Les Schaffer is an professional astro-physicist.
Will soon copy to list Caudwell's discussion of quantum mechanics.
Charles
^^^^^^
Dialectics/Phil of Math / quantum mechanics
________________________________
* To: [EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>
* Subject: Dialectics/Phil of Math / quantum mechanics
* From: Charles Brown <[EMAIL PROTECTED]
________________________________
I've been mugging up on this too :>) and a physics professor, Erwin
Marquit,
told me:
"When I discuss quantum physics, I never refer to an observer, but to the
objective recording of an interaction by an instrument. Observation by a
human plays no role in the result, so it makes no difference whether
humans
are present or not. The human may or may not be serving as part of the
instrumentation and the result will be independent of this factor. "
Maybe this is the "unravelling" of the inadequate way the we have "always"
been forced to think of change of position, displacement, as a series of
positions at rest. Maybe it only "comes out" at this elementary level. It
is
sort of what comes up with Zeno's paradox. How can a thing have a position
AT REST and be moving at the same time ? Motion has been _simulated_ as a
series of "at rests" but that really is a contradiction, because if
something is moving , it is not at rest.
So maybe it is that at such an "elementary" level, the traditional fiction
for portraying motion comes undone in the form of no simultaneous and
definite position( at rest) and velocity ( moving).
CB
* From: Daniel Davies <[EMAIL PROTECTED]
the participant/observer problem is epistemological; it's about what you
can
and can't know. It's agnostic between an interpretation under which there
is a genuine underlying reality which you can't observe properly, and one
under which there is no underlying reality until it's observed. The HUP
isn't agnostic in this way and isn't (as I understand it) an
epistemological
claim. It says that a quantum really doesn't have a simultaneously
defined
position and momentum.
One important thing to remember (I'm mugging up on this this weekend for
an
argument with Steven Landsburg) is that quantum probability is very
different from classical probability. When a particle is superposed in
two
states, that isn't at all the same thing as saying that it's in one state
with probability x and in the other state with probability y.
dd
-----Original Message-----
From: PEN-L list [mailto:[EMAIL PROTECTED] Behalf Of Devine,
James
Sent: 24 October 2004 17:36
To: [email protected]
Subject: Re: Dialectics/Phil of Math / quantum mechanics
What's the difference between the Heisenberg Uncertainty Principle (the
HUP)
and the participant-observer problem in sociology?
Jim Devine [EMAIL PROTECTED] http://myweb.lmu.edu/jdevine
________________________________
To: [EMAIL PROTECTED]
Subject: Re: Dialectics/Phil of Math / quantum mechanics
From: Les Schaffer <[EMAIL PROTECTED]>
Date: Tue, 26 Oct 2004 10:44:37 -0400
User-agent: KMail/1.7
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On Monday 25 October 2004 18:01, Charles Brown wrote:
I've been mugging up on this too :>) and a physics professor told me:
"When I discuss quantum physics, I never refer to an observer, but to the
objective recording of an interaction by an instrument.
this goes some way towards healing the quantum-classical split. there are
still problems remaining.
the reason is this: an "objective recording of an interaction by an
instrument", meaning a classical observation, can in principle be analyzed
quantum mechanically. so for example, when a photon hits a recording film
and
it creates a white spot. we can think of that classically as recording the
photon's position in some kind of photon propagation experiment. but
nothin
prevents us from analyzing this film recording event. in that case, there
are
silver chloride atoms, and an interaction with a photon, and some
probabilities for atoms making transitions to excited states, and so on
and
so forth.
there is also the notion of quantum decoherence (charles: we'll talk more
about it offlist). this also renders more classical the results of quantum
"paradoxes". however, there is still disagreement in the physics community
about whether even this solves the problem completely, meaning "in
principle". many agree it solves a lot of the problem "in practice".
in brief, quantum mechanics does not specify a dividing line between
quantum
and classical behavior. it is a two-layered approach to physics. there is
an
almost classical part, like a schrodinger equation, describing the time
evolution of a "state", and there is the part which connects "states" with
"observations" in the macro (classical) world. classical mechanics does
not
have this split in principle. its the part that takes a quantum state and
renders unto us what we can observe that is the source of the oddities. in
classical mechanics, i solve the equations of motion for the
earth-moon-sun
system in terms of their positions and momentum, and the solution is
rendered
in terms of those position/momentum variables. those numbers are directly
connected, in principle, with our observations, and so we know there WILL
BE
a total lunar eclipse this coming wednesday evening.
Maybe this is the "unravelling" of the inadequate way the we have
"always"
been forced to think of change of position, displacement, as a series of
positions at rest.
i think there is something to this, certainly in terms of getting off of
the
point-particle picture as the total description of material reality.
however, QM also contains other kinds of "can't do this" prescriptions,
called
"incompatible observables", like position and momentum.
so, for example, QM also says you cannot measure precisely an electron's
intrinsic spin in two mutually orthogonal directions, say east and north.
there is no classical analogue to this intrinsic spin, and so can't be
analyzed further in terms of some things like a point's position and
momentum.
daniel davies wrote:
One important thing to remember (I'm mugging up on this this weekend for
an
argument with Steven Landsburg) is that quantum probability is very
different from classical probability. When a particle is superposed in
two
states, that isn't at all the same thing as saying that it's in one state
with probability x and in the other state with probability y.
the difference is this: the superposition is in the "quantum amplitude",
or
state, the time evolution of which can be almost classical.
however connecting this amplitude to observations requires taking the
"complex
magnitude" of this amplitude, and so you can get interference patterns and
all kinds of goodies. this is what i refered to above as the two-tiered
approach. going from amplitude to probabilty of observation is the screwy
part.
an historical note: Heisenberg came first came to a notion of a quantum
state
and a quantum kinematical description of micro particles that made sense
of
radiation lines from excited atoms (among other things). in examining this
new description, he and Bohr noticed oddities, and the uncertainty
principle
was born as a way of making sense of the new description. sometime later,
it
was asked what is the meaning of this quantum amplitude, and Born answered
that the complex modulus was a probability thing. so historically this was
taken in two somewhat distinct seperate steps. in very crude terms,
Heisenberg came to the idea that something like position was better
described
as a matrix of numbers rather than a lone number, and Born figured out how
to
go from this matrix and state description to the measurement and
observation
of properties.
there is a famous -- within the physics community -- quotation from Murray
Gell-mann (quarks) about Bohr and his Copenhagen interpretation: "Niels
Bohr
brainwashed a whole generation of theorists into thinking that the job
(interpreting quantum theory) was done 50 years ago."
more recently Gerard t'Hooft (Nobel Prize for proof of renormalizability
of
electro-weak theory) has argued for a new look at the principles and
interpretation. for example: http://arxiv.org/pdf/quant-ph/0212095 (for
non-physics people, see beginning and end sections). here is a slide show
of
one of his talks
http://online.kitp.ucsb.edu/online/kitp25/thooft/oh/01.html
and links to the accompanying talk:
http://online.kitp.ucsb.edu/online/kitp25/thooft/
les schaffer
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