Richard Rhodes - The Making of the Atomic Bomb

Sommerfeld brought with him to Göttingen in the early summer of 1922 his most promising student, a twenty-year-old Bavarian named Werner Heisenberg, to hear Bohr as visiting lecturer there. “I shall never forget the first lecture,” Heisenberg wrote fifty years later, the memory still textured with fine detail. “The hall was filled to capacity. The great Danish physicist… stood on the platform, his head slightly inclined, and a friendly but somewhat embarrassed smile on his lips. 435Summer light flooded in through the wide-open windows. Bohr spoke fairly softly, with a slight Danish accent…. Each one of his carefully formulated sentences revealed a long chain of underlying thoughts, of philosophical reflections, hinted at but never fully expressed. I found this approach highly exciting.”

Heisenberg nevertheless raised pointed objection to one of Bohr’s statements. Bohr had learned to be alert for bright students who were not afraid to argue. “At the end of the discussion he came over to me and asked me to join him that afternoon on a walk over the Hain Mountain,” Heisenberg remembers. “My real scientific career only began that afternoon.” 436It is the memory of a conversion. Bohr proposed that Heisenberg find his way to Copenhagen eventually so that they could work together. “Suddenly, the future looked full of hope.” 437At dinner the next evening Bohr was startled to be challenged by two young men in the uniforms of the Göttingen police. One of them clapped him on the shoulder: “You are arrested on the charge of kidnapping small children!” They were students, genial frauds. 438The small child they guarded was Heisenberg, boyish with freckles and a stiff brush of red hair.

Heisenberg was athletic, vigorous, eager—“radiant,” a close friend says. “He looked even greener in those days than he really was, for, being a member of the Youth Movement… he often wore, even after reaching man’s estate, an open shirt and walking shorts.” 439In the Youth Movement young Germans on hiking tours built campfires, sang folk songs, talked of knighthood and the Holy Grail and of service to the Fatherland. Many were idealists, but authoritarianism and anti-Semitism already bloomed poisonously among them. When Heisenberg finally got to Copenhagen at Eastertime in 1924 Bohr took him off on a hike through north Zealand and asked him about it all. “‘But now and then our papers also tell us about more ominous, anti-Semitic, trends in Germany, obviously fostered by demagogues,’” Heisenberg remembers Bohr questioning. “ ‘Have you come across any of that yourself?’” That was the work of some of the old officers embittered by the war, Heisenberg said, “but we don’t take these groups very seriously.” 440

Now, as part of the “unique cooperation” Bohr would speak of, they went freshly to work on quantum theory. Heisenberg seems to have begun with a distaste for visualizing unmeasurable events. As an undergraduate, for example, he had been shocked to read in Plato’s Timaeus that atoms had geometric forms: “It saddened me to find a philosopher of Plato’s critical acumen succumbing to such fancies.” 441The orbits of Bohr’s electrons were similarly fanciful, Heisenberg thought, and Max Born and Wolfgang Pauli, his colleagues at Göttingen, concurred. No one could see inside an atom. What was known and measurable was the light that came out of the atomic interior, the frequencies and amplitudes associated with spectral lines. Heisenberg decided to reject models entirely and look for regularities among the numbers alone.

He returned to Göttingen as a Privatdozent working under Born. Toward the end of May 1925 his hay fever flared; he asked Born for two weeks’ leave of absence and made his way to Heligoland, a stormy sliver of island twenty-eight miles off the German coast in the North Sea, where very little pollen blew. He walked; he swam long distances in the cold sea; “a few days were enough to jettison all the mathematical ballast that invariably encumbers the beginning of such attempts, and to arrive at a simple formulation of my problem.” 442A few days more and he glimpsed the system he needed. It required a strange algebra that he cobbled together as he went along where numbers multiplied in one direction often produced different products from the same numbers multiplied in the opposite direction. He worried that his system might violate the basic physical law of the conservation of energy and he worked until three o’clock in the morning checking his figures, nervously making mistakes. By then he saw that he had “mathematical consistency and coherence.” And so often with deep physical discovery, the experience was elating but also psychologically disturbing:

At first, I was deeply alarmed. I had the feeling that, through the surface of atomic phenomena, I was looking at a strangely beautiful interior, and felt almost giddy at the thought that I now had to probe this wealth of mathematical structures nature had so generously spread out before me. I was far too excited to sleep, and so, as a new day dawned, I made for the southern tip of the island, where I had been longing to climb a rock jutting out into the sea. I now did so without too much trouble, and waited for the sun to rise.

Back in Göttingen Max Born recognized Heisenberg’s strange mathematics as matrix algebra, a mathematical system for representing and manipulating arrays of numbers on matrices—grids—that had been devised in the 1850s and that Born’s teacher David Hilbert had extended in 1904. In three months of intensive work Born, Heisenberg and their colleague Pascual Jordan then developed what Heisenberg calls “a coherent mathematical framework, one that promised to embrace all the multifarious aspects of atomic physics.” 443Quantum mechanics, the new system was called. It fit the experimental evidence to a high degree of accuracy. Pauli managed with heroic effort to apply it to the hydrogen atom and derive in a consistent way the same results—the Balmer formula, Rydberg’s constant—that Bohr had derived from inconsistent assumptions in 1913. Bohr was delighted. At Copenhagen, at Göttingen, at Munich, at Cambridge, the work of development went on.

The bow of the Carpathians as they curve around northwestward begins to define the northern border of Czechoslovakia. Long before it can complete that service the bow bends down toward the Austrian Alps, but a border region of mountainous uplift, the Sudetes, continues across Czechoslovakia. Some sixty miles beyond Prague it turns southwest to form a low range between Czechoslovakia and Germany that is called, in German, the Erzgebirge: the Ore Mountains. The Erzgebirge began to be mined for iron in medieval days. In 1516 a rich silver lode was discovered in Joachimsthal (St. Joachim’s dale), in the territory of the Count von Schlick, who immediately appropriated the mine. In 1519 coins were first struck from its silver at his command. Joachimsthaler, the name for the new coins, shortened to thaler, became “dollar” in English before 1600. Thereby the U.S. dollar descends from the silver of Joachimsthal.

The Joachimsthal mines, ancient and cavernous, shored with smoky timbers, offered up other unusual ores, including a black, pitchy, heavy, nodular mineral descriptively named pitchblende. A German apothecary and self-taught chemist, Martin Heinrich Klaproth, who became the first professor of chemistry at the University of Berlin when it opened its doors in 1810, succeeded in 1789 in extracting a grayish metallic material from a sample of Joachimsthal pitchblende. He sought an appropriate name. Eight years previously Sir William Herschel, the German-born English astronomer, had discovered a new planet and named it Uranus after the earliest supreme god of Greek mythology, son and husband of Gaea, father of Titans and Cyclopes, whose son Chronus with Gaea’s help castrated him and from whose wounded blood, falling then on Earth, the three vengeful Furies sprang. To honor Herschel’s discovery Klaproth named his new metal uranium. It was found to serve, in the form of sodium and ammonium diuranates, as an excellent coloring agent of ceramic glazes, giving a good yellow at 0.006 percent and with higher percentages successively orange, brown, green and black. Uranium mining for ceramics, once begun, continued modestly at Joachimsthal into the modern era. It was from Joachimsthal pitchblende residues that Marie and Pierre Curie laboriously separated the first samples of the new elements they named radium and polonium. The radioactivity of the Erzgebirge ores thus lent glamour to the region’s several spas, including Carlsbad and Marienbad, which could now announce that their waters were not only naturally heated but dispersed tonic radioactivity as well.