A Brilliant Darkness

Ettore’s friend Werner Heisenberg has sometimes been accused of knowing more about Ettore’s fate than he ever let on. Some even claim that Ettore rejoined Werner in 1938 to give him a helping hand. Because something remarkable happened to Heisenberg six years after Ettore visited Leipzig. He was rehabilitated by the Nazi regime.

In 1933 Heisenberg had opposed Deutsche Physik, leading to a major schism in the regime. God knows what pressures he was under when Ettore visited. He was inevitably against equating relativity with “Jewish physics” and other such imbecilities. But at the same time he was a right-wing ultranationalist and must have been pained at being rejected by such a pro-German movement as the Nazis. By comparison his collaborator Pascual Jordan was enjoying life as a Nazi storm trooper. Ambivalence and a certain jealousy must have been Heisenberg’s feelings toward the regime in the period between 1933 and 1938. Regrettably, his bond to his country and its people was indeed tantamount to a bond with the Nazis.⁷⁴

So in 1939, when the Nazi establishment finally ruled in his favor and against Deutsche Physik, he jumped with open arms at the offer of leading the German atomic project—the so-called Uranium Club.

Later Heisenberg justified himself by saying that under the prevailing winds he was certain Hitler would win the war and Nazism become an unavoidable nuisance. He only wanted to safeguard the values of science and culture under the order of the “Thousand Year Reich.” Poor excuse. Particularly as this was not about Greek philosophy and the solipsism of quantum mechanics—he could have been the reason Hitler won the war. Asked by Hitler’s advisers how big the new bomb being built by his club would be, he replied, “The size of a pineapple” (strange choice of fruit). If Signorina Tebalducci got it right, Ettore was much involved in the fruit salad.

Uranium, I don’t need to tell you, went on to become a major character in this play. Ida Noddack was right when she argued in 1934 that bombarding uranium with neutrons need not produce heavier elements. Instead it causes a dramatic fission into two much smaller pieces (krypton with Z = 36 and barium with Z = 56), releasing a large amount of energy (see Figure E.1). The process was only unambiguously revealed in 1938 and 1939 by Lise Meitner, Otto Hahn, and Fritz Strassmann. Lise Meitner was an Austrian Jew, in a serious predicament after the Anschluss, forcing her to do a runner to Sweden while this important discovery was being made. Thus both sides of the conflict knew about the new phenomenon at first hand.

Yet, uranium had a panoply of further twists in store, and we shouldn’t criticize Fermi too hastily for having missed them. The Boys, of course, had been wrong, but in 1934 nothing heavier than an alpha particle had ever been chipped from a nucleus. Moreover, this made complete sense using the nuclear theory of Ettore and Heisenberg, which everyone revered at the time. A full revision of nuclear theory was required, and I have to wonder how aware of this Ettore might have been, so critical was he of his own work.

In the end, the new theory was provided by Meitner’s nephew Otto Frisch and the not-so-senile Niels Bohr. Surprisingly, uranium behaves like a “liquid drop” when fission takes places (see Figure E.2). But even with this extraordinary revelation, the mystery wasn’t fully solved. Fission was confirmed independently by several groups but the full fission dataset was self-contradictory, particularly concerning the dissimilar actions of fast and slow neutrons. Even the identity of the two fragments wasn’t fully clear (they eventually turned out to be krypton-92; i.e., with A = 92, and barium-141). Uranium was a real mess.

Physicists puzzled and scratched their heads . . . until Niels Bohr—again!—had an epiphany (obviously Carlsberg is good for you). Playing a game of analogies with other elements and the behavior of liquid drops, Bohr remembered that uranium exists in nature as a mixture of two isotopes: about 99.3 percent has A = 238 (Uranium-238) but 0.7 percent has A = 235 (uranium-235). He then understood in a flash that when uranium is bombarded with slow neutrons—such as those first exposed at the Via Panisperna pond—it is the minority component that undergoes fission.

This means that three neutrons had to be emitted; just count the neutron and proton content of mother and daughter nuclei (see Figure E.3). To Bohr’s shock, he realized that these neutrons were then free to restart the process, hitting other uranium nuclei and initiating a chain reaction: 1 fission, 3 fissions, 9, 27, 81, 243, 729, etc. . . . (see Figure E.4). All that was needed was to purify the minority isotope of uranium and to work out the “critical mass” for a chain reaction. The path to Little Boy—dropped on Hiroshima on August 6, 1945—had been unveiled.

Figure E.3: The minority component, uranium-235 (92 protons and 143 neutrons) hit by a neutron splits into krypton-92 (36 protons and 56 neutrons) and barium-141 (56 protons and 85 neutrons.) This leaves three spare neutrons, which are emitted.

Figure E.5: Nonetheless the process long suspected by Fermi also occurs. Uranium-238 does follow the pattern predicted by Ettore’s theory. It absorbs the neutron to then undergo beta decay into neptunium. A few days later, neptunium, in turn, beta decays into plutonium.

Yet, there was a second, even more incredible twist in the uranium plot: Mussolinium exists. Although fission is the main interaction channel, when uranium- 238 is bombarded with slow neutrons it does undergo the process Fermi had suspected since 1934 (see Figure E.5). Ausonium and hesperium are nowadays called neptunium and plutonium. The first decays into the second in a couple of days, but the latter survives tens of thousands of years (but not billions of years, which is why we don’t see it in nature). The “explosive” news was that plutonium, like the minority uranium-235, undergoes fission and chain reaction. When it turned out to be easier to produce plutonium than to purify uranium-235, the route to Fat Man—dropped on Nagasaki on August 9, 1945—was also found.

Which takes us back to Fermi. By 1938, with the racial laws in full swing, life in Rome had become untenable. Learning that he’d been awarded the Nobel Prize, Fermi spent the rest of that day buying expensive watches, as an unobtrusive way to transfer wealth abroad. He went to Sweden with his wife and children to collect the award and then on to an “extended” visit to the United States. He never returned. His father-in-law died in the holocaust. The Fermis resented Italy forever.

Nomadic years followed, as the Fermis remained refugees never sure of their future. Enrico even buried his Nobel Prize money in the basement of his house in New Jersey, not trusting banks not to freeze his assets. He continued his nuclear physics research, first at Columbia, then in Chicago, finally catching up with fission. And thus he became embroiled in the Manhattan Project.

There was never any synergy between Fermi and the United States army. When a first meeting was arranged to raise the army’s awareness of the new weapon, Fermi was announced as, “There’s a wop outside.” More insulting were the ridiculous questions he had to field from the generals. “How can an energy source possibly burn no oxygen?” But “how easy would it be to load the magazine of a rifle with uranium?” And just “how practical would it be to join two subcritical uranium masses to produce a supercritical explosion in the middle of a battlefield?” Meanwhile, Heisenberg was discussing pineapples with a more sympathetic audience. Fermi was quoted as saying, regarding the United States army, that “even if we present them with a ready-made nuclear weapon on a tray, the chances are fifty-fifty they’ll still get it wrong.”

Fermi didn’t believe Bohr’s hypothesis that it was uranium-235 that underwent spontaneous fission with slow neutrons. He was wrong. But it was both a strength and a weakness that Fermi was so pigheaded, because his alternative line of research would prove very fruitful. He set about searching for a chain reaction using unpurified uranium. The critical mass was huge and it would never make a bomb; however, Fermi hit upon the idea of building a “reactor” instead. And after much work he succeeded. Crucially, he found the right neutron moderator—the substance used to slow them down—choosing graphite instead of the more obvious heavy water (i.e., water containing hydrogen with A = 2, or deuterium). He requisitioned enough graphite to supply the entire United States with pencils for a year. But it was far simpler than the complex purification process of heavy water, which the Germans were pursuing.⁷⁵

In a victory of ant over grasshopper, criticality was achieved on February 12, 1942, at 3:25 pm, in what became the first nuclear reactor. The “pile” had been built at the University of Chicago (in a squash court under the football stadium) without much consideration for safety. Fermi was sure that he could control the chain reaction and avoid a disastrous meltdown by judicious use of his beloved slide ruler. Italian pomposity has ever since compared Fermi to Prometheus, who harnessed fire; but I prefer the parallel with his housewife mother, who built her own pressure cooker.

Still, why would a nuclear reactor be so useful at a time of war? This is where the unexpected avenue to Fat Man opened up. A reactor of unenriched uranium had its chain reaction powered by the minority uranium component, but the slow neutrons also interacted with the majority uranium-238. In the process they produced copious transmutations into plutonium, which had a low critical mass for a chain reaction. Here was a choice method to industrially produce large amounts of plutonium, which could then be turned into bombs.

There is little evidence that Fermi ever felt guilty about what he’d done. Later, after the bombs were dropped in Japan, Oppenheimer is reputed to have said that he only felt sorry they hadn’t been used in Germany. No comment, one way or the other, ever emerged from Fermi. He only regretted he’d missed the fission of uranium while in Rome: It humiliated him to his grave; but he was insensitive to more moral pains. He died of stomach cancer, possibly from radiation exposure, at the age of fifty-three.

But perhaps we shouldn’t be so judgmental—those were hard times. And it’s true that the Allied nuclear project was spurred on by the knowledge that the enemy was active in the field. In 1940, Heisenberg understood the physics of fission better than Fermi, in particular the question of uranium isotopes and what to do with plutonium. But in the end he was beaten by a small detail: the neutron moderator. Slowing down neutrons was essential for the success of a reactor. Heavy water was the German choice,⁷⁶ but purifying heavy water is hard (there’s a lot of water available, it’s true, but there’s a lot less heavy water in natural water than there is uranium-235 in natural uranium). Heisenberg never got anywhere with his “uranium machine” apart from an accidental chemical blast (some compounds of uranium are chemically very explosive). The German army at once congratulated him on his success—before he admitted what had actually happened.⁷⁷

Indirectly, however, Heisenberg was essential to the success of the Allied atomic project. Seeing a difficult but open trail leading to the bomb in 1941, he went to consult Bohr, his mentor and father figure, in Copenhagen. Unfortunately, long gone were the days when they roamed the mountains discussing quantum mechanics—Bohr was openly anti-Nazi, as well as half-Jewish. They went for a walk in the park, so that their conversation wouldn’t be bugged. There have been so many contradictory accounts of this meeting that it’s pointless to present any one version. Did Heisenberg ask Bohr for help? Did he try to get intelligence about the other side? Did he promise Bohr that Germany wouldn’t attempt the bomb in exchange for similar assurances from the Allies (suggesting a worldwide physicist strike)? Whatever happened, Bohr was furious and the two had a massive spat. Most likely it was all a big misunderstanding; Heisenberg certainly had to mince his words. But the effect was to convince Bohr (a pacifist) that Germany was close to the bomb, which made him go through the roof and pressure the Allies to move for ward.

Two years later, Bohr was evacuated by the RAF to join the Allied war effort.⁷⁸ A Mosquito bomber, capable of flying at high altitude, was adapted to carry him in its bomb bay. Unfortunately, Bohr forgot to turn on his oxygen and fainted, forcing the pilot to fly at sea level, at grave risk of interception. The plan was to open the bay and let Bohr parachute into the North Sea should the plane be shot down. He’d then be rescued by commandos. In the end no one noticed the Mosquito and this wasn’t necessary. When he traveled to the United States later that year, Bohr saw that his words had been heeded. Nuclear weapons would soon be built.

Physicist Rudolph Peierls said of Heisenberg, “He had agreed to sup with the devil and perhaps found that there was not a long enough spoon.” These were the barbed fruits of quantum mechanics and nuclear theory—but such were the times. I doubt Ettore linked up with Heisenberg or was kidnapped by the Allies. He must have been the only one of the Via Panisperna Boys who was spared tough decisions; all the others must have felt the lack of a long enough spoon. But they reacted to it very disparately—and some of the divisions were unavoidably provoked by the issue of race.

Emilio Segrè, for example, married a German Jewish woman who narrowly missed the holocaust. The two lived in Palermo after he was appointed there, but when the Italian racial laws came into force, Segrè was summarily dismissed. Fortunately this happened while he was visiting and being courted by Berkeley University, so all he and his wife had to do was stay put in California.

During the war, Segrè became a leading figure in the Manhattan Project. After the early “oversight” at Via Panisperna, it’s one of the little twists of fate that he was one of the official discoverers of plutonium, or Mussolinium, as it might have been called. New elements seem to have been one of his life’s obsessions: Before plutonium he discovered the first artificial element, technetium, and he also discovered astatine. In Los Alamos he distinguished himself by proving that Thin Man (a plutonium gun bomb) wouldn’t work; and thus Fat Man was built, saving the United States from the embarrassment of a fizzle over Nagasaki.

After the war, he identified the antiproton, for which he was awarded the Nobel Prize in 1959. He returned to Rome in 1974 where he had a reputation for bragging moronically about his participation in the Manhattan Project. He died at the age of eighty-four, not before having Ettore’s famous letter to him published in the press.

With utter chaos developing in Italy, Edoardo Amaldi came to the United States in 1939 in search of a job. It didn’t work out, and he ended up weathering the war with his family in Italy. After the war, with the Boys disbanded, and in the position of being one of the few physicists without undue fascist associations, he found himself the natural carrier of the beacon—much diminished but not yet extinguished—left by Corbino and Fermi. He was a cofounder of CERN, of which he was president, and he also founded the Italian physics funding body and national laboratory. He spent his later years campaigning for nuclear disarmament, dying at the age of eighty-one in Rome, where he kept his cattedra for forty-one years.

Perhaps more interesting is the later life of Franco Rasetti. Already dissatisfied with physics (as attested by his trip to Morocco during Via Panisperna’s moment of glory), Rasetti became outright disgusted by his colleagues’ involvement in the war effort. He was invited to work on the Manhattan Project, but refused on moral grounds. He pointedly fell out with the rest of the Boys and after the war vehemently opposed all scientific involvement in military technology. When asked why, his standard reply, according to several sources, was, “Because war is stupid.”

Rasetti eventually moved to Canada—that eternal refuge of the sane—until he abandoned physics altogether. Like many other physicists of Ettore’s generation (such as Max Delbruck and Francis Crick, of DNA fame) he moved into biological sciences after the war, becoming first a botanist, then a geologist and paleontologist. He lived to the age of one hundred, dedicating himself “with much satisfaction” to the Cambrian paleontology of Canada, United States, and Sardegna, the botany of the Alps and the Italian orchidaceas. His old-age letters belie a disenchantment with the world and a soft cynicism that must have brought him closer to Ettore than they ever were at Via Panisperna.

In contrast to Rasetti, Ettore’s best friend, Giovanni Gentile Jr., would die very young. He went to Milan as part of the same concorso that sent Ettore to Naples. From then on he was very depressed, possibly because of his friend’s demise, but also due to a liaison with a much older woman who wasn’t kind to him. He was Ettore’s age almost to the day: They often joked that they were twins. He didn’t vanish, but it’s a sad coincidence that he died (of an abscess and subsequent septicemia) at just thirty-five: in March 1942—four years almost to the day after Ettore’s disappearance.

His premature death at least meant he didn’t have to witness the end of fascism and the fate of his father, the brain of the regime. With the 1943 downturn in Italy’s war fortunes and her subsequent invasion by allied forces, Mussolini tried—and failed—to stand up to Hitler and sign a peace treaty. In July 1943, with bombs already falling over Rome, the Italian king finally intervened, recouping his long-lost power and ordering the arrest of Mussolini, to the great joy of the Italian people. The new Italian government then signed a peace treaty with the allies and declared war on Germany. By which point civil war was inevitable.

Freed from jail by SS commandos, Mussolini was put in charge of part of northern Italy, occupied by Germany, in what became known as the Republic of Salò. In this German protectorate his delusions of grandeur returned with a vengeance. Giovanni Gentile Sr. remained loyal to Mussolini and was a leader in Salò. However, in this period he became conciliatory, attempting a reunification of Italy and its academic institutions, speaking passionately of Italian ideals to a nation torn by civil strife. In April 1944, Senator Gentile was assassinated outside his house by a group of partisans posing as philosophy students.

With the advance of the Allies and the growing presence of saboteurs behind the lines, the state of Salò finally collapsed in April 1945. Mussolini and his close assistants were captured and executed by partisans, their corpses displayed in a Milan square, where just a few months earlier a similarly gruesome spectacle had been performed by fascists. Civil war is not pretty. And thus was fascism brought to an end.

A less dramatic casualty of the fall of fascism was Professor Antonino Lo Surdo. Having won what looked like his last battle against Senator Corbino, succeeding him as head of the Physics Department in Rome, he was badly punished for his politics after the war. In the self-satisfied words of Segrè, “He lived to see the collapse of fascism and the waning of the influence he had acquired in the last years of the dictatorship.” Destitute of all power or scientific relevance, he died in 1949, forgotten by all. Were it not for the Mr. North evil-eye jokes, no one would have heard of him today.

Another early member of the party who found himself in trouble after the war was Ettore’s Zio Quirino. He was head of the Italian Physics Society until 1946, when his early fascist associations forced him to resign (he’d joined the party in 1926). He continued to be critical of Einstein’s theory of relativity but never succeeded in disproving the principle of the constancy of the speed of light, despite several attempts. However he did manage to produce a “gravity shielding device” in a series of experiments that have never been reproduced (much to the chagrin of UFO fans). He died in Bologna in 1957 after keeping a low political profile.

But perhaps the only Boy to have a life almost as colorful as Ettore’s was Bruno Pontecorvo, the man who proposed neutrino oscillations and, in the end, opened the gateway to the detection of Ettore’s neutrino. In 1936, Pontecorvo moved to France to work with the Joliot-Curies. Being Jewish, after the establishment of racial laws in Italy he found himself unable to return. He remained in Paris until the Nazis invaded, after which he moved to the United States, where he developed the first industrial application of slow neutrons.⁷⁹ He was never invited to work on the Manhattan Project, due to his outspoken Marxist beliefs.

After the war, however, Pontecorvo worked on the British nuclear project, having become a subject of Her Majesty in 1948. Then in 1950 he went on holiday to Italy, and while there boarded a plane for Stockholm without warning. In Sweden he disappeared, but western intelligence sighted him a few days later near the Soviet border in Finland, surrounded by KGB agents. Was this Ettore all over again? The BBC reported, “The British intelligence service MI5 has been brought into the hunt for missing atomic scientist Bruno Pontecorvo who has not been seen for about seven weeks.”

Confirmation that he had fled, not been kidnapped, came only in 1955 when he appeared at a news conference in Russia. At a time when the exodus across the iron curtain happened overwhelmingly in the opposite direction, his declarations were deeply inflammatory. He explained that he’d moved away from the West because “[the West] was intent on a new war using atomic and nuclear weapons as a means for achieving world domination.”

In the Soviet Union, Pontecorvo became a leading scientist, winning a Stalin Prize and two Orders of Lenin. He worked almost exclusively on neutrinos, proposing the phenomenon of neutrino oscillations that would lead to the solution of the solar neutrino puzzle. He also pioneered experimental research on the Majorana neutrino, resurrecting Ettore’s idea and labeling it the central problem in neutrino physics. Universally known as Bruno Maksimovich, he was famed for attracting hordes of pretty women and leading a happy life in the “socialist” paradise. It was in a Marxist vein that he suggested in his 1972 book that if Ettore had had to earn his bread like the rest of the people, maybe his tragedy would never have happened.

Pontecorvo is the only Panisperna Boy I ever personally met. We encountered one another at the Ettore Majorana Center in 1992, the year before he died and three years after the fall of the Berlin Wall. He had Parkinson’s disease and was in dreadful shape. Over dinner he expressed disillusionment and kept insisting he’d made a terrible blunder when he moved to the Soviet Union. We tried to calm him down, to no avail. He died in Dubna in 1993 at the age of eighty, thoroughly embittered.

This book could not be more open-ended, which is why I had the drive to write it; I hate eternal truths. We don’t know what happened to Ettore, and we don’t know if the neutrino is Majorana. But who cares? As Einstein and Infeld once put it, science is a bad thriller, one in which we never get to know whodunit.

Even if an experiment proved the neutrino to be Majorana, we can be sure that before another hundred years have passed a different experiment will demonstrate that Ettore’s construction is still only a crude approximation. Reality is always far deeper and more complex, and our little steps will inevitably seem naïve and raw with the benefit of hindsight. In this sense the neutrino can never be Majorana. Or Dirac. Or whatever. The lack of a definite answer is not just the end of this book, it’s the name of the game.

And as with the neutrino, Ettore’s story is also elusive. Even if we found out for sure what actually happened to him, we’d never know why he did it—which is far more important. This absence of a final truth shouldn’t sadden us: At least we don’t harbor delusions of omniscience. When I got on that plane to Sicily, I promised myself only this: I won’t raise my leg and urinate over my little territory in Ettoreland; I won’t invent a solution that is not needed.

I would love to know if neutrinoless double beta decay happens; it would be fascinating to board a time machine to that day in March 1938. But access to omniscience wouldn’t solve our problems, it would only create new ones—stressing that it’s only a mirage. I’m happy to live in ignorance as long as an effort has been made; it’s glimpses of temporary answers that spur us onward, creating tension and life. This is no fabricated disbelief. So I might as well tell you what inspired me to write this book: what particular newspaper clipping made me jump on that plane to Sicily. It was a matter of an image.

Bruno Pontecorvo proposed neutrino oscillations from behind the iron curtain, and we have now proved their existence. The sun isn’t sick. A healthy flux of neutrinos emanates from its core, but some oscillate into another reality. Gargantuan experiments have proved this temporary truth all around the world: in Japan, Switzerland, France, Italy, and the United States. One of these projects, the NEMO experiment, uses large masses of seawater, two kilometers beneath the surface off the eastern Sicilian coast, in effect employing a cubic kilometer of deep seawater as a neutrino target. The purity of this water, like the purity of Antarctica ice, makes it an ideal film for a neutrino camera. It’s peaceful down there, at least if you ignore the bioluminescence coming from the occasional abyssal fish.

While the detectors were being lowered into these Faustian depths, scientists were surprised by a cacophony of sonar clicks that couldn’t possibly be caused by neutrinos. Could this be the intangible dark matter? Or something even creepier than Ettore’s neutrino? Many a wild physics theory was proposed, until finally someone had the good sense to call in the marine biologists.

It turned out that the clicking ultrasounds were the characteristic mating signals of sperm whales, an endangered species long thought to be extinct in the Mediterranean. But in fact the hulking mammals had been there all these years, withdrawn into the depths of the ocean, disgusted by life on its surface. The world’s largest toothed animal, carrying the heaviest brain, had sought refuge in the same deep waters that may have welcomed Ettore, if he did commit suicide. Even if he didn’t physically end up there, Ettore certainly moved to a “whales’ world”—to a different planet, emigrated to Mars.

The whales screech in an alien language of peace known only to them, making way for the scientists, who install detectors that might one day prove Ettore’s theory. For decades the whales have been beyond detection. And so has he.