X-Message-Number: 11224
From: 
Date: Sat, 6 Feb 1999 21:41:28 EST
Subject: quantum states & identity

Apologies to those who are uninterested, but I am trying to wrap up some
sections of my draft book, and possibly any physicists on the list might help.

Tipler (THE PHYSICS OF IMMORTALITY) rests his case for the "identity" of
replicas, despite differing locations, on the alleged identity of systems in
the same quantum state.  He specifically refers to thermodynamics. I see (said
the blind man) more than one problem with this view.

First, he appears to mean that two molecules (say) in the same quantum state
will behave identically, despite differing histories and trajectories. That's
all right for the diffusion experiment he discusses, because we are only
concerned with statistical averages. Nevertheless, gas molecules and photons
etc. do have trajectories, even in quantum theory, and if (say) we are talking
about the Compton effect (a photon scattered by an electron), then we can only
talk about the trajectory of the particular photon involved, not just any old
photon of the same energy. Photons ARE (at least sometimes) distinguishable
from each other.

Second, he seems to use "quantum state" in ambiguous ways. In discussing
diffusion, he speaks of molecules in the "ground state" as being in the "same"
quantum state. But "ground state" does not fully specify a molecule. Elsewhere
in his book, he acknowledges (I think) that "quantum state" refers to the
precise point or region in phase space occupied by the system at a given
moment. For example, a fully specified quantum state for a water molecule
would have to include directions of the axes. And, as I understand it (or
possibly misunderstand it) the phase space includes coordinates of spatial
location, hence "quantum state" MUST explicitly acknowledge the relevance of
location. 

Third, in light of "quantum entanglement," the past histories of systems
apparently do (or at least might) affect the total quantum state; and in SOME
interpretations a change of state of a previously entangled system at a
distance could (instantly) change the state of the system being observed. 

Is a puzzlement. At least to me. Any help?

Incidentally, Tipler has interesting comments on memory, similar to some made
by Donaldson. In particular, our memories of specific events may often be only
fragments, or even fragments of previous fragments, which when called upon are
fleshed out on a probabilistic basis, so that frequently our recall has
substantial elements of fiction. So--would you rather be revived with the same
partly fictional memories you had when frozen, or with veridical memories?
Which would more nearly represent your "true" self? Probably many of us would
prefer, at least initially upon revival, to be as nearly the same as possible,
but that just defers the question.

Robert Ettinger
Cryonics Institute
Immortalist Society
http://www.cryonics.org

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