**From:** Matt Mahoney (*matmahoney@yahoo.com*)

**Date:** Wed Aug 18 2010 - 23:03:27 MDT

**Next message:**John Clark: "Re: [sl4] The Many Worlds of Hugh Everett"**Previous message:**John K Clark: "[sl4] The Many Worlds of Hugh Everett"**In reply to:**John K Clark: "[sl4] The Many Worlds of Hugh Everett"**Next in thread:**John Clark: "Re: [sl4] The Many Worlds of Hugh Everett"**Reply:**John Clark: "Re: [sl4] The Many Worlds of Hugh Everett"**Reply:**John K Clark: "Re: [sl4] The Many Worlds of Hugh Everett"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ] [ attachment ]

Thanks for the excellent book review.

One point where I disagree with Everett is the need for an uncountable infinity

of universes rather than a countable infinity. Everett must have been aware that

the observable universe has a finite description length (about 10^122 bits). The

universe we observe is surely the result of applying the anthropic principle to

an enumeration of Turing machines.

-- Matt Mahoney, matmahoney@yahoo.com

________________________________

From: John K Clark <johnkclark@fastmail.fm>

To: sl4 sl4 <sl4@sl4.org>

Sent: Tue, August 17, 2010 10:53:29 PM

Subject: [sl4] 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 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, 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-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, "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 me 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

-- John K Clark johnkclark@fastmail.fm

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