Talk:Afshar experiment/Archive 1

message: OK, page created.  I consolidated information which was spread (in many case, as multiple verbatim or near-verbatim copies of the same information) across many pages.  The pages I edited to consolidate this information include:
* Wavefunction collapse
* Copenhagen interpretation of quantum mechanics
* Double-slit experiment 
* Niels Bohr
* Wave-particle duality
* Bohr-Einstein debates
* Complementarity
* Transactional interpretation (Minor change: Link updated)
* Interpretation of quantum mechanics
I also removed red links to other suggested names for this page.
Next: Get rid of some links from Double-slit experiment which only apply to the Afshar experiment. Samboy 10:26, 21 Dec 2004 (UTC)
replies: text: Done.  Samboy 12:30, 21 Dec 2004 (UTC)

message: The Afshar experiment demonstrates that a coherent path distribution must be assumed to predict the number of photons incident on measurement spaces where path information is being observed, but it does not demonstrate that the coherent path distribution is actually realized across the surface of measurement spaces where path information is being observed.
All Figure number references in this article are references to Afshar’s Figure numbers in his paper “Sharp complementary wave and particle behaviours in the same welcher weg experiment”:
http://www.irims.org/quant-ph/030503/
In Afshar’s experiment, the two holes can be considered emitters in the sense that he pumps photons through these two holes with his laser, and these photons have to go somewhere. Assuming the Copenhagen Interpretation of different path distribution functions (coherent versus decoherent) for different type of measurements (visibility versus path information), one might ask the question how do these photons get distributed in experiments involving complementary measurement spaces (i.e. how many photons get mapped into each measurement space). This question is also relevant in an experiment that involves only a single measurement space where path information is being measured. The answer of course is that a global coherent path distribution function across all measurement spaces must be assumed to predict the photons incident on each measurement space. The number of photons incident on a measurement space is predicted by integration of the global coherent path distribution function across the surface of the measurement space. But the Copenhagen Interpretation indicates the predicted number of photons incident on a measurement space where we are measuring path information don’t actually exhibit a coherent distribution locally.
So when Afshar says that he has visibility of interference on the photons incident on the lens, if he means that a coherent distribution predicts the number of photons incident on the lens surface, then this is correct. But if he is saying that the photons incident on the lens surface actually exhibit a local coherent distribution across the surface of the lens, then this is incorrect.
In Afshar’s experiment there are 13 measurement spaces. There are 6 measurement spaces where visibility information is being observed corresponding to the 6 wires. There are 7 measurement spaces where path information is being observed corresponding to the 7 portions of the lens segmented by the wires. The number of photons incident on each of the wires is very low because the wires are very thin and Afshar has placed them at the point of maximum destructive interference of the coherent path distribution function. The number of photons incident on each of the lens segments can be predicted by integration of the coherent path distribution function across the face of the lens segment. If the results for all of the lens segments are added up, the result is very close to the value for the whole lens when the wires are absent, since only the portions of the total lens where there is maximum deconstructive interference in the coherent path distribution function are omitted in this integration process.
 
Afshar’s interpretation of his experiment seems to be that since the wires are very thin and he has carefully placed them at the points of maximum destructive interference, he can treat his experiment as a single measurement space. Since he is observing interference in the photons incident at the wires, he concludes that there must also be interference present in the photons incident on the lens, since he believes both sets of photons are part of the same measurement space.
 
Even though the wires are very thin, the photons incident on the wires must be treated separately from the photons incident on the lens, since different types of measurements are being made in the two cases, and therefore the photons exhibit different behaviors for the two cases. For the photons incident on the wires, visibility information is being observed, and therefore the photons incident on the wires go through both holes with a corresponding coherent path distribution that exhibits interference in the vicinity of the wires. For the photons incident on the surface of the lens, path information is being observed, and therefore the photons incident on the lens only go through one hole with a corresponding decoherent path distribution.
 
The argument that the local path distribution across each of the 7 lens segments must be decoherent consists of the following four points:
1) The photons only go through one hole and are resolved at the detectors. Therefore any interference pattern in front of the lens cannot be explained by self-interference.
2) The only other way to explain a coherent path distribution in front of the lens is for a single hole to be emitting a coherent path distribution function. Hopefully we would all agree that this is about as likely as hearing the sound of one hand clapping.
3) If a single hole is (somehow magically) emitting a coherent path distribution function, then it would manifest itself in an interference pattern at the detector image. 
4) Since there is no interference pattern at the detector image in Figure 8a, a single hole must not (somehow magically) be emitting a coherent path distribution function.
The third point above is illustrated by Figure 8b where Afshar has induced some of the characteristics of a coherent distribution sourced by a single hole by placing the wires in front of the lens at the points of maximum destructive interference. The image in Figure 8b clearly indicates interference at the detector. The interference pattern is also still clearly visible in Figure 8c, but it does seem to be attenuated somewhat from Figure 8b. Afshar’s explanation for this attenuation is that less photons are incident on the wires in Figure 8c than in Figure 8b, which is certainly true. In summary, Figures 8b and 8c indicate an interference pattern, but this interference is the result of placing the wires in front of the lens. Figure 8a illustrates clearly that there is no interference pattern at the detector without the wires present.
So how does Afshar explain his claim of a coherent distribution across the face of the lens? His explanation seems to be a superposition behavior in the neighborhood of the holes (that the photon goes through both holes exhibiting interference and it also goes through only one hole exhibiting path information). There is a superposition of states before the wave function collapses. Before the wave function collapses, there is a possibility that the photon goes through both holes with a corresponding coherent path distribution, and there is the possibility that the photon goes through one hole with a corresponding decoherent path distribution. Afshar seems to be assuming a superposition of two states at the two holes, but only a single potential path distribution. When we make an observation, the wave function will collapse in a way that depends on the nature of the measurement we are making. If we are measuring visibility information, the wave function will collapse such that the photon goes through both holes with a corresponding coherent path distribution. If we are measuring path information, the wave function will collapse such that the photon goes through one hole with a corresponding decoherent path distribution.
 
Afshar attributes far too much magic to the thickness and placement of his wires. A couple of examples with different thickness and placement are provided below to illustrate this point. Both of these examples assume a peak-to-peak distance of u = 1.4 mm for the consecutive fringes similar to Afshar’s first experiment illustrated in Figure 1.
 
For the first example, replace the wires with thin strips with a width of 1.4 mm leaving these strips centered about the maximum point of deconstructive interference. These strips will block some of the portions of the lens where the value for a coherent path distribution is less than the value for a decoherent path distribution (i.e. some of the valleys of a coherent distribution). All portions of the lens where the value for a coherent path distribution is greater than the value for a decoherent path distribution will be left exposed (i.e. all peaks of a coherent distribution). Next determine the predicted attenuation of the radiant flux at the image based on a decoherent path distribution either by calculation, simulation, or experimental measurement. Finally open the second hole and measure the actual attenuation in radiant flux at the image and compare with the value predicted in the previous step. The measured results will be much less than the value predicted by assuming a decoherent path distribution. 
 
For the second example, keep these same strips, but move them to a position where they are centered about the peaks of a coherent distribution instead of the valleys of a coherent distribution. These strips will now block some portions of the lens where the value for a coherent path distribution is greater than the value for a decoherent path distribution (i.e. some of the peaks of a coherent distribution). All portions of the lens where the value for a coherent path distribution is less than the value for a decoherent path distribution will be left exposed (i.e. all of the valleys of a coherent distribution). Go through all of the same steps as in the first example. This time the measured results for the reduction in radiant flux at the image will be much greater than the value predicted by assuming a decoherent path distribution.
 
Both of these examples demonstrate the same results as the Afshar experiment (i.e. a coherent path distribution function must be assumed to prediction the reduction in photons incident on the detectors). Therefore there is no magic in using very thin wires placed at the points of maximum deconstructive interference.
 
In summary, the Afshar experiment demonstrates that a coherent path distribution function must be assumed to predict the number of photons incident on measurement spaces where path information is being observed. According to the Copenhagen interpretation, the assumed coherent path distribution function actually collapses into a decoherent path distribution function across the surface of measurement spaces where path information is being observed. The Afshar experiment provides no evidence that the Copenhagen interpretation is incorrect.
Originally contributed by User:63.226.32.16 to Talk:Double-slit_Experiment; I copied it here since it is appropriate to place here Samboy 19:38, 22 Dec 2004 (UTC)
thread_title:  Afshar Experiment: A Dissenting Opinion 

message: The bottom line for the above Dissenting Opinion is the following false conclusion (quoted):
"According to the Copenhagen interpretation, the assumed coherent path distribution function actually collapses into a decoherent path distribution function."
Unfortunately, the major error in this argument is a misunderstanding of what the Wavefunction collapse actually means. Without going into mathematical details, a coherent superposition state can only collapse into an observable with a coherent distribution when a measurement is made. There is no "collapse" from a coherent wavefunction to a decoherent state because upon measurement a coherent wavefunation Psi is mapped into an observable within |Psi|^2 via a projection, and not into some other decoherent distribution, say |Psi_1|^2 + |Psi_2|^2 . If the above quotation were true, then we could not observe an interference pattern in a double slit experiment, or immediately after the wires in my experiment, by direct observation, but we do! We cannot change the definition of wavefunction collapse to an arbitrary and mathematically inaccurate one, just to save Complementarity! Afshar 00:06, 23 Dec 2004 (UTC)
replies: text: It is quite telling that the anonymous writer of the Dissenting Opinion (whose name is actually Alex), having now realized that his definition of the wavefunction collapse was indeed erroneous, has again attempted to “correct”his conclusion by replacing the pervious version with the following: "According to the Copenhagen interpretation, the photons predicted by the assumed coherent path distribution function actually exhibit a decoherent path distribution function locally across the surface of measurement spaces where path information is being observed." I'm afraid, the more he awkwardly tries to avoid self-contradiction, the more his lack knowledge on even the most rudimentary QM formalism and language becomes apparent. There is no such thing as "coherent path distribution function" in QM.  I suggest that he formally study QM before making more clumsy statements. Need I say more?! Afshar 07:50, 23 Dec 2004 (UTC)
thread_title: Afshar's Response

message: This article looks great with the pictures and the mathematical formulas! Samboy 23:46, 23 Dec 2004 (UTC)
thread_title:  The pictures look great 

message: The relevant definitions need to preceed (e.g. V , Imax) and so on, in order for the critique to make any sense to the non-specialist reader of the article. CSTAR 00:02, 24 Dec 2004 (UTC)
thread_title:  Definitions 

message: "Addendum: A brief response to Afshar's criticism can be found at 
http://www.physicsforums.com/archive/t-62460_Afshar_2_slit_experiment--peer_review.html
(see rkastner's third posting)"
I moved the above entry by 70.21.61.81 to this page, simply beacuse I have not yet responded to Kastner on the main Wiki page. After I enter my rebuttal, we can have Kastner's response to my official rebuttal. Let's not replace Wiki entries with Weblog links. Thanks! --Afshar | Talk 04:28, 18 Mar 2005 (UTC)
thread_title: Weblog Entries

message: Here is the question posed by Unruh. 
He asks "Yes, the lens acts as a "Fourier transform" device, but again so what?"
----------
From: Bill Unruh 
Sent: Friday, April 29, 2005 1:33 PM
To: Danko Georgiev
Again, your interpretation I agree makes no sense. The "which way"
infomation IS there in the images, just as it is there in the original pinholes. I would certainly not advise him to give you the $1000 based on this argument.  While he is wrong, he is not wrong in the way you have outlined it.
The fact that IF you were to place a screen before the lens, you would see an interference pattern, is irrelevant to whether or not the photons falling on the detectors convey "which way " information.
Yes there is a Airy disk. but so what. Yes, the lens acts as a "Fourier transform" device, but again so what. The natural propagation of the light also acts as a fourier transform. And the lens can be set up to compensage for the natural propagation transform to give you back the original image.
Bill Unruh
----------
My reply is:
Dear Bill,
You simply don't understand the essence of my argument.
The existence of light "wave" implies that there is no "which way". 
The application of Fourier transform between the two focal planes of the lens COMPLETELY MIXES THE TWO CHANNELS. In the Fourier transform you don't preserve the one-to-one mapping between the object and the image, but you introduce many-to-one mapping. Also the Fourier transform requires interference therefore if there is inteference of photon wavefunctions between the lens focal planes the final image certainly does not preserve the which way info. In order the interference to be absent between the two focal planes of the lens the photon wavefunctions for passage through slit A and B should be not coherent i.e. there must be already some "which way" marker as say different wavelength [color filter on the pinhole] or different polarization [polarization filter on the pinhole].
Danko
------------
*[Bill Unruh's response, from e-mail CC/ed to afshar@rowan.edu by Bill]
Since you decided to post an answer to a private reply to you to this whole
list, I will respond in the same way.
a) EM waves are linear. Thus the image at the detectors is precisely the
sum of the images from the waves emitted at the two slits. Those
independent images are that if the wave came from pinhole 1, the image
(yes, with diffraction pattern) falls entirely on detector 1, and the image
from pinehole 2 falls entirely on detector 2. This is an elementary result
of fourier optics. Yes, there is interference in the intermediate region,
interference which comes from precisely the linearity of the waves, but
that is irrelevant.
On the basis of your fourier optics, the Green's function of the EM field
is precisely such that the image at detector 1 depends only and solely on
the amplitude at slit 1, and that at detector 2 depends only and solely on
that at slit 2.
b) What has "classical straight ray" arguments got to do with anything. Who
discusses them but you? The argument is not based on "classical straight
ray" arguments. It is based on the wave nature of light throughout.
You may be getting confused when the term "which way" is used. It is NOT
which way the photon went between the slit and the detector. That is NOT
what "which way" refers to. It refers to whether or not the photon came
through slit 1 or slit 2. That is all. It has nothing to do with what the
photon did in the space between the slits and the detectors. You may have
gotten misled by the use of the word "way" in "which way" and thought that
it referred to a complete path. It does not. In this context it would
better be phrased as "which slit". It is ONLY which slit the light came out
of that is being determined, not anything about how it travelled between
the slit and the detector.
----------------------------------
**Dear All,
Above is an exchange between Bill Unruh (a veteran physicist) and Danko Georgiev (AKA The Fake) in which Bill rejects his utter nonsense. Although Bill disagrees with me, I applaud his defense of truth, which in this case happens to be the defense of my arguments regarding which-way info in the images. The likes of Georgiev MUST be rejected and marginalized by all real scientists in the interest of scientific advancement, all personal differences aside. I have no problem with considering unorthodox ideas (after all some may consider me as unorthodox,) but after one realizes an individual is fake, and it takes no more than a couple of exchanges for a pro., the individual must be warned, and if stubborn, BANNED from professional forums. Therefore, I shall make recommendations to PhilSci and arXiv archives, as well as Wikipedia to put his name on their blacklist. I would also encourage you to do so. Sorry Danko, but you brought this unto yourself after my repeated warnings...--Afshar | Talk 15:46, 30 Apr 2005 (UTC)
replies: text: What you have written is worth consideration, but please read wikiquette.  Your treatment of Afshar is quite impolite, and it is better to work cooperatively here (and in fact, policy).  (Afshar, I'd also suggest you read it, since it appears this has become heated.)   — Cortonin | Talk 06:01, 10 May 2005 (UTC)
replies: text:  Dear Cortonin, I couldn't care less about the manner in which Danko characterizes me. As any competent physicist would immediately notice, his "paper" is nothing but a hodge-podge of copied and pasted and mostly ill-understood concepts in Fourier optics, denounced by Unruh and myself (yes unfortunately I did read it). It is not impolite to call something what it is. It may be a bit blunt, but in this case, it is a no-brainer: Danko's "paper" is a joke, and an affront to serious physicists. As much as I respect the amateurs getting at it, I cannot ignore an ignorant person insisting on wrong concepts and total abuse of the professional lingo. What would you think if someone recommends that you use the Umbilical Cord to wrap up your gifts? Would you say "sure, a cord is a cord, is a cord"?! No, you would smile, and try to correct the individual, but if he still insists on that idea, you'd be entirely justified to dismiss him as a mere jester, deserving not a single minute of your time. Sadly, that is the case with Danko. Too sad really... Regards.--Afshar | Talk 13:26, 10 May 2005 (UTC)

text: Dear Danko, I noticed you have withdrawn your submission from the PhilSci archive. If indeed you removed it on your own initiative, I applaud that. It is a good first step in the right direction. Also, I did see your "improved" paper, but it still suffers from the same shortcomings as the original one. At any rate, best of luck to you.--Afshar | Talk 14:11, 10 May 2005 (UTC)
thread_title:  Reply to Unruh question