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George F. Smoot, winner of the Nobel Prize in Physics, 2006, celebrating with colleagues at Lawrence Berkeley National Laboratory. October 3 2006. (Source)

George Fitzgerald Smoot III (born February 20, 1945) is an American astrophysicist and cosmologist awarded the 2006 Nobel Prize in Physics with John C. Mather for "their discovery of the black body form and anisotropy of the cosmic microwave background radiation".

This work helped cement the big-bang theory of the universe using the COBE (Cosmic Background Explorer) satellite. According to the Nobel Prize committee, "the COBE-project can also be regarded as the starting point for cosmology as a precision science". [1]




Smoot was born on 20 February 1945 in Yukon, Florida. He studied mathematics before switching to the Massachusetts Institute of Technology where he obtained dual bachelor's degrees in mathematics and physics in 1966, and a doctorate in particle physics in 1970.[2]

Although Smoot attended MIT, he was not the same Smoot who was laid end to end to measure the Harvard Bridge between Cambridge and Boston[3][4]; this was his cousin[5] Oliver R. Smoot[6], an MIT alumnus who served as the chairman of the American National Standards Institute.

Initial research

George Smoot then switched to cosmology, and went to Lawrence Berkeley National Laboratory where he collaborated with Luis Walter Alvarez on the experiment HAPPE, a stratospheric balloon for the detection of antimatter in the upper atmosphere, which was predicted by the now obscure steady state theory of cosmology.

He then took up an interest in cosmic microwave background radiation (CMB), previously discovered by Arno Allan Penzias and Robert Woodrow Wilson in 1964. There were, at that time, several open questions about this, relating directly to fundamental questions about the structure of the universe. Certain models predicted the universe as a whole was rotating, which would have an effect on the CMB: its temperature depending on the direction of observation. With the help of Alvarez and Richard A. Muller, Smoot developed a differential radiometer which measured the difference in temperature of the CMB between two directions 60 degrees apart. The instrument, which was mounted on a Lockheed U-2 plane, made it possible to determine that the overall rotation of the universe was zero (within the limit of accuracy of the instrument). It did, however, detect a variation in the temperature of the CMB of a different sort. This dipole pattern (meaning that the CMB appears to be at a higher temperature on one side of the sky than on the opposite side) has been explained as a Doppler effect of the Earth's motion relative to the area of CMB emission, which is called the last scattering surface. Such a doppler effect arises because the Sun (and in fact the Milky Way as a whole) is not stationary, but rather is moving at nearly 600 km/s with respect to the last scattering surface. This is probably due to the gravitational attraction between our galaxy and a concentration of mass like the Great Attractor.

Participation in COBE

At that time, the CMB appeared to be perfectly uniform excluding the distortion caused by the Doppler effect as mentioned above. This result contradicted observations of the universe, with various structures (galaxies, galaxy clusters, etc.) that indicate that the universe was relatively inhomogenous on a small scale. However, these structures formed slowly. Thus, if the universe is inhomogenous today, it would be inhomogenous at the time of the emission of the CMB as well, observable today through weak variations in the temperature of the CMB. It was the detection of these anisotropies that Smoot was working on in the late 1970s. He then proposed to NASA a project involving a satellite equipped with a detector that was similar to the one mounted on the U-2, but was more sensitive and not influenced by air pollution. The proposal was accepted and gave rise to the satellite COBE, and cost US$ 160 million. COBE was launched on November 18, 1989, after a delay owing to the destruction of the Space Shuttle Challenger. After more than two years of observation and analysis, the COBE research team announced on 23 April 1992 that the satellite had detected tiny fluctuations in the CMB, a breakthrough in the study of the early universe. [7]

The success of COBE was the outcome of prodigious team work involving more than 1,000 researchers, engineers and other participants. John Mather coordinated the entire process and also had primary responsibility for the experiment that revealed the blackbody form of the CMB measured by COBE. George Smoot had main responsibility for measuring the small variations in the temperature of the radiation[8].

Smoot collaborated with San Francisco Chronicle journalist Keay Davidson to write the general-audience book Wrinkles in Time [9], first published in 1994, that chronicled his team's efforts.

Cosmic microwave background temperature data were extracted from the released FITS files and then combined into two linear combinations. The first is a weighted sum of the 53 and 90 GHz channels which gives the highest signal-to-noise ratio for cosmic temperature variations but includes the Milky Way Galaxy as well. In the second linear combination, a multiple of the 31 GHz map is subtracted from a weighted sum of the 53 plus 90 GHz channels to give a "reduced map" that gives zero response to the observed Galaxy, zero response to free-free emission, but full response to variations in the cosmic temperature. These maps have been smoothed with a 7 degree beam, giving an effective angular resolution of 10 degrees. An all-sky image in Galactic coordinates is plotted using the equal-area Mollweide projection. The plane of the Milky Way Galaxy is horizontal across the middle of each picture. Sagittarius is in the center of the map, Orion is to the right and Cygnus is to the left.

The following image just shows the reduced map (i.e., both the dipole and Galactic emission subtracted). The cosmic microwave background fluctuations are extremely faint, only one part in 100,000 compared to the 2.73 degree Kelvin average temperature of the radiation field. The cosmic microwave background radiation is a remnant of the Big Bang and the fluctuations are the imprint of density contrast in the early universe. The density ripples are believed to have given rise to the structures that populate the universe today: clusters of galaxies and vast regions devoid of galaxies."

Recent projects

After COBE, Smoot took part in another experiment involving a stratospheric balloon, MAXIMA, which was more precise than COBE, and refined the measurements of the anistrophies of the CMB. He is also a collaborator in SNAP, a satellite which is proposed to measured properties of dark energy, and data from the Spitzer Space Telescope in connection with far infrared background.

Original text translated from French language article.

  1. ^ Information for the public (PDF). The Royal Swedish Academy of Sciences (2006-10-03). Retrieved on 2006-10-05.
  2. ^ MIT Press Office (2006-10-03). Nobelists' work supports big-bang theory. Press release. Retrieved on 2006-10-03.
  3. ^ George Smoot. The SMOOT as unit of Length. Retrieved on 2006-10-07.
  4. ^ Talk of the Nation (2006-10-06). Winning the Nobel Prize. National Public Radio. Retrieved on 2006-10-07.
  6. ^ All Things Considered (2005-12-07). Smoot, Namesake of a Unit of Length, Retires. National Public Radio. Retrieved on 2006-10-07.
  7. ^ Smoot, G. F et al., Structure in the COBE differential microwave radiometer first-year maps, Astrophysical Journal 396, L1 (1992)
  8. ^ Press release: Pictures of a newborn Universe
  9. ^ Wrinkles in Time by George Smoot and Keay Davidson, Harper Perennial, Reprint edition (October 1, 1994) ISBN 0380720442


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