Arno A. Penzias, who fled Nazi Germany in childhood, settled in the United States and in 1978 shared the Nobel Prize in physics for helping find vital early evidence of the Big Bang Theory about the creation of the universe, died Jan. 22 at an assisted-living center in San Francisco. He was 90.

The cause was complications from Alzheimer’s disease, said his son, David Penzias.

Along with a Bell Laboratories colleague, astronomer Robert W. Wilson, Penzias conducted groundbreaking work widely considered fundamental to one of the landmark discoveries of modern science. Their efforts offered support for the current theory of the origin and development of the entire universe and all that lies within it.

In the work for which they were eventually honored with the Nobel, Penzias and Wilson built and operated a highly sensitive radio telescope. With it, they picked up faint emanations permeating space — radiation, many scientists think, produced by the cataclysmic explosion known as the Big Bang and that set the universe into motion.

The atoms and molecules that compose the universe are themselves composed of particles that carry electrically charged particles. In motion, charged particles may generate electromagnetic radiation.

Light is only one of the many forms of such radiation. It has long been collected from distant places on Earth and in the heavens by optical telescopes. But radiation of other frequencies and wavelengths, undetectable by the eye, can be gathered, detected and amplified by what are known as radio telescopes.

Such devices are akin to their optical counterparts but detect radiation at other frequencies and gather information unavailable to optical telescopes. Antennas, analogous to those that can pick up TV or radio signals, serve as the signal-gathering lenses or mirrors of these telescopes.

The discovery made by Penzias and Wilson came from pointing their device at the sky, and detecting a mysterious and unexplained electromagnetic background that in the world of microwave technology appeared at first as mere noise.

It was in 1964, at the Bell Labs in Holmdel, N.J., that Wilson and Penzias made their celebrated discovery. They pointed toward the heavens their antenna, shaped like a huge, stylized horn, and even they were startled by what they found.

The mysterious radiation they collected from space in the form of microwave signals from space came not, as had been suspected, from some single, narrow region of the cosmos. Instead, it came from everywhere. Although faint and no longer possessed of the titanic energies that had created and once characterized it, the radiation pervaded the universe.

Their discovery helped dispel what was known as the steady-state theory, the long-held view of a placid, unchanging universe, and led to the widespread adoption of the more dynamic and dramatic Big Bang Theory. The Nobel citation honored them “for their discovery of cosmic microwave background radiation.” (A third scientist, Pyotr Kapitsa of the Academy of Sciences in Moscow, also shared the prize that year for an unrelated discovery involving low-temperature physics.)

Curiously and interestingly, the same cosmic signals that led to Penzias and Wilson’s discovery had been, to some extent, detected and detectable before.

In the original over-the-air TV sets, the signals from the cosmos, scientists say, formed at least part of the hissing, crackling static that could be witnessed after broadcasting ceased for the night, or on an unused channel.

An early response to the puzzle of the origins of the microwave background was to consider all possible sources, terrestrial and interstellar, of these extraneous signals, and then to rule out the ones shown not to meet the necessary criteria.

Ultimately, scientists have come to accept this pervasive microwave energy as a vestige of the Big Bang, a faint, perhaps cryptic message from the time of creation, thought to be more than 13 billion years ago.

In an episode that demonstrates the often mundane aspects of scientific research, Penzias and Wilson noted the pigeon droppings repeatedly found at a sensitive part of their antenna. This departure from the sterile perfection of their equipment was — in its turn and along with the other possibilities — duly ruled out as a contributor, albeit a sort of scatological one, to the mysterious background.

Arno Penzias was born in Munich on April 26, 1933. His father, who owned and operated a leather wholesale business, provided what Penzias described as a comfortable middle-class living for his family. His mother, a Catholic, had converted to her husband’s Jewish faith.

His family was sent to the Polish border in 1938 as part of a Nazi program to deport Jews of Polish background and who did not hold German passports. By his account, the family missed the deadline by an hour at the border and was turned back, on grounds that no more immigrants were to be accepted.

That, the family believed, may have saved their lives. When his father was ordered to leave the country within six months, he began making arrangements for his sons to leave for Britain as part of the kindertransport program to rescue German-Jewish children.

On leaving home in 1939, 6-year-old Arno said he told his slightly younger brother in German, “Jetzt sind wir allein” — “now we are alone.”

The family was reunited soon thereafter in England before sailing to the United States in December 1939 on a ship, on which his father had presciently booked passage 18 months earlier. They settled in the Bronx the next month, where his parents became superintendents of an apartment building. His father later worked in the carpentry shop of the Metropolitan Museum of Art, and his mother cleaned homes and did sewing at a coat factory.

“Arno was always a thinker and very ambitious,” his father told the Palm Beach Post after his son received the Nobel. He recalled that Arno, on his own, found out that he was eligible to attend Brooklyn Technical High School, which had a renowned science and engineering program. From the Bronx, Arno trekked three hours a day on transit by foot and subway to the school. “He just thought [school] would give him more,” his father said. “The travel didn’t mean anything to him.”

Arno became a naturalized citizen in 1946, adding “Allan,” the Americanized name he liked to be called, as his middle name. At his father’s behest, he studied chemistry in the hope of earning a good living in engineering. But during his freshman year at tuition-free City College of New York, he switched to physics because he was bored by chemistry.

“Physics was unglamorous then,” he told the New Yorker. “This was before Sputnik. … The top kids seemed to be attracted to it for aesthetic reasons. I didn’t get into it, at first, for those reasons, but I found that, as I studied it, it was something I liked. The competition was extraordinarily tough.”

He graduated in 1954, then spent two years working on radar in the Army Signal Corps, before obtaining a master’s degree in physics in 1958 and a doctorate four years later, both from Columbia University.

Much of his early work, including his Army service, involved him with microwave research and technology, and that placed him on the path that led to the Nobel. At Columbia, the physics department was deeply engaged in microwave research with a faculty that included some of the luminaries of the field. Under one Columbia mentor, Charles Townes, an inventor of the maser, he was immersed in the study of microwaves and radio astronomy.

In 1961, Penzias joined Bell Laboratories, the research center maintained by the old Bell System, and it studied the fundamental science behind such technologies as microwaves, electronic signals and modern telecommunications.

The renowned laboratories in Holmdel, he said, had one-of-a-kind facilities that “made it an ideal place” to finish the radio astronomy observations he had begun but not completed during his Columbia Ph.D. work.

For example, Bell already had a large antenna suitable for radio astronomy. That antenna had been intended for use in communication with Earth satellites. Penzias described it as a superb tool for pursuing his own interests, and it became available to him. He remained at Bell for 37 years, working in such areas as interstellar chemistry before moving up the management ranks.

In the mid-1990s, he moved to Silicon Valley, where he became prominent as a thinker on the development of new technologies and an adviser to start-up companies.

His first marriage, to Anne Barras, ended in divorce. In 1996, he wed Sherry Levit, a Silicon Valley executive. In addition to his wife, of San Francisco, survivors include three children from his first marriage, David Penzias of Newton, Mass., Mindy Dirks of Monte Sereno, Calif., and Rabbi L. Shifra Weiss-Penzias of Santa Cruz, Calif.; two stepchildren, Carson Levit and Victoria Zaroff, both of San Francisco; a brother; 12 grandchildren; and three great-grandchildren.

A book Penzias published in 1989, “Ideas and Information,” may seem to have particular relevance at a time of increasing interest in such topics as artificial intelligence. “In essence,” he wrote in his Nobel biographical statement, “the book depicts computers as a wonderful tool for human beings but a dreadful role model for what we humans know as intelligence. In other words, ‘If you don’t want to be replaced by a machine, don’t try to act like one!’ ”