Philip Morrison, who died Friday at his home in Cambridge, Mass., at 89, was a physicist who assembled the first atomic bomb for the Manhattan Project.

An outspoken pacifist after VJ Day – “I have always said that one nuclear war is plenty,” he said – Morrison turned to high-energy astronomy and became a pioneer in the search for extraterrestrial intelligence.

Blessed with a restless mind that sought out scientific arcana promiscuously, Morrison was a leading popular science writer. For more than 30 years, Morrison was the main book reviewer for Scientific American magazine, often writing with his second wife, Phylis. He also co-wrote the book “Powers of Ten” and narrated the film, and he created the PBS series “Ring of Truth,” which illustrated scientific concepts with graphic demonstrations – such as burning a pile of 32 jelly doughnuts, the equivalent of the energy expended daily by a rider in the Tour de France.

Morrison was born in Somerville, N.J., in 1915 and raised in Wilkensburg, Pa., just outside of Pittsburgh. A bout of polio left him with permanently weakened legs and lungs. His father was a gadget enthusiast who got his young son interested in radio when he brought home an early crystal set. By the time Morrison was 12, he had a broadcasting license and, armed with textbooks and his own microscope, had also educated himself in biology.

After majoring in physics at Carnegie Tech, Morrison began graduate work in physics at the University of California at Berkeley under J. Robert Oppenheimer, in 1936. Shortly after earning his Ph.D. in theoretical physics, with a dissertation on the behavior of gamma rays and energy fluctuations in the electromagnetic field, Morrison was recruited to work on the Manhattan Project. He first worked at the Metallurgical Laboratory at the University of Chicago, and later transferred to Los Alamos, where he assembled the core of the “Fat Man” bomb.

On July 16, 1945, Morrison observed the first atomic detonation from about 10 miles off. He recorded the experience in a starkly worded official report. “What I saw first was a brilliant violet glow entering my eyes by reflection from the ground and from the surroundings generally,” he wrote. “I observed through the welding glass, centered at the direction of the tower an enormous and brilliant disk of white light.”

Soon afterward, Morrison traveled to Tinan Island in the Pacific, where he assembled the bomb that was dropped on Nagasaki, Japan, on August 9, 1945. A letter he helped draft was parachuted from the bomber, addressed to a former Berkeley colleague, Ryokichi Sagane of the University of Tokyo, warning that America was capable of building many more such bombs. The letter never reached its destination, but Japan surrendered days later.

Morrison was named to the government team that traveled to Nagasaki immediately after the Japanese surrender. He called the devastation “matchless in human misery,” and swore off working on weapons for the rest of his career.

After the war, Morrison became involved in creating the first fast plutonium reactor meant for producing electricity. He named it Clementine, for its remote location – “in a cavern, in a canyon.”

While he compared fears that using atomic energy would lead to more atomic bombs to the idea that electricity should be outlawed because of electric chairs, Morrison also was an outspoken foe of atomic weapons. He became identified with a group of scientists who supported placing atomic energy under international control.

Fearing, he later wrote, that academic freedom at Berkeley would suffer as Cold War tensions increased, Morrison took a job at Cornell, where he remained until the mid-1960s. In the early 1950s, it was disclosed that he had briefly joined a communist organization in the 1930s, and he was forced to testify before the Senate’s internal security subcommittee in 1953. Little came of the affair, although there were calls at the time for his dismissal from Cornell.

Having moved his research focus to cosmology from nuclear physics, he investigated the sources of cosmic rays, as well as communications in cells and the origins of helium isotopes in rocks. In 1959, with physicist Giuseppe Cocconi, he proposed a systematic radio telescope study of the heavens in order to detect alien life. The concept of SETI, or search for extraterrestrial intelligence, became a widespread scientific quest, although he pronounced himself unsurprised that it had not yielded any discoveries.

In 1965, Morrison moved permanently to MIT, where he focused on the study of supernovae, as well as black holes and quasars, which he proposed were giant pulsars. He also became more involved with science education and helped to develop science kits to demonstrate fundamental scientific principles to children. He contributed to popular magazines and wrote books for general readers, including “Nothing Is Too Wonderful To Be True” (1994) and “The Ring of Truth: An Inquiry Into How We Know What We Know” (1987). In support of tighter control of nuclear weapons, he contributed in 1979 to “In The Price of Defense: A New Strategy for Military Spending,” an influential book in the disarmament camp.

What struck general readers was how widely he cast his intellectual net. In one essay, written on appropriate technology for the Whole Earth Review in 1998, Morrison described an irrigation system employed by Louis XIV: “The Sun King had his engineers construct fourteen huge waterwheels, each forty feet across, all mounted on a kind of ornate barge, turning steadily in the strong current midstream of the wide Seine. They pumped water through cast-iron pipes up the hill to the aqueduct high above. Marly-la-Machine was noisy with its pumps and their drive rods. Though its power output was only about that of a mid-sized auto engine, when it was brought into use during the 1680s it was likely the most powerful concentration of mechanical power in the world.”

He claimed to have written 1,500 book reviews, and publishers sent him so many books that he gave them away in place of treats on Halloween.

Philip Morrison

Born November 7, 1915, in Somerville, N.J.; died April 22 at home in Cambridge, Mass., of respiratory failure aggravated by childhood polio; survived by his stepson, Bert Singer.