The Pope of Physics

by Gino Segrè

  On September 1 and 2, the Italian Council of Ministers announced the expulsion of Jews teaching at any level of Italian schools, including of course universities. Jews who were already attending university would be allowed to complete their studies, but no new Jewish students were allowed to enroll. This was the tipping point for many.

  The Fermis heard the news of the anti-Semitic edict while vacationing in the Dolomites. A heretofore reluctant Laura recognized that this was only the first of many more restrictions to come. She was also familiar with German racial laws that defined children with a Jewish mother as Jewish. Laura agreed, if only for the children’s sake, to immigrate to the United States.

  The first step in making the move was for Fermi to obtain a position at a major American university. On September 4 he wrote letters to four of the country’s leading institutions, carefully mailing each of them from a different resort village lest the sight of all of them addressed to the United States from one small post office arouse suspicion. The decision to immigrate had finally been made, although the destination and other details remained to be decided. The Fermis returned to Rome in mid-September.

  Early responses to Fermi’s inquiries for a position were uniformly positive. Confident that further correspondence would result in at least one mutually acceptable offer, Laura and Enrico began making preparations to leave Italy in January 1939.

  One of the things Fermi had never done, though Bohr had repeatedly invited him, was to attend one of the weeklong informal conferences at the famed Theoretical Physics Institute in Copenhagen. It was a ritual journey made by most nuclear physicists, and Fermi now viewed it as a fitting farewell to Europe. The decision was providential.

  While there, Bohr broke rules of secrecy and divulged to Fermi that he was likely to receive the 1938 Nobel Prize in Physics. Bohr had a valid reason for alerting Fermi. Germany had prohibited its citizens from accepting a Nobel Prize of any sort as a protest for the 1936 Nobel Peace Prize having been awarded to the German dissident Carl von Ossietsky. Given Italy’s and Germany’s rapprochement, Bohr inquired if Italy would similarly force Fermi to reject a Nobel Prize. He assured Bohr that Mussolini had not yet adopted this policy.

  On the way back from Copenhagen, Fermi stopped briefly in Belgium. From there, on October 21, he telegraphed his acceptance of the offer made by the head of Columbia University’s department of physics. The next day he followed up with a letter entreating the chairman not to publicize his acceptance of a permanent professorship “for reasons easily understood.” If the Mussolini government knew of his intent to leave the country permanently, they could throw up barriers to any passport requests.

  Furthermore, he did not want to jeopardize the future of other physicists. It could do harm to Amaldi and the small group of scientists who had made Via Panisperna so vital. His thoughts were also fixed on his country’s Jewish physicists. As he wrote to Columbia’s chair, “Making use of my writing from Belgium, I want to ask about positions for some young Italian physicists who have been deprived of their positions because of the racial laws.” The list of five was Fano, Pincherle, Racah, Rossi, and Segrè—all Jewish. It was an act of thoughtfulness and caring.

  The offer from New York had been the most appealing to Fermi. Appreciative of their strong neutron physics experimental group, Fermi was familiar with the environs, having spent the summer there in 1936. He was also sure Laura would feel more at home in New York City’s cosmopolitan atmosphere than in a small city such as Ann Arbor, Michigan.

  When Fermi returned from his Copenhagen/Belgium trip, he requested a six-month leave of absence from the University of Rome. His public stance was that he would be away at Columbia only for the spring term. The acceptance of a permanent professorship concurrent with a plan of long-term immigration was known only to Rasetti and Amaldi. Fermi also shared with them the prospect of a Nobel Prize.

  Fermi had asked Columbia for a long-term visa for the family, one that would pave the road to permanent residency in the United States. A six-month American tourist visa was still relatively easy to obtain in 1938, although longer than that was difficult for non–northern Europeans. Quotas were not kind to Italians and other “southerners.” Fermi, who prepared meticulously in all matters, did not want to leave anything to chance. Thanks to strong backing from Columbia University, the desired visa was granted.

  With things falling into place, the expected phone call from Stockholm came at six in the evening on November 10. It was official: Fermi had won the Nobel Prize. The citation was read to him over the telephone. He was elated by the acknowledgment; in addition, the prize money would provide a handsome nest egg for settling in the new country.

  It also meant a change of plans. Instead of leaving directly from Italy for New York, the Fermi family would leave a month earlier from England—after the Stockholm ceremonies in December. They would not return to Rome. That way they would not be required to change the prize money into lire and would be able to take the full amount, approximately $45,000, with them, thereby skirting Italian laws stipulating that not more than $50 could be taken out of the country.

  Shortly afterward, having heard the news, the Amaldis and other friends came knocking at the door to lead an exuberant celebration. Ginestra insisted on a feast, which was duly organized and enjoyed. The joy felt by the small group was tempered by other news. The Fermis and their friends had heard it on the radio on that same day.

  On November 11, in banner headlines, Il Corriere della Sera, Italy’s leading newspaper, announced: THE LAWS FOR THE DEFENSE OF THE RACE APPROVED BY THE COUNCIL OF MINISTERS. New civil statutes defined who was a Jew and proclaimed that mixed marriages such as the one between Enrico and Laura were forbidden. Children who had resulted from such a marriage would be regarded as Jews unless they had been baptized before October 1, 1938.

  Simultaneously, the situation in Germany disintegrated. The November 11 New York Times ran a three-column headline, NAZIS SMASH, LOOT AND BURN JEWISH SHOPS AND TEMPLES UNTIL GOEBBELS CALLS HALT. On the two-day rampage of Kristallnacht (Night of Broken Glass), more than a thousand synagogues throughout Germany were burned to the ground. The number of Jews killed in this pogrom, Europe’s worst since the Middle Ages, varies from hundreds to thousands depending on whether one counts direct fatalities or ones in the ensuing year.

  There was no question in either Laura’s or Enrico’s mind that they had made the right decision. They went into high gear now that the Nobel Prize was official. Because of his frequent travels, Fermi had a valid passport, but Laura and the children, ages seven and two, did not. Italian Jews had been ordered to surrender their passports and have race recorded in them, but Fermi, with the help of an influential friend, managed to have his wife’s renewed without the damning notation. This was fortunate because Laura, already nervous, would have otherwise been far more so.

  Fermi had applied to Il Duce for a needed travel permit. Asking about the delay in receiving it, Fermi wrote on December 3 to Mussolini’s private secretary that it would be “a great honor to be received by Il Duce” before his imminent departure for Stockholm and then Columbia University “so I can take eventual directives on actions that I might take in scientific circles of those countries.” The chances of a meeting with Mussolini on three days’ notice were nil. Clearly Fermi was ingratiating himself. He did not want to impart the slightest hint to the Italian government that his exodus would be permanent.

  The day before their departure on December 5, 1938, the Fermis took an extraordinary step. They went to their local parish, named after Saint Roberto Bellarmine, the cardinal inquisitor who had summoned Galileo to Rome in 1616 and ordered him to abandon Copernican notions. The Fermis were about to undergo another kind of conversion. In the presence of the Amaldis and of Edoardo Amaldi’s father, Ugo, Laura was baptized by the parish priest. Then Laura and Enrico were married in a Catholic ceremony. The official document lists Nella and Giulio as having been baptized on February 28, 1936, a week after Giulio’
s birth. In 1936, in the face of Germany’s strict racial laws, it had been considered prudent by many to baptize Jewish children in Italy. Now in 1938, it was prudent to record a Christian marriage. In one fell swoop, the union of Laura and Enrico and the status of their children was legitimized.

  On the morning of the sixth of December, Fermi attended his last faculty meeting. It was announced there that two towering figures of mathematics, Federico Enriques and Tullio Levi-Civita, would no longer be teaching at the University of Rome because they were Jewish. This was another crippling blow for Italy’s contribution to that discipline.

  That evening at nine, the Fermis boarded the train for the forty-eight-hour trip to Stockholm. Only Rasetti and the Amaldis were at the station to see them off. As they boarded, Rasetti said in a subdued tone, “I hope I’ll see you soon.” Amaldi, braced for the separation, had intuited that Fermi would have left Italy even if Laura had not been Jewish. He and Ginestra sadly bade farewell to their dear friends and respective collaborators.

  Fermi had planned for every obstacle. The trip, with the exception of a short delay at the German border, went smoothly. Little Nella, sensing tension when an official slowly examined their passports, was told that everything was fine. During the two long days and nights on the train, her father’s calm demeanor reassured her.

  Fermi received his Nobel Prize from King Gustavus V of Sweden on December 10. In his acceptance, Fermi summarized his work of the previous four-plus years. Describing the Boys’ presumed discovery of transuranics, he said they had found “one or more elements of atomic number larger than 92; we used to call the elements 93 and 94 in Rome with the names of Ausonium and Hesperium respectively.” He added that Hahn and Meitner had been able to trace “elements up to atomic number 96.” All those claims of transuranic elements would soon be proved wrong. Some detractors say Fermi got the Nobel for a faulty discovery. But his years of productive research, particularly showing the world the power of slow neutrons, suggest otherwise. Nevertheless, he never quite forgave himself for his mistake about transuranics.

  The Nobel Prize award ceremony was simpler and shorter than usual because prizes in chemistry, physiology, and medicine were not awarded that year. Only Fermi and Pearl Buck were on the stage, the American author having received 1938’s Literature Prize. At one point in the ceremonies, walking respectfully backward after accepting his prize from the king, Fermi mistakenly almost sat in Pearl Buck’s lap. A quick maneuver on his part saved Buck’s dignity—and his own.

  The Italian press criticized Fermi for not wearing his Royal Academy uniform and for shaking the king’s hand rather than giving him a Fascist salute. They relegated Fermi’s receiving the Nobel Prize to their newspapers’ back pages. An occasion that should been a source of national pride instead almost turned into an embarrassment. The press was pro-Hitler and didn’t want to cover an award shunned by Germans. Fortunately, Fermi did not have to worry anymore about the Italian press, nor about dictates from Fascist officials.

  On December 24, Christmas Eve, the Fermis sailed from Southampton to New York. The underground and the foreign antifascist press had questioned Fermi’s official line that the family was leaving Italy for only six months. They reported that Fermi was leaving Italy permanently because of his wife’s Judaism. A banner headline in the January 4 New York Herald Tribune proclaimed: FERMI, WINNER OF NOBEL PRIZE, TO SETTLE IN U.S. A subhead stated: NOTED PHYSICIST, NOW HERE, LEFT ITALY BECAUSE OF THE RECENT ANTI-SEMITIC LAWS.

  The displeasure from Italy was immediate. The next day, at Il Duce’s demand, Luigi Federzoni, the president of Italy’s Royal Academy and a staunch Fascist, telegraphed Fermi, who had safely arrived on American soil two days earlier. Fermi’s reply was as instantaneous as Federzoni’s inquiry: “I thank you for the courteous communication that surprised me since it is known that my visit to America is in no way connected to racial questions but is determined only by scientific reasons, just like my preceding five visits. Please deny in my name any other interpretation.” Fermi’s rebuttal was forwarded to Mussolini the same day. In his transmittal memo to Mussolini, Federzoni commented that the Nobel Prize winner’s reply was “without special warmth.”

  PART 3

  HELLO, AMERICA

  19

  FISSION

  The very same day, perhaps at the very same hour, that the Fermi family was boarding the ocean liner bound for America, another event took place in Sweden that would forever alter the world’s scientific and human domain. It was predicated on Fermi’s recognition of the power in slow neutrons.

  Two physicists, an aunt and her nephew, were talking and walking in the snowy Scandinavian woods on the day of Christmas Eve. Vacationing together over the holiday, they were on the cusp of discovering the mechanism of fission. Both Lise Meitner and Otto Frisch were Jewish and part of the vast diaspora seeking refuge after the rise of Nazism. Meitner, born in Vienna, received a doctorate in physics at its university, the second woman to have ever done so. She had been in Sweden only a few months, after having escaped from Germany in July 1938. Frisch, who had also studied at the University of Vienna, was the son of Meitner’s sister. He had worked first in Germany, but emigrated once Hitler was elected. For the past four years, Frisch had been conducting nuclear research at the Bohr Institute in Copenhagen.

  When Meitner had moved to Berlin in her twenties, she met Otto Hahn, a young German chemist, and the two of them combined interests in radioactivity. They would collaborate for the next thirty years at the Kaiser Wilhelm Institute for Chemistry. Meitner was charged with establishing a physics branch in the Institute. Within a decade she had been so successful that she became one of the first women to receive the title of Professor.

  In the early 1930s, by now internationally known, Meitner assisted the Rome group in shifting their focus from atomic to nuclear physics. Franco Rasetti remembered her tutelage fondly. “She taught me how to prepare the polonium, how to extract and separate the polonium from radium, how to evaporate it on the beryllium foil and so on.”

  Apolitical like Fermi, Meitner had thought being Jewish would not harm her career and believed her conversion to Protestantism in 1908 had removed it as an issue. She was naïve: being Jewish did make a difference when Hitler came to power in 1933. The Führer’s distinction was racial, not religious. According to Nazi dogma she was a Jew. Since the Kaiser Wilhelm Institute was an independent entity, Meitner’s research continued unimpeded, but her teaching privileges at the University of Berlin, a state-controlled institution, were instantly rescinded.

  For a few years she felt relatively safe as an Austrian rather than a German citizen. That protection ceased after the Anschluss, the March 12, 1938, annexation of her homeland. Her Austrian passport was no longer valid, and Germany, with emigration restrictions in force, would not issue her a new one. On the fourth of July, she was informed that a new policy prohibiting German scientists from leaving would soon be enforced, essentially trapping her. Her appointment at the Kaiser Wilhelm would surely be terminated soon. The vise was tightening.

  Eight days later on July 12, after elaborate planning and clever stratagems, Meitner illegally crossed a remote border into Holland. She had worked at her laboratory until eight that evening, warding off any suspicions about her escape. At age fifty-nine, with only ten German marks in her pocket, she leaped into the void of uncertainty that faced all such refugees. Her only security, other than her formidable talents, was a diamond ring given to her at the last minute by Hahn; it had been his mother’s.

  From Holland, Meitner flew to Copenhagen and continued on to Sweden, where Bohr had arranged a position for her in Stockholm. She was safe, but work would not be the same since the research facilities were far inferior to those she had left behind. When Laura Fermi met her in Stockholm in December, she thought Meitner was “a worried, tired woman with the tense expression all refugees had in common.”

  Meitner shared not only family roots and religion with her young nephew, but al
so—perhaps more important—a love for physics. When Frisch joined Meitner in Kungälv, a small town in southwestern Sweden, on the morning of December 23, 1938, he found his aunt rereading a letter she had received from Hahn three days earlier. She asked her nephew to read it. Meitner had absorbed its contents but was still trying to discern their implications.

  In Berlin, Hahn and his younger associate Fritz Strassmann had been studying the effects of bombarding uranium with slow neutrons. The experiments had revealed an anomalous end product occasionally emerging: a radioactive isotope of barium. Since the barium nucleus has only 56 protons while uranium has 92, this seemed impossible. How could absorbing a neutron cause a uranium nucleus to change by 36 units of electrical charge? Meitner had written back to Hahn immediately, “Your radium results are very startling. A reaction with slow neutrons that leads to barium!” Hahn and Strassmann themselves realized how startling it was to find barium. When they published their finding, they admitted it went against all previous experiences in nuclear physics.

  After he read the letter from Hahn, Frisch told his aunt that Hahn must have made a mistake. She replied that the experienced chemist was too careful for that. But if that wasn’t the case, what did the experiment mean? On December 24, aunt and nephew went out for a walk in the quiet woods near the inn to clear their heads and discuss the incongruity. And there, they came up with a possible solution.

  The conventional picture of the nucleus was that strong interactions create an effective barrier, essentially preventing anything more massive than an alpha particle from exiting. Two protons might escape but not thirty-six.