by Peter Byrne
In July 1979, in what may very well have been their last communication, Wheeler wrote to Everett:
Thank you for your letter of too many weeks back. I think you got a great subject going and I am overjoyed at the thought of your getting back and going to bat for it!11
On that same day, Wheeler copied Everett and DeWitt on a letter to the director of the Institute for Theoretical Physics at University of California, Santa Barbara:
Hugh Everett who did that fascinating Everett interpretation of quantum mechanics and who ought to be got back into it to go on with it has written to me indicating that he might conceivably get free to spend a period at the Institute.
I have written Bryce DeWitt about this and believe that it has real possibilities for quite fruitful interactions.12
DeWitt replied to Wheeler,
There is nothing in Bohr’s description that is not contained in Everett. Everett, however, would amplify Bohr’s statement. When Bohr says that an elementary act of measurement (or quantum interaction or what have you) is ‘brought to a close by an irreversible act of amplification,’ Everett would add that the process of one ‘world’ splitting into many is simultaneously brought to completion.
Everett in fact delves deeper by pointing out that nowhere does Bohr give a rigorous definition of ‘irreversible’ or make a distinction between ‘irreversible in practice’ and ‘irreversible in principle.’ Some might say that therein lies Bohr’s strength, that the distinction has no operational significance.
Everett suggests (and I believe) that it is a mistake to transform the wonderful lessons that Bohr has taught us into points of dogma. The history of physics has taught 1. that one should never be dogmatic, 2. that one should never hesitate to push a formalism to its ultimate logical conclusions however absurd. In the case of the formalism of quantum mechanics one cannot say that the interferences are there at one moment but gone the next.
All that Everett is really trying to say is that the interferences are in principle always there. As David Deutsch so aptly puts it: ‘Quantum theory is the Everett interpretation.’ The theory may ultimately be proved wrong, but at the present time you cannot have one without the other.13
Despite Wheeler’s enthusiasm, Everett made no effort to re-ignite his theoretical career. In 1980, two years before his death, he wrote a letter to physics enthusiast L. David Raub:
I certainly still support all of the conclusions of my thesis…. Dr. Wheeler’s position on these matters has never been completely clear to me (perhaps not to John either). He is, of course, heavily influenced by Bohr’s position … It is equally clear to me that, at least sometimes, he wonders very much about that mysterious process, ‘the collapse of the wave function.’ The last time we discussed such subjects at a meeting in Austin several years ago he was even wondering if somehow human consciousness was a distinguished process and played some sort of critical role in the laws of physics.
I, of course, do not believe any such special processes are necessary, and that my formulation is satisfactory in all respects. The difficulties in finding wider acceptance, I believe, are purely psychological. It is abhorrent to many individuals that there should not be a single unique state for them (in the world view), even though my interpretation explains all subjective feelings quite adequately and is consistent with all observations.14
Decades later, Deutsch summed up why the many worlds model is so important in the history of physics and philosophy:
Everett was before his time, not in sense that his theory was not timely—everybody should have adopted it in 1957, but they did not. Above all, the refusal to accept Everett is a retreat from scientific explanation. Throughout the 20th century a great deal of harm was done in both physics and philosophy by the abdication of the original purpose of those fields: to explain the world. We got irretrievably bogged down in formalism, and things were regarded as progress which are not explanatory, and the vacuum was filled by mysticism and religion and every kind of rubbish. Everett is important because he stood out against it, albeit unsuccessfully; but theories do not die and his theory will become the prevailing theory. With modifications.15
35 Wheeler Recants
Given for one instant an intelligence which could comprehend all the forces by which nature is animated and the respective situation of the beings who compose it—an intelligence sufficiently vast to submit these data to analysis—it would embrace in the same formula the movements of the greatest bodies of the universe and those of the lightest atom; for it, nothing would be uncertain and the future like the past would be present to its eyes.
Pierre Simon Laplace,18141
In 1972, Max Jammer was researching the final chapters of The Philosophy of Quantum Mechanics. He wrote to Wheeler asking for Everett’s address. The professor had lost track of his whereabouts, replying, “Bohr did not take to [Everett’s] way of describing q. mechanics, as he also earlier had not accepted Feynman’s way of ascribing q. mechanics.”2
Was he still carrying Everett’s torch?
Jammer later learned the McLean address from DeWitt, who also told him about the existence of the long thesis. He wrote to Everett,3 who replied at length, recounting the influences on this thinking when he wrote the original thesis. He said his theory was the simplest explanation of quantum mechanics available, but accepting it was “a matter of taste.” He said he had sent his last copy of the long thesis to DeWitt for publication. And that the only other copy was locked in a file drawer along with the doctoral thesis on EPR of his business partner, Reisler. When they had started DBS, the two physicists had locked up their respective dissertations, agreeing not to talk about quantum mechanics for ten years, “when presumably we could afford the luxury of such a diversion.”4
Everett’s spirits must have been lifted by the attention being paid to his theory. But the failure of Lambda weighed heavily upon him; he was sexually obsessed; and alcoholism was slowly degrading his ability to perform intellectually. Then, Wheeler, his mentor, and once his strongest advocate, publicly disowned him. Why? Let’s revisit 1957 and take it from there.
The power of Bohr
In the spring of 1957 Bohr and his inner circle categorically rejected Everett’s “heretical” quantum model because—above all other considerations—it violated Bohr’s prohibition on talking about reality as quantum mechanical, as fundamentally non-classical. Wheeler went on to publish his enthusiastic endorsement of Everett’s work in Reviews of Modern Physics, but he was distressed about having unsuccessfully challenged Bohr, and he soon found an opportunity to reaffirm his loyalty.
In October 1957, Bohr received the first Atoms For Peace award in Washington D.C. The $100,000 award was sponsored by the Ford Motor Company to honor scientists working on peaceful uses for atomic energy. Wheeler’s and Bohr’s work on fission had made the atomic bomb possible, and Wheeler was a prime architect of the hydrogen fusion bomb, but these credentials did not hurt them with Atoms for Peace, which asked Wheeler to make the keynote speech.5 Delivered in best-courtier fashion, it cast Bohr as the epitome of civilized man. According to Wheeler, Bohr’s interpretation of quantum mechanics was “the most revolutionary scientific concept of this century,” presumably surpassing Einstein’s contributions.
Wheeler had invited Everett to the Atoms for Peace award dinner. But he declined to attend; if he had gone, he probably would have gagged when Wheeler lauded Bohr’s institute as a place where, “young men come from all over the world to work in an atmosphere free of envy and jealousy, one that could be described in the words of Sir William Rowan Hamilton’s poem, ‘Yet with an equal joy let me behold, Thy truth’s chariot o’er that way by others rolled.’” In Copenhagen, said Wheeler, “the climate of ideas opens the way to new advances in physics.” This was, at best, wishful thinking on Wheeler’s part. After the Second World War, Bohr’s institute had become more of a temple or ideological fortress than a laboratory for new ideas.
As long as the world of physics talked of E
verett behind closed doors, Wheeler could live with being associated to the upstart theory. But, after DeWitt started up his Everett bandwagon, the world at large started paying attention to the Everett-Wheeler theory of multiple universes. Wheeler was torn. He did not deny that the theory had merit, but the attachment of his good name to it harmed his standing with committed Copenhagenists, such as Rosenfeld and Heisenberg. Many prominent physicists, including Feynman, thought many worlds was a ludicrous idea. And espousing a belief in multiple universes was not necessarily consistent with the image of rationality that Cold War scientists typically strove to project.
But if Wheeler was to repudiate Everett, he might end up looking the fool if an experimental proof of the theory ever panned out.
So, he vacillated.
Trieste, Italy, 1972
The “Symposium on the Physicists Conception of Nature in the Twentieth Century” in Trieste was attended by two score of the finest quantum thinkers of the day, including, Wigner, Heisenberg, Dirac, Bell, Lamb, Rosenfeld, Schwinger, Cooper, and Chen Ning Yang. Wheeler came to the cosmopolitan seaport having just passed the magic age of 60, when physicists often celebrate a festschrift, call it a day, and become emeritus. But he was hyper-energetic, joyously churning out strange ideas in the service of uniting gravity and the quantum. He had recently named the gravitational singularities at the heart of quantum cosmology “black holes.” He continued to obsess about “quantum foam” seething with electromagnetic geons and gravitational wormholes. He was fascinated by the relationship of the probabilistic chaos of the microscopic universe to the macroscopic order of our classical world. And, quixotically, he desired for all of these new ideas to fit into Bohr’s complementary mould.
Wheeler arrived in Trieste on the heels of having published a massive textbook, Gravitation, written with Misner and Kip Thorne. He referred repeatedly to Gravitation in a lengthy, provocative paper he delivered on the intersections of general relativity and the quantum in which he catalogued milestones in the evolution of quantum mechanics from Planck to Bohr to Heisenberg, Dirac, von Neumann, Feynman, and, finally, to Everett, whose relative states theory allowed physicists to treat the whole universe as quantum mechanical.
After equating Everett with quantum giants, Wheeler suggested that entire universes can float in “superspace,” a foamy space-time geometry without the dimension of time. Probability waves representing histories of whole universes propagate through superspace scattering off black holes. Within this mathematical framework, Wheeler postulated the existence of “leaves of history,” i.e. alternative histories of the universe: multiple, co-existing universes. Each universe exists on a “classical leaf in history in superspace” and has “quantum spread.” Due to the nature of gravitational collapse, “There is also not the slightest possibility to travel to another leaf of history.”6
He was describing a type of many worlds theory:
No one can deny the ‘co-existence of alternative histories of the universe’ who accepts the existence of quantum fluctuations in the geometry of space.7
It was the superposition principle writ large.
One has only to recall the famous double slit electron interference experiment to see the same principle in a simpler context. The ‘co-existence of two histories’ of the electron is the very heart of the observed interference. No one has ever successfully contested it.8
Philosophically, Wheeler did not care for the notion of a Big Crunch, the prediction that our universe will ultimately collapse into a black hole, squashing the laws of physics as we know them (he was writing long before it was discovered that we probably live in an outwardly accelerating universe). Confronted by the prospect of oblivion and anarchy in the foundations of physics, Wheeler harkened back to ancient Grecian themes of eternal change as the ultimate physical law. He postulated that the deepest laws of physics will survive the gravitational collapse of our universe:
It is difficult to find any other way to summarize the situation as it now appears than this: ‘There is no law except the law that there is no law;’ or more briefly, ‘Ultimate MUTABILITY is the central feature of physics.’9
Searching for a philosophical tether in a multiversian reality roiled by chaos, uncertainty, the end of time, Wheeler was becoming more and more attached to Bohr’s principle that the act of observation changes the object observed. In Trieste, he called for the concept of “observer” to be replaced by “participator.” He then abandoned the concept of the wave function as physically real. He reached back 2,500 years, to quote Parmenides of Elea, a poet who spoke of possible worlds brought into being by observation: “What is, … is identical with the thought that recognizes it.”10
And Leibniz:
Although the whole of this life were said to be nothing but a dream and the physical world nothing but a phantasm, I should call this dream or phantasm real enough if, using reason well, we were never deceived by it.11
This was basically a restatement of Wigner’s idealist philosophy that human consciousness creates physical reality. Everett believed the reverse: that physical reality creates human consciousness, which is why his theory of quantum entanglement does not require human participation as a sine qua non.
Strasbourg, France, 1974
Two years later, Wheeler gingerly removed Everett from his list of quantum greats. The occasion was “A Colloquium on Fifty Years of Quantum Mechanics,” held at the University of Louis Pasteur, Strasbourg. It was attended by more than a dozen physicists, including a young French man, Jean Marc Lévy-Leblond. Wheeler’s presentation was called, “Include the Observer in the Wave Function?”12
The most striking feature of Everett’s universal wave function is that it includes the observer. In Strasbourg, Wheeler attacked the core of the many worlds model by excluding the observer from the wave function. In doing so he referred to Wigner’s argument that wave mechanics only describes correlations between conscious observations. According to Wigner, and now Wheeler, observers of quantum systems cannot stand outside a wave function, but neither can they be part of a wave function as they must observe it. If this seems confusing: it is. Wheeler summed up: “There has to be a wave function for the universe but there can’t be a wave function for the universe: that is the dilemma.”13
Wheeler was concerned that if one adopts the use of a deterministic universal wave function, “predictability perishes.” And yet we experience the world probabilistically. Clearly, he no longer believed his claim of two decades previous that Everett’s universal wave function explained the “appearance” of probability in a branching universe. He now called Everett’s claim “extreme.”14 Desiring to keep probability, he was ineluctably drawn toward an amalgam of the Wigner-von Neumann postulate of conscious intervention as creating physical reality, and Bohr’s admonition that, Wheeler paraphrased, “an observation is only complete when there is an [external] observer.”15
Hence, the observer cannot be included in the wave function, Wheeler concluded, attacking a pillar of Everett’s theory: that reality does not require the participation of an observer. Wheeler cast away Everett’s main physical idea: that the observer is included in the wave function, i.e. that the whole universe is quantum mechanical. Rather, he said, the universal wave function is “beyond the reach of the laws of physics itself.”
Wigner seized gladly upon Wheeler’s quasi-spiritual conversion, writing, probably with some relief, that his friend no longer supported Everett.16 Wigner himself rejected the many worlds theory on the basis that “it can neither be confirmed nor refuted.”17 Of course, the same could be said for his own theory that conscious impressions form the “primitive reality.”18
Hand washing contest
Several years later, Lévy-Leblond sent Everett a copy of a paper he had presented at Strasbourg, “Towards a Proper Quantum Theory.”19 In his cover letter, Lévy-Leblond said that, at the symposium, Wheeler had
suggested that I directly ask your opinion on what I believe to be a crucial questio
n concerning the ‘Everett & no-longer-Wheeler’ (if I understand correctly!) interpretation of Qu. Mech.20
Lévy-Leblond had his own interpretation of Everett’s interpretation:
The question is one of terminology: to my opinion there is but a single (quantum) world, with its universal wave function. There are not ‘many worlds,’ no ‘branching,’ etc., except as an artifact due to insisting once more on a classical picture of the world.
Uncharacteristically, Everett answered Lévy-Leblond, writing that his offering “is one of the more meaningful papers I have seen on this subject, and therefore deserving of a reply.”21 Specifically Referring to of Lévy-Leblond’s analysis of the many worlds theory, Everett wrote, “In this case, your observations seem entirely accurate (as far as I have read).”
On those pages, Lévy-Leblond had written:
To me, the deep meaning of Everett’s ideas is not the coexistence of many worlds, but, on the contrary, the existence of a single quantum one. The main drawback of the ‘many-worlds’ terminology is that it leads one to ask the question of ‘what branch we are on,’ since it looks as if our consciousness definitely belonged to one world at a time. But this question only makes sense from a classical point of view … It becomes entirely irrelevant as soon as one commits oneself to a consistent quantum view, exactly as the question of the ether was deprived of meaning, rather than answered, by a consistent interpretation of relativity theory.22