R.I.P. Arno Penzias (1933-2024) | In the Dark


Yesterday I heard the sad news of the death, at the age of 90, of American physicist and radio astronomer Arno Penzias.

I’ve used the above image hundreds of times in popular talks. It shows Robert W. Wilson (left) and Arno A. Penzias (right) standing in front of the famous horn antenna that (accidentally) discovered what we now know to be the cosmic microwave background, radiation left over after the Big Bang.

Penzias and Wilson made their historic measurements in 1964, published their results in 1965, and received the Nobel Prize for Physics in 1978. At the time of this experiment, the scientists were working at Bell Telephone Laboratories at Holmdel, New Jersey, on Project Echo. The antenna was built to receive radio signals bounced off a passive satellite in a low Earth orbit to check the feasibility of satellite radio communication. They found excess noise in their receiver, which was eventually identified as a relic of a time when the Universe was extremely hot. Coincidentally, the theory of this yet undiscovered radiation was being worked on by Bob Dicke and his group in Princeton at about the same time (and also in New Jersey). Discussions ensued, and the discovery paper by Penzias & Wilson appeared in the Astrophysical Journal in 1965 beside a paper by Dicke et al. giving the theoretical interpretation.

The discovery of the cosmic microwave background was probably the most important result in observational cosmology after that of the Hubble expansion and it paved the way for the establishment and further development of the Big Bang theory. One of the two discoverers of the CMB has now left us, leaving a priceless legacy.

Rest in peace, Arno Allan Penzias (1933-2024)

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