## Metadata - Author: [[Louisa Gilder]] - Full Title: The Age of Entanglement - Category: #books ## Highlights - Bohr shakes his head, smiling: “My life from the scientific point of view passes off in periods of over-happiness and despair…as I know that both of you understand…of feeling vigorous and overworked, of starting papers and not getting them published”—his face is earnest—“because all the time I am gradually changing my views about this terrible riddle which the quantum theory is.” “I know,” says Sommerfeld, “I know.” Einstein’s eyes almost close; he is nodding. “That is a wall before which I am stopped. The difficulties are terrible.” His eyes open. “The theory of relativity was only a sort of respite which I gave myself during my struggles with the quanta.” ([Location 1069](https://readwise.io/to_kindle?action=open&asin=B001MYJ3BU&location=1069)) - James Franck, the beloved experimentalist, described Bohr deep in thought “in the early years”: “One thinks of Bohr when one had a discussion with him. Sometimes he was sitting there almost like an idiot. His face became empty, his limbs were hanging down, and you would not know this man could even see…. There was absolutely no degree of life. Then suddenly one would see that a glow went up in him and a spark came, and then he said: ‘Now I know.’…I am sure it was the same with Newton too.” ([Location 1116](https://readwise.io/to_kindle?action=open&asin=B001MYJ3BU&location=1116)) - Einstein wrote back, “What applies to jokes, I suppose, also applies to pictures and to plays. I think they should not smell of a logical scheme, but of a delicious fragment of life, scintillating with various colors according to the position of the beholder. “If one wants to get away from this vagueness one must take up mathematics. And even then one reaches one’s aim only by becoming completely insubstantial under the dissecting knife of clarity. Living matter and clarity are opposites—they run away from one another. We are now experiencing this rather tragically in physics.” ([Location 1884](https://readwise.io/to_kindle?action=open&asin=B001MYJ3BU&location=1884)) - Against Heisenberg’s wishes, the wave nature of quantum subjects has here overwhelmed their particle nature. Waves do not have a specific position and momentum; these two attributes are linked in exactly the same way that Heisenberg’s principle describes (a wave in a tiny box—a specific position—caroms off its walls in a wild and jumbled mess; a wave left to spread out in the world—a blurred position—has room to have a specific momentum). ([Location 1973](https://readwise.io/to_kindle?action=open&asin=B001MYJ3BU&location=1973)) - But Heisenberg did not want to think about waves at all. About particles, he wrote in his paper, “In the strong formulation of the causal law—‘If we know the present exactly, we can predict the future’—it is not the conclusion but rather the premise which is false.” ([Location 1977](https://readwise.io/to_kindle?action=open&asin=B001MYJ3BU&location=1977)) - Bohr wanted to make it clear that, despite the mild sound of “complementarity,” he was talking about a violent disjunction. We have “only the choice between Scylla and Charybdis”—the boat-crunching rock and the man-eating whirlpool: particle phenomena and wave phenomena—“depending on whether we direct our attention to the continuous [smooth] or the discontinuous [quantized] features of the description.” ([Location 2029](https://readwise.io/to_kindle?action=open&asin=B001MYJ3BU&location=2029)) - The measurement problem is one symptom of the nonseparability of quantum systems; another, to which the conversation naturally turned, is the uncertainty principle—uncertainty is what you get when you try to treat nonseparable things as separate. ([Location 2119](https://readwise.io/to_kindle?action=open&asin=B001MYJ3BU&location=2119)) - “What is it that we human beings depend on? We depend on our words. We are suspended in language,” Bohr famously said years later. “Our task,” he maintained, “is to communicate.” His old friend Aage Peterson explained that “Bohr was not puzzled…by questions as to how concepts are related to reality. Such questions seemed sterile to him.” For Bohr, there was no meaning beyond the fabric of classical words spun, weblike, over the quantum abyss. ([Location 2163](https://readwise.io/to_kindle?action=open&asin=B001MYJ3BU&location=2163)) - Born and Schweitzer meet often in the ensuing days for long tramps in the snow. They talk about physics. They talk about Schweitzer’s hospital where he lives in equatorial West Africa. He is raising money for it by playing Bach throughout Europe for six months. Born, finally, begins to heal. ([Location 2250](https://readwise.io/to_kindle?action=open&asin=B001MYJ3BU&location=2250)) - Rutherford himself in 1920 had predicted a “neutron,” a neutral twin to the (positive) proton, which would solve many of the mysteries of how atoms, especially the heavier ones, held together. James Chadwick, the assistant director of the Cavendish Lab, found this neutron twelve years later, in February 1932. But it was not Pauli’s neutron. He did not give up hope, and neither did Ehrenfest’s student Enrico Fermi, who that year published his great theory of beta decay (an otherwise mysterious change of an atomic nucleus), made possible by what he called Pauli’s “little neutron”—the neutrino. (Nearly a quarter of a century later, half a world away in the postwar Los Alamos labs in New Mexico, the neutrino was found; its finders fired off a telegram to Pauli telling him the good news.) At the Cavendish, back in 1932, two more members of Rutherford’s team—the laconic John Cockcroft, who was known to be working two and a half full-time jobs around the Cavendish simultaneously, and Ernest Walton, a nimble experimentalist who could repair watches—were greasing up a homemade “accelerator” in the former library of the laboratory to do something even more spectacular. In 1928, the twenty-five-year-old Gamow had realized that the proton, because of its wave nature, might tunnel into the nucleus of an atom, splitting it apart—even though, viewed as a particle, it had no chance of doing so. Rutherford stormed good-naturedly in and out, giving orders, encouragement, or distraction, occasionally shocking himself by hanging his wet coat on a live terminal or lighting overdry tobacco and sending it up “like a volcano with a great cloud of smoke, flames, and piles of ash,” as the experimentalist next door to Cockcroft and Walton noticed with amusement. And on either April 13 or 14—Cockcroft and Walton in their notebooks wrote down different dates—he observed the two pieces of a lithium atom hit their fluorescent screen. We’ve split the atom! This jubilant cry was soon heard at the newspapers—the atom, the unsplittable, had been split. Things fall apart; the center cannot hold. ([Location 2517](https://readwise.io/to_kindle?action=open&asin=B001MYJ3BU&location=2517)) - As far as this formalism is concerned, these two atoms, no matter how far they separated, ceased to be individuals after their interaction. “I would not call that one but rather the characteristic trait of quantum mechanics,” wrote Schrödinger, “the one that reinforces its entire departure from classical lines of thought. By the interaction, the two representatives have become entangled.” Thus the word and concept of entanglement entered physics. ([Location 3228](https://readwise.io/to_kindle?action=open&asin=B001MYJ3BU&location=3228)) - In quantum mechanics—which Bohm analyzed in three parts, as quantized motion, statistical causality, and indivisible wholeness—“I came closer to my intuitive sense of nature.” ([Location 3545](https://readwise.io/to_kindle?action=open&asin=B001MYJ3BU&location=3545)) - As Bell had predicted, entanglement was moving with familiar celerity from its previous condition of impossibility to a dismissible state of triviality. ([Location 4671](https://readwise.io/to_kindle?action=open&asin=B001MYJ3BU&location=4671)) - Every step—from the entanglement abstractly inherent in Schrödinger’s wave equation to EPR, when Einstein imagined just what this implied, to Bell’s closer scrutiny, finding a testable conflict, to Horne, Shimony, Clauser, and Holt’s blueprint for bringing that conflict into the lab—was a step closer to incarnation. But this story had so far rested in the hands of the theorists. Nineteen sixty-nine was the year in which the experimentalists took command of the age of entanglement. ([Location 4691](https://readwise.io/to_kindle?action=open&asin=B001MYJ3BU&location=4691)) - Zeilinger, though unusually appreciative of Einstein, Schrödinger, and the man sitting beside him for their clear understanding of “the radical changes in our worldview that quantum mechanics necessitates,” liked the austerity of the Copenhagen interpretation. He was drawn to the idea that the wavefunction might be simply a description of knowledge (or even, in soon-to-be-popular terminology, information), at which point the paradoxes mostly disappear, and it depends on the theorist whether any reality or causes should be sought in the nonlocality or nonseparability beneath this curtain of processing information. Zeilinger, for his part, was beginning to suspect that the lesson of quantum mechanics was that “there is no difference between epistemology and ontology: being and knowing are intertwined.” ([Location 5272](https://readwise.io/to_kindle?action=open&asin=B001MYJ3BU&location=5272)) - of motion as being in different “reference frames”: the classic example compares “the moving-train reference frame” with “the platform reference frame.” And the concept of simultaneity, two things occurring “at exactly the same time,” has meaning only for observers in the same reference frame. ([Location 5708](https://readwise.io/to_kindle?action=open&asin=B001MYJ3BU&location=5708))