The Scientist at Ground Zero, 1945

Today is the 100th anniversary of the birth of Julius Robert Oppenheimer. Julius was his father’s name, but Oppenheimer never used it. He first signed letters Bob, then Robert, and to close friends he was known as Oppie or Opje. In later years, the name Julius appears mostly on his FBI documents.

During the two years I was at the Institute for Advanced Study in Princeton, from 1957 to 1959, I saw Oppenheimer, in one way or another, every day. I also saw him several times later on -- in Paris, in the Virgin Islands, in New York -- before his death at age 62 in 1967. I certainly do not claim to have been a close friend -- he was “Dr. Oppenheimer” to me -- but I probably saw more of him than many of the physicists of my generation.

In the years since he died, I’ve often asked myself what Oppenheimer’s legacy was. If it were Einstein, I would simply say that his legacy was much of 20th century physics. Or if it were Werner Heisenberg and Erwin Schrodinger, I could say that quantum mechanics was their legacy. But when Oppenheimer began doing theoretical physics in the late 1920s, the theories of quantum mechanics and relativity had already been invented. A vast new scientific terrain had opened up, and physicists like Oppenheimer exploited it. It was very good physics, but it wasn’t comparable to inventing the original theories.

So what did Oppenheimer actually do? Among other things, he and a colleague put forward in the 1930s the first theory of what later became known as black holes. And he was undoubtedly one of the great physics teachers of the 20th century.

But his most visible legacy is the development of the American atomic bomb, which began in earnest in 1942 when Gen. Leslie Groves was appointed head of what became known as the Manhattan Project.

Oppenheimer, who had done some work on the bomb as a consultant of sorts, made a very favorable impression on Groves, who unexpectedly appointed him director of the laboratory in Los Alamos, N.M., where the work was being done. (The site was known to Oppenheimer, who had a ranch in the Pecos Mountains near Santa Fe, a long horseback ride from Los Alamos.)

Oppenheimer was a surprising choice not only because he had no experience organizing large scientific projects but because he had once belonged to several communist-front organizations. Nonetheless, he was Groves’ choice, and it turned out to be an act of genius.

I am persuaded that if Oppenheimer had not been the director of Los Alamos, the atomic bomb would not have been built in time to play a role in World War II. With his charisma, he was able to persuade what was probably the most talented group of scientists ever assembled on a single project to come to a location he could not reveal and to work on something whose nature he could only hint at. Once there, these young people -- the average age was 29 -- were caught up in his vision.

During these years, Oppenheimer mastered every detail of the enormously complex project and worked himself to his limits. By the end, he weighed about 115 pounds.

When the first atomic bomb was finally tested on July 16, 1945, in the New Mexico desert, no one knew whether it would work, or whether it would ever be used in the war. But within a month, two atomic bombs were dropped on Japan. “We knew the world would not be the same,” Oppenheimer said.

Several years later, Oppenheimer gave a speech in which he said that because of the bomb, physicists had “known sin.” He did not say that he had known sin, but that they all had, making many of the people who had worked on the bomb angry. After the war, Oppenheimer worked to moderate the consequences of this new weapon. He hoped the Russians could be persuaded to join in some attempt at international control. But after Hiroshima, Stalin was determined to get the bomb.

Oppenheimer’s career in government ended during the McCarthy era in 1954, when his clearance was taken away after a security hearing -- really a trial -- which most scientists thought was grossly unfair. The Atomic Energy Commission panel that held the hearing, complaining about his lack of enthusiasm for the hydrogen bomb and his apparent lack of straightforwardness about his left-wing past, used a variety of extralegal devices, including listening in on private conversations between Oppenheimer and his lawyers, to press their case.

It was many years before the divisive effects of this hearing faded away. The generation directly affected is also disappearing, and for the younger generation it is now ancient history. Nonetheless, I think part of Oppenheimer’s legacy should be a recognition of the consequences when a nation allows its security apparatus to run amok.

Jeremy Bernstein, a physicist and former staff writer for the New Yorker, is the author of “Oppenheimer: Portrait of an Enigma” (Ivan R. Dee, 2004).