In four photographs of Albert Einstein, taken over a 30-year span between 1911 and 1942 and reproduced in Silvan Schweber’s “Einstein & Oppenheimer: The Meaning of Genius” (Harvard, 432 pages, $29.95), he positions himself, whether in a group or alone, so that his left hand is caught by the camera. He holds that hand in a distinctive gesture, with his thumb and forefinger joined to form a little ellipse. Though he tends to face away from the camera, as though indifferent to appearances, he is clearly at pains to keep that left hand visible. The gesture is as much a signal as a symbol.

In “Einstein & Oppenheimer,” his unusual exercise in comparative biography, Mr. Schweber, an emeritus professor of physics and the history of ideas at Brandeis, explains that Einstein adopted the gesture from Hindu and Buddhist practices. Both the Hindu god Vishnu and the Buddha himself are often portrayed with their left hands in this posture; known in Sanskrit as the vitarka gesture, it represents “compassionate teaching” as well as, for Buddhists, the union of wisdom and method. In Einstein’s case, it serves as a sign not of the public figure he had become but of the man hidden within.

A generation separated Albert Einstein (1879-1955) from his younger colleague J. Robert Oppenheimer (1904-67), and yet, this was the least of the differences between them. Einstein saw himself as a “lone traveller.” He was convinced that great discoveries come out of solitary effort or, as he put it, that “pure thought can grasp reality.” Oppenheimer, by contrast, functioned best in collaboration; he was a brilliant organizer who created the School of Theoretical Physics at Berkeley in the 1930s, served as chief scientific adviser to the Manhattan Project, which produced the first atomic bombs, and, after the war, for the last 20 years of his life, directed — and transformed — the Institute for Advanced Study at Princeton (where he was, in effect, Einstein’s boss).

Mr. Schweber draws out the contrasts between these two extraordinary men in great detail, but he’s really interested in something more fundamental, which their parallel careers exemplify. He wishes not only, as his subtitle suggests, to explore “the meaning of genius” but in fact “to banish the term,” especially with regard to Einstein. “Calling Einstein a ‘genius’ dwarfs the background against which his work was done,” he argues. Though Einstein saw himself as “a loner,” his epochal discoveries of 1905 — of which the special theory of relativity is only the most celebrated — did not emerge out of “pure thought” alone. Einstein drew on the scattered insights and discoveries of others; he was active in conferences and maintained a far-flung and intensive correspondence. Even in the Bern patent office he remained in the thick of things. None of this, of course, diminishes Einstein’s achievements; as Mr. Schweber emphasizes, it is simply the way groundbreaking research works. Scientific discovery is collaborative even in seclusion.

The real interest of Mr. Schweber’s account — and what makes his dual biography unusual — is the emphasis he places not on Einstein’s or Oppenheimer’s scientific achievements, which have been often enough described, but on their later careers, when both found themselves, for different reasons, strangely sidelined. Though both men remained very much in the public eye — Einstein as a sage and Oppenheimer as an articulate spokesman for science — they spent the last 25 years of their lives simultaneously immersed in but apart from the scientific community. Einstein made no fundamental contributions after 1935, largely because of his obsessive quest to formulate a unified field theory and thereby dislodge quantum mechanics, which he detested. And Oppenheimer, despite important research on what would later come to be known as “black holes,” abandoned research after 1946 in favor of administrative pursuits.

Mr. Schweber describes Einstein’s fate as “tragic,” but this assessment seems a bit exaggerated, particularly when compared with Oppenheimer’s. There was a wholeness to Einstein’s personality, and to his vision of reality, which Oppenheimer, a more complex and fragmented figure, simply lacked. For all his outward success, Oppenheimer seems to have been thwarted at every turn. A breakdown in 1925 led him to take up physics; the failure of the Acheson-Lilienthal Plan to control atomic energy prompted him to give up active research, and the revocation of his security clearance during the McCarthy era provided a final public humiliation. Mr. Schweber describes these crises well, drawing on letters, transcripts, and public statements, and yet, it seems a stretch, too, to depict Oppenheimer as “tragic.” For all his flaws, Oppenheimer displayed a disciplined nobility to an ideal of service; he made no lasting discoveries, as did Einstein, but he devoted his considerable brilliance — what Mr. Schweber terms his “collective charisma” — to encouraging the brilliance of others.

I’m not sure that Mr. Schweber, despite his best efforts, succeeds in dispelling the aura of “genius,” particularly in the case of Einstein. He compares Oppenheimer to a brilliant orchestra conductor while Einstein is “the Mozart” of physics, an unaccountable phenomenon. In 1954, Einstein wrote that “the eternal mystery of the world is its comprehensibility.” He himself embodied such mystery. Even today, more than 50 years after his death, he remains baffling and transparent at once.

eormsby@nysun.com