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By Root 1930 0

his elder colleague. In response to the criticisms, Wheeler delayed granting Everett his Ph.D. and compelled him to modify the thesis substantially. Everett was to cut out those parts blatantly critical of Bohr’s methodology and emphasize that his results were meant to clarify and extend the conventional formulation of quantum theory. Everett resisted, but he had already accepted a job in the Defense Department (where he would soon play an important behind-the-scenes role in the Eisenhower and Kennedy administrations’ nuclear-weapons policy) that required a doctorate, so he reluctantly acquiesced. In March of 1957, Everett submitted a substantially trimmed-down version of his original thesis; by April it was accepted by Princeton as fulfilling his remaining requirements, and in July it was published in the Reviews of Modern Physics.1 But with Everett’s approach to quantum theory having already been dismissed by Bohr and his entourage, and with the muting of the grander vision articulated in the original thesis, the paper was ignored.2

Ten years later, the renowned physicist Bryce DeWitt plucked Everett’s work from obscurity. DeWitt, who was inspired by the results of his graduate student Neill Graham that further developed Everett’s mathematics, became a vocal proponent of the Everettian rethinking of quantum theory. Besides publishing a number of technical papers that brought Everett’s insights to a small but influential community of specialists, in 1970 DeWitt wrote a general level summary for Physics Today that reached a much broader scientific audience. And unlike Everett’s 1957 paper, which shied away from talk of other worlds, DeWitt underscored this feature, highlighting it with an unusually candid reflection regarding his “shock” on learning Everett’s conclusion that we are part of an enormous “multiworld.” The article generated a significant response in a physics community that had become more receptive to tampering with orthodox quantum ideology and ignited a debate, still going on, that concerns the nature of reality when, as we believe they do, quantum laws hold sway.

Let me set the stage.

The upheaval in understanding that took place between roughly 1900 and 1930 resulted in a ferocious assault on intuition, common sense, and the well-accepted laws that the new vanguard soon began calling “classical physics”—a term that carries the weight and respect given to a picture of reality that is at once venerable, immediate, satisfying, and predictive. Tell me how things are now, and I’ll use the laws of classical physics to predict how things will be at any moment in the future, or how they were at any moment in the past. Subtleties such as chaos (in the technical sense: slight changes in how things are now can result in huge errors in the predictions) and the complexity of the equations challenge the practicality of this program in all but the simplest situations, but the laws themselves are unwavering in their viselike grip on a definitive past and future.

The quantum revolution required that we give up the classical perspective because new results established that it was demonstrably wrong. For the motion of big objects like the earth and the moon, or of everyday objects like rocks and balls, the classical laws do a fine job of prediction and description. But pass into the microworld of molecules, atoms, and subatomic particles and the classical laws fail. In contradiction of the very heart of classical reasoning, if you run identical experiments on identical particles that have been set up identically, you will generally not get identical results.

Imagine, for example, that you have 100 identical boxes, each containing one electron, set up according to an identical laboratory procedure. After exactly 10 minutes, you and 99 cohorts measure the positions of each of the 100 electrons. Despite what Newton, Maxwell, or even a young Einstein would have anticipated—would likely have been willing to bet their lives on—the 100 measurements won’t yield the same result. In fact, at first blush the results will look random,