Pandora's Keepers (6 page)

A tall Scandinavian with a large head and hands, bushy eyebrows, big jowls, and unruly combed-back hair, Bohr had a quiet,
unassuming demeanor that masked a lively and profound mind of great creativity, subtlety, and humanity. He looked rather ponderous,
but when people drew near him his blue eyes sparkled, exuding the warmth and charm of his personality. His great kindness
and reluctance to hurt anyone’s feelings, coupled with his insistence on not letting any inexact or wrong statement pass,
led to his frequent comment: “I am not saying this in order to criticize, but this is sheer nonsense!”
³³

As a talker, Bohr found it very hard to get to the point. He thought of the implications of everything he said so much that
he was unwilling to make any statement without qualifying it. It didn’t help that he spoke in a mumbling voice not much above
a whisper. An equally laborious writer, he preferred talking to writing. He also could be absentminded. But if he sometimes
seemed scatterbrained about what was right before him, Bohr was stunningly acute when it came to what could not be seen. He
possessed a powerful mind and formidable theoretical insight into physical processes.

Bohr was as much a philosopher as a physicist. He loved paradoxes. When faced with an apparently insoluble problem, he always
said, “Every great and deep difficulty bears in itself its own solution. It forces us to change our thinking in order to find
it.”
³⁴
Unlike most physicists of his day, who kept science and moral concerns quite separate, Bohr generalized this concept of “complementarity”
to fields outside of physics, including politics, believing that rational inquiry, conducted in an open society and led by
an informed elite, could harmonize technological progress with humanistic values and smooth out conflicts between nations.
He was also deeply aware of the dangers that scientific innovation could pose to society. This concern, which Bohr felt with
great intensity, was called
der Kopenhagener Geist
(“the Spirit of Copenhagen”) by other physicists. Bohr was widely admired both for his scientific accomplishments and for
his humanity; it was on account of both that he enjoyed immense prestige among physicists.
³⁵

Outside the walls of his Copenhagen institute, Bohr fought his anxiety by working tirelessly on behalf of scientists fleeing
Nazi persecution: finding out who was in need, raising funds to assist them, circulating lists of names to institutions that
might find jobs for them. As the head of the Danish Committee for the Support of Fugitive Intellectuals and Scientists, which
he helped organize in 1933, Bohr had become the head dispatcher of an “underground railroad” that delivered many of Europe’s
most brilliant scientists to Britain and America. Every year, he traveled to both countries to sell “his refugees,” including
a trip to Princeton in the spring of 1939.

Bohr spent his time at Princeton that last spring before World War II analyzing the theoretical implications of fission. The
big question of the moment was whether additional neutrons—what physicists called “secondary neutrons”—were also released
by fission. If they were (and there were enough of them), these secondary neutrons could split still other uranium atoms in
a multiplying chain reaction—proving true the idea that had come to Leo Szilard while walking on a London street back in September
1933.

Bohr hoped a chain reaction was impossible. He began studying the problem with a young Princeton physicist named John Wheeler
in February 1939. He and Wheeler worked in Fine Hall, a Georgian brick pile on Princeton’s campus housing the physics and
mathematics departments. Bohr’s office had bookshelves on one wall, a blackboard on another, and large windows looking out
onto a green lawn on another. Bohr began each day standing at the blackboard. Soon he began drawing and writing equations,
erasing figures with the sleeve of his coat. He probed and stabbed at the bowl of his pipe as he paced his office for hours,
littering the floor with matchsticks. Sometimes he paced the hallway that circled the second floor of Fine Hall, thinking
as he walked. Back in the office, Bohr broke one piece of chalk after another in bouts of furious writing at the board. At
the end of the day, he would lift the edge of the rug on the hardwood floor and kick broken bits of chalk under it. Otherwise,
he would be scolded for messiness by the cleaning lady.

There was a large radio in the common room, and each afternoon at four Bohr would have tea with other faculty members and
all of them would listen intently to news of the intensifying crisis in Europe. War seemed inevitable. Bohr took it all in
with remarkable equanimity. The Western democracies were making the mistakes now, he remarked, but the Nazis would be making
the mistakes in the end.
³⁶

Amid this tension-filled atmosphere, Bohr and Wheeler pondered the secrets of fission, formulating a hypothesis that fit the
known facts. They knew that natural uranium consisted of two isotopes. More than 99 percent of uranium atoms consisted of
an isotope of atomic weight 238, and less than 1 percent were of atomic weight 235. They also knew that elements of odd atomic
weight tended to be less stable than those of even atomic weight. They reasoned then that only the rare isotope U-235 was
fissioning when its nucleus was penetrated by a neutron while secondary neutrons would mostly be absorbed by U-238, which
would not fission. The two isotopes were chemically identical and could be separated only by mechanisms that depended on the
difference in their weight. Since the weights were so close—differing by only three parts in 238—it seemed an impossible task
to separate the two in any meaningful quantities. Bohr was relieved to conclude that a fission bomb could not be constructed
without separation and that the world was safe from destruction after all.

Despite Bohr’s conclusion, Szilard labored to keep the possibility of a chain reaction secret. He felt so strongly about the
need for secrecy that he decided to withhold his own groundbreaking research from publication. Such self-denial was one way,
he thought, of preventing the Nazis from realizing fission’s military potential. Another way was to urge other scientists
to do the same. This was a major departure from the scientific ethos of the day. Science was open; no scientist hid results;
there was no progress without publication. It was quite unaffected by national boundaries.

Szilard learned that neutron experiments were being done by Frédéric Joliot in Paris, so he wrote Joliot, imploring him not
to publish his results. “If more than one neutron were liberated, a sort of chain reaction would be possible,” he confided
to Joliot. “In certain circumstances this might then lead to the construction of bombs which would be extremely dangerous
in general and particularly in the hands of certain governments,” he broadly hinted. Szilard closed the letter, “In the hope
that there will not be sufficient neutrons emitted by uranium, I am…,” but then crossed out this closing, simply signed the
letter, and mailed it.
³⁷
Joliot refused his request, publishing his results in a European scientific journal later that spring.

Undeterred, Szilard approached Fermi, who was working separately on his own neutron experiments. Although the two had started
out together in the Columbia laboratory, it had not worked out—their temperamental differences made collaboration impossible.
Szilard preferred brainstorming to manual labor, whereas Fermi expected everyone to roll up his sleeves. Szilard’s research
assistant at Columbia, Bernard Feld, noted that Szilard made intuitive leaps from Point A to Point D, whereas Fermi moved
methodically from Point A to Point B.
³⁸
Szilard believed neutron research might be applicable to military purposes, whereas Fermi doubted anything militarily useful
would result from it. Szilard was disposed to constantly reevaluate premises; Fermi was by nature cautious and careful.
³⁹

Fermi considered Szilard a brilliant but very peculiar man who enjoyed startling people. He was certainly startled when Szilard
walked into his Pupin Hall office one afternoon and told him that it was his duty to withhold results of his neutron experiments
until it was clear whether they were potentially dangerous. This was especially important, Szilard argued, because astute
reporters had gotten on the trail after Bohr had announced Hahn’s fission results at the Washington conference in early February.
With fission, “hope is revived that we may yet be able to harness the energy of the atom,” the
New York Times
reported on February fifth. The February sixth issue of
Newsweek
also reported on fission. The
Times
’ science correspondent, William Laurence, buttonholed Fermi after a meeting of the American Physical Society at Columbia
on February twenty-fourth, and inquired whether uranium could be used to make an atomic bomb. The unusually long silence that
followed made Laurence feel that he had asked something important.

“We must not jump to hasty conclusions,” Fermi said carefully. “This is all so new. We will have to learn a lot more before
we know the answer. It will take many years.”

How many? Laurence replied.

“At least twenty-five, possibly fifty years,” answered Fermi.

“Supposing Hitler decides that this may be the very weapon he needs to conquer the world,” Laurence persisted. “How long then?”

Fermi was guarded, but to Laurence the implications were clear. Fission meant a chain reaction, and a chain reaction meant
an atomic bomb.
⁴⁰

When Szilard learned from Rabi the next day that Fermi had publicly discussed the possibility of a chain reaction, he was
horrified. He rushed to Fermi’s office; he wasn’t there. Szilard went back to Rabi and asked him to tell Fermi that “these
things ought to be kept secret.”

Szilard sought out Rabi again the following day:

I said to him: “Did you talk to Fermi?” Rabi said, “Yes, I did.” I said, “What did Fermi say?” Rabi said, “Fermi said ‘Nuts!’”
So I said, “Why did he say ‘Nuts!’?” and Rabi said, “Well, I don’t know, but he is in and we can ask him.” So we went over
to Fermi’s office, and Rabi said to Fermi, “Look, Fermi, I told you what Szilard thought and you said ‘Nuts!’ and Szilard
wants to know why you said ‘Nuts!’” So Fermi said, “Well… there is the remote possibility that neutrons may be emitted in
the fission of uranium and then of course perhaps a chain reaction can be made.” Rabi said, “What do you mean by ‘remote possibility’?”
and Fermi said, “Well, ten percent.” Rabi said, “Ten percent is not a remote possibility if it means that we may die of it.
If I have pneumonia and the doctor tells me that there is a remote possibility that I might die, and it’s ten percent, I get
excited about it.”
⁴¹

“We both wanted to be conservative,” Szilard noted, “but Fermi thought that the conservative thing was to play down the possibility
that this may happen, and I thought the conservative thing was to assume that it would happen and take the necessary precautions.”
⁴²

Szilard grew increasingly frantic that spring the more he thought about fission. For weeks he rushed about the Columbia University
labs and faculty offices, bearing witness to the great and dreadful events he foresaw. He was anxious—almost desperate—to
prove or disprove a chain reaction. Half in hope and half in fear, he set up an experiment on the night of March third. The
setting was the vaultlike laboratory on the seventh floor of Pupin. The experiment was designed to reveal pulses on an oscilloscope
that could be expected from the neutrons of split uranium atoms. All Szilard had to do was flip a switch and watch the oscilloscope
screen. If pulses appeared on the screen, it would mean that secondary neutrons were emitted in the fission of uranium—and
that would confirm a chain reaction.

Szilard flipped the switch, saw the dreaded pulses, and watched them for several minutes with mounting horror. Then he flipped
off the switch and walked back in silence to his hotel. “That night,” Szilard later recalled, “there was very little doubt
in my mind that the world was headed for grief.”
⁴³

T
HE SAME NIGHT
that Szilard conducted his experiment at Columbia University proving a chain reaction, he phoned Edward Teller with the ominous
news. Teller remembered the moment vividly many years later. “I was at the piano, attempting with the collaboration of a friend
and his violin to make Mozart sound like Mozart, when the telephone rang. It was Szilard, calling from New York. He spoke
to me in Hungarian, and he said only one thing: ‘I have found the neutrons,’” and hung up.
¹
Teller understood just what Szilard’s laconic message meant. And he shared Szilard’s sense of dread. “All my worries about
nuclear energy—the full realization that it was coming, and coming very soon, and that it would be very dangerous” was clear
to Teller. “My sleep that night was uneasy,” he recalled.
²