Arno Allan Penzias was born on the 26th of April, 1933, in Munich, Germany. It was a fractious time for Germany, and downright dangerous for anyone of Jewish descent, which Penzias was; his grandparents had come from Poland and were prominent members of the Reichenbachstrasse Synagogue. Fortunately for the family, his parents saw which way the wind was blowing and evacuated Arno and his brother Gunther to Britain as part of the Kindertransport Rescue Operation. Their father and mother, Karl and Justine (Eisenreich) Penzias, were also able to get out before the borders closed, eventually making their way (as so many Jewish refugees did) to New York City, where they settled in the Garment District.
The younger Penzias had shown a fascination and aptitude for science at a young age, so his choice of a major was never really in doubt. He went to City College of New York, graduating with a degree in physics in 1954 and ranking near the top of his class. For a time after graduating he worked as a radar officer in the U. S. Army Signal Corps, but the pull of research drew him back into academia. In 1962, he earned a Ph.D. in microwave physics from Columbia University, studying with the inventor of the maser, Charles Townes.
Penzias then got a job with Bell Labs in Holmdel, New Jersey, where he worked on developing receivers for the (then) brand-new field of microwave astronomy. He teamed up with Robert Wilson, an American astronomer, to develop a six-meter-diameter horn reflector antenna with a seven-centimeter ultra-noise receiver, at that point by far the most sensitive microwave detector in the world.
And while using that antenna in 1964, he and Wilson discovered something extremely odd.
At a wavelength of 7.35 centimeters, corresponding to a temperature of around three degrees Kelvin, there was a strong microwave signal -- coming from everywhere. It seemed to be absolutely uniform in intensity, and was present in the input no matter which direction they aimed the antenna. It was so perplexing that Penzias and Wilson thought it was an artifact of some purely terrestrial cause -- at first, they thought it might be from pigeon poo on the antenna. Even after ruling out whatever they could think of (and cleaning up after the pigeons), the signal was still there, a monotonous hiss coming from every spot in the sky.
Before publishing their findings, they started looking for possible explanations, and they found a profound one. Almost twenty years earlier, physicists Ralph Alpher, Robert Herman, and Robert Dicke had predicted the presence of cosmic microwave background radiation, the relic left behind by the Big Bang. If the Big Bang model was correct, the unimaginably intense electromagnetic radiation generated by the beginning of the universe would have, in the 13.8-odd billion years since, been "stretched out" by the expansion of the fabric of spacetime, increasing its wavelength and dropping into the microwave region of the spectrum. Alpher, Herman, and Dicke had predicted that the relic radiation should be under twenty centimeters in wavelength, and should be isotropic -- coming from everywhere in space at a uniform intensity.
That's just what Penzias and Wilson had observed.
In July of 1965, they published their results in the Astrophysical Journal, and suddenly Penzias and Wilson found themselves famous.
At the time, there were two competing theories in cosmology -- the Big Bang model and the Steady-State model. The latter theorized that the universe was expanding (that much had been undeniable since the discovery of red shift and Hubble's Law) but that as space expanded, matter was continuously being created, so the universe had no fixed start point. Steady-State was championed by some big names in cosmological research -- Hermann Bondi, Thomas Gold, and Fred Hoyle amongst them -- and trying to figure out a way to discern which was correct had become something of a battle royale in astronomical circles.
But now Penzias and Wilson had made an accidental discovery, coupled it with a pair of (at the time) obscure papers making predictions about the temperature and wavelength of background radiation, and in one fell swoop blew the Steady-State model out of the water.
In 1978 Penzias and Wilson were awarded the Nobel Prize for research that changed the way we see the universe.
Since then, the cosmic microwave background radiation has been studied in phenomenal detail, and we've learned a great deal more about it -- starting with the fact that it isn't perfectly isotropic. There are tiny but significant irregularities in the temperature of the radiation, something that has yet to be fully explained. But the majority of the implications of the discovery have stood firm for nearly seventy years; 13.8 billion years ago, spacetime started to expand, and everything we see around us -- all the matter and energy in the universe -- condensed out of that colossally powerful event. And coming from everywhere in the sky, like a ghostly afterimage of an explosion, is the radiation left behind, stretched out so much that it is outside of the range of human vision, and can only be detected by a telescope tuned to the microwave region of the spectrum.
On Monday, the 22nd of January, 2024, Arno Penzias died at the venerable age of ninety. The world has lost a brilliant and innovative thinker whose contributions to science are so profound they're hard even to estimate. The boy who escaped Nazi Germany with his family in the nick of time grew up to be a man who listened to the sky, and in doing so forever altered our understanding of how the universe began.