The Quark and the Jaguar

W.H. Freeman, 1994

Version 0.1

Note just added: John Gribbon defends the idea of "nonlocality" which Gell-Mann tries to reject.

Ch.11 begins Murray Gell-Mann's popular exposition of quantum mechanics. He accepts as a working hypothesis that quantum mechanics is "exactly correct" p.136. This would preclude the new "back-action" idea I have professed elsewhere which involves a violation of today's quantum mechanics as the essential signature of all living organizations of matter. Gell-Mann's main concerns are to show that nonlocality with its faster-than-light and backwards-in-time "spooky" influences are illusory, and to show how the familiar classical world (of heavy objects moving predictably given initial conditions) emerges from weird quantum reality. It is Gell-Mann's goal to exorcise any remnants of what he considers to be a superstitious "anthropocentric" magical view of fundamental physical reality.

physicists are only now approaching a really satisfactory interpretation, one that affords a deep understanding of how the quasiclassical domain of everyday experience arises from the underlying quantum-mechanical character of nature. p.136

I agree with Gell-Mann when he says that the

original interpretation of quantum mechanics, restricted to repeated experiments performed by external observers, is far too special ... especially since it has become increasingly clear that quantum mechanics must apply to the whole universe.

There is no external observer with a measuring apparatus which is outside of the entire universe. As in Godel's theorem, the universe measures itself. There is, at least on the surface, only one universe so that

there is no opportunity for repetition, for observing many copies of the universe. p.137

Is Gell-Mann rejecting the many-worlds interpretation of quantum mechanics in this remark? Not necessarily, because it is part of the traditional many-worlds meta-theory that each observer stuck in one universe cannot get information about the universe next door. However, David Albert in his book, The Quantum Mechanics of Experience, casts doubt on that assumption which is apparently implicit in Gell-Mann's meta-theory.

In any case the universe presumably couldn't care less whether human beings have evolved on some obscure planet to study its history; it goes on obeying the quantum-mechanical laws of physics irrespective of observation by physicists. p.137

On the other hand, if the quantum properties of matter are fundamentally mental or "qualia-like", then the quantum wavefunction of the universe, modified from "back-action" of the metric on it, is what Stephen Hawking has called "The Mind of God". Our minds are then "reduced" projections from the God-Mind and, on this magical view, the universe may indeed care about us. This is, of course, only a scientific conjecture, not a revealed truth.

Bohr's original Copenhagen interpretation seemed to require

a classical domain apart from quantum mechanics ... to many of us today it seems bizarre ... it is proposed that the quasiclassical domain emerges from the quantum mechanical laws, including the initial condition at the beginning of the universe. Understanding how that emergence comes about presents a major challenge. p.137

Gell-Mann and his former student, James Hartle, do not like the term "many worlds" but prefer to talk about "many alternative histories of" presumably one universe. The distinction is delicate, if not obscure operationally, since there must be a quantum amplitude for each possible metric geometry. One can imagine small regions of spacetime in which the three-dimensional part of the metric fluctuates as "quantum foam" at the Planck scale along a specific, but nonunique, way of ordering time. Gell-Mann's remarks on this on p.138 are very unclear to me.

the many worlds are described as being "all equally real," whereas we believe it is less confusing to speak of "many histories, all treated alike except for their different probabilities p.137

Gell-Mann appears to contradict himself since he earlier said that there are not "many copies of the universe". Therefore, he cannot be thinking of probability as the fraction of systems in an ensemble haviing a given property. He must be using a more subtle notion of probability that applies to a single system. He dies not give enough explanation here to really understand what he is trying to say. The book fails here, as elsewhere, as a popular work. The book "How is Quantum Field Theory Possible" by Sunny Auyang does discuss the idea of probability for single systems. I have not tried to relate Auyang's deeper analysis to Gell-Mann's point of view, but that would be a worthwhile exercise for students of modern theoretical physics. Indeed, David Bohm's meta-theory (in which there is only one actual universe on a branch with many possible empty branches) is conceptually clearer. The empty branches are objectively real and can in principle interfere with the occupied branch causing new phenomena in the course of evolution.

to be continued