Common misunderstanding of Copenhagen Interpretation of QM
#13
(13-Jun-2013, 02:42 AM)Kanad Kanhere Wrote: About the placement of the detector, its very important. This can be observed by just moving the screen very close to the two slits. Interference pattern doesn't occur in that case [refer this experiment]

Please bear with me for one more post. I can understand how moving the screen close to the double slits will reduce the interference pattern. My question is about the detector. Let us fix the distance between the double slits and the screen. Let us place a detector in between the plane of the double slits and the plane of the screen like it is shown in the video in the earlier post. Turn the detector on.

1) Now slide the detector closer towards the plane of the double slits. What will the pattern in the screen look like? Will it be more closer to the non-interference pattern (ie just two sharp bands on the screen)?

2) Now slide the detector closer towards the plane of the screen. What will the pattern in the screen look like? Will it be more closer to the interference pattern?
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#14
(13-Jun-2013, 06:57 AM)Captain Mandrake Wrote: Please bear with me for one more post. I can understand how moving the screen close to the double slits will reduce the interference pattern. My question is about the detector. Let us fix the distance between the double slits and the screen. Let us place a detector in between the plane of the double slits and the plane of the screen like it is shown in the video in the earlier post. Turn the detector on.

1) Now slide the detector closer towards the plane of the double slits. What will the pattern in the screen look like? Will it be more closer to the non-interference pattern (ie just two sharp bands on the screen)?

2) Now slide the detector closer towards the plane of the screen. What will the pattern in the screen look like? Will it be more closer to the interference pattern?

Yes to both questions, as per my understanding.
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#15
(13-Jun-2013, 12:10 PM)Kanad Kanhere Wrote:
(13-Jun-2013, 06:57 AM)Captain Mandrake Wrote: Please bear with me for one more post. I can understand how moving the screen close to the double slits will reduce the interference pattern. My question is about the detector. Let us fix the distance between the double slits and the screen. Let us place a detector in between the plane of the double slits and the plane of the screen like it is shown in the video in the earlier post. Turn the detector on.

1) Now slide the detector closer towards the plane of the double slits. What will the pattern in the screen look like? Will it be more closer to the non-interference pattern (ie just two sharp bands on the screen)?

2) Now slide the detector closer towards the plane of the screen. What will the pattern in the screen look like? Will it be more closer to the interference pattern?

Yes to both questions, as per my understanding.

My understanding is also the same. That is why I think that the light from the detector shined on the photon/electron from the double slits is causing the collapse of the wave function of the photon/electron. Back to the point 1) you made in an earlier post.

Quote:I don't think if I shine a beam of light on another beam of light, it will cause a wavefunction collapse of either of the beams.

Similar to the collapse of the wave function of photon/electron by the light from the detector wouldn't one beam collapse the wave function of photons in the other beam? Googled this question and found this link to another forum.

http://www.thenakedscientists.com/forum/...ic=27154.0

There are a lot of comments on that topic. All seem to say that nothing will happen under most circumstances. Only under extreme conditions do interesting things happen.

Now I am confused. Did the light from the detector collapse the wave function of photon/electron from the double slit?
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#16
(14-Jun-2013, 12:21 AM)Captain Mandrake Wrote: Now I am confused. Did the light from the detector collapse the wave function of photon/electron from the double slit?

Its better to think this way: act of detection causes the wavefunction collapse. Now what constitutes as an act of detection is an open problem (measurement problem).

Not all detectors work by shining light. Photon detectors could actually be just markers that polarize the light in a specific way to facilitate which-slit-detection later.
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#17
(10-Jun-2013, 05:33 AM)Kanad Kanhere Wrote: The Copenhagen interpretation (CI), one of the popular interpretations of quantum mechanics (QM), is often used by people to assert evidence towards involvement of "consciousness" in workings of the universe at a very fundamental level.

Some people tend to do that. Like how we hear people quoting Einstein's God does not play dice totally out of context to support their faith. And funny thing is that they do not have any idea about the EPR paradox. People like von Neumann used the word consciousness in QM but that can be just a prerequisite for any measurement. There is nothing supernatural about it.

Quote:Its also important to note that none of this interpretations yet have any meaningful contribution to physics per se because they do not offer any new falsifiable testable predictions.

Karl Popper's idea of scientific theory being falsifiable is kind of backdated. Because to falsify a correct theory you need to consider scenarios which cannot occur because if it does the theory will no longer be correct! Rather than falsifiability its the accuracy of the prediction which should be within the limits of the theory.

Quote:Coming back to CI, one of the primary reason, IMO, that causes the claimed misunderstanding is because of the famous thought experiment Schrodinger's cat.

This misunderstanding happens because there is no real collapse in the closed system mentioned in the experiment.

Quote:The biggest error is usage of the word "observation" in the above text. Because of its inherent anthropocentric nature its easy to mistake that CI claims to involve consciousness, associated with the act of observation, in the so called wavefunction collapse.

Exactly. Because a conscious observation mentioned by von Neumann is done from the outside and hence relevant only for open systems.

Quote:For example in the double slit experiment the destruction of interference pattern can be achieved via placing particle detectors close to the slits. How CI explains this behavior is that the act of detection by the particle detectors causes a wavefunction collapse of the particle, which makes interference of the wavefunction impossible.

AHEM that is not true. When you observe a photon the energy of the photon becomes delocalized and absorbed. Hence assuming that the wavefunction collapsed to measured eigenstate does not make any sense. The photon does not exist at that point.
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#18
(01-Sep-2013, 07:05 AM)Warl0ck Wrote: Karl Popper's idea of scientific theory being falsifiable is kind of backdated. Because to falsify a correct theory you need to consider scenarios which cannot occur because if it does the theory will no longer be correct! Rather than falsifiability its the accuracy of the prediction which should be within the limits of the theory.

Umm.. That didn't make sense. Although its indeed a concern whether Scientists indeed give enough importance to falsifiability (discussed here), falsifiability is still not outdated and infact I would say can never be so.

Explaining the Phenomena is indeed The goal for Science. Infact accuracy of predictions itself implies some sort of falsifiability at play. It is summarized very well by this intelligent quote by Neils Bohr.

(01-Sep-2013, 07:05 AM)Warl0ck Wrote: AHEM that is not true. When you observe a photon the energy of the photon becomes delocalized and absorbed. Hence assuming that the wavefunction collapsed to measured eigenstate does not make any sense. The photon does not exist at that point.

The discussion is in context of Copenhagen Interpretation and that only. And as far as my understanding goes CI does rely on wave collapse! Various interpretations use various other schemes to explain the relevant behavior though.
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#19
Quote:Umm.. That didn't make sense.

I don't want to go into a philosophical debate since Karl Popper himself accepted that falsifiability is not enough to credit a scientific theory. For scientists the falsifiability of a theory is not that important. The falsifiability of a theory is given more importance when we are dealing with pseudoscience. Just think, if it was that important for a scientific theory then why so many physicists are still working on (and swearing by) String theory?

Quote:The discussion is in context of Copenhagen Interpretation and that only. And as far as my understanding goes CI does rely on wave collapse! Various interpretations use various other schemes to explain the relevant behavior though.

There is no version of Copenhagen Interpretation on record which can be called official. But if we put it aside then yes it does talk about wavefunction collapse, again whose mechanism it can't explain. What I was pointing out is the mistake of using that particular interpretation on photon. This is a common misconception even with QM veterans. Please understand that the interpretation of QM is not mainstream QM. Unless you learn about QM from Shankar's book, you'll find that almost all mainstream books take the approach of non Interpretation or rather shut up and calculate (borrowing Feynman's words ;-).

By the way you might want to have a look at http://arxiv.org/abs/0806.3547 where Copenhagen Interpretation again takes a punch to its belly.
If it was so, it might be; and if it were so, it would be; but as it isn't, it ain't. That's logic. ~ Twiddledee
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#20
(01-Sep-2013, 11:42 PM)Warl0ck Wrote: Just think, if it was that important for a scientific theory then why so many physicists are still working on (and swearing by) String theory?

Then we should also note as to why string theorists face so much resistance from likes of Lawrence Krauss - for lack of falsifiable predictions. Scientists are spending a lot of effort on it because its promising. But it will never be accepted till its falsifiable predictions are verified. Until then it will always have the status of "in the works".

A theory ofcourse needs lot more than falsifiability. But Falsifiability is still an important aspect of Scientific Method.

(01-Sep-2013, 11:42 PM)Warl0ck Wrote: There is no version of Copenhagen Interpretation on record which can be called official. But if we put it aside then yes it does talk about wavefunction collapse, again whose mechanism it can't explain. What I was pointing out is the mistake of using that particular interpretation on photon. This is a common misconception even with QM veterans. Please understand that the interpretation of QM is not mainstream QM. Unless you learn about QM from Shankar's book, you'll find that almost all mainstream books take the approach of non Interpretation or rather shut up and calculate (borrowing Feynman's words ;-).

By the way you might want to have a look at http://arxiv.org/abs/0806.3547 where Copenhagen Interpretation again takes a punch to its belly.

Its true that most books follow 'shut up and calculate' approach. The intent of this post wasn't to support or popularize CI, the intent was to bust its usage by woo peddlers as a "proof" for 'consciousness being the source of everything'.

Thanks for your link. I will go through the paper in detail later. A quick skim didn't seem to be against wavefunction collapse. Eraser experiments are common and not really against it as per my knowledge.
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#21
** Because to falsify a correct theory you need to consider scenarios which cannot occur because if it does the theory will no longer be correct! **

The way I read it there seems to be a confusion between falsifiable theory and falsified theory (I do not imply that you do not know the difference). It is just that the theory or more precisely the hypothesis has to be falsifiable. If it is falsifiable then the scenarios under which it will be falsified can naturally follow from the way the hypothesis is framed. For example the hypothesis that the gravitational force between two masses is inversely proportional to the square of the distance between the masses is falsifiable (double the distance between two masses and show that force decreases by a factor other than four) but not falsified.
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#22
Came across this paper titled "Consciousness and the double-slit interference pattern: Six experiments" on the web on this topic. The paper claims that consciousness does affect the outcome of the double-slit experiment.

http://www.deanradin.com/papers/Physics%...0final.pdf

The abstract is quoted below.

Quote:A double-slit optical system was used to test the possible role of consciousness in the
collapse of the quantum wavefunction. The ratio of the interference pattern’s double-slit spectral
power to its single-slit spectral power was predicted to decrease when attention was focused toward
the double slit as compared to away from it. Each test session consisted of 40 counterbalanced
attention-toward and attention-away epochs, where each epoch lasted between 15 and 30 s. Data
contributed by 137 people in six experiments, involving a total of 250 test sessions, indicate that on
average the spectral ratio decreased as predicted (z=-4:36, p=6·10-6). Another 250 control
sessions conducted without observers present tested hardware, software, and analytical procedures
for potential artifacts; none were identified (z=0:43, p=0:67). Variables including temperature,
vibration, and signal drift were also tested, and no spurious influences were identified. By contrast,
factors associated with consciousness, such as meditation experience, electrocortical markers of
focused attention, and psychological factors including openness and absorption, significantly
correlated in predicted ways with perturbations in the double-slit interference pattern. The results
appear to be consistent with a consciousness-related interpretation of the quantum measurement
problem.

The experiment described in the paper is really bizzare. This is how consciousness was brought into the experiment.

Quote:During a test session, participants were instructed by
the computer to direct their attention toward the double-slit apparatus or to withdraw their attention and relax. To
announce the attention-toward task, a computer-synthesized voice said, ‘‘Please influence the beam now’’; for
attention away, it said, ‘‘You may now relax.’’

Apparently it is not the measurement that interferes with the experiment. Just someone thinking about influencing the experiment is sufficient. How the experimenter figures out if the person claiming to be thinking about influencing the experiment is actually thinking about it is not very clear?

How do these papers get published?

PS: Have not read the entire paper. Just the abstract and the experimental procedure.
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#23
(06-Sep-2013, 08:46 AM)Captain Mandrake Wrote: The paper claims that consciousness does affect the outcome of the double-slit experiment.

http://www.deanradin.com/papers/Physics%...0final.pdf
...
How do these papers get published?

Wariness is recommended for any claims of the Institute of Noetic Sciences (whose claim to notoriety is the tall claims of pre-cognition). Some quick Googling also showed that the journal in which it is published is something the online physics community considers adding to the list of 'faux scientific journals'. As for the Institute of Noetic Sciences, its claims that strain credulity feature prominently in the supposedly 'non-fiction' movie I Am which includes in itself a digest of woo-woo from disparate sources, a take-down of which can be the subject of another thread.
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