements of dozens of exploding stars (called Type 1a supernovae) to determine their distances. This indicated how rapidly the universe is slowing down. The idea was that in a decelerating universe, observers would see the cosmos expanding at an increasingly slower rate over time. Hence, in a flagging universe, the peak brightness of ever more-distant supernovae would decline predictably with distance, just as the taillights of a receding automobile moving at progressively slower speeds (but never stopping) would fade predictably with increasing distance. Instead they found just the opposite: Although remote supernovae did in fact decline in brightness with distance, the decline was much greater than predicted. The universe wasn’t putting on the brakes—it was flooring it. The only conclusion to be drawn is that we are being carried away from these far flung supernovae (and they from us) at an ever-increasing rate. The team’s findings were soon confirmed by a competing group of astronomers, and both groups earned Science magazine’s “Breakthrough of the Year for 1998.”

Now astronomers are beginning to view the CMB findings in light of an accelerating universe. Measurements of the CMB irregularities indicate that the universe is close to being flat, that is, the universe is not curved, and that it will expand forever at a continually decelerating rate. But the supernovae findings clearly contradict this. Moreover, the total amount of matter (visible and dark), as measured in the CMB results, accounts for only 30 percent of the matter needed to slow and reverse universal expansion. Therefore, in an accelerating universe, some form of additional energy is required to account for the 70 percent deficit. Astronomers refer to this unaccounted-for-energy as “dark energy.” It is one of the biggest challenges in cosmology today.

“People have contemplated the origin and evolution of the universe since before the time of Aristotle,” said Smoot. “Although cosmology has been around since the time of the ancients, historically it has been dominated by theory and speculation. Very recently, the era of speculation has given way to a time of science. The advance of knowledge and of scientific ingenuity means that at long last, we can actually test our theories.”