John Wheeler, who helped invent the theory of nuclear fission and who coined the phrase "black hole," died Sunday in Hightstown, N.J., at the age of 96.

The cause was pneumonia, according to his daughter, Alison Wheeler Lahnston.

Wheeler was born in Jacksonville, Fla., and received his doctorate from John Hopkins University in 1933. He went on to teach physics at Princeton and the University of Texas, and also worked on developing the atomic bomb with the Manhattan Project during the Second World War.

He regretted that the bomb was not created in time to change the course of the war in Europe, where his brother Joe died in 1944 while serving in Italy.

Before the war, he collaborated with Danish physicist Niels Bohr, who had come to the United States in 1939 to discuss the theory of relativity with Albert Einstein, but ended up spending more time talking fission, Wheeler once told the New York Times.

Within a few weeks of meeting, the two had sketched out how nuclear fission worked. In their fission theory, Bohr and Wheeler explained that the atomic nucleus, which contains protons and neutrons, is like a drop of liquid. The liquid drop starts vibrating when a neutron from another disintegrating nucleus hits it, then bends into a peanut shape and breaks in two.

Wheeler also coined the term "wormhole," which describes tunnels in space-time, in 1957 while working on expanding Einstein's relativity theory. He came up with the term "black hole" in 1967 while giving a speech on the theory of gravitational collapse.

In 1979, he unsuccessfully tried to have parapsychology — the study of paranormal incidents such as extrasensory perception and psychokinesis — expelled from the American Association for the Advancement of Science. The organization chose to continue its paranormal studies.

Wheeler won numerous accolades for his research, including the Atomic Energy Commission's Enrico Fermi award in 1968 and the Wolf Prize in physics in 1997.

In 1935, Wheeler married his wife Janette, who died in October 2007 at 99. He is survived by his three children, Alison and Letitia Wheeler Ufford, both of Princeton, as well as James English Wheeler of Ardmore, Pa. Wheeler is also survived by eight grandchildren, 16 great-grandchildren, six step-grandchildren and 11 step-great-grandchildren.