Jack Steinberger, who shared the 1988 Nobel Prize in physics for expanding understanding of the ghostly neutrino, a staggeringly ubiquitous subatomic particle, died Saturday at his home in Geneva. He was 99.

His wife, Cynthia Alff, confirmed the death.

The ancient Greeks proposed that there was one invisible, indivisible unit of matter: the atom. But modern physics has found more than 100 smaller entities lurking within atoms, and observations of their dizzying interactions compose the Standard Model of what is now taken to be the order of the universe.

The neutrino’s existence was first proposed in 1931, to fill holes in a theory about the makeup of the universe, but finding one proved maddeningly difficult. It has no electrical charge, travels at the speed of light and has almost no mass. Each second, trillions of neutrinos pass unimpeded through every human being. Not until 1956 — when ways to smash atoms and examine the debris were developed — was one detected.

Six years later, Dr. Steinberger joined with two fellow Columbia University physicists, Melvin Schwartz and Leon Lederman, to show that two types of neutrinos existed. Just as significant, they devised a method to produce a beam composed of vast numbers of neutrinos at very high energies. The beam could be used to study one of the basic forces of nature: the weak interaction, virtually the only influence to which neutrinos respond.

This weak interaction is one of the four fundamental interactions of nature, along with the strong interaction, which binds an atom’s nucleus together, as well as electromagnetism and gravitation. It is responsible for the radioactive decay and nuclear fusion of subatomic particles, and is called weak because its strength is surpassed by both the strong force and electromagnetism. Gravitation is weaker still.

In bestowing the physics prize on the three men, the Nobel awards committee said they had “opened entirely new opportunities for research into the innermost structure and dynamics of matter.’’

Hans Jakob Steinberger was born May 25, 1921, in Bad Kissingen in Bavaria, Germany, one of three sons of Ludwig and Berta Steinberger. His father was a cantor and religious teacher to the town’s small Jewish community; his college-educated mother supplemented the family income by giving English and French lessons.

With the rise of the Nazis and the enactment of laws barring Jewish children from attending public schools and from seeking higher education, his parents arranged for him and his older brother to go to the United States with the help of the American Jewish charities, which had offered to find homes for 300 German refugee children.

The brothers were placed in separate but nearby foster homes in the Chicago area. Jack settled into the home of a wealthy grain broker named Barnett Faroll, who several years later arranged for the boys’ parents and younger brother to join them in Chicago, rescuing them from the Holocaust, Dr. Steinberger wrote. He later attended the University of Chicago.

After the Japanese bombed Pearl Harbor in December 1941, he joined the Army, which sent him to the Massachusetts Institute of Technology to study physics so that he could work on developing radar bomb sights. After his discharge, with financial help from the GI Bill, he returned to the University of Chicago, where he found his niche as an experimental physicist working under Enrico Fermi and Edward Teller. He was awarded a PhD in 1948.

He next spent a year at the Institute for Advanced Study in Princeton, N.J., working under J. Robert Oppenheimer, the so-called father of the atomic bomb. The theoretical physics he pursued there did not fulfill him, and he grabbed at a chance to join the radiation laboratory at the University of California, Berkeley.

At Berkeley, though, he refused to sign a loyalty oath disavowing the Communist Party, even though he was not a Communist, and was asked to leave. Throughout his life, he joined other scientists to speak out against nuclear testing and American militarism. He declined to do weapons work.

Dr. Steinberger joined the Columbia faculty in 1950. In “The Second Creation: Makers of the Revolution in Twentieth-Century Physics’’ (1986), Robert Crease and Charles Mann characterized the university at that time as “the dominant center of particle physics in the United States, and thus the world.’’

Schwartz came up with the idea of the neutrino beam, and by February 1960 he had worked out the structure of an experiment at Brookhaven National Laboratory on Long Island.

Meanwhile, Dr. Steinberger had deserted his Columbia colleagues and was working on essentially the same experiment at the European Council for Nuclear Research, known as CERN, in Geneva. A miscalculation derailed this effort, and Dr. Steinberger returned to Brookhaven.

President Reagan awarded Dr. Steinberger the National Medal of Science in 1988.

Dr. Steinberger’s marriage to Joan Beauregard ended in divorce. In addition to Alff, he is survived by two sons from his first marriage, Joseph and Ned; two children from his second marriage, Julia and John; and four grandsons.