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[edit] Timeline of cosmic microwave background astronomy

Thermal (non-microwave background) temperature predictions:

• 1896 - Charles Edouard Guillaume estimates the "radiation of the stars" to be 5.6K.<ref>Guillaume, C.-E., 1896, La Nature 24, series 2, p. 234, cited in "History of the 2.7 K Temperature Prior to Penzias and Wilson" (PDF)</ref>
• 1926 - Sir Arthur Eddington estimates the non-thermal radiation of starlight in the galaxy ".. by the formula E = σT⁴ the effective temperature corresponding to this density is 3.18º absolute .. black body"<ref>Eddington, A., The Internal Constitution of the Stars, cited in "History of the 2.7 K Temperature Prior to Penzias and Wilson" (PDF)</ref>
• 1930s - Cosmologist Erich Regener calculates that the non-thermal spectrum of cosmic rays in the galaxy has an effective temperature of 2.8K
• 1931 - Term microwave first used in print: "When trials with wavelengths as low as 18 cm. were made known, there was undisguised surprise+that the problem of the micro-wave had been solved so soon." Telegraph & Telephone Journal XVII. 179/1
• 1934 - Richard Tolman shows that black-body radiation in an expanding universe cools but remains thermal
• 1938 - Nobel Prize winner (1920) Walther Nernst reestimates the cosmic ray temperature as 0.75K
• 1941 - Andrew McKellar uses the excitation of CN doublet lines to measure that the "effective temperature of space" is about 2.3 K

• 1946 - Robert Dicke predicts ".. radiation from cosmic matter" at <20 K, but did not refer to background radiation <ref name=Kragh>Helge Kragh, Cosmology and Controversy: The Historical Development of Two Theories of the Universe (1999) ISBN 0-691-00546-X. "In 1946 Robert Dicke and coworkers at MIT tested equipment that could test a cosmic microwave background of intensity corresponding to about 20K in the microwave region. Howver, they did not refer to such a background, but only to 'radiation from cosmic matter'. Also this work was unreleated to cosmology, and is only mentioned because it suggests that by 1950 detection of the background radiation might have been technically possible, and also because of Dicke's later role in the discovery". See also Robert H. Dicke, Robert Beringer, Robert L. Kyhl, and A. B. Vane, "Atmospheric Absorption Measurements with a Microwave Radiometer" (1946) Phys. Rev. 70, 340–348</ref>
• 1946 - George Gamow calculates a temperature of 50 K (assuming a 3-billion year old Universe)<ref>George Gamow, The Creation Of The Universe p.50 (Dover reprint of revised 1961 edition) ISBN 0-486-43868-6</ref>, commenting it ".. is in reasonable agreement with the actual temperature of interstellar space", but does not mention background radiation.

Microwave background radiation predictions:

• 1948 - Ralph Alpher and Robert Herman estimate "the temperature in the Universe" at 5 K. Although they do not specifically mention microwave background radiation, it may be inferred.<ref>Helge Kragh, Cosmology and Controversy: The Historical Development of Two Theories of the Universe (1999) ISBN 0-691-00546-X. "Alpher and Herman first calculated the present temperature of the decoupled primordial radiation in 1948, when they reported a value of 5 K. Although it was not mentioned either then or in later publications that the radiation is in the microwave region, this follows immediately from the temperature .. Alpher and Herman made it clear that what they had called "the temperature in the univerese" the previous year referred to a blackbody distributed background radiation quite different from sunliight".</ref>
• 1949 - |Ralph Alpher and Robert Herman re-re-estimate the temperature at 28 K.
• 1955 - Tigran Shmaonov finds excess microwave emission with a temperature of roughly 3K
• 1960s - Robert Dicke re-estimates a microwave background radiation temperature of 40K (ref: Helge Kragh)
• 1964 - A. G. Doroshkevich and Igor Dmitrievich Novikov write an unnoticed paper suggesting microwave searches for the black-body radiation predicted by Gamow, Alpher, and Herman
• 1965 - Arno Penzias, Robert Wilson, Bernie Burke, Robert Dicke, and James Peebles discover the cosmic microwave background radiation, eventually confirmed at approximately 2.7K
• 1966 - Rainer Sachs and Arthur Wolfe theoretically predict microwave background fluctuation amplitudes created by gravitational potential variations between observers and the last scattering surface (see Sachs-Wolfe effect)
• 1968 - Martin Rees and Dennis Sciama theoretically predict microwave background fluctuation amplitudes created by photons traversing time-dependent potential wells
• 1969 - R. A. Sunyaev and Yakov Zel'dovich study the inverse Compton scattering of microwave background photons by hot electrons (see Sunyaev-Zel'dovich effect)
• 1983 - Researchers from the Cambridge Radio Astronomy Group and the Owens Valley Radio Observatory first detect the Sunyaev-Zel'dovich effect from clusters of galaxies
• 1990 - The Cosmic Background Explorer (COBE) satellite shows that the microwave background has a nearly perfect black-body spectrum and thereby strongly constrains the density of the intergalactic medium.
• 1992 - The COBE satellite discovers anisotropy in the cosmic microwave background.
• 1995 - The Cosmic Anisotropy Telescope performs the first high resolution observations of the cosmic microwave background.
• 1999 - The BOOMERanG experiment makes higher quality maps at intermediate resolution, and confirms that the Universe is "flat".
• 2003 - The Very Small Array produces yet higher quality maps at high resolution (covering small areas of the sky).
• 2003 - The WMAP satellite produces an even higher quality map at low and intermediate resolution of the whole sky (WMAP provides no high-resolution data, but improves on the intermediate resolution maps from BOOMERanG).
• 2004 - The Arcminute Cosmology Bolometer Array Receiver produces a higher quality map of the high resolution structure not mapped by WMAP.
• 2005 - The Arcminute Microkelvin Imager and the Sunyaev-Zel'dovich Array begin the first surveys for very high redshift clusters of galaxies using the Sunyaev-Zel'dovich effect.

[edit] Future

• 2008 The Clover Project will give an improved precision intermediate and high resolution map, and measure the B-mode polarization
• 2009 The Planck (satellite) will give improved precision at all resolutions

[edit] Notes