Re: Is State Vector Reduction a 'Process'?
- From: rof@xxxxxxxxxxxx
- Date: Fri, 10 Jun 2005 06:22:40 +0000 (UTC)
Arnold Neumaier <Arnold.Neumaier@xxxxxxxxxxxx> writes:
>rof@xxxxxxxxxxxx wrote:
>> Arnold Neumaier <Arnold.Neumaier@xxxxxxxxxxxx> writes:
>>
>>>rof@xxxxxxxxxxxx wrote:
>>
>> I may have confused the official Copenhagen interpretation with
>> what Bohr, Heisenberg, von Neumann and so on believed. As Scerir
>> pointed out in this thread, Heisenberg said "The discontinuous change
>> in the probability function, however, takes place with the act
>> of registration, because it is the discontinuous change
>> of our knowledge in the instant of registration that has its
>> image in the discontinuous change of the probability function.",
>> Hiesenberg, "Physics and Philosophy", 1958
>I commented that already. the 'acto of registration' happens on the
>photographic plate or in the eye, not in the mind, and is simply
>the irreversible magnification due to dissipation by interaction with
>a macroscopic detector. It is objective and has no connection to
>any 'knowledge'.
>... only that your interpretation of what he said in terms of
>knowledge is a postmodern interpretation, and either the
>Copenhagen interpretation nor Heisenberg's intention.
My apologies for taking so long to reply. Various collegiate
matters have occupied my attention for the last week.
Anyway, to summarize:
Heisenberg said "it is the discontinuous change of our knowledge
in the instant of registration that has its image in the discontinuous
change of the probability function."
My interpretation of this is: it is the discontinuous change of our
knowledge in the instant of registration that has its image in the
discontinuous change of the probability function.
Your interpretation of it is: it is _not_ the discontinuous change
of our knowledge in the instant of registration that has its image
in the discontinuous change of the probability function. It has no
connection to any 'knowledge'.
Then you declare that your arguments are excellent, and
that my interpretation of what Heisenberg said is "a postmodern
interpretation".
Now, what appears to me to be happening here is that your position,
that Heisenberg believed that collapse "is objective and has no
connection to any 'knowledge'", is entirely incorrect, and that
Heisenberg said so himself, and that when confronted with this fact,
you gave the impression that his statements required "interpretation".
You then "interpreted" his statement to mean exactly the opposite
of what he said. Then you accused me of having a distorted
interpretation because I took Heisenberg at his word, and
proceeded to insult me by calling my interpretation postmodern.
Heisenberg was even more explicit about the connection to knowledge,
which you deny he believed in:
"This probability function represents a mixture of two things,
partly a fact and partly our knowledge of a fact. It represents a
fact in so far as it assigns at the initial time the probability
unity (i.e., complete certainty) to the initial situation: the
electron moving with the observed velocity at the observed position;
'observed' means observed within the accuracy of the experiment.
It represents our knowledge in so far as another observer could
perhaps know the position of the electron more accurately. The error
in the experiment does - at least to some extent - not represent a
property of the electron but a deficiency in our knowledge of the
electron. Also this deficiency of knowledge is expressed in the
probability function." Heisenberg, Physics and Philosophy
He said this in chapter three, and goes on to say:
"We can, for instance, predict the probability for finding the
electron at a later time at a given point in the cloud chamber. It
should be emphasised, however, that the probability function does
not in itself represent a course of events in the course of time.
It represents a tendency for events and our knowledge of events."
A little further, he says:
"The observation ... breaks the determined continuity of the
probability function by changing our knowledge of the system."
You will, of course, deny that you intended any insult when
you used the word postmodern, and you will claim that everything
Heisenberg said above is completely consistent with your
interpretation, which is that the wavefunction has nothing
at all to do with knowledge. Then you'll claim that your
position is not absurd, despite the fact that it obviously
is. You will probably focus on the occurrence of the word
"fact" in Heisenberg's quote above, and claim that its
appearance demonstrates that you are right, while
ignoring the parts where he says things like "the probability
function ... represents a tendency for events and our knowledge of
events."
Now, I should point out here that your claim that your arguments
are excellent is incorrect; that they are, as I said they would be,
unconvincing even to yourself. You have adopted a position where
you interpret a statement to mean its opposite, and you have done
this not because you find that it is an excellent argument, but
because you can't allow yourself to change your mind in public,
because you fear that there is some humiliation associated with
that. Let me assure you that anybody whose respect for you drops
when he sees you change your mind is a person whose respect is
not worth having. A reasonable person would have more respect
for you if you showed the ability to change your mind, and
therefore learn, rather than sticking to a position long
after it has become ridiculous.
By the way, when you claimed that Heisenberg didn't think the
'act of registration' happened in the mind:
>... the 'act of registration' happens on the
>photographic plate or in the eye, not in the mind, and is simply
>the irreversible magnification due to dissipation by interaction with
>a macroscopic detector.
you were wrong.
Heisenberg agrees with me that the "act of registration"
does indeed occur in the mind of the observer, and not on the
photographic plate:
"Therefore, the transition from the 'possible' to the 'actual' takes
place during the act of observation. If we want to describe what
happens in an atomic event, we have to realize that the word 'happens'
can apply only to the observation, not to the state of affairs
between two observations. It applies to the physical, not the
psychical act of observation, and we may say that the transition
from the 'possible' to the 'actual' takes place as soon as the
interaction of the object with the measuring device, and thereby
with the rest of the world, has come into play; it is not connected
with the act of registration of the result by the mind of the
observer. The discontinuous change in the probability function,
however, takes place with the act of registration, because it is
the discontinuous change of our knowledge in the instant of
registration that has its image in the discontinuous change of the
probability function."
The act which we are talking about is, according to Heisenberg,
"the act of registration of the result by the mind of the observer",
and it is this that corresponds to the "discontinuous change in the
probability function". What happens at the photographic plate is
the transition from 'possible' to 'actual'.
Since this all happens in a chapter called "The Copenhagen
Interpretation of Quantum Theory", and since Heisenberg is, I hope
you will agree, competent to tell us what the Copenhagen interpretation
is, perhaps you would be kind enough to acknowledge that I have
told you something about the Copenhagen interpretation that you
didn't previously know, namely that according to that interpretation,
collapse is associated with the "act of registration of the result
by the mind of the observer".
You can read the chapter online at:
http://www.marxists.org/reference/subject/philosophy/works/ge/heisenb3.htm
>> With due respect, and I sincerely mean no offense, I believe
>> that you have been infected
>Whatever I am infected with, I hope it is highly infectuous
>and incurable, so that it spreads and has a lasting effect.
You have become infected with it precisely because it is
highly infectious, and because it has spread far and has
had a lasting effect.
It is, however, not incurable, although the patients
certainly don't like the medicine.
>> with the mental disease that I
>> ranted about in an earlier post:
>> http://groups-beta.google.com/group/sci.physics.research/msg/69ca190957f25c12?dmode=source
>This is a long post, I cannot recognize myself reflected in it.
>Neither do I recognize signs of a mental disease in my behavior.
It is extremely rare that one spots a mental disease in oneself,
but let me assure you that you are a textbook case.
>> My understanding is that this is why you react so negatively to the
>> suggestion that the wavefunction describes knowledge.
>I followed the historical development of the interpretations of QM
>quite closely, reading hundreds of papers, to be able to make up my
>own mind of how _I_ should interpret QM (and other physics).
>In the discussions on s.p.r., I share my insights for those who might
>wish to learn from it. I simply think that phrasing objective
>descriptions in a psychological language, making them dependent on
>mental processes, is neither necessary to understanding nor does it
>serve any useful purpose. There is nothing inherently absurd about
>this assessment.
These are your boasts about how well-read you are (despite your
rather poor knowledge of the Copenhagen interpretation), your
beliefs and your opinions. You cannot claim that your interpretation
was shared by the founders of quantum mechanics. I will acknowledge
that you are a strict conformist, but what you are conforming to
is the modern desire to rid physics of any reference to subjective
experience, and thereby achieve "purity". This desire spreads like
a disease, which comes complete with instructions to ridicule
those who insist, as did Heisenberg, Bohr and von Neumann, that
subjective experience must be considered carefully and not
ignored. Objectivity has become a religion, and those who
insist that physicists should completely ignore subjective
experience have become fanatical and have been allowed to take over.
>>>>A definition
>>>>of measurement isn't missing because measurement is the
>>>>acquisition of new knowledge.
>>
>>>This is not a good definition since it is never specified what
>>>constitutes acquisition of knowledge.
>>
>> Acquisition of knowledge is what happens when you look at the
>> measuring device and see where the pointer is pointing. That's
>> perfectly precise for a normal person, but it seems insufficient
>> to somebody who wants to know about "the real objective world".
>It seems that it is sufficient for you. But it is insufficient for me.
>I want a mathematical model of reality within which one can clearly
>say what exists, what is an experiment, an observer, a measurement,
>a record, etc., in such a way that one can predict in principle which
>experiments give outcomes with which accuracy.
>Such arguments are common in qunatum mechanical foundations (e.g.
>discussions of the Heisenberg microscope) but currently based on
>informal notions of experiment, observer, measurement, record
>only.
>My goal is to put the foundations of physics on a basis similarly to
>the foundations of mathematics, where the whole logical process of
>coherent deduction can be modelled on a metalevel and gives clarity
>to the foundations of mathematics that is missing in physics.
>And I think that such foundations are possible and will provide the
>same clarity for physics.
Well, they are not possible. What you are looking for is an ontology.
I will explain in the other thread, "Why physicists should pay
attention to the mind", where it is that you can find the proof
that this task is hopeless. You will, however, have to pay attention
to the mind to understand the proof.
>> Of course, if this is pointed out to them, they
>> deny it, saying "Why not at all - I am the most
>> reasonable of fellows.
>Everyone who has a sensible point of view argues that way,
>including you.
Reasonableness is to be demonstrated in one's words
and actions. One should not proclaim that one is great
and reasonable, that one has read hundreds of papers
and has excellent arguments. A person may seek to
acquire credibility by stating that they deserve it,
but such a person actually deserves less credibility.
One should give one's arguments and let others judge
if they are good or bad; if one has read many papers,
it should be shown by giving knowledgeable answers.
>Your argument sounds as if you are not claiming that the wave function
>collapse is about the change of real knowledge of real minds,
>but about how knowledge should change if someone observes something
>and acts completely rational. But then it becomes a moral statement
>completely outside science.
>However, the collapse was formulated by the founders as a necessity to
>make sense of quantum mechanics, and not as a postulate about moral
>standards for maintaining knowledge in minds.
Now, morality is about good and evil. The question of how one
should use the knowledge one has to make the best predictions
about the results of experiments is a strategic question, which
has nothing to do with good or evil, and hence has nothing
to do with morality. You must have confused "What I have to do
in order to accomplish task X" with "What it makes me a good person
to do." It seems to me that it would require an almost
superhuman ability to become confused, to make that mistake.
It is certainly not an excellent argument.
>>>Furthermore, knowledge depends on subjective decisions to trust
>>>a measurement. If we discard one as an artifact, there is no
>>>collapse. How can the collapse depend on such subjective issues?
>>
>> In the "wavefunction represents knowledge" interpretation, the
>> wavefunction is not an objective thing,
>How then can a non-objective thing change in time in an objective way???
>(Please don't be offended by the three ?s!)
Consider, for example, a random walk in one dimension. Suppose I
see where the particle is at time 0 and you see where it is at
time 1. At time 10, we both look at where the particle is, but
don't look at it between the first time we see it and the final
time. We each use the same equation to describe the time-evolution
of the probability distribution for the position of the
particle, and hence the probability distribution evolves in
an objective way (recall - objective means the same for
everybody, subjective means differs from person to person). The
probability distribution, however, is subjective, because
you use a different one to mine - yours is a delta function
at time 1, while mine is a delta function at time 0 and is
spread out at time 1. That is an example of how a non-objective
thing can change in time in an objective way.
>> but different observers
>> will use different wavefunctions, depending on what knowledge they
>> have about the system.
>If I know nothing about an experiemnt, which wave function should I use?
>Should I use instead of a pure state the microcanonical ensemble,
>suggested by many statistical mechanics treatments as noninformative
>prior? Then I make observations and find that they are not in accordance
>with the predictions of my ensemble since it is born of ignorance
>rather than knowledge...
You will use a density matrix if you know absolutely nothing about
the preparation of the system.
>> The "collapse" is what happens when the
>> observer receives new knowledge, and updates his mathematical
>> representation of his knowledge to reflect the new knowledge that
>> he has.
>This must be a ficticious observer invented to suit your interpretation.
>A real observer with a real mind has no wave function in his mind --
>that changes unitarily according to a differential equation whose
>solution requires a computing capacity much beyond the mind's power, and
>once it sees a measurement (any look out of the window, or only a
>careful look at the detector needle to be sure of the third decimal?)
>it computes the solution of the corresponding eigenvalue problem to
>find out how the wave functions must be collapsed to be consistent.
>At least you won't find that when interrogating the most competent
>experimental physicists who know how they update their knowledge.
Your sneering isn't justified. The statement regarding collapse
above is exactly what the Copenhagen interpretation states. If
you claim that you weren't sneering, then you have to also claim
that you really thought I was suggesting that people solve
Schrodinger's equation in their mind in the course of
everday life. You did not really think that.
>> Recall that subjective doesn't mean simply bad.
>I never assumed that. But subjective means outside the realm of science,
>unless that subjectivity can be explained and predicted by models of how
>it arises from something objective, such as the subjective
>observer-dependence in special and general relativity.
So you appear to be saying that you think the processes in
the brain provide a sufficient explanation of subjective
experience. If you do, then you cannot claim that von Neumann
agrees with you:
"It is inherenly entirely correct that the measurement or the related
process of the subjective perception is a new entity relative to
the physical environment and is not reducible to the latter. Indeed,
subjective perception leads us into the intellectual inner life of
the individual, which is extra-observational by its very nature."
von Neumann, Mathematical Foundations of Quantum Mechanics, p. 418
>>>At the time of Bohr, von Neumann and Wigner, the collapse meant
>>>something objective, though it might have been related to the mind
>>>in some unspecified way.
>>
>> I have to disagree with that, although I do not mean it in an
>> adversarial way. The relation to the mind was perfectly clear and
>> very specific for these people, at least by the '50s. Also, since
>> they understood that the wavefunction represented knowledge, the
>> collapse wasn't an objective thing for them.
>Please support your claims by solid evidence!
I do support my claims with solid evidence, but you consistently
pretend that I haven't, which is a dishonest thing for you to
do. The quotations from Heisenberg above where he explicitly
says that collapse corresponds to the reception of knowledge
by the observer, and von Neumann's statements about psycho-physical
parallelism, are solid evidence.
>>>>>Von Neumann takes the collapse as an axiom, hence also testifies to its
>>>>>reality.
>>>>
>>>>He uses it as an axiom, but that doesn't mean that he claimed that
>>>>the wavefunction didn't represent knowledge.
>>
>>>But he certainly didn't claim that the wavefunction does represent
>>>knowledge.
>>
>> As I quoted before,
>>
>> "Let us assume that we do not know the state of a system, S, but
>> that we have made certain measurements about the state of S and
>> know their results. In reality, it always happens this way, because
>> we can learn something about the state of S only from the results
>> of measurements. More precisely, the states are only a theoretical
>> construction, only the results of measurements are actually available,
>> and the problem of physics is to furnish relationships between the
>> results of past and future measurements." p. 337
>>
>> This is exactly a claim that the wavefunction represents
>> knowledge.
>I cannot understand how you can possibly arrive at this statement.
>If your claim were true, what von Neumann actually said (first sentence)
>would mean: ''Let us assume that we do not know what we know (the state
>of S)'', and then he deduces correctly from this (obviously false)
>premise everything he likes.
No; if my claim were true, what von Neumann said would not mean that.
You are using an argument of the form: "If what you said were true,
then X", where X is a contradiction. However, you didn't even attempt
to show how X would follow from the antecedent. You merely stated
that X would follow, as though the fact that you stated it were
a sufficient proof.
>>>No. A proposition is a statement that is true or false,
>>>or undecidable. It has nothing to do with whether or not
>>>anyone knows (or claims to know) its truth or falsehood.
>>
>> Logic, which includes the propositional calculus, is the formal
>> science of inference, and inference can only be done by the mind.
>No. It is routinely (and more reliably) done by computers.
...
>> The desire to assert that logic has nothing to do with the mind is,
>> I believe, rooted in the primitive notion of nobility,
>No. For example, it can be rooted in the fact that logic can
>be performed by microchips, which have little to do with mind as
>commonly understood.
I previously said:
>>I have to anticipate how somebody could reject something as
>>simple as this. The only thing I can think of is that somebody
>>might claim that, since computers can be programmed to do
>>symbolic manipulation, logic has nothing to do with thinking.
>>
>>The problem with this argument is that the fact that computers
>>can do the symbolic manipulation associated with formal logic
>>indicates only that logic can be represented by symbolic
>>manipulations, but establishes nothing about what those
>>symbolic manipulations describe. Logic was established
>>in its present form because those symbolic manipulations
>>describe certain rules of correct thinking.
Now, you did exactly what I predicted - said that logic can be done
by computers and therefore has nothing to do with thinking. You
ignored the fact that I had anticipated this argument and explained
why it is wrong. I will explain again, in more detail, why it is
wrong, and I would ask that the next time you reply, you either
address the argument that I give, or admit that logic does have a
connection to the mind.
The more detailed version of the explanation is:
Yes, computers can do symbolic manipulation, and the
rules of inference and deduction, by which we produce
new knowledge from existing knowledge, have been
characterized accurately enough to be expressed
symbolically. However, the fact that computers can
manipulate symbols does not mean that logic is not
a characterization of inference as done by thinking
people.
I said: The formal system X describes Y.
You said: The formal system X does not describe Y because X
can be implemented in a computer.
In the present case, X refers to symbolic logic and Y refers
to inference, which is what happens when a person goes from
the knowledge that "All men are mortal" and the additional
knowledge that "Socrates is a man" to the knowledge that
"Socrates is mortal".
We could, however, replace X with "The Euler equations", and
Y with "Fluid dynamics", and your argument would just be
as invalid:
Me: The Euler equations describe fluid dynamics
You: The Euler equations don't describe fluid dynamics because the
Euler equations can be implemented in a computer.
In fact, when we use computers to do symbolic logic, we program
them with rules which are specifically chosen because they
match "natural inference", meaning inference done by humans
in the course of their thinking. The rules of symbolic logic
were constructed to describe correct deductive thought, and
computers can be used to manipulate the symbols to produce
conclusions that we trust because we know that, if we carefully
examine each symbolic manipulation that the computer does,
it will agree with a deduction that a human could have
made without the help of the computer.
Please let me know if you understand this, or if I have to
explain it in further detail.
>> I was
>> asserting that von Neumann was aware that we only know the results
>> of measurements,
>I agree with this assertion. It is in flat contradiction with your claim
>that the wave function represents our knowledge. For a wave function
>needs infinitely many bits to specify, while the results of measurements
>(according to what you just stated, the _only_ thing we know about the
>system) can be coded in the finite number of bits making up a protocol.
Any wavefunction that can be written down by a human has a finite
Kolmogorov complexity, otherwise the human wouldn't be able to
write it down. Finite Kolmogorov complexity means finite information.
>> "More precisely, the states are only a theoretical construction,
>> only the results of measurements are actually available, and the
>> problem of physics is to furnish relationships between the results
>> of past and future measurements. To be sure, this is always
>> accomplished through the introduction of the auxilliary concept
>> "state", but the physical theory must then tell us on the one hand
>> how to make from past measurements inferences about the present
>> state, and on the other hand, how to go from the present state to
>> the results of future measurements." p. 337
>>
>> What he is saying is that, in quantum mechanics, what we call
>> a "state" is actually a theoretical construction
>but with the same objective status as mass, temperature, momentum,
>charge distribution, etc. of an object. These are also theoretical
>constructs used to organize our observations.
Almost, but not quite. Different observers will assign different
states to the same system, so it is not quite as objective
as mass or temperature.
>> Basically, you are saying that knowledge is a dirty thing,
>No. You read this into my statements. Knowledge has nothing to
>do with cleanliness. Dirty things can be washed; I wouldn't know
>how to wash knowledge.
Bravo, Arnold. You truly are the master of the metaphor.
>Knowledge is what we (think we) know. This may be a number of
>experimental results to within some accuracy, an approximate
>description of a quantum mechanical state, the rough
>temperature distribution in a room, the behavior of a piece of
>equipment according to the manufacturer's manual (perhaps
>corrected by our own calibration experiments), the weight,
>length and age of the persons working in a room, etc.
>It is (in some idealization) something describable in a finite
>string of symbols.
>On the other hand, fundamental physics is about the mathematical
>model of Nature resulting from such information. This model
>(von Neumann's ''theoretical construction'') is inferred from
>observations and contains more accurate parts, less accurate parts,
>probably a few mistaken parts, and completely unknown parts -
>it is like a 17th century world map, but instead for the
>physical phenomenon under study. The objective state of the
>system is one of the polethora of states compatible with the
>asvailable information - which one, we don't know. But if we know
>sufficiently much, all compatible states are approximately the same,
>so working with any particular of them will give good predicitions.
>Nothing here prevents one of taking the system to be the whole universe.
>The state of the universe must simply be compatible with all details
>we observed in the parts of the universe accessible to our experiments.
It would be helpful if you took care to distinguish between your
own personal interpretation of quantum mechanics and the interpretation
which you claim von Neumann had. Here, I will point out that while
you claim that "fundamental physics is about the mathematical model
of Nature", von Neumann claims that "the problem of physics is
to furnish relations between the results of past and future
measurements." p.337
You will, mostly likely claim that these two positions are compatible,
but they indicate a completely different way of looking at the
task of physics. You want a mathematical model of nature itself,
and think that measurements and their results should be a part
of the model, and shouldn't have any privileged status within
the theory. You are demanding more from fundamental physics than
von Neumann did, who simply wanted relations between the
results of measurements.
>> Also, when you say "I don't buy this," are you saying that
>> you don't believe that von Neumann held this opinion,
>> namely that the principle of psycho-physical parallelism
>> tells us that we can consider what we are observing
>> to be within our own bodies? Because he did:
>>
>> "We wish to measure a temperature. ... [we can] say: this
>> temperature is measured by the thermometer. ... we can
>> calculate the resultant length of the mercury column,
>> and then say: this length is seen by the observer. Going
>> still further, and taking the light source into consideration ...
>> we would say: this image is registered by the retina of the
>> observer. And were our physiological knowledge more precise
>> than it is today, we could go still further, tracing the
>> chemical reactions which produce the impression of this image on
>> the retina, in the optic nerve tract and in the brain, and then in
>> the end say: these chemical changes of his brain cells are
>> perceived by the observer." p.419
>>
>> "That this boundary can be pushed arbitrarily into the interior
>> of the body of the observer is the content of the principle
>> of the psycho-physical parallelism." p.420
>Von Neumann says that collapse happens in each particular physical
>system (defined by its boundary), but that consistency requires that
>if we regard a particular system as part of a bigger system then
>the collapse of the larger system must give, for the smaller system,
>results compatible with the collapse of the smaller system considered
>by itself. This is nothing more than an obvious compatibility
>condition. It has nothing to do with the nature of the two systems,
This is not correct. The boundary separates the observed system
from the observer, and von Neumann is very clear about this:
"We must always divide the world into two parts, the one being
the observed system, the other the observer." p.420
Please note that he says "must".
Please acknowledge that, according to von Neumann,
the boundary separates the observed system from the observer,
and does not merely separate one physical system from another.
Please acknowledge that von Neumann's view, that the task of
physics is to provide relations between the results of
experiments, is crucial to understanding why the boundary,
between the observer and the observed system, must be
placed somewhere. It is quite clearly the observer who
has access to the results of measurements, and who
seeks the relations between them, and that is why there
has to be a boundary between the observer, who examines
the results, and the observed system, which furnishes
the observer with the results.
It is only if you reject von Neumann's view, that the task of physics
is to provide relations between the results of experiments, and
suppose instead that the task of physics is to describe "what's really
going on", that you can think that measurements and their results
don't have a privileged role within physics. It is only if you
think that measurements don't have a privileged role, that you
can drop the demand that the boundary be placed somewhere.
Now you have done this - rejected von Neumann's view of
physics, and you demand an ontology, that is, a description
of the world as it really is in itself and considered
in isolation from the manner in which we know about it,
namely through the results of experiments. As I said
earlier, I will tell you in the other thread where you
can find the proof that your dream is hopeless.
For the moment, please acknowledge that this is indeed what you are
trying to do, and that von Neumann didn't consider your task - a
description of nature in which measurements and the observer have
no privileged role - to be a part of physics.
>You might care to notice that von Neumann carefully avoids to invoke
>either the 'mind' or the observer's 'knowledge'.
He refers to the "process of the subjective perception" on page
418, and, on page 421, divides the world into three parts:
'I [is] everything up to the retina of the observer, II his
retina, nerve tracts and brain, III his abstract "ego."'
By the 'abstract "ego"' he refers to the mind of the observer.
I recommend that you read the relevant parts of the book
before making statements about what he doesn't refer to.
>Von Neumann simply argues that the collapse is consistent with the
>psycho-physical parallelism (to the extent that one can define the
>latter by the assertion that the ''boundary can be pushed arbitrarily
>into the interior of the body of the observer'').
That is not how he defines the principle of psycho-physical
parallelism. He defines it, on page 419, as the principle
"that it must be possible to describe the extra-physical
process of the subjective perception as if it were in
reality in the physical world - i.e., to assign to its
parts equivalent physical processes in the objective
environment, in ordinary space."
>... argument does not require a body or a brain; it is true wherever
>the boundary is placed, for example when the boundary is placed
>between the exposed photographic plate and the process developing
>the plate to see the picture.
>Thus the psycho-physical parallelism is completely inessential for
>the interpretation of the collapse.
He says, on page 418, that the principle of psycho-physical parallelism
"is a fundamental requirement of the scientific viewpoint". On
page 421, he says "The danger lies in the fact that the principle
of the psycho-physical parallelism is violated, so long as it
is not shown that the boundary between the observed system and
the observer can be displaced arbitrarily in the sense given
above."
Clearly, he doesn't want the principle to be violated, and regards
it as rather important, unlike you. Your claim that he considered
it "completely inessential for the interpretation of the collapse"
is incorrect. In fact, he devotes the rest of the chapter, indeed
the rest of the book, to showing that the collapse postulate does
not in fact violate the principle of psycho-physical parallelism.
In doing so, he clearly separates the world into three parts -
one being everything outside the observer's brain, another
being the observer's brain, and the third being the observer
himself, namely the observer's mind, or as he calls, it
the 'abstract "ego"'. I highly recommend that physicists
read this book. It's a very good book.
>> He also didn't have the "subjective means bad" attitude of modern
>> physicists, and was aware that what we deal with in physics is
>> not "the real world", but rather with subjective observations:
>> "Indeed experience only makes statements of this type: an observer
>> has made a certain (subjective) observation; and never any like
>> this: a physical quantity has a certain value." p.420
>Von Neumann is more careful in his use of language than you in your
>interpretation of his words.
>There is a difference between 'experience' and 'experiment'.
>The former is a psychological concept; the latter is a concept
>of physics.
>An experience produces subjective sensory perceptions;
>an experiment produces recorded values of physical quantities.
And the first is bad, and banned from discussion of physics,
while the second is good, and may be talked about.
>> For him, the distinction between the observer and the observed
>> was of fundamental importance in quantum mechanics; this is
>> the so-called quantum/classical boundary:
>> "That is, we must always divide the world into two parts,
>> the one being the observed system, the other the observer. ...
>> The boundary between the two is arbitrary to a large extent. ...
>.. to such an extent that his observer can be an inanimate object
>like a camera or a thermometer.
No; he spends considerable time in chapter six explaining that the
subjective experience of the observer is very important and has to
be considered carefully, to avoid violating the principle of
psycho-physical parallelism. You keep pretending that this is not
the case, claiming that he never mentions the mind, when in fact
he does, and claiming that he considered subjective experience
unimportant, when he thinks it's important enough to devote an
entire chapter to.
You want to give the impression that von Neumann agreed with your
interpretation, because you can thereby claim some credibility for
your personal views. However, von Neumann's interpretation of
quantum mechanics was that it is there to furnish us with relations
between the results of experiments, while your interpretation is
that measurements have no privileged role in physics, and that
quantum mechanics is there to give us a description of the world
as it really is. These viewpoints are in complete opposition.
>> but this does not change the fact that in each method of description
>> the boundary must be placed somewhere, if the method is not to
>> proceed vacuously, i.e., if a comparison with experiment is to be
>> possible." p.420
>>
>> So, from von Neumann's point of view, to use a "wavefunction of the
>> universe" would be to proceed vacuously.
>Only in this last statement I agree with your interpretation of
>his position.
At last. I was beginning to think that you would continue to stick
to the "von Neumann agrees with me" story until you found yourself
saying that true is false.
>At this point my view of quantum mechanics differs from his.
>And with good grounds.
The grounds are the following:
You want a description of the world in which the observer is just
another subsystem of the whole world, and in which measurement
has no privileged role.
Von Neumann believed that the task of physics is to furnish
relations between the results of experiments, and so measurements
and their results must have a privileged role in the formalism.
Von Neumann's view is only consistent if there is a boundary
between the observer and the observed system.
You do not recognise this boundary as important because you
fundamentally disagree with von Neumann about what the
task of physics is. You believe that the task of physics
is to describe the world as it really is, and so it should
be possible to describe the entire world as it really is,
and hence have a "wavefunction of the universe."
Is this accurate?
R.
.
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