The existence of a Cosmic Microwave Background was theoretically predicted by George Gamow and his associates, but played no role in the accidental discovery of the 2.7 degree cosmic microwave background radiation by Penzias and Wilson while they were testing a new type of satellite communications antenna at the Bell Telephone Laboratories in Holmdel, NJ. An earlier measurement of the cosmic microwave background at Bell Labs went unnoticed except by Russian scientists, who misunderstood the paper to be reporting a negative result. Meanwhile, not far away, Robert Dicke and his colleagues at Princeton University were building a radiometer to verify Dicke’s prediction that it might be possible to detect the microwave remnants of the big-bang. But they were beaten by Penzias and Wilson’s serendipitous Nobel Prize winning discovery that led to the final demise of the steady-state theory. An even earlier measurement of optical absorption lines by interstellar cyanogen gave the first clues to the existence of a cosmic background radiation, but its meaning was not recognized until after the 1965 experimental discovery of the microwave background at Bell Labs.

This chapter explores what is known as the Cosmic Microwave Background (CMB), what it is, how it was discovered and our recent efforts to measure and map it. In general, the analysis finds remarkably good overall agreement with predictions of the now-standard “lambda CDM” model of a universe, in which there is both cold dark matter (CDM) to spur structure formation, as well as dark-energy acceleration that is well-represented by a cosmological constant, lambda. From this we can infer 13.8 Gyr for the age of the universe.