The subject involved quantum mechanics and the speaker was a prominent physicist. When questions were invited, I asked, “Would quantum mechanics be better or worse if everything Niels Bohr did after 1921 were eliminated?” The audience broke out in laughter; the speaker snickered, but did not answer my question. Bohr is a giant of 20th century physics. He effectively built the Institute for Theoretical Physics in Denmark that opened in 1921 and, like the Lord of the Manor, presided over everything. “Faust in Copenhagen” (Viking, 320 pages, $25.95) is about those promising young physicists who descended on Denmark during the late 1920s and early ’30s.

The year 1932 was special: In a British laboratory the neutron was found; American physicists meanwhile discovered the antiparticle, the positron, and the deuterium. Particle accelerators made their appearance in both countries. In April of that year, many of the illustrious Copenhagen alumni returned to Bohr’s institute to talk physics, enjoy entertainment, and have fun. It was the centennial of Goethe’s death and the entertainment came from a skit based on Faust. The fun came from the script, written largely by Max Delbrück, in which physicists including Bohr and Wolfgang Pauli became Faustian characters. Gino Segrè, a physicist at the University of Pennsylvania, uses the Goethe celebration as the touchstone of his delightful new book.

For the physicists who gathered in Copenhagen in 1932, the glory days of the institute were slipping into the past. Copenhagen had been the hub of physics from 1925 through 1929 when quantum mechanics was created. Almost all the principal architects of this theoretical achievement — Wolfgang Pauli (born 1900), Werner Heisenberg (born 1901), and Paul Dirac (born 1902) — were barely out of childhood, while Erwin Schrödinger (born 1887) was, by comparison, an old man. Each of these physicists, titans all, come alive in Mr. Segrè’s book.

The author is wonderfully successful in exposing their characters and showing the reader how their individual approaches to physics differed. Mr. Segrè does not stop with the principals. Other illustrious physicists, Lise Meitner, Paul Ehrenfest, and Max Delbrück appear prominently. Physicists and non-physicists alike will be drawn into the aura of these great 20th-century scientists and will leave the book with a deeper appreciation of who these people were and what they did.

Mr. Segrè’s treatment of Bohr in particular, I believe, will raise provocative questions. Physicists heap admiration on the giants of the discipline. Bohr receives an uncommon intensity of veneration that begs the question, “Why?” Mr. Segrè provides part of the answer: Bohr was kind, considerate, generous, and “the most loved theoretical physicist of the twentieth century.” I cannot vouch for the amorous inclinations of physicists, but I have talked to many who knew Bohr and without exception they exude an unusual level of admiration for the man. Bohr qua man with charm vs. Bohr qua great physicist are, however, two different things. Mr. Segrè’s treatment of the latter is mixed.

For example, Mr. Segrè writes, “[Ehrenfest’s] original work might not have been on the level of Bohr’s or Einstein, but then whose was?” To put Bohr’s original work on the level of Einstein’s is, I believe, impossible to justify. After 1921, what was Bohr’s original work? Bohr surrounded himself with bright young physicists and they did physics collaboratively. But who did what?

Mr. Segrè also shows Bohr as an obstructionist. Bohr rejected Einstein’s particle of light, proposed in 1905, until well into the 1920s. He was so opposed to the light-particle concept that he talked Hendrik Kramers, one of his bright assistants, out of proposing a Compton-type experiment to prove the particle concept several months before Compton did it. (Compton won the Nobel Prize forthiswork).TheBohr, Kramers, and John Slater paper, known as the BKS paper, published in 1924, was a mess. Bohr apologized for it later. He proclaimed electron spin to be wrong after Sam Goudsmit and George Uhlenbeck proposed it. Of course, both the particle of light (named the photon in 1926) and electron spin are now indispensable parts of physics.

Bohr asked Heisenberg to withdraw his 1927 paper that gave birth to the Uncertainty Principle. Heisenberg refused. He was also slow to recognize the significance of antielectrons — a direct implication of Dirac’s famous 1928 paper. As I. I. Rabi said, Bohr was always trying to do away with the conservation of energy as he did in the BKS paper. He challenged energy conservation in stellar interiors, with beta decay, and in the interiors of nuclei. Pauli, Heisenberg, and Dirac teased him about this, but to no avail. In 1929, Pauli wrote to Bohr, “Do you intend to mistreat the poor energy law further?” Ernest Rutherford added his objections. Reading all this, one is prompted to ask: Was Bohr’s intuition in physics all that great?

Bohr contributed nothing to the powerful formalism of quantum mechanics. He did, however, provide the Copenhagen interpretation of quantum mechanics, including the Principle of Complementarity in 1927. Again, I take issue with Mr. Segrè when he writes, “The Bohr interpretation still stands [today], as solidly as ever.” The Copenhagen interpretation never did stand solidly: Pauli, Heisenberg, and Dirac tolerated it; contemporary physicists pay no attention to it.

Bohr was a charming man and a great organizer. His institute provided a haven where the brightest minds in physics flourished. Twentieth-century physics was the benefactor. For that the man deserves enormous credit. But as a physicist, particularly after 1921, he falls short of greatness.

Mr. Rigden is a professor of physics at Washington University in St. Louis.