In Memoriam: Arno Penzias, Nobel physicist who confirmed Big Bang theory

•  KATIE HAFNER

NEW YORK: Arno A. Penzias, whose astronomical probes yielded incontrovertible evidence of a dynamic, evolving universe with a clear point of origin, confirming what became known as the Big Bang theory, died on Monday in San Francisco. He was 90.

His death, in an assisted living facility, was caused by complications of Alzheimer’s disease, his son, David, said.

Dr. Penzias (pronounced PEN-zee-as) shared one-half of the 1978 Nobel Prize in Physics with Robert Woodrow Wilson for their discovery in 1964 of cosmic microwave background radiation, remnants of an explosion that gave birth to the universe some 14 billion years ago. That explosion, known as the Big Bang, is now the widely accepted explanation for the origin and evolution of the universe. (A third physicist, Pyotr Kapitsa of Russia, received the other half of the prize, for unrelated advances in developing liquid helium.) Until Dr. Penzias and Dr. Wilson published their observations, the Big Bang theory competed with the steady-state theory, which envisioned a more static, timeless expanse growing into infinite space, with new matter formed to fill the gaps.

Dr. Penzias and Dr. Wilson’s discovery finally settled the debate. Yet it was the serendipitous product of a different investigation altogether. In 1961, Dr. Penzias joined AT&T’s Bell Laboratories in Holmdel, N.J., with the intention of using a radio antenna, which was being developed for satellite communications, as a radio telescope to make cosmological measurements.

“The first thing I thought of was — study the galaxy in a way that no one else had been able to do,” he said in a 2004 interview with the Nobel Foundation. In 1964, while preparing the antenna to measure the properties of the Milky Way galaxy, Dr. Penzias and Dr. Wilson, another young radio astronomer who was new to Bell Labs, encountered a persistent, unexplained hiss of radio waves that seemed to come from everywhere in the sky, detected no matter which way the antenna was pointed. Perplexed, they considered various sources of the noise. They thought they might be picking up radar, or noise from New York City, or radiation from a nuclear explosion. Or might pigeon droppings be the culprit?

Examining the antenna, Dr. Penzias and Dr. Wilson “subjected its electric circuits to scrutiny comparable to that used in preparing a manned spacecraft,” Walter Sullivan wrote in The New York Times in 1965. Yet the mysterious hiss remained.

The cosmological underpinnings of the noise were finally explained with help from physicists at Princeton University, who had predicted that there might be radiation coming from all directions left over from the Big Bang. The buzzing, it turned out, was just that: a cosmic echo. It confirmed that the universe wasn’t infinitely old and static but rather had begun as a primordial fireball that left the universe bathed in background radiation.

The discovery, Dr. Penzias said years later, intensified his interest in astronomy. He and Dr. Wilson went on to detect dozens of types of molecules in interstellar clouds where new stars are formed.