The Many Worlds of Hugh Everett III: Multiple Universes, Mutual Assured Destruction, and the Meltdown of a Nuclear Family

by Peter Byrne

  He asserted that experimental results have no meaning in Everett’s scheme; and that, “He talks of correlation but can never build that up by ψ [wave functions].” Everett penciled next to this statement, “Obviously hasn’t completed reading of thesis! It does just that.”

  Also in May, Alexander Stern, an American physicist-engineer in residence at Bohr’s institute, wrote to Wheeler saying he had just given a seminar on Everett’s “erudite, but inconclusive and indefinite paper,” and that Bohr had opened the discussion. Reflecting the tenor of that discussion, Stern commented that Everett,

  lack[s] an adequate understanding of the measuring process. Everett does not seem to appreciate the FUNDAMENTALLY irreversible character and the FINALITY of a macroscopic measurement…. It is an INDEFINABLE interaction.”13

  Stern flatly stated that wave collapse does not contradict the Schrödinger equation—as if the construct of wave collapse was included in the complementary model. Without bothering to comment on Everett’s technical arguments, he asserted that Everett’s “preconceived model of the universe” was “untenable.” And he objected to the claim that observers can be replaced by servo-mechanisms. In response to a suggestion made by Wheeler (in a previous letter to Stern) that physics needs to develop mathematical models akin to game theory, “that will include the observer,” Stern pointed out that behavioral decisions made in games are inherently subjective, whereas measurement in physics is objective. But it was the determinism of Everett’s theory that was grounds enough for dismissing it without further ado. Stern said that by “exclud[ing] probability from wave mechanics [he fails to] understand the concept of ‘observer.’” For Stern, as for Bohr, the macroscopic observer is by definition external to the microscopic quantum system observed. Therefore, complained Stern: “Wave mechanics without probability excludes physicists.”

  Blinded by his assumption that measurement requires an external observer, Stern failed to appreciate that Everett was totally eliminating the role of external observation so crucial to Bohr’s interpretation. He concluded:

  If Everett’s universal wave equation demands a universal observer, an idealized observer, then this becomes a matter of theology … The subjective aspect of physics, which some scholars and philosophers have claimed to detect but have not understood, has its origin in the fact that physics must make contact with reality which is, after all, the way the world appears to us, and can be understood by us.

  Like many of Everett’s critics, past and present, Stern was troubled by Everett’s treatment of the Born probabilities as non-objective features of the universe:

  I do not follow him when he claims that … one can view the accepted probabilistic interpretation of quantum theory as representing the subjective appearances of observers.

  For Stern, indeterminism was quantum mechanics; he was not prepared to accord any validity to a theory that challenged the status quo, simply on the basis that it was not the status quo.14

  Within Everett’s basement archive are two pages of “comments” on Stern’s letter:

  Technically, ‘observer’ can be applied to any physical system capable of changing its state to a new state with some fairly permanent characteristics which depend upon the object system (with which it interacts), i.e., any measuring apparatus could be called observer …

  Stern’s remarks about [my] misunderstanding of [the] fundamental irreversibility of [the] measurement process indicate rather clearly that he has had insufficient time to read the entire work. Several rereadings on his part seem to be called for. Also, Stern is quite guilty in these remarks of begging the question – one of the fundamental motivations of the paper is the question of how can it be that [many] measurements are ‘irreversible,’ the answer to which is contained in my theory, but is a serious lacuna in the other theory.

  Wheeler had seriously miscalculated: Bohr and his circle were not even remotely open to such a radical idea as a universal wave function. In a lengthy and conciliatory letter, Wheeler replied to Stern:

  I fully recognize that there are many places in Everett’s presentation that are open to heavy objection, and still more that are subject to misinterpretation…. I would not have imposed upon my friends the burden of analyzing Everett’s ideas … if I did not feel that the concept of ‘universal wave function’ offers an illuminating and satisfactory way to present the content of quantum theory. I do not in any way question the self consistency and correctness of the present quantum mechanical formalism when I say this.

  On the contrary, I have vigorously supported and expect to support in the future the current and inescapable approach to the measurement problem. To be sure, Everett may have felt some questions on this point in the past, but I do not. Moreover, I think I may say that this very fine and able and independently thinking young man has gradually come to accept the present approach to the measurement problem as correct and self consistent, despite a few traces that remain in the present thesis draft of a past dubious attitude.

  So, to avoid any possible misunderstanding, let me say that Everett’s thesis is not meant to question the present approach to the measurement problem, but to accept and generalize it.15

  Wheeler went on to clarify that in Everett’s theory there is no such thing as an external observer. Mounting a spirited defense, he equated Everett’s universe to the deterministic universe of Laplace, with the caveat that,

  No one seriously believed that it would be a practical possibility ever to know at one moment the position and velocity of every particle, but it was convenient to postulate that these quantities nevertheless had well-defined values.16

  Likewise with Everett’s universal wave function, which, in theory, contains the coordinates of every particle in the universe.

  Wheeler insisted that the logical consequences of the theory were, for the time being, confined to a mathematical “model for our world,” which, in his opinion, had not yet been shown to physically correspond to the real world. The question of the reality or unreality of that correspondence was what Wheeler was urging Everett and Bohr to struggle out, in accord with one of Wheeler’s favorite sayings, “The kind of physics that occurs does not adjust itself to the available words; the words evolve in accordance with the kind of physics that goes on.”17

  Wheeler copied Everett on his reply to Stern, attaching another pedagogical warning,

  I have no escape from one sad but important conclusion: that your thesis must receive heavy revision of words and discussion, very little of mathematics, before I can rightfully take the responsibility to recommend it for acceptance…. I feel that your work is most interesting and am sure that it will receive discussion of a scope comparable to that which has attended Bohm’s publications. But in your case I must ask that the bugs be got out and the sources of misunderstanding be clarified before the job is made public, not afterwards.

  I hope you will realize that I mean this as what is called here your ‘promoter,’ and one actively interested in your reputation and promising future.18

  Continuing his flurry of letter writing, Wheeler wrote to Allen Shenstone, chairman of the physics department at Princeton,

  I think [Everett’s] very original ideas are going to receive wide discussion…. Since the strongest present opposition to some parts of it comes from Bohr, I feel that acceptance in the Danish Academy would be the best public proof of having passed the necessary tests.19

  Wheeler reported to the National Science Foundation:

  I have to say that I am more and more impressed by Everett’s originality, mathematical ability, talent for expressing himself clearly orally and in writing, and self-sustaining research drive. His thesis … develops an idea quite original with him, to treat the problem of observation in quantum mechanics by including the observer himself within the framework or the mathematical formalism. Then the equations themselves become completely deterministic and the unavoidable indeterminism of all quantum systems comes in on a much more subtle level. The mathematics h
as many new features …. [but the] interpretation and the words that go with the formalism to show how to use it and what it means, make a much more difficult problem….

  I feel Everett’s very original work is destined to become widely known…. I think of Everett as an example of a National Science Fellowship at its best. The man has an independent status, with no boss to tell him what to do. He is working side by side with the faculty in the pursuit of learning. He is an independent scholar in his own right.20

  And he mailed Bohr a copy of “Septet of Sibyls,” enclosed with a note telling his mentor that he had urged Everett, “to discuss the issues with you directly and arrive at a set of words to describe his formalism.”21

  The situation was delicately balanced. Wheeler was proceeding full steam preparing for the upcoming Chapel Hill conference on quantum mechanics and general relativity, and he wanted to highlight the universal wave function. But if Bohr was adamantly against it, he would have trouble showcasing it. Unfortunately, Everett was getting ready to start working at the Pentagon, and he was not eager to rewrite his thesis.

  As May wound down, Petersen sent Bohr’s copy of Everett’s dissertation back to Wheeler with a note suggesting that Bohr would soon write to him “about his attitude regarding the epistemological situation in quantum physics and especially about the status of the observers in the complementary mode of description.”22 Obviously, Bohr and Petersen were more concerned with correcting Wheeler’s deviation than in becoming convinced by him that Everett was correct, or, worse, that Bohr’s philosophy of physics was wrong.

  Wheeler and Everett conferred by telephone in late May, and Everett agreed to visit Bohr with the caveat that he had to return to Washington to start work at the Weapons Systems Evaluation Group by June 15. Wheeler cabled Bohr with this news. Petersen cabled back that a “longer stay is desirable.” He also wrote to Everett explaining that, “It would be very helpful to us if, as a background to your criticism, you gave a thorough treatment of the attitude behind the complementary mode of description and as clearly as possible stated the points where you think this approach is insufficient.”23

  Referring to Petersen’s request that he bone up on complementarity, Everett replied: “I have not done this yet, but while I am doing it you might do the same for my work.” He said he’d like to visit Copenhagen in a few months, and that he was enclosing another copy of his thesis, since,

  Judging from Stern’s letter to Wheeler … there has not been a copy in Copenhagen long enough for anyone to have read it thoroughly, a situation which this copy may rectify. I believe that a number of misunderstandings will evaporate when it has been read more carefully (say 2 or 3 times).24

  Everett was not to get to Copenhagen for three years. And when he did, the meeting with Bohr was, as he recalled at the cocktail party, “that was a hell of a—doomed from the beginning.”25

  18 The Battle with Copenhagen, Part II

  Physicists are to some extent sleepwalkers, who try to avoid [interpretive] issues and are accustomed to concentrate on concrete problems. But it is exactly these questions of principle which nevertheless interest nonphysicists and all who wish to understand what modern physics says about the analysis of the act of observation itself…. The heart of the matter is the difficulty of separating the object and the observer.

  Fritz London, Edmond Bauer, 1939.1

  In the summer of 1956, Everett took a job with the top secret Weapons Systems Evaluation Group at the Pentagon. Gore became pregnant and they married. Shortly after the January 1957 conference on gravitation at Chapel Hill (which Everett did not attend), he got together with Wheeler to edit and condense the dissertation,2 making it, in the professor’s phrase, “javelin proof.”3

  In March, preprints of the truncated dissertation and Wheeler’s supporting article were sent to a score of prominent physicists, including Bohr, Schrödinger, Oppenheimer, Rosenfeld, and Wiener. A few weeks later, Bohr dropped Wheeler a note,

  I have not found time to write to you and Everett about the papers you kindly sent me. It appears that the argumentation contains some confusion as regards the observational problem and … Aage Petersen will write to Everett about our discussions.4

  Days later, Petersen wrote to Everett,

  As you can imagine, the papers have given rise to much discussion at the Institute…. I think that most of us here look differently upon the problem and don’t feel those difficulties in quantum mechanics which your paper sets out to remove. Accordingly, we cannot agree with you and Wheeler that the relative state formulation entails a further clarification of the foundations of quantum mechanics.5

  Petersen was adamant: there was no point in talking about a measurement problem because it is irrelevant:

  There can on this view be no special observational problem in quantum mechanics – in accordance with the fact that the very idea of observation belongs to the frame of classical concepts…. There is no arbitrary distinction between the use of classical concepts and the formalism since the large mass of the apparatus compared with that of the individual atomic objects permits the neglect of quantum effects which is demanded for the account of the experimental arrangement….

  Of course, I am aware that from the point of view of your model-philosophy most of these remarks are besides the point. However, to my mind this philosophy is not suitable for approaching the measuring problem. I would not like to make it a universal principle that ordinary language is indispensable for definition or communication of physical experience, but for the elucidation of the measuring problems hitherto met with in physics the correspondence approach has been quite successful.6

  So now we have the curious situation in which Wheeler and Everett had cut nearly three-quarters of the original paper. The chapter on information theory was gone. (Stern had thought this chapter to be the “best in the book.”) Much of the colorful language that Everett used to bring his theory alive in “ordinary” terms was excised, as was his criticism of Bohr. The edit did clarify the significance of applying a universal wave function to gravitation. In fact, the revised dissertation was reframed as, “the task of quantizing general relativity,” which had not been Everett’s primary goal. But fearful for his doctorate, Everett allowed Wheeler to basically dictate what was to remain intact of his original thesis, while removing all mention of splitting. And now Bohr, through Petersen, was complaining that the math was not explained in terms of ordinary language, the language of classical physics, Copenhagen-speak.

  Everett replied to Petersen, angrily,

  Lest the discussion of my paper die completely, let me add some fuel to the fire with …. criticisms of the ‘Copenhagen interpretation.’ First of all, the particular difficulties with quantum mechanics that are discussed in my paper have mostly to do with the more common (at least in this country) form of quantum theory, as expressed for example by von Neumann, and not so much with the Bohr (Copenhagen) interpretation. The Bohr interpretation is to me even more unsatisfactory [with its] strange duality of adhering to a ‘reality’ concept for macroscopic physics and denying the same for the microcosm.

  Now I do not think you can dismiss my viewpoint as simply a misunderstanding of Bohr’s position…. I believe that basing quantum mechanics upon classical physics was a necessary provisional step, but that the time has come … to treat [quantum mechanics] in its own right as a fundamental theory without any dependence on classical physics, and to derive classical physics from it …. We should no longer regard quantum mechanics as a mere appendage to classical physics tacked on to cover annoying discrepancies in the behavior of microscopic systems.

  Let me mention a few more irritating features of the Copenhagen Interpretation. You talk of the massiveness of macro systems allowing one to neglect further quantum effects (in discussions of breaking the measuring chain), but never give any justification for this flatly asserted dogma. [And] there is nowhere to be found any consistent explanation for this ‘irreversibility’ of the measuring process
. It is again certainly not implied by wave mechanics, nor classical mechanics either. Another independent postulate?7

  In April 1957, H. J. Groenewold of Natuurkundig Laboratorium der Rijks-Universiteit te Groningen wrote a long critique of the edited thesis (“relative states” preprint) in which he “profoundly disagree[d]” with its premise and conclusion. In his letter to Everett and Wheeler, Groenewold said that in the summer of 1956 he had “borrowed” a copy of “Wave Mechanics Without Probability,” and that the preprint of “‘Relative State’ Formulation of Quantum Mechanics” was “much improved.” Believing that this preprint was an abstract of a likewise improved long thesis, he asked to read that, too!8

  Groenewold wrote,

  I fully sympathize with the idea of describing the measuring process on purely physical systems without including living observers. So the ‘measuring chain’ has to be cut off. But it is extremely fundamental that the [cut] off is made after the measuring result has been recorded [in a] permanent way, so that it no longer can be essentially changed if it is observed on its turn…. This recording has to be more or less irreversible and can only take place in a macrophysical (recording) system.