Discovery of cosmic microwave background radiation

This article concerns the accidental discovery of cosmic microwave background radiation. Although predicted by earlier theories, it was first found accidentally by Arno Penzias and Robert Woodrow Wilson as they experimented with the Horn Antenna.

History

By the middle of the 20th century cosmologists concerned with the creation of the universe had evolved two leading theories to explain their views. Some astronomers supported the steady-state theory, which stated that the universe has always existed and will continue to survive without noticeable change. Others believed in the Big Bang theory which expressed that the universe was created in a massive explosion about 16 billion years ago.

At Holmdel, New Jersey, in 1964, Arno Penzias and Robert Wilson were experimenting with a supersensitive, 20 foot (6 m) horn antenna originally built to detect radio waves bounced off echo balloon satellites. To measure these faint radio waves, they had to eliminate all recognizable interference from their receiver. They removed the effects of radar and radio broadcasting, and suppressed interference from the heart in the receiver itself by cooling it with liquid helium to −269 °C, only 4 °C above absolute zero.

When Penzias and Wilson reduced their data they found a low, steady, mysterious noise that persisted in their receiver. This residual noise was 100 times more intense than they had expected, was evenly spread over the sky, and was present day and night. They were certain that the radiation they detected on a wavelength of 7.35 centimeters did not come from the Earth, the Sun, or our galaxy. After thoroughly checking their equipment, the noise remained. Both concluded that this noise was coming from outside our own galaxy--although they were not aware of any radio source that would account for it.

At that same time, Robert H. Dicke, Jim Peebles, and David Wilkenson, astrophysicists at Princeton University just 40 miles (60 km) away, were preparing to search for microwave radiation in this region of the spectrum. Dicke and his colleagues reasoned that the Big Bang must have scattered not only the matter that condensed into galaxies but also must have released a tremendous blast of radiation. With the proper instrumentation, this radiation should be detectable.

When a friend told Penzias about a preprint paper he had seen by Jim Peebles on the possibility of finding radiation left over from an explosion that filled the universe at the beginning of its existence, Penzias and Wilson began to realize the significance of their discovery. The characteristics of the radiation detected by Penzias and Wilson fit exactly the radiation predicted by Robert H. Dicke and his colleagues at Princeton University. Penzias called Dicke at Princeton, who immediately sent him a copy of the still-unpublished Peebles paper. Penzias read the paper and called Dicke again and invited him to Bell Labs to look at the Horn Antenna and listen to the background noise. Dicke, Penzias, and Wilson visited the antenna and immediately recognized the significance of their discovery--they had stumbled on to the "embers" of creation predicted by their Princeton colleagues.

To avoid potential conflict, they decided to publish their results jointly. Two notes were rushed to the Astrophysical Journal Letters. In the first, Dicke and his associates outlined the importance of cosmic background radiation as substantiation of the Big Bang Theory. In a second note, jointly signed by Penzias and Wilson titled, "A Measurement of Excess Antenna Temperature at 4080 Megacycles per Second," they noted the existence of the residual background noise and attributed a possible explanation to that given by Dicke in his companion letter.

In 1978, Penzias and Wilson were awarded the Nobel Prize for Physics for their joint discovery.

Bibliography

• Aaronson, Steve. "The Light of Creation: An Interview with Arno A. Penzias and Robert W. Wilson." Bell Laboratories Record. January 1979, pp. 12-18.
• Abell, George O. Exploration of the Universe. 4th ed., Philadelphia: Saunders College Publishing, 1982.
• Asimov, Isaac. Asimov's Biographical Encyclopedia of Science and Technology. 2nd ed., New York: Doubleday & Company, Inc., 1982.
• Bernstein, Jeremy. Three Degree Above Zero: Bell Labs in the Information Age. New York: Charles Scribner's Sons, 1984.
• Chown, Marcus. "A cosmic relic in three degrees," New Scientist, September 29, 1988, pp. 51-55.
• Crawford, A.B., D.C. Hogg and L.E. Hunt. "Project Echo: A Horn-Reflector Antenna for Space Communication," The Bell System Technical Journal, July 961, pp. 1095-1099.
• Disney, Michael. The Hidden Universe. New York: Macmillan Publishing Company, 1984.
• Ferris, Timothy. The Red Limit: The Search for the Edge of the Universe. 2nd ed., New York: Quill Press, 1978.
• Friedman, Herbert. The Amazing Universe. Washington, DC: National Geographic Society, 1975.
• Hey, J.S. The Evolution of Radio Astronomy. New York: Neale Watson Academic Publications, Inc., 1973.
• Jastrow, Robert. God and the Astronomers. New York : W. W. Norton & Company, Inc., 1978.
• Kirby-Smith, H.T. U.S. Observatories: A Directory and Travel. Guide. New York: Van Nostrand Reinhold Company, 1976.
• Learner, Richard. Astronomy Through the Telescope. New York: Van Nostrand Reinhold Company, 1981.
• Penzias, A.A., and R. W. Wilson. "A Measurement of the Flux Density of CAS A At 4080 Mc/s," Astrophysical Journal Letters, May 1965, pp. 1149-1154.

External links and references

• "Astronomy and Astrophysics Horn Antenna. (http://www.cr.nps.gov/history/online_books/butowsky5/astro4k.htm)". National Park Service, Department of the Interior

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