From: Matt Mahoney (matmahoney@yahoo.com)
Date: Wed Aug 18 2010 - 23:03:27 MDT
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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