by Peter Byrne
Bell observed,
Then there is the surprising contention of Everett and DeWitt that the theory ‘yields it own interpretation.’ The hard core of this seems to be the assertion that the probability interpretation emerges [as the Born rule] without being assumed…. I am unable to see why, although of course it is a perfectly reasonable choice with several nice properties.
Everett penciled: “re-read Proof!”
Channeling Schrödinger’s fear of jellyfishication (lack of preferred basis), Bell wrote,
Thus the structure of the wave function is not fundamentally tree-like. It does not associate a particular branch at the present time with any particular branch in the past any more than with any particular branch in the future.
Everett replied that his branching wave functions were time-reversible: “tree both ways! branching only relative to choice of bases.”
When Bell continued,
And the essential claim is that this does not matter at all. For we have no access to the past. We have only our ‘memories’ and ‘records.’
Everett wrote: “correct” and “still unique measure.”
Dissatisfied, Bell concluded,
The Everett theory provides a resting place for those who do not like the pilot wave trajectories but who would regard the Schrödinger equation as exact. But a heavy price has to be paid. We would live in a present which had no particular past, nor indeed any particular (even if predictable) future. If such a theory were taken seriously it would hardly be possible to take anything else seriously. So much for the social implication.
In the margin, Everett scrawled “?Ha what difference from probabilistic? also no unique past!” (In other words, the efficacy of the Born rule does not require a non-branching past.)
Bell wrote another paper critiquing Everett in 1976. But, overall, he was intrigued by the no-collapse stance—he just could not come to terms with a multiplicity of worlds—and he frankly admitted to not being able to follow Everett’s technical argument on how the classical world of our experience emerges from a superposition of all possible universes.
Bell died in 1990, even as the work of Everett-inspired decoherence theorists5 was starting to gain currency. That such a profound thinker paid serious attention to the many worlds theory was testimony to its growing relevance.
Everett’s nemesis, Leon Rosenfeld, was infuriated.
Rosenfeld’s campaign
In the wake of DeWitt’s high-profile endorsement of Everett in Physics Today, Bohr’s philosophical legacy was in jeopardy. His amanuensis, Rosenfeld, viewed the ascendancy of Everett’s theory as the tip of a poisoned spear aimed at the heart of Copenhagenism. After reading Bell’s preprint on Everett, Rosenfeld grabbed for his pen, horrified that a physicist of Bell’s stature was taking the idea of a universal wave function seriously.
My dear Bell,
Many thanks for the preprint of your last paper which I did read because you are one of the very few heretics from whom I always expect to learn something, and, indeed, I found this new paper of yours exceedingly instructive. To begin with, it is no mean achievement to have given Everett’s damned nonsense an air of respectability by presenting it as a refurbishing of the idea of preestablished harmony.6 … Is it not complacent of you to think that you can contemplate the world from the point of view of God?7
Bell’s critical analysis of Everett was distressing to Rosenfeld, but he was utterly appalled when Frederick J. Belinfante of Purdue University wrote in partial favor of the relative state heresy.
In the basement archive, there are yellowing typescripts of two papers on quantum measurement written by Belinfante. Everett read them, penciling comments. These papers formed the core of a book published by Belinfante in 1975 on quantum measurement and time reversal.8 “Measurements in Objective Quantum Theory” attempts to salvage the standard interpretation of wave function collapse in quantum mechanics by claiming to solve the measurement problem with help from Everett. To achieve this (supposed) feat, Belinfante employed a “re-interpretation” of Everett, which excluded branching universes and a universal wave function.
Leon Rosenfeld, date unknown.
Using a “technically ingenious” argument,9 Belinfante claimed that Everett eliminated the contradiction between the Schrödinger equation and wave function collapse by showing the irreversibility of memory records. For Belinfante, Everett’s relative states formulation was a “handy tool” for making predictions without having to call upon a postulate of wave function reduction.
But he cast aside Everett’s universal wave function, reinterpreting his theory:
The essential point is that the universe as we know it is just one arbitrary member of an entire ensemble of universes, and that the laws of physics are probability laws for this big ensemble, and therefore are not determinate for ‘our’ universe.10
Everett scrawled his view of Belinfante’s reinterpretation: “Nonsense.” But when Belinfante said it was not necessary to accept von Neumann’s wave collapse postulate, as Everett obtained the same measurement result using his non-collapse model, he cheerfully inscribed: “right on.” And where Belinfante critiqued Mott’s explanation of a single track emerging from a spherical wave by a process of wave reduction, Everett made an approving check mark.
After crediting Everett for breaking ground on the measurement problem, Belinfante disparaged the core of the many worlds theory, “not claiming that it would be illogical, but stressing its unpracticability and its superfluousness.” Echoing a sentiment evinced by many of those who have studied Everett, Belinfante remarked, “It is impossible to say that this point of view would be definitely wrong (i.e. illogical). Most people ‘do not like it.’” His main objection was that “Everett’s claim that his ψ would describe the universe is a hoax, and fortunately is a hoax,” because it is impossible to calculate a universal wave function in real life.
In a series of semi-hysterical letters written to Belinfante during the summer of 1972 (after he read Belinfante’s preprint), Rosenfeld labeled Everett’s “heresy” a “muddle,” commenting,
With regard to Everett neither I nor even Niels Bohr could have any patience with him, when he visited us in Copenhagen more than 12 years ago in order to sell the hopelessly wrong ideas he had been encouraged, most unwisely, by Wheeler to develop. He was undescribably [sic] stupid and could not understand the simplest things in quantum mechanics…. I would suggest that Occam’s Razor could be most profitably used to rid us of Everett or at least his writings.11
In a subsequent letter,12 he railed against the “pitfall” of trying to “rescue” Everett’s “wooly thinking.” But a few months later, Rosenfeld reconsidered his opposition:
As to the case of Everett, I see your logical point, and have therefore to grant you unrestricted right to adopt Everett’s point of view for the sake of argument.13
He relented because he realized that Belinfante had modified Everett’s theory to support an interpretation that it in no way supports. Of Belinfante’s modifications, Everett scrawled, “baby with wash.”
Ultimately, Belinfante’s “translation” of Everett did not take off, not the least because he attempted to resolve the inconsistencies in his own approach by arguing that quantum indeterminacy is evidence for the existence of God.14
Pulp science fiction
By the mid 1970s, Everett’s theory was becoming a touchstone for physicists exploring non-collapse approaches. By 1980, it was widely considered to be one of most important papers ever written on quantum measurement. Whether or not one agreed with the reality of multiple universes, the genie was uncorked: the monocracy of the Copenhagen interpretation had been rudely and successfully challenged, and branching universes were no longer figments of science fiction.
As physicist Wojciech Zurek, a pioneer in decoherence theory, says, “Everett gave us permission to think about the universe quantum mechanically.”15
Even physicists who think that branching universes are bunk cr
edit Everett with exposing the illogic of Bohr’s ontological divide between the microscopic and the macroscopic—as making the quantum world real.16
Everett’s small collection of annotated physics papers is a firm indication that he was proud of his theory. He seldom spoke of his achievement, but he was undoubtedly delighted by its rebirth. He remained perplexed that the best minds in physics could not follow his derivation of the Born Rule from the quantum formalism; but not perplexed enough, unfortunately, to work on improving the theory.
In his library he kept a book by British cosmologist P. C. W. Davies. He made the checkmark of approval by Davies’ brief description of his theory as based on increasing and decreasing entropy.17 And not long before he died, he bought a copy of The Dancing WuLi Masters, An Overview of the New Physics, by Gary Zukov. In it, he flagged the pages explaining the “Everett-Wheeler-Graham” theory of many worlds as mystical, although he had stated firmly that his theory was “unmystical.”
His joy overflowed in December 1976 when the pulp science fiction magazine Analog ran a four-page article (“The Garden of the Forking Paths”) explicating the “Everett-Wheeler” interpretation, largely drawn from DeWitt’s Physics Today article.
Everett ordered multiple copies of the magazine, sending them to friends, including Wheeler, who had already begun to publicly dissociate himself from the many worlds interpretation. Being praised in Analog probably added salt to Wheeler’s festering wound. The article was in a section called “Quantum Physics and Reality.” It ended with a quote from Jorge Luis Borge’s story, The Garden of Forking Paths, the same quote that had inspired Cooper and, also, graced the preface of The Many Worlds Interpretation of Quantum Mechanics:
… a picture, incomplete yet not false, of the universe as Ts’ui Pên conceived it to be. Different from Newton and Schopenhauer, … [he] did not think of time as absolute and uniform. He believed in an infinite series of times, in a dizzily growing, ever spreading network of diverging, converging and parallel times. This web of time—the strands of which approach one another, bifurcate, intersect or ignore each other through the centuries – embraces every possibility. We do not exist in most of them. In some you exist and not I, while in others I do, and you do not, and in yet others both of us exist. In this one, in which chance has favored me, you have come to my gate. In another, you, crossing the garden, have found me dead. In yet another, I say these very same words, but am an error, a phantom.18
34 Austin
[My] theory is therefore capable of supplying us with a complete conceptual model of the universe, consistent with the assumption that it contains more than one observer.
Hugh Everett III, 19561
Spring, 1977
Shortly after Wheeler relocated to the University of Texas in Austin, he and DeWitt invited Everett to give a seminar on the many worlds interpretation. Even though he loathed public speaking, Everett was excited: In April, he packed Nancy, Liz, and Mark into his second-hand Cadillac Seville and drove from Virginia to a motel.
While their father in Austin lectured, Mark and Liz tooled about in a VW Beetle drinking beer with a soldier friend of Liz’s stationed nearby.2
The talk packed the university hall with curious students and teachers. An exception to the school’s no-smoking policy was made for Everett. Dressed in his trademark black suit, he explained the basics of the theory, answering questions in a staccato voice as he paced back and forth, chain smoking and gesticulating. At one point he went off on a tangent to promote Pugh’s recently published book on the biological origin of human values.
In an after-talk lunch at a beer-garden, a young, British graduate student named David Deutsch sat next to Everett. He was researching quantum gravity with Wheeler and DeWitt. DeWitt had introduced him to Everett’s theory, and after first disbelieving it, Deutsch became one of its firmest advocates. He is now recognized as a pioneer in the field of quantum computation, which, he argues, is made possible by the existence of many universes.3
Deutsch recalled that Everett was,
Full of nervous energy, high-strung, extremely smart, very much in tune with the issues of the interpretation of quantum mechanics despite having left academic life many years before. I find that this is unusual: normally, people who leave become ‘rusty’ in time.
He was extremely enthusiastic about many universes, and very robust as well as subtle in its defense, and he did not speak in terms of ‘relative states’ or any other euphemism.
Deutsch asked him about the preferred basis problem. Everett said he did not think the question of how a preferred basis emerges was a problem; each universe, he said, is defined by the energetic structure of its system as a whole. In other words, the preferred basis is not something extra that you have add to the formalism, it emerges out of the theory naturalistically.4 Deutsch is not alone in holding that the entanglement of a quantum system with the larger environment—the decoherence phenomenon—solves the preferred basis problem in the many worlds theory, not the least by prohibiting communication between branching—or decohering—universes.
Deutsch did not ask his lunch partner about the related problem of his derivation of probability; but he eventually agreed with DeWitt that Everett’s probability measure did not work; he has several times tried to improve upon it. In recent years, Deutsch, who works with the University of Oxford’s Center for Quantum Computation, has teamed up with a vibrant group of “Everettians” in the department of philosophy. Together, they are tackling the many worlds interpretation, searching to bridge gaps in the theory and, perhaps, to develop a new theory of quantum probability.
Only on Tuesdays
Returning to McLean, the Everetts invited the Misners over to celebrate the latter’s 18th wedding anniversary. After numerous cocktails, Everett and Misner (pushed by Susanne Misner) made the rambling tape recording where Everett recollected the origins of his theory. He said that Wheeler had recently “confessed” to him that he reserved the right to disbelieve the many worlds theory once a month, on a Tuesday. Wheeler was being circumspect. He had already taken pains to distance himself from Everett, and he was about to publicly disown him in a series of papers called “Law Without Law.”
Years later, Deutsch cut to the chase:
Wheeler told me that he was always implacably opposed to the theory—what he supported was Everett. He wanted Everett’s idea to become known, not because he thought it was true, but because it was a jumping off point to look at the logic of wave collapse, which Wheeler did not think was the right approach to the measurement problem.5
Shortly after the Austin trip, Paul Benioff, a researcher at the Argonne National Laboratory in Illinois sent Wheeler a paper critiquing the mathematics of the “Everett-Wheeler” derivation of probability as “vacuous.” Wheeler forwarded the paper to Everett along with a copy of his reply to Benioff, which noted,
The point you make is obviously important … I should add that Everett’s Princeton PhD thesis was on a topic entirely conceived by him and ought to be called the Everett Interpretation not the Everett Wheeler Interpretation. Though I have difficulty subscribing to it today, I still feel it is one of the most important contributions made to quantum mechanics in recent decades.6
Everett circled the word “difficulty,” scrawling “only on Tuesdays.” A few weeks later, Wheeler copied Everett on another letter to Benioff7 (who had written a second paper on the many worlds theory) asking him to please stop referring to the Everett-Wheeler theory. For Benioff’s edification, he enclosed a reprint of his new paper (dismissing Everett’s theory), “Include the Observer in the Wave Function?”
Everett was incensed; he slash-penciled corrections all over Benioff’s first paper, which examined the many worlds probability measure from Graham’s point of view, not from Everett’s. Everett wrote: “I made identification with Mathematics of Probability, and short-circuited all such nonsense. Only understanding of isomorphism is required!” Once again, his derivation of the Born rule was not b
eing understood. Asked to referee Benioff’s paper for Foundations of Physics, Everett drafted a reply letter rejecting it “in toto.” Then he (diplomatically) revised the letter, saying that he did not have time to review it.8
A year after the Austin trip, Nancy drafted a letter to Wheeler, thanking him for forwarding the Benioff papers and letters, and apologizing for her husband’s inability to correspond with him. She never mailed this letter.9 Another year passed, and one evening the Everetts watched Wheeler host a PBS television show on Einstein. Inspired, Nancy picked up the old draft, slightly rewrote it, had Everett sign it, and mailed it off.
It was an odd letter, written in the third person. It read, in part,
There are two things about Hugh that perhaps need clearing up. One is, tho’ it appears he plays hard-to-get by refusing to correspond, the truth is, he feels the written word is totally inadequate in comparison to a one-to-one conversation. This is why the meeting in Austin two years ago with Bryce DeWitt, [and Deutsch] was such a great thing for him to participate in….
Far from being totally unconcerned, Hugh may even feel some gratification to be receiving a small measure of recognition for his work done under your counsel…. Now we read in Physics Today that even more is being done to expedite the flow and exchange of ideas what with the Institute forming in Santa Barbara. (Hugh always thought Santa Barbara a lovely spot).10