How the Hippies Saved Physics: Science, Counterculture, and the Quantum Revival Page 5
The enrollment-driven pragmatism, so stark in American physics departments after World War II, was anything but a “dumbing down.” The second and third editions of Schiff’s acclaimed textbook, for example, contained homework problems—aimed at entry-level graduate students—that would have stumped leading physicists only a decade or two earlier. The quarter century during which this Cold War style reigned witnessed an extraordinary buildup of calculating skill. All the same, an intellectual trade-off slipped by unnoticed, with wide-ranging implications. For every additional calculation of baroque complexity that physics students tackled during the 1950s and 1960s, they spent correspondingly less time puzzling through what all those fancy equations meant—what they implied about the world of electrons and atoms. The fundamental strangeness of quantum reality had been leeched out.
Not everyone in the United States adopted the mantra of “shut up and calculate” after the war. But the few groups that tried to retain the prewar style rapidly became exceptions that proved the rule. Throughout the hot summer months of 1954, for example, about a dozen physicists gathered in New York City to discuss the foundations of quantum mechanics. Even as most of their colleagues were too busy rewriting their lecture notes, editing their textbooks, and revising their examinations to drop nearly any mention of such interpretive material, this group pressed on, unconvinced that all was well with the central pillar of modern physics.42
More than a fascination with quantum mysteries brought these physicists together. Most shared the same politics as well. The group had been convened by Hans Freistadt, a native of Vienna who had fought in the U.S. Army during World War II. By the early 1950s he was an instructor at the sleepy Newark College of Engineering in New Jersey, the latest stop in his wanderings following his dramatic testimony before the Joint Congressional Committee on Atomic Energy back in 1949. Yes, he had confirmed, he was a member of the Communist Party, and yes, he continued, he had indeed received one of the first fellowships from the Atomic Energy Commission (AEC) to pursue graduate studies in physics. His studies had concerned strictly unclassified material. All the same, the headline-grabbing revelation, and the political firestorm that ensued, nearly ended the AEC fellowship program.43
Joining Freistadt to ponder quantum mysteries in the 1954 discussion group was Byron Darling. Until recently a tenured professor of physics at Ohio State University, Darling found himself out of work after testifying before the House Un-American Activities Committee (HUAC) during its March 1953 investigation of “Communist methods of infiltration” of the educational system. The committee had accused Darling of past membership in the Party; he pleaded the Fifth Amendment. Although he had signed his university’s anti-Communist loyalty oath, had answered every question put to him by the university’s investigating committee, and had stated categorically that he was not nor had ever been a member of the Communist Party, Ohio State dismissed him for failing to answer all of HUAC’s questions. He left Columbus for New York City, where he passed the time during the summer of 1954 talking about possible alternatives to quantum theory with Freistadt and company, before taking up a new post at the University of Laval in Quebec.44
Nearly all the other members of Freistadt’s discussion group shared a clear leftist orientation. Some had even left tenure-track jobs in the United States to work overseas for a few years, returning just in time to join the discussions in New York that summer. Freistadt’s seminar produced two publications, both written by him. The first, published in the Marxist cultural magazine Science and Society before the sessions began, was filled with predictable talk of the “doctrinaire” thinking shown by “modern scientists in capitalist countries,” whose “positivist obscurantism” had landed quantum theory in its current state of “crisis.” The other, a technical review article on a variant of quantum mechanics, was published as a supplement to an Italian physics journal and promptly forgotten for the next twenty years. Fired from jobs or castigated in the media for their alleged political activities, the group members’ politics and their unpopular research interests each marked them as clearly outside the discipline’s mainstream. In that climate, they could find little traction for their work.45
Twenty years later, another informal discussion group convened, likewise bent on exploring the big metaphysical questions raised by quantum mechanics. Like Freistadt’s group, the Fundamental Fysiks Group, established in Berkeley in the spring of 1975, was peopled with physicists on the margins. Yet for all the similarities, the two groups left rather different footprints. Where Freistadt’s group toiled in obscurity, members of the Fundamental Fysiks Group became media darlings, publishing a series of best-selling books and leaving a genuine imprint on physics research and curricula throughout the country.
The divergence in outcomes for the two discussion groups, otherwise so similar in makeup and structure, illuminates how quickly conditions had changed for physicists by the early 1970s. Politics had thwarted the career trajectories of most members of the Fundamental Fysiks Group, but not the personal politics of red-baiting as in Freistadt’s day. Rather, they were caught at the wrong place at the wrong time, bystanders of a systematic political upheaval that rocked the physics profession from top to bottom. Freistadt’s circle had labored on the fringes of boom times for American physicists. By the time members of the Fundamental Fysiks Group found each other, the boom times had turned to bust.
When trouble came for physicists, it came fast. All too quickly, the assumptions that had driven the enrollment boom broke down. As tensions with the Soviets cooled and resources dried up, military patrons and congressional leaders revisited long-standing priorities. No longer did calls ring out to produce scientific “manpower” at all costs. The Pentagon’s return on decades of investment in open-ended basic research—which had justified, and paid for, nearly all graduate training in physics—struck a new generation of analysts as rather lackluster. Years into the slog of the Vietnam War, meanwhile, antiwar protesters grew more brazen, taking over campus buildings and planting pipe bombs, all part of a campaign to force the Pentagon out of the higher-education business. (Physics laboratories provided some of their favorite targets, potent symbols of the “mutual embrace” between academic scientists and military paymasters.) Caught between hardnosed Pentagon accountants on the one hand and raised-fist radicals on the other, physics had nowhere to go but down.46
Nearly every field suffered cutbacks in the realigned political and budgetary landscape, but none more than physics. Since World War II, the discipline had become more reliant than any other on federal funding. When trouble hit, physicists’ enrollments plummeted faster and deeper than any other field: down fully one-third from their peak in just five years, falling to one-half by decade’s end. (Fig. 1.6.) Demand disappeared even more quickly. Records from the Placement Service of the American Institute of Physics tell the grim tale. The service had arranged job interviews between prospective employers and physics students since the early 1950s. As late as the mid-1960s, the service had registered more employers than students looking for jobs. By 1968, the balance had tipped: 989 applicants registered, with only 253 jobs on offer. And then the bottom fell out. In 1971, the Placement Service registered 1053 applicants competing for just 53 jobs.47
Into that state of wreckage trod the young physicists who would form the Fundamental Fysiks Group. Like it or not, they would not follow physics careers like the ones their teachers had enjoyed. The ways and means of being a physicist came unmoored in a way they hadn’t been for two generations. No longer would the attitude of “shut up and calculate” hold sway unchecked. Sitting around the large conference table at the Lawrence Berkeley Laboratory, with few other demands on their time, they sought to recapture the sense of excitement, wonder, and mystery that had attracted them to physics in the first place, just as it had animated the founders of quantum mechanics. They might not have enjoyed secure employment, but they fervently believed one thing: physics could be fun again.
FIGURE 1.6. Num
ber of physics PhDs granted in the United States, 1900–1980. (Illustration by Alex Wellerstein, based on data from the American Institute of Physics and the National Science Foundation.)
Chapter 2
“Spooky Actions at a Distance”
In a theory in which parameters are added to quantum mechanics to determine the results of individual measurements, without changing the statistical predictions, there must be a mechanism whereby the setting of one measuring device can influence the reading of another instrument, however remote. Moreover, the signal involved must propagate instantaneously.
—John S. Bell, 1964
One recent development dominated the Fundamental Fysiks Group’s deliberations: a striking theorem published in the mid-1960s by the Irish physicist John S. Bell. The iconoclastic Bell had long nursed a private disquietude with quantum mechanics. His physics teachers—first at Queen’s University in his native Belfast during the late 1940s, and later at Birmingham University, where he pursued doctoral work in the mid-1950s—had shunned matters of interpretation just as vehemently as their American colleagues did at the time. The “ask no questions” attitude frustrated Bell, who remained unconvinced that Bohr had really vanquished the last of Einstein’s critiques long ago and that there was nothing left to worry about. At one point in his undergraduate studies, his red shock of hair blazing, he even engaged in a shouting match with a beleagured professor, calling him “dishonest” for trying to paper over genuine mysteries in the foundations, such as how to interpret the uncertainty principle. Certainly, Bell would grant, quantum mechanics worked impeccably “for all practical purposes,” a phrase he found himself using so often that he coined the acronym “FAPP.” But wasn’t there more to physics than FAPP? At the end of the day, after all the wavefunctions had been calculated and probabilities plotted, shouldn’t quantum mechanics have something coherent to say about nature?1
In the years following his impetuous shouting matches, Bell tried to keep these doubts to himself. At the tender age of twenty-one he realized that if he continued to indulge these philosophical speculations, they might well scuttle his physics career before it could even begin. He dove into mainstream topics, working on nuclear and particle physics at Harwell, Britain’s civilian atomic energy research center. Still, his mind continued to wander. He wondered whether there were some way to push beyond the probabilities offered by quantum theory, to account for motion in the atomic realm more like the way Newton’s physics treated the motion of everyday objects. In Newton’s physics, the behavior of an apple or a planet was completely determined by its initial state—variables like position (where it was) and momentum (where it was going)—and the forces acting upon it; no probabilities in sight. Bell wondered whether there might exist some set of variables that could be added to the quantum-mechanical description to make it more like Newton’s system, even if some of those new variables remained hidden from view in any given experiment. Bell avidly read a popular account of quantum theory by one of its chief architects, Max Born’s Natural Philosophy of Cause and Chance (1949), in which he learned that some of Born’s contemporaries had likewise tried to invent such “hidden variables” schemes back in the late 1920s. But Bell also read in Born’s book that another great of the interwar generation, the Hungarian mathematician and physicist John von Neumann, had published a proof as early as 1932 demonstrating that hidden variables could not be made compatible with quantum mechanics. Bell, who could not read German, did not dig up von Neumann’s recondite proof. The say-so of a leader (and soon-to-be Nobel laureate) like Born seemed like reason enough to drop the idea.2
Imagine Bell’s surprise, therefore, when a year or two later he read a pair of articles in the Physical Review by the American physicist David Bohm. Bohm had submitted the papers from his teaching post at Princeton University in July 1951; by the time they appeared in print six months later, he had landed in São Paulo, Brazil, following his hounding by the House Un-American Activities Committee (HUAC). Bohm had been a graduate student under J. Robert Oppenheimer at Berkeley in the late 1930s and early 1940s. Along with several like-minded friends, he had participated in freewheeling discussion groups about politics, worldly affairs, and local issues like whether workers at the university’s laboratory should be unionized. He even joined the local branch of the Communist Party out of curiosity, but he found the discussions so boring and ineffectual that he quit a short time later. Such discussions might have seemed innocuous during ordinary times, but investigators from the Military Intelligence Division thought otherwise once the United States entered World War II, and Bohm and his discussion buddies started working on the earliest phases of the Manhattan Project to build an atomic bomb. Military intelligence officers kept the discussion groups under top-secret surveillance, and in the investigators’ eyes the line between curious discussion group and Communist cell tended to blur. When later called to testify before HUAC, Bohm pleaded the Fifth Amendment rather than name names. Over the physics department’s objections, Princeton’s administration let his tenure-track contract lapse rather than reappoint him. At the center of a whirling media spectacle, Bohm found all other domestic options closed off. Reluctantly, he decamped for Brazil.3
In the midst of the Sturm und Drang, Bohm crafted his own hidden variables interpretation of quantum mechanics. As Bell later reminisced, he had “seen the impossible done” in these papers by Bohm. Starting from the usual Schrödinger equation, but rewriting it in a novel way, Bohm demonstrated that the formalism need not be interpreted only in terms of probabilities. An electron, for example, might behave much like a bullet or billiard ball, following a path through space and time with well-defined values of position and momentum every step of the way. Given the electron’s initial position and momentum and the forces acting on it, its future behavior would be fully determined, just like the case of the trusty billiard ball—although Bohm did have to introduce a new “quantum potential” or force field that had no analogue in classical physics. In Bohm’s model, the quantum weirdness that had so captivated Bohr, Heisenberg, and the rest—and that had so upset young Bell, when parroted by his teachers—arose because certain variables, such as the electron’s initial position, could never be specified precisely: efforts to measure the initial position would inevitably disturb the system. Thus physicists could not glean sufficient knowledge of all the relevant variables required to calculate a quantum object’s path. The troubling probabilities of quantum mechanics, Bohm posited, sprang from averaging over the real-but-hidden variables. Where Bohr and his acolytes had claimed that electrons simply did not possess complete sets of definite properties, Bohm argued that they did—but, as a practical matter, some remained hidden from view.4
Bohm’s work had captivated members of Hans Freistadt’s 1954 discussion group, that bunch of bedraggled leftist physicists who dove into quantum physics and philosophy as a welcome break from their run-ins with HUAC and related red-baiters. In fact, Freistadt devoted his long review article to Bohm’s approach to hidden variables. Quite independently, Bohm’s papers fired Bell’s imagination as well. Soon after discovering them, Bell gave a talk on Bohm’s papers to the Theory Division at Harwell. Most of his listeners sat in stunned (or perhaps just bored) silence: Why was this young physicist wasting their time on such philosophical drivel? Didn’t he have any real work to do? One member of the audience, however, grew animated: Austrian émigré Franz Mandl. Mandl, who knew both German and von Neumann’s classic study, interrupted several times; the two continued their intense arguments well after the seminar had ended. Together they began to reexamine von Neumann’s no-hidden-variables proof, on and off when time allowed, until they each went their separate ways. Mandl left Harwell in 1958; Bell, dissatisfied with the direction in which the laboratory seemed to be heading, left two years later.5
Bell and his wife Mary, also a physicist, moved to CERN, Europe’s multinational high-energy physics laboratory that had recently been established in Geneva. Once again he pursued
cutting-edge research in particle physics. And once again, despite his best efforts, he found himself pulled to his hobby: thinking hard about the foundations of quantum mechanics. Once settled in Geneva, he acquired a new sparring partner in Josef Jauch. Like Mandl, Jauch had grown up in the Continental tradition and was well versed in the finer points of Einstein’s, Bohr’s, and von Neumann’s work. In fact, when Bell arrived in town Jauch was busy trying to strengthen von Neumann’s proof that hidden-variables theories were irreconcilable with the successful predictions of quantum mechanics. To Bell, Jauch’s intervention was like waving a red flag in front of a bull: it only intensified his resolve to demonstrate that hidden variables had not yet been ruled out. Spurred by these discussions, Bell wrote a review article on the topic of hidden variables, in which he isolated a logical flaw in von Neumann’s famous proof. At the close of the paper, he noted that “the first ideas of this paper were conceived in 1952”—fourteen years before the paper was published—and thanked Mandl and Jauch for all of the “intensive discussion” they had shared over that long period.6
Still Bell kept pushing, wondering whether a certain type of hidden-variables theory, distinct from Bohm’s version, might be compatible with ordinary quantum mechanics. His thoughts returned to the famous thought experiment introduced by Einstein and his junior colleagues Boris Podolsky and Nathan Rosen in 1935, known from the start by the authors’ initials, “EPR.” Einstein and company had argued that quantum mechanics must be incomplete: at least in some situations, definite values for pairs of variables could be determined at the same time, even though quantum mechanics had no way to account for or represent such values. The EPR authors described a source, such as a radioactive nucleus, that shot out pairs of particles with the same speed but in opposite directions. Call the left-moving particle “A,” and the right-moving particle “B.” A physicist could measure A’s position at a given moment, and thereby deduce the value of B’s position. Meanwhile, the physicist could measure B’s momentum at that same moment, thus capturing knowledge of B’s momentum and simultaneous position to any desired accuracy. Yet Heisenberg’s uncertainty principle dictated that precise values for certain pairs of variables, such as position and momentum, could never be known simultaneously.7