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Arno Penzias, co-discoverer of the Big Bang's afterglow, dies at age 90

Arno Penzias (right) and Robert Woodrow Wilson, who co-discovered the afterglow of the Big Bang. The Bell Lab employees, who won the 1978 Nobel Prize in physics for their discovery, are shown standing in front of their microwave antenna at Bell Labs in Holmdel, N.J., on Oct. 17, 1978.
Arno Penzias (right) and Robert Woodrow Wilson, who co-discovered the afterglow of the Big Bang. The Bell Lab employees, who won the 1978 Nobel Prize in physics for their discovery, are shown standing in front of their microwave antenna at Bell Labs in Holmdel, N.J., on Oct. 17, 1978.

Physicist Arno Penzias, who co-discovered the cosmic microwave background, helping to confirm the Big Bang theory of the universe's beginning, died on Monday at age 90.

In the 1960s, Penzias and colleague Robert Woodrow Wilson were working at Bell Labs in Holmdel, N.J., on a new type of microwave antenna shaped like a giant horn. They planned to use the ultrasensitive system to study radio emissions from the Milky Way. What they eventually found instead was a signal that originated from outside our galaxy that turned out to be the smoking gun proof for the Big Bang theory.

While there was an eventual "eureka moment," it didn't come quickly.

While testing the receiver, Penzias and Wilson picked up an unexplained hiss in the microwave portion of the spectrum. At first, the pair thought the interference could be coming from New York City, just north of the antenna, or perhaps an echo from a nuclear bomb test conducted years earlier in the Pacific Ocean. But the signal seemed to be emanating from every part of the sky, which seemed to preclude those possibilities.

Another guess was that the interference might be coming from a pair of pigeons nesting in the antenna horn — or, more precisely, from their poop. After cleaning out what Penzias euphemistically described as "a layer of white, sticky, dielectric substance coating the inside of the antenna," the results were the same. The interference persisted.

"We looked for anything in the instrument or in the environment that might be causing the excess antenna noise," Wilson was quoted by Smithsonian magazine as saying in 2014. "Among [other] things, we searched for radiation from the walls of the antenna, especially the throat, which is the small end of the horn. We constructed a whole new throat section and then tested the instrument with it."

Eventually, Penzias and Wilson concluded that they had stumbled on something hypothesized some 15 years earlier by three physicists led by George Gamow. Gamow and his colleagues built on the work of Edwin Hubble, who had shown in 1929 that the universe was expanding. They argued that reversing the clock meant there was a beginning to the universe and that billions of years later, we ought to still be able to see (and hear) what remained from a time just after the initial "bang."

Penzias had learned that Princeton professor Robert Dicke had predicted that this afterglow from the Big Bang would be found throughout the universe as a sort of background radiation. That was what Penzias surmised he and Wilson had found.

Upon publishing their findings, Penzias and Wilson settled a scientific dispute that had been raging for years. Despite Hubble's discovery of an expanding universe, there were still prominent doubters, such as British astronomer Fred Hoyle, who favored an alternative known as the Steady State model.

With the discovery of the cosmic background, the Steady State was all but dead.

Nobel Prize recognized "a crucial piece of evidence for how the universe was created"

In 1978, Penzias and Wilson were awarded the Nobel Prize in physics for what the Nobel website describes as their "fortuitous discovery of a form of radio noise that bathes the cosmos." The discovery, it said, "provided a crucial piece of evidence for how the universe was created."

Penzias, who was Jewish, was born in Germany in 1933 just as the Nazis were coming to power. His family fled six years later. "In the late spring of 1939, shortly after my sixth birthday, my parents put their two boys on a train for England; we each had a suitcase with our initials painted on it, as well as a bag of candy," he recalled in a 2005 Nobel laureate bio. They told me to be sure and take care of my younger brother. I remember telling him, "jetzt sind wir allein" ("now we are alone") as the train pulled out."

His mother and father joined him in England and the family eventually settled in the Bronx. Penzias later attended City College of New York. He planned to become an engineer, but a professor dangled the idea of physics.

"He said, 'Physicists think they can do anything an engineer can do,'" Penzias recalled to NPR in 2014. So, he decided to give it a try.

He later spent two years in the U.S. Army Signal Corps as a radar officer before going to graduate school at Columbia University, eventually earning a doctorate in physics in 1961.

It was then that he joined Bell Labs.

Penzias later rose through the ranks at the premier research facility, spending four decades at the company. Toward the end of his career, he talked himself into a job in Silicon Valley, where he vetted technology startups for his employer. "I hit upon the idea of turning what I had been enjoying most into a full time job: helping to shape new ideas, and bring them to practical fruition," Penzias said in a 2005 Nobel laureate bio.

"The more I thought about it, the more attractive this plan for my post-retirement life became," he said.

The achievement of Penzias and Wilson fundamentally changed the way we view our universe.

Charles Bennett, an astronomer at Johns Hopkins University in Baltimore, is one of hundreds of scientists still studying the cosmic microwave background, mostly with space-based instruments such as the Wilkinson Microwave Anisotropy Probe (WMAP) and, previously, COBE, the Cosmic Background Explorer.

Speaking to NPR in 2014, Bennett said: "Penzias and Wilson rocked my world."

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Scott Neuman is a reporter and editor, working mainly on breaking news for NPR's digital and radio platforms.