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Cosmologist George Smoot contributed to our understanding of the Universe on the largest scales and at the earliest observable times by measuring temperature variations in the cosmic microwave background. His key experiment in 1992 reported detecting these ‘ripples’ in the microwave sky. Smoot’s discovery, for which he won a share of the Nobel Prize in Physics in 2006, revealed the long-anticipated traces of the formation of structures including stars and galaxies (G. F. Smoot et al. Astrophys. J. 396, L1–L5; 1992). This work led to many similar experiments, which used ever-more-precise measurements to cement our modern description of the Universe. Smoot has died aged 80.
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The cosmic microwave background is the radiation from the Big Bang, which marked the beginning of the Universe 13.8 billion years ago. Smoot led the design of the detector that flew on NASA’s Cosmic Background Explorer (COBE) satellite. The data it collected gave a snapshot of variations in the density of matter in the hot, young Universe only about 400,000 years after the Big Bang. The amplitude of these variations aligned closely with predictions assuming that today’s galactic structures were formed under the gravitational influence of dark matter, rather than plasma, from that early time.
Smoot was born in Yukon, Florida, the son of a hydrologist and a science teacher. In 1966, he earned degrees in physics and mathematics at the Massachusetts Institute of Technology (MIT) in Cambridge. He remained at MIT for his PhD in experimental particle physics, before joining the research group of Nobel laureate Luis Alvarez at the University of California, Berkeley, and the Lawrence Berkeley National Laboratory, where he built his research career.
Smoot was using a high-altitude weather balloon to study cosmic rays, until it crashed into the ocean. His team then explored new research directions, in particular Big Bang cosmology. In the early 1970s, prompted by a theoretical paper from one of us (J. Silk Nature 215, 1155–1156; 1967), he began to study the relic microwave radiation. “My physics colleagues dismissed this work as speculation,” he wrote in his Nobel lecture. “It seemed to me a field ripe for observations that would be important no matter how they came out.” Early results using differential microwave radiometers (DMRs) on U-2 spy planes made it possible to measure how the motion of the Solar System makes one side of the sky seem hotter than the other.
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