# The Many Worlds of Hugh Everett

I've just finished this book and its one of the most enjoyable things I've read in a long time. Being a staple of science fiction and the only interpretation of quantum mechanics to enter the popular imagination it's a little surprising that "The Many Worlds of Hugh Everett" by Peter Byrne is the first biography of the originator of that amazing idea. Everett certainly had an interesting life, he was a libertarian and a libertine, became a cold warrior who with his top secret clearance was comfortable with the idea of megadeath, became wealthy by started one of the first successful software companies until alcoholism drove him and his company into the ground. Everett died of heart failure in 1982 at the age of 51, he was legally drunk at the time. He requested that his body be cremated and his ashes thrown into the garbage. And so he was.

Byrne had an advantage other potential biographers did not, the cooperation of his son Mark, a successful rock musician and composer whose music has been featured in such big budget movies as American Beauty, Hellboy, Yes Man, all three of the Shrek movies and many others. Mark gave Byrne full access to his garage which was full of his father's papers that nobody had looked at in decades.

Everett was an atheist all his life, after his death Paul Davies, who got 1,000,000 pounds for winning the Templeton religion prize, said that if true Many Worlds destroyed the anthropic argument for the existence of God. Everett would have been delighted. Nevertheless Everett ended up going to Catholic University of America near Washington DC. Although Byrne doesn't tell us exactly what was in it, Everett as a freshman devised a logical proof against the existence of God. Apparently it was good enough that one of his pious professors became very upset and depressed with "ontological horror" when he read it. Everett liked the professor and felt so guilty he decided not to use it on a person of faith again. This story is very atypical of the man, most of the time Everett seems to care little for the feelings of others and although quite brilliant wasn't exactly lovable.

Everett wasn't the only one dissatisfied with the Copenhagen Interpretation which insisted the measuring device had to be outside the wave function, but he was unlike other dissidents such as Bohm or Cramer in that Everett saw no need to add new terms to Schrodinger's Equation and thought the equation meant exactly what it said. The only reason those extra terms were added was to try to rescue the single universe idea, and there was no experimental justification for that. Everett was unique in thinking that quantum mechanics gave a description of nature that was literally true.

John Wheeler, Everett's thesis adviser, made him cut out about half the stuff in his original 137 page thesis and tone down the language so it didn't sound like he thought all those other universes were equally real when in fact he did. For example, Wheeler didn't like the word "split" and was especially uncomfortable with talk of conscious observers splitting, most seriously he made him remove the entire chapter on information and probability which today many consider the best part of the work. His long thesis was not published until 1973, if that version had been published in 1957 instead of the truncated Bowdlerized version things would have been different; plenty of people would still have disagreed but he would not have been ignored for as long as he was.

Byrne writes of Everett's views: "the splitting of observers share an identity because they stem from a common ancestor, but they also embark on different fates in different universes. They experience different lifespans, dissimilar events (such as a nuclear war perhaps) and at some point are no longer the same person, even though they share certain memory records." Everett says that when a observer splits it is meaningless to ask "which of the final observers corresponds to the initial one since each possess the total memory of the first" he says it is as foolish as asking which amoeba is the original after it splits into two. Wheeler made him remove all such talk of amoebas from his published short thesis.

Byrne says Everett did not think there were just an astronomically large number of other universes but rather an infinite number of them, not only that he thought there were a non-denumerable infinite number of other worlds. This means that the number of them was larger than the infinite set of integers, but Byrne does not make it clear if this means they are as numerous as the number of points on a line, or as numerous as an even larger infinite set like the set of all possible clock faces, or maybe an even larger infinity than that where easy to understand examples of that sort of mega-infinite magnitude are hard to come by. Neill Graham tried to reformulate the theory so you'd only need a countably infinite number of branches and Everett at first liked the idea but later rejected it and concluded you couldn't derive probability by counting universes. Eventually even Graham seems to have agreed and abandoned the idea that the number of universes was so small you could count them.

Taken as a whole Everett's multiverse, where all things happen, probability is not a useful concept and everything is deterministic. However for observers like us trapped in a single branch of the multiverse, observers who do not have access to the entire wave function and all the information it contains but only a small sliver of it, probability is the best we can do. That probability we see is not part of the thing itself but is just a subjective measure of our ignorance.

Infinity can cause problems in figuring out probability but Everett said his theory could calculate what the probability any event could be observed in any branch of the multiverse, and it turns out to be the Born Rule (discovered by Max Born, grandfather of Olivia Newton John) which means the probability of finding a particle at a point is the squaring of the amplitude of the Schrodinger Wave function at that point. The Born Rule has been shown experimentally to be true but the Copenhagen Interpretation just postulates it, Everett said he could derive it from his theory it "emerges naturally as a measure of probability for observers confined to a single branch (like our branch)". He proved the mathematical consistency of this idea by adding up all the probabilities in all the branches of the event happening and getting exactly 100%. Dieter Zeh said Everett may not have rigorously derived the Born Rule but did justify it and showed it "as being the only reasonable choice for a probability measure if objective reality is represented by the universal wave function \[Schrodinger's wave equation\]". Rigorous proof or not that's more than any other quantum interpretation has managed to do.

Everett wrote to his friend Max Jammer:

> "None of these physicists had grasped what I consider to be the major accomplishment of the theory- the "rigorous" deduction of the probability interpretation of Quantum Mechanics from wave mechanics alone. This deduction is just as "rigorous" as any deductions of classical statistical mechanics. \[...\] What is unique about the choice of measure and why it is forced upon one is that in both cases it is the only measure that satisfies the law of conservation of probability through the equations of motion. Thus logically in both classical statistical mechanics and in quantum mechanics, the only possible statistical statements depend upon the existence of a unique measure which obeys this conservation principle."

Nevertheless some complained that Everett did not use enough rigor in his derivation. David Deutsch has helped close that rigor gap. He showed that the number of Everett-worlds after a branching is proportional to the conventional probability density. He then used Game Theory to show that all these are all equally likely to be observed. Everett would likely have been delighted as he used Game Theory extensively in his other life as a cold warrior. Professor Deutsch gave one of the best quotations in the entire book, talking about many worlds as a interpretation of Quantum Mechanics "is like talking about dinosaurs as an interpretation of the fossil record".

Everett was disappointed at the poor reception his doctoral dissertation received and never published anything on quantum mechanics again for the rest of his life; instead he became a Dr. Strangelove type character making computer nuclear war games and doing grim operational research for the pentagon about armageddon. He was one of the first to point out that any defense against intercontinental ballistic missiles would be ineffectual and building an anti-balistic missile system could not be justified except for "political or psychological grounds". Byrne makes the case that Everett was the first one to convince high military leaders through mathematics and no nonsense non sentimental reasoning that a nuclear war could not be won, "after an attack by either superpower on the other, the majority of the attacked population that survived the initial blasts would be sterilized and gradually succumb to leukemia. Livestock would die quickly and survivors would be forced to rely on eating grains potatoes and vegetables. Unfortunately the produce would be seething with radioactive Strontium 90 which seeps into human bone marrow and causes cancer". Linus Pauling credited Evert by name and quoted from his pessimistic report in his Nobel acceptance speech for receiving the 1962 Nobel Peace prize.

Despite his knowledge of the horrors of a nuclear war Everett, like most of his fellow cold warrior colleagues in the 50's and 60's, thought the probability of it happening was very high and would probably happen very soon. Byrne speculates in a footnote that Everett may have privately used anthropic reasoning and thought that the fact we live in a world where such a war has not happened (at least not yet) was more confirmation that his Many Worlds idea was right. Incidentally this is one of those rare books where the footnotes are almost as much fun to read as the main text.

Hugh's daughter Liz Everett killed herself a few years after her father's death, in her suicide note she said "Funeral requests: I prefer no church stuff. Please burn be and DON'T FILE ME. Please sprinkle me in some nice body of water or the garbage, maybe that way I'll end up in the correct parallel universe to meet up with Daddy". And so she was.

John K Clark