## A nearly forgotten man of many universes

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**The Many Worlds of Hugh Everett III**

by Peter Byrne

Oxford University Press; 456 pp. $45

Quantum mechanics (hereinafter QM) is famously odd. As Peter Byrne notes in this book:

A century has passed since Max Planck and Albert Einstein discovered the quantum world. The basic quantum paradoxes — uncertainty, non-locality, and the measurement problem — are either unsolved or remain highly contentious.

The measurement problem is especially knotty. Down in the subatomic realm, each of the particles that constitute matter is smeared out over a volume of space in a manner described mathematically by a "wave function." When an observer interacts with this wave function by taking a measurement, the wave function suddenly manifests as a particle with a position and speed to which numbers can be assigned. It ceases to be a quantum-mechanical phenomenon and becomes a "classical" one. This seems to give the observer's consciousness a privileged position in our description of the world.

As well as making physicists deeply uncomfortable, this state of affairs raises difficult philosophical problems. Does QM describe all of reality? Including the observer? Then this peculiar "collapse of the wave function" when a measurement is made should itself be susceptible to a QM explanation. Or is the observer a classical "island" in a QM world? And what if there is more than one observer? Which observer's consciousness then causes the wave function to collapse? Could the consciousness of, say, a mouse, cause the collapse? (This precise question was asked by a skeptical Albert Einstein in his last public lecture.) Could a smart machine?

As Byrne has told us, these are still open questions, so much so that Oxford University offers a degree course in Physics and Philosophy. The associated research group is, the university's course description says, "extremely active." Some of the best minds on the planet have been working on the QM paradoxes for decades.

Among those first-class minds was the one belonging to Hugh Everett III, an American who lived from 1930 to 1982, mostly near Washington, D.C. In this biography of Everett, Peter Byrne interleaves Everett's personal story with an account of the main trends in thinking about QM across the second half of the 20th century.

Everett's contribution to the QM debates was of an unusually one-off character. He worked on his doctoral thesis at Princeton through 1954-5, finally submitting its 137 typed pages to his adviser, John Wheeler, in January 1956. The title of the thesis was "Quantum Mechanics by the Method of the Universal Wave Function." After Wheeler had absorbed the paper and recommended some small changes it was distributed, under a different title, to leading physicists, including Niels Bohr.

Wheeler was a first-rank physicist of the previous generation. (His dates are 1911-2008.) Like most such, he revered Niels Bohr, the godfather of QM. Bohr had taken a utilitarian view of the QM paradoxes, a view much influenced by linguistic philosophy and wary of metaphysics: asking not "What physical reality underlies these observations?" but "What future observations can be predicted from these?" This view is known as the Copenhagen Interpretation, from the location of Bohr's research institute.

Bohr and other Copenhagenists reacted rather strongly against Everett's ideas. As a result, Wheeler pressured his student to revise the thesis. Everett, anxious to get his doctorate, did so. The thesis, drastically reduced — by 75 percent, says Byrne — at last appeared in a scholarly journal in July 1957. The world of physics took no notice of it. Wheeler reminisced in his old age that Everett "was disappointed, perhaps bitter, at the non-reaction to his theory." Everett had in fact already left Academia to embark on a career in what Eisenhower later, in his farewell address, called "the military industrial complex." He had also acquired a wife and baby daughter.

Everett never published another word on QM after 1957. The remaining 25 years of his life were spent working in the then-new fields of operations research, game theory, and computing. Some of this work was for the U.S. Department of Defense in the depths of the Cold War, under a very high level of security clearance.

In 1964 he founded an independent consultancy, then left it in 1973 to found another one. His consultancy work began as a continuation of his defense studies, in the gruesome calculus of megadeath nuclear exchanges, on contract to the Pentagon. It ended in the equally gruesome — though admittedly less lethal — calculus of Affirmative Action, applying mathematical models to seek patterns of "discrimination" in hiring, housing, and education on behalf of civilian federal agencies. Everett's career traveled, you might say, along a geodesic in the U.S.A.'s curved sociocultural space during the third quarter of the 20th century, from Mutual Assured Destruction to War on Poverty. Along the way he wrecked his health, though not quite his marriage, with heroic levels of smoking, drinking, eating, and philandering.

A forgotten doctoral thesis; an unremarkable non-academic career; an early death; why does Everett deserve the attentions of a biographer? The answer is in that 1957 thesis, and its attack on the measurement problem in QM.

To restate the problem: QM describes the corner of the universe we are investigating — a single particle perhaps; or, in Erwin Schrödinger's famous thought experiment, a cat — using a wave function, a mathematical construction that implies a smeared-out reality at the sub-microscopic level. When an observer makes an observation, all the fuzziness instantly vanishes to give him a classical measurement. This schema leads to the aforementioned puzzles and paradoxes.

Everett's solution was very audacious. He posited a "universal wave function" that encompasses both the observer, his consciousness,
and the phenomena he observes. However, the collapse of the wave function to some one particular co-ordinate does not happen. Rather, as the wave
function evolves through time, it constantly splits off new universes, one for each coordinate point. There is no collapse. The fact that observer
A takes measurement M is nothing to do with interaction between A and the universal wave function. They are already, and for ever,
interacting — "entangled." All that happened was that the universe split in two at the instant of observation (as it is always
doing, observed or not) and the version of A that we know about was carried off willy-nilly on the branch associated with co-ordinate M. A copy of
him, A2, was carried off on a different branch, with a different measurement. So were innumerable other copies. The universal wave function
governs them all. Actually, it *is* them.

This was the germ of what later became known as the Many Worlds Interpretation of QM. Though it sounds preposterous to a lay person, it has some features that strongly recommend it to theorists, not only removing the privileged status of consciousness but even banishing probability from the subatomic realm. Probability is bothersome, philosophically and scientifically (though not mathematically). MWI restores a pleasingly "classical" — determinist, materialist — quality to physics.

The cost is of course those ever-spawning copies of the universe. The notion was more than some commentators could bear — notably the late Martin Gardner, who pooh-poohed MWI in a famous 2001 article.

There is also the small matter of evidence for the existence of these other universes. Are they in fact physically real? Everett, an atheist and a materialist, was as little inclined to metaphysics as his nemesis Bohr, though for different reasons. When cornered on this point by a sympathetic Defense Department colleague in 1959 though, he allowed "a 70 percent probability" that the multitude of universes are all real.

Martin Gardner notwithstanding, the MWI is now a modest industry within theoretical physics, with conferences, celebrities, and contending schools of thought. It has become entangled, so to speak, with the growing efforts to develop quantum computers, which should in theory be able to perform complex calculations at blinding speed. (Though the last time I spoke to a researcher in the field, he was exulting at having persuaded his quantum computer to multiply 3 by 7.) It would be absurd for a nonspecialist to offer an opinion about the validity of MWI, but a great many very smart people are taking it seriously.

Peter Byrne's book tells us everything essential, and is altogether a fine work of investigative biography. He has trawled through stacks of boxes in Everett's son's basement, and spoken to as many associates and acquaintances of Everett as he could find. His explanations of QM are more lucid than the average.

It is a shame that OUP, like every other publisher, has now got out of the editing business, so that we are insulted with "criteria" as a single noun, "lay" for "lie," "ex-patrioted" for "expatriate," and other gross infelicities of grammar and usage. I wish, too, that Byrne had done less editorializing on behalf of his New Left opinions about feminism, militarism, the "culture of consumerism," and the rest — all very bold in 1957, but drearily conformist nowadays. These minor irritations aside, though, I found this book a well-researched and worthwhile read.