Re: vol 97, issue 15 reaction

[Russell Standish]

On Fri, Jul 08, 2011 at 10:49:39AM -0600, peggy miller wrote:
> Hi -- reacting to quantum mechanics discussion.
> Question -- I probably need to go back and reread my quantum and complexity
> books, but asking anyway -- I can accept quantum particles gain a state when
> being measured, but that only shows the influence of observation on quantum
> particles. How do we prove that they have "no state" when not being
> observed? Maybe they are observed by something else, or reacting to other
> influences causing an existence and behavior that we simply call "no state".
>
>

Your terminology of "state" here is confusing and non-standard. All
quantum particles have state, which is a vector in a Hilbert space (eg
a wavefunction). When a measurement is performed, afterwards the
particle's state is aligned with one of the eigenvectors of the
measurement operator, which corresponds to a particular classical outcome.


--

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Prof Russell Standish                  Phone [phone] (mobile)
Principal, High Performance Coders
Visiting Professor of Mathematics      [hidden email]
University of New South Wales          http://www.hpcoders.com.au
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[Bruce Sherwood]

To which I would add this: The difficult experiments that deal with
this subtle issue are relatively recent, and until it became possible
to carry them out, I believe that it was possible to argue that the
system was already in the finally observed state before the
measurement confirmed what state that was. I gather that everyone
agreed that what state you would observe was probabilistic, but that
there was disagreement on whether the final state had already been
determined before the measurement was carried out. We now know that a
system can indeed be in a superposition of eigenstates before the
measurement selects out one of these. At least that's my understanding
of the significance of the recent experiments, as discussed in
Zeilinger's recent book, The Dance of the Photons. (Invitations are
hereby issued to others to correct or refine this view.)

Bruce

P.S. There are hints from other participants on this list that
postings get lost or misplaced. I saw Russell's response to Peggy
without ever having seen her note. I looked in the archives and saw
her note and Russell's response, so the archives are correct. But
there seems to be a screw loose in the machinery.

On Fri, Jul 8, 2011 at 5:28 PM, Russell Standish <[hidden email]> wrote:

> On Fri, Jul 08, 2011 at 10:49:39AM -0600, peggy miller wrote:
>> Hi -- reacting to quantum mechanics discussion.
>> Question -- I probably need to go back and reread my quantum and complexity
>> books, but asking anyway -- I can accept quantum particles gain a state when
>> being measured, but that only shows the influence of observation on quantum
>> particles. How do we prove that they have "no state" when not being
>> observed? Maybe they are observed by something else, or reacting to other
>> influences causing an existence and behavior that we simply call "no state".
>>
>>
>
> Your terminology of "state" here is confusing and non-standard. All
> quantum particles have state, which is a vector in a Hilbert space (eg
> a wavefunction). When a measurement is performed, afterwards the
> particle's state is aligned with one of the eigenvectors of the
> measurement operator, which corresponds to a particular classical outcome.
>
>
> --
>
> ----------------------------------------------------------------------------
> Prof Russell Standish                  Phone [phone] (mobile)
> Principal, High Performance Coders
> Visiting Professor of Mathematics      [hidden email]
> University of New South Wales          http://www.hpcoders.com.au
> ----------------------------------------------------------------------------
>
> ============================================================
> FRIAM Applied Complexity Group listserv
> Meets Fridays 9a-11:30 at cafe at St. John's College
> lectures, archives, unsubscribe, maps at http://www.friam.org
>

============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
lectures, archives, unsubscribe, maps at http://www.friam.org

[Russell Standish]

On Fri, Jul 08, 2011 at 11:06:32PM -0600, Bruce Sherwood wrote:

> P.S. There are hints from other participants on this list that
> postings get lost or misplaced. I saw Russell's response to Peggy
> without ever having seen her note. I looked in the archives and saw
> her note and Russell's response, so the archives are correct. But
> there seems to be a screw loose in the machinery.
>

Check your spam box. That is where I found your email ...

--

----------------------------------------------------------------------------
Prof Russell Standish                  Phone [phone] (mobile)
Principal, High Performance Coders
Visiting Professor of Mathematics      [hidden email]
University of New South Wales          http://www.hpcoders.com.au
----------------------------------------------------------------------------

============================================================
FRIAM Applied Complexity Group listserv
Meets Fridays 9a-11:30 at cafe at St. John's College
lectures, archives, unsubscribe, maps at http://www.friam.org