The Physics
Factbook
An encyclopedia of scientific essays

Temperature of the Cosmic Microwave Background Radiation

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Bibliographic Entry Result
(w/surrounding text)
Standardized
Result
Rotham, Tony. Instant Physics: From Aristotle To Einstein. New York: Fawcett, 1995. "It's temperature is now at only 3 K above absolute zero" 3 K
"Cosmic Background Radiation." McGraw-Hill Encyclopedia of Science & Technology. New York: McGraw Hill, 1973. "… the radiation is redshifted from the visible by a factor on the order of 1000 into the microwave region, with a characteristic temperature of 3 K" 3 K
Talcott, Richard. "Seeking the Seeds of Today's Cosmos." Astronomy. July 1994: 23. "… they found fluctuations of about 40 millionths of a kelvin in the overall 2.73 kelvin background" 2.73 K
Rowan-Robinson, Michael. Cosmology. Oxford: Clarendon Press, 1977. "… 2.7 K black-body cosmic microwave background" 2.7 K
Cowen, Ron. "Taking the Temperature of the Far Cosmos." Science News. 10 September 1994: 15. "The temperature of the relic radiation in nearby regions of space, 2.73 kelvins, exactly matches the predicted cooling" 2.73 K

Going through different sources, I found the cosmic background radiataion varies from 2.7 K to 3 K. After further study, I believe the cosmic background radiation should be around 2.7 K because the texts that state this value give more accurate and detailed information than other texts. All of my research sources agree that the cosmic background radiation must have been thermalized when the universe was denser and hotter than it is now. Isotropic and homogeneous expansion of the universe automatically preserves the thermal character of the radiation, with no need for a thermalizing agent: expansion simply lowers the temperature.

Astronomers have discovered some tiny fluctuations in the temperature of the background radiation. Big Bang cosmologies help them to predict how the temperature changed with time. According to Big Bang, the temperature of the microwave background increases linearly with redshift, a measure of the distance to faraway objects. To test these prediction, Antoinette Songaila of the Institute for Astronomy in Hawaii and her co-workers measured the temperature of the background radiation at a time corresponding to 4 billion years after the Big Bang. Within experimented errors, the team found that one cloud -- at 7.58 kelvin -- matches the temperature predicted for the microwave background at that distance. The other cloud has a temperature some 3 kelvin higher. Cowie notes that the number give only an upper limit on the microwave background. Local effects also contribute to the excitement of carbon atoms in each cloud, and this may explain the higher temperature in the second cloud. As a whole, the measurement are consistent with the Big Bang theory.

In conclusion, the information I gather tells me the early universe was hot, the temperature of cosmic background radiation was higher than today's. However, the universe has cooled considerably since its birth and the temperature of the relic radiation in nearby regions of space, 2.73 kelvin, exactly matches the predicted cooling.

Silin Yang -- 1997

Bibliographic Entry Result
(w/surrounding text)
Standardized
Result
Schwarzschild, Bertram. "WMAP Spacecraft Maps the Entire Cosmic Microwave Sky With Unprecedented Precision." Physics Today. Vol. 56, No. 4 (April 2003): 21. "The cmB [cosmic microwave background] is the relic radiation from the 'moment' of first transparency, 4 × 105 years after the Big Bang, when the opaque plasma pervading the cosmos finally became cool enough (about 3000 K) to let neutral hydrogen survive. The thousandfold cosmic expansion since then has redshifted this ubiquitous, largely undisturbed radiation to a blackbody temperature of 2.725 K, with random anisotropies of only a few parts in 105 from point to point on the sky." 2.725 K

Editor's Supplement -- 2003