The Many Worlds of Hugh Everett '' by Peter Byrne
This is a well written enjoyable book, and 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 who ate drank and smoked too much and exercised too little, became a cold warrior with a top secret clearance, was comfortable with the idea of megadeath and became wealthy by starting 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 only 51. He was legally drunk at the time. He requested 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.
After Everett’s death Paul Davies, who won the Templeton religion prize and received 1,000,000 pounds, said if Many Worlds reflects the true nature of reality then it destroys the anthropic argument for the existence of God. Everett was an atheist all his life so he 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 the man wasn't exactly lovable.
Everett wasn't the only one dissatisfied with the Copenhagen Interpretation of Quantum Mechanics which insisted that in any measurement, for reasons never made clear, the wave equation could never be applied to the measuring device used; 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 and needed no modification. The only reason to add in stuff and complicate an already complicated equation 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 advisor, made him cut out about half the stuff in his original 137 page thesis published in 1957 and tone down the language so it didn't sound like he thought all those other universes were equally real, when in fact that’s exactly what he thought. For example, Wheeler didn't like the word "split" and was especially uncomfortable with talk of conscious observers splitting, so the following quote was too radical and made Wheeler far too uncomfortable for him to allow it to appear in the published thesis:
“As an analogy one can imagine an intelligent amoeba with a good memory. As time progresses the amoeba is constantly splitting, each time the resulting amoebas having the same memories as the parent. Our amoeba hence does not have a life line, but a life tree. The question of identity or non identity of two amoebas at a later time must be rephrased. At any time we can consider two of them, and they will have common memories up to a point (common parent) after which they will diverge[...] The same is true if one accepts the hypothesis of the universal wave function. Each time an individual splits he is unaware of it, and any single individual is at all times unaware of his "other selves" with which he has no interaction from the time of splitting.”
Even worse, Wheeler made Everett remove the entire chapter on information and probability from his thesis before he got his PHD 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 probably 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 an observer splits it is meaningless to ask "which of the final observers corresponds to the initial one since each possesses 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 amebas 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, and was equal to or greater than the number of points on a line. 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, and today everybody agrees with that but even among Many World adherents there is disagreement over whether there are an infinite number of worlds or just an astronomically large number to an astronomically large power of them. It depends largely on if space and time are continuous or discrete, that is to say if there is structure smaller than the Planck Length of 1.6*10^-35 meters, and nothing changes in less than the Planck Time of 5.4*10^-44 seconds.
According to Everett, taken as a whole, the multiverse must be completely deterministic because Schrodinger's wave equation is. 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 and can only see a small sliver of it, probability is the best we can do. Probability is just a measure of our ignorance.
Infinity can cause problems in figuring out probability but Everett said his theory could calculate what the probability of an event could be observed in any branch of the multiverse, and it turns out to be the Born Rule (discovered in 1926 by Max Born, grandfather of pop singer Olivia Newton John) which means the probability of finding a particle at a point is the square 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 does not derive the rule, it is just assumed as a starting axiom. 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 showed the mathematical consistency of his idea by proving that all the probabilities are always positive Real Numbers between zero and one and in all the branches all the probabilities of an event happening always add up to exactly 1 ( because something is certain to happen). 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 an interpretation of Quantum Mechanics "is like talking about dinosaurs as an interpretation of the fossil record".
More recently Sean Carroll and others have pointed out the only assumption that Many Worlds makes is that everything evolves according to the Schrodinger equation, and Occam's Razor is about an economy of assumptions not an economy of results, and all those worlds are not an assumption, they are just the result of what happens if you think Schrodinger's equation means what it says. However Schrodinger's equation is completely deterministic so the real question is not why does the Born Rule work but why do we need to use probabilities at all? Carroll says the reason is "self location". Many Worlds says that if somebody flips a coin then the universe branches and in one branch the coin lands heads and the other tales, but until you are able to actually look at the coin you won't know which branch you're on, so you'd have to resort to probability, in this case 50-50.
Everett was disappointed at the poor reception his doctoral dissertation received and never published anything on Quantum Mechanics again; 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-ballistic 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, Everett said "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 food would be seething with radioactive Strontium 90 which seeps into human bone marrow and causes cancer". Chemist Linus Pauling credited Evertt 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 high and would likely happen very soon. Byrne speculates in a footnote that Everett may have privately used anthropic reasoning and thought the fact we live in a world where such a war has not happened yet , not even in 1962 during the Cuban missile crisis where the human race came closer to extinction than it ever has before or since, was more confirmation that his Many Worlds idea was right. Incidentally this is one of those very 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 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.