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Science Forum Index » Physics - Research Forum » complementarity (particle-wave duality)
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| Guest |
 Posted: Tue Apr 01, 2008 9:35 pm |
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31-MAR-2008
Some quick questions:
Does the detection of light, say at a ccd, constitute a measurement,
before an observer accesses the data and views the image?
If not, does the sensor record both particle AND wave natures of
light, regardless of the experimental setup?
I'm assuming that, as in a classical camera, until digital images are
rendered visible to an observer, the recorded information is just
Shrodinger's film... it seems consistent that complementary realities
can happily co-exist until I crack open my CVS disposable 35mm or
offload the data from my digital camera and look at the results.
Since the ordinary spatial image one eventually recovers and observes
classically is a manifestation of the particle nature of light (i.e.
the photoelectric effect), is it possible in subsequent sequential
(and presumably irreversible) measurements, to extract a meaningful
wave description from the particle image, without violating first
principles? I'm not sure how we'd do that with film since it would
require a second sensor in a scanner, but with digital it seems
somehow logical...
In other words, if the optical instrument attached to the sensor is
affecting the propagation of light as a wave, insofar as there are
diffraction effects owing to apertures etc. ahead of the sensor,
wouldn't the measure of these effects indicate that yes, particle and
wave nature are preserved simultaneously in detection, and then
separated in time by choice in some later observation?
Any clarification very much appreciated,
mark jonathan horn |
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| Arnold Neumaier |
| Posted: Fri Apr 04, 2008 9:44 am |
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mark_horn@sbcglobal.net schrieb:
Quote: 31-MAR-2008
Some quick questions:
Does the detection of light, say at a ccd, constitute a measurement,
before an observer accesses the data and views the image?
Yes. Any interaction with a macroscopic object described by
thermodynamics is dissipative and hence a measurement.
Arnold Neumaier |
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| Igor Khavkine |
| Posted: Fri Apr 04, 2008 9:44 am |
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On Apr 2, 3:35 am, mark_h...@sbcglobal.net wrote:
Quote: 31-MAR-2008
Some quick questions:
Does the detection of light, say at a ccd, constitute a measurement,
before an observer accesses the data and views the image?
Yes. So, there is no "Schroedinger's film" scenario, which you've
proposed.
Quote: If not, does the sensor record both particle AND wave natures of
light, regardless of the experimental setup?
First of all, it is better to all together drop the idea of the
particle-wave dichotomy for light, for electrons, or for anything
else. Photons, electrons, etc. are neither particle nor waves. They
are quanta respectively of the electromagnetic field, the Dirac field,
etc. Now, that may not say much to you if you are not familiar with
advanced quantum theory. But, this does show that they are more
complicated objects that in some cases can be approximately described
as particles and in other cases approximately described as waves. What
this should also tell you is where to look for a more precise
description of the quantum behavior of light.
Now, one might rephrase your question as follows: does the CCD sensor
capture enough information to reconstruct the incoming light beam at
a later time? The answer is no. For example, the CCD does not record
phase or polarization information of the light, nor many other
properties. What it does do is capture the image carried by the light
beam with enough detail to make it fairly realistic to the human eye.
Hope this helps.
Igor |
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| Gerry Quinn |
| Posted: Sun Apr 06, 2008 10:38 am |
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In article <7eeab9c4-1476-4f4a-bed2-88099879e999@
13g2000hsb.googlegroups.com>, mark_horn@sbcglobal.net says...
Quote: 31-MAR-2008
Some quick questions:
Does the detection of light, say at a ccd, constitute a measurement,
before an observer accesses the data and views the image?
As Arnold says, interaction with an object such as a CCD is enough to
provide a thermodynamically irreversible measurement, more or less
equivalent to that made by a human observer.
Quote: If not, does the sensor record both particle AND wave natures of
light, regardless of the experimental setup?
If you want to preserve the system in a pure state (i.e. the sort of
quantum superposition state in which quantum interference can be
demonstrated) you need something more sophisticated than a CCD - you
need, in fact, a measuring device that can completely erase its
measurements without trace if called upon to do so (an un-measuring
device, if you like).
Quote: I'm assuming that, as in a classical camera, until digital images are
rendered visible to an observer, the recorded information is just
Shrodinger's film... it seems consistent that complementary realities
can happily co-exist until I crack open my CVS disposable 35mm or
offload the data from my digital camera and look at the results.
Schrodinger's Cat is much misinterpreted. If a CCD is good enough to
make an irreversible measurement, a cat is even better. The cat paradox
demonstrates only that there is no obvious point at which we can say
"here is where the wave function collapses". From your perspective, of
course, different possibilities exist until you look at the result. But
these possibilities will no longer be interfering with each other; your
expectations are no different from those of a nineteenth-century
physicist who also knows that he cannot predict exactly what he will see
until he opens the box. Whatever causes quantum physics to turn into
classical physics - most people nowadays would call this decoherence -
is happening in the box before it's opened. It happens in your CCD
also.
Quote: Since the ordinary spatial image one eventually recovers and observes
classically is a manifestation of the particle nature of light (i.e.
the photoelectric effect), is it possible in subsequent sequential
(and presumably irreversible) measurements, to extract a meaningful
wave description from the particle image, without violating first
principles? I'm not sure how we'd do that with film since it would
require a second sensor in a scanner, but with digital it seems
somehow logical...
In other words, if the optical instrument attached to the sensor is
affecting the propagation of light as a wave, insofar as there are
diffraction effects owing to apertures etc. ahead of the sensor,
wouldn't the measure of these effects indicate that yes, particle and
wave nature are preserved simultaneously in detection, and then
separated in time by choice in some later observation?
All you have at the end of this experiment is a record of the results
obtained when thousands of photons passed through a double slit. You
can deduce from the conditions of the experiment and the result obtained
that individual photons - if we choose to describe the experiment in
terms of individual photons - must be doing something that cannot be
explained classically. But all we have left of each photon is a record
of a measurement at some pixel of the CCD at a particular time. Once
that measurement is made, any further quantum magic by that photon is
killed stone dead.
- Gerry Quinn |
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