1934 : Richard Tolman shows that blackbody radiation
in an expanding universe cools but retains its thermal distribution and
remains a blackbody.
1941 : Andrew McKellar uses the excitation of CN doublet lines to
measure that the ``effective temperature of space'' is about 2.3 K
1948: George Gamow, Ralph Alpher, and Robert Herman predict that a Big
Bang universe will have a blackbody cosmic microwave background
with temperature about 5 K
1955: Tigran Shmaonov finds excess microwave emission with a
temperature of roughly 3 K. So do several other researchers,
starting with Andrew McKellar's 1941 observations of the excitation of
interstellar CN molecules,
but they do not follow through sufficiently,
until Penzias and Wilson in 1964 .
1964 : A.G. Doroshkevich and Igor Novikov write an unnoticed paper
suggesting microwave searches for the blackbody radiation predicted
by Gamow, Alpher, and Herman
1965: Arno Penzias and Robert Wilson discover the 3 K cosmic microwave
background radiation. Through the connection of Bernie Burke, Robert Dicke,
James Peebles, Roll, and Wilkinson learn of and interpret the measurement.
1966: Rainer Sachs and Arthur Wolfe theoretically predict microwave
background fluctuation amplitudes created by gravitational
potential variations between observers and the last scattering surface
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
1990: The COBE
satellite shows that the microwave background has a
nearly perfect blackbody spectrum and thereby strongly supporting the hot
big bang model, the thermal history of the Universe and constrains
the density of the intergalactic medium
1992: The COBE
satellite discovers anisotropy in the cosmic microwave background,
this strongly supports the big bang model with gravitational instability
as the source of large scale structure. This discovery energizes and motivates
the field in both theory and experiment leading to an explosion of activity.
2000: CMB anisotropy observations show that the Universe's
curvature is small and that the Universe is flat for practical purposes.
The CMB anisotropies begin to fulfill their promise of determining
cosmological parameters first to 10% sensitivity and later more accurately.
2001: MAP (Microwave Anisotropy Probe) launched as a NASA MidEX mission.
(Max Planck Surveyor formerly known as COBRAS/SAMBA) to be launched
as an ESA (European Space Agency) Mission.