Talk:Double-slit experiment/Archive 1

message: Just throwing this out there, but what if interference pattern that occurs from the double slit experiment is independent of time?  That is to say that while we perceive the electrons/photons/whatever to be shot one-at-a-time, the particles themselves do not due to their high-speed and therefore the Lorentz contraction of time.  So while we see a "gun being fired", the particles behave as if they were in a wave of particles all being shot at once.  So, it's not so much a probability-wave as a time-independent-wave (atemporal-wave).  That would seem to coincide with general relativity and the double slit in time experiment mentioned below.  Any answers?  —Preceding unsigned comment added by 159.153.140.10 (talk) 00:42, 29 September 2007 (UTC)
thread_title:  Double slit free of time 

message: # In the double-slit experiment, does it matter whether more than one light source is used?
# Has there been any significant discussion regarding the possibility that photons fluctuate between positive and negative intensity?
--η[ υωρ] 08:14, 19 Nov 2004 (UTC)
thread_title:  Interference 

message: I've added a link to a pretty good analysis of Afshar's work to the page.  It is written in layman's terms.  Basically, since the wires are thin, the light is mostly particles as it hits the lens and the wires don't make the light very "wavy".  Interesting discussion there; I think it's worth having here just as Afshar's experiment is worth having here.  Samboy 08:16, 21 Dec 2004 (UTC)
replies: text: Dear Samboy, the link you have added is that of Lubos Motl (a colleague of mine at Harvard), whose Wikipedia user name is Lumidek. Please take a look at the above Nov. 27 discussion on this page where link [1] and [2] are in fact the same link you have provided. I met with Lubos and discussed our differences. In fact it was him who suggested that I write an article for Wikipedia, which I intend to do soon. Briefly, he must meet the same challenge as Aurelien mentioned in the pervious post, as his argument in his link is NOT rigorously worked out. Please take a look at my weblog to see my detailed response. Therefore, I have moved the link here, as this particualr argument was already settled back in November. Afshar 08:34, 21 Dec 2004 (UTC)
replies: text: I think the way to handle this, at this point, is to place all of the information about your (Afshar's) experiment available in a single page and simply link to it from other pages.  I certaintly think your experiment is (to put it mildly) notable enough to merit its own page.  I also agree that there is going to be a lot of controversey about this discovery; any new discovery in Science is met with great skepticism.  Einstein never accepted Quantum Mechanics, after all.  On the other hand, this skepticism is healthy because many seemingly great discoveries are later on sown to be nothing; Cold fusion being a well-known example.  The fact that this experiment has generated so much controversey shows how notable it is.  I think it is best for all sides to be heard.  And I certaintly don't see any retraction from Lumidek about his blog entry! Samboy 09:12, 21 Dec 2004 (UTC)
replies: text:  Dear Samboy, I do not shy away from controversy in the least bit, and like you, believe it is a healthy aspect of the scientific process--as long as the participants are both objective and knowledgeable in the field. I appreciate your prudent act of getting a separate page started. However, I do not think it should turn into a forum. There already are hundreds of fora (including my own) where discussions on the experiment have been raging for months. As for Lobus' retraction, suffice it to say that he has toned down his comments considerably (actually, changed his weblog comments after our meeting) and as you can see in his discussion there, he admits that "Shahriar may have found a statement due to Bohr in the libraries or archives that was proven incorrect by this experiment." The statement he refers to is in fact the very description of Complementarity in Bohr's own words (published in the journal Nature), and personally verified by the eminent historian of physics Prof. Gerald Holton of Harvard. That is good enough for me! Afshar 09:49, 21 Dec 2004 (UTC)
replies: text: I think the new page will minimize the kinds of conflicts.  I have now reinstated this link at the bottom of the new Afshar experiment page, along with three blog entries with a more positive viewpoint on your experiment.  I think this is far more NPOV than just a link to Motl's blog entry.  And, yes, just as evolutionists have to put up with nonsense about creationism on the evolution page, we have to look at dissenting views here too. Samboy 10:44, 21 Dec 2004 (UTC)
replies: text: I agree that it is more factual this way. Sounds pretty fair! Afshar 11:00, 21 Dec 2004 (UTC)

text: Let me add one more comment. Using the name of Harvard University may certainly be appealing, but it can also be used as in . Don't get me wrong, I think that Viktor Kozeny, the founder of the Harvard funds, is a very bright and in some sense nice guy! But on the other hand, Harvard funds is not related to Harvard university. Shahriar, I am not sure whether it is quite an honest and scientific approach if you repeat so many times that you're Harvard faculty, especially if it does not seem to be true. If you want to see the list of Harvard physics faculty, open . Did they forget you?  --Lumidek 19:43, 21 Dec 2004 (UTC)
replies: text: Dear Lumidek, where have I ever said that I am a Harvard Faculty?! You MUST produce evidence for such a claim if you care about your credibility with the public. This is not the first time you have attributed inaccurate statements to me, some of which I have responded to in your Blog. You make rash and irresponsible comments like this all the time, as others (whom I will not mention here) have also complained. I have every legal right to use Harvard's name as the place where the experiment was actually performed and announced while I was a Research Scholar. So, I kindly ask you to stop this kind of ridiculous personal attacks before it gets too ugly. It is really unbecoming of a Harvard "faculty" member. --Afshar 20:34, 21 Dec 2004 (UTC)
replies: text: Dear Shahriar, your question "where I ever said that I am a Harvard faculty" is unfortunately very easy to answer. If you look in the second paragraph of this section, you will find your text "Dear Samboy, the link you have added is that of Lubos Motl (a colleague of mine at Harvard), whose Wikipedia user name is...". Also, the very first sentence of the article Afshar experiment says "In March 2004, Shahriar S. Afshar announced at Harvard University the..." which undoubtedly creates the (wrong) impression that Harvard University has something to do with your statements. Moreover, you repeatedly call your experiment "the Harvard experiment". No actual scientist from Harvard would use the name "Harvard" even with 10% frequency of yours. If you want to go far enough and think that you have the right to call your experiment "the Harvard experiment", we may try to ask the responsible people at Harvard. Incidentally, the authentic URL of the list of Research Scholars at Harvard is here: , not at Google. --Lumidek 20:49, 21 Dec 2004 (UTC)
replies: text: Dear Lobus, we were both Research Scholars while I was there, that makes us colleagues. You have called me a colleague in the past yourself, and if you have changed your opinion on that it is your choice. By the "Harvard experiment" I have meant to distinguish between the high flux investigation that was performed at Harvard and the single photon version performed at Rowan university. If it makes you feel better, simply replace "the high flux experiment conducted and verified at Harvard" with "Harvard experiment". As for associating my work with Harvard, the "responsible people" have already clarified the legal boundaries in a written document provided to my legal team at IRIMS.-- Afshar 20:59, 21 Dec 2004 (UTC)
replies: text: Dear Shahriar, if were were both research scholars in 2003, then you can call us "former colleagues", but not "colleagues". On my blog, sorry to tell you, I used the word "colleague" as a kind of joke - I am often using this word for crackpots - various crackpots who want to claim that they falsified theory of relativity, quantum mechanics, or perhaps energy conservation or anything like that - to point out that they definitely consider themselves to be our colleagues which I find entertaining - as long as it remains on the level of jokes. I don't believe that you were allowed to use Harvard's trademarks for your experiments. Incidentally, if you search for the word "colleague" in , you will see that I used exactly the same word for Viktor Kozeny - and my guess is that you will understand that it's not quite serious. --Lumidek 21:36, 21 Dec 2004 (UTC)
replies: text: Dear Lubos, in that case I am sorry I took you seriously! Only time will tell who is more entertaining...--Afshar 21:39, 21 Dec 2004 (UTC)
replies: text: Dear Shahriar, I am happy that we can end this discussion with a happy end - the time will tell (if it has not already told). I agree with your whole last comment, except for your spelling of my first name, and I wish you happy holidays. --Lumidek 21:45, 21 Dec 2004 (UTC)
thread_title:  I've added a link to a pretty good analysis of Afshar's work 

message: In the current article it is stated:
:The waves interfering must be coherent, i.e., the light has the same frequency and is in the same phase. In Young's experiment, this was achieved by passing the light through the first slit, and thereby diffracting it, producing a coherent wave; this is more typically achieved now by using a laser, and removing the first slit.
Was the above procedure fully explained and justified by classical wave mechanics? According to classical wave mechanics, light consisting of a spectrum of colors is a superposition of electromagnetic waves with different wavelength. Does classical wave mechanics allow superposition of electromagnetic waves that closely match in wavelength, but are not in the same phase? Does classical wave mechanics predict interference patterns when the lightsource is a narrow band of the spectrum, but not perfectly monochromatic?
Quantum electrodynamics allows unlimited superposition, so according to quantum electrodynamics incoherent lightsources remain incoherent after the first (single) slit. What does classical mechanics allow, and should an article on double slit experiment present an interpretaton both in terms of classical wave mechanics and in terms of quantum electrodynamics? -Cleon Teunissen | Talk 09:44, 23 Mar 2005 (UTC)
thread_title:  What exactly is changed as light negotiates a single diffracting slit? 

message: Cleon Teunissen | Talk 10:24, 7 Apr 2005 (UTC)
thread_title:  coherency and pinholes 

message: The article says that the experiment can also be performed with beams of electrons or atoms; it would be nice if some more detail could be added for this (when were the experiments performed, what kinds of atoms were used, etc.) Cwitty 23:54, 4 November 2005 (UTC)
thread_title: Beams of electrons or atoms?

message: Say if we can do this experiment at home. (anon User:210.201.31.246 on 21 Feb 2006)
:Yes you can. linas 00:12, 22 February 2006 (UTC)
thread_title:  at home 

message: I have a PhD in QM, but it's some years (20 plus) since I used it, so I'm rusty. Can I ask you guys for feedback on a basic question? One thing that always bugged me about most explanations of electron diffraction in the two slits experiment was that they were based on the single-particle approximation, with the electron being the particle and the slits being modelled as an external potential, so the only wavefunction being considered is that of the single electron.  Now, in reality the slits are gaps in some kind of physical device made of, guess what, electrons and nuclei, so the electron that is passing through the slits is actually interacting, under the influence of electromagnetic forces, with all of the other electrons and nuclei that form the boundaries of the slits. That interaction will be mediated by photon exchange, in a way that is linked to the relative speed of the electron being diffracted, and it should be more properly modelled as a many-body wavefunction. Has anyone investigated whether the diffraction effects could reflect the wave-nature of the electromagnetic intereaction between the electron and the screen containing the slits? It seems to me that this could, in principle, allow for diffraction effects even if each electron definitely went through only one slit. (unsigned question from User:81.155.67.43 on 31 March 2006)
:Interesting question. Several answers:
:-- As long as the simplest theory of twoslit diffraction is sufficient to explain the outcome, there is no incentive to look for more complex explanations. Occam's razor.
:-- You might find that the Mott problem to be the many-body treatment that you are looking for, although it is for cloud chambers and not the double-slit. Although it actually solves the opposite problem: it explains the abscence of a "diffraction effect", as it were. You might also find the Renninger experiment intriguing.
:--There are quantum effects when the size of the particle being scattered is non-negligable with regard to the size of the slit. These have been experimentally measured and theoretically confirmed for the diffraction of large molecules through very very small slits. 
:But your suggestion founders: a many-body wavefunction is inherently quantum mechanical; and adds to the confusion of "wheres the electron" the additional confusion of "which electron are you talking about, they're all indistiguishable?" In a certain sense, many-body quantum mechanics aka QFT is even more mired in subtle confusions when it comes to the interpretation of quantum mechanics. linas 23:51, 31 March 2006 (UTC)
replies: text: I see your question, and raise you one. What effect do the particles hiting the mask have on quantum state of the particles making up the edge of the slit? Is there any way to seperate the 'negative' effect of a hole in the mask material not gaining the charge of the particles from the 'positive' effect of the particles selected by the slits?Shalaid 03:39, 18 September 2007 (UTC)
thread_title: A basic question

message: I would like to know how large/small the slits need to be. Actually there could be several articles referenced from here
relating to the different variations of this experiment (and
well yes, there are many references:-)
According to basic description the slits should be less than a wavelength. I think we were told in College that slits could be 
made (or were made) by cutting in covered glass.
But I have a recollection that the experiment at that time
(1964) was meant to demonstrate that light after the slits would
behave differently, as if one beam.
So you can see this is more a request for more explanation.
Thank you for this article, the many references and the
interesting inspiring writing.
    Donald Axel
--d-axel 09:20, 12 May 2006 (UTC)
thread_title:  Request for more description of Young's experiment 

message: One sentence in the article is too vague to be meaningful.
A very easy way to see the interference pattern is to look at light in the background through a slit made by common objects such as two pencils. The interference pattern of lighted bands and obscure bands is evident to anyone.
# What is "the interference pattern" supposed to refer to? The aforesaid pattern produced by double slits? You don't need additional apparatus to see what is there, so the sentence most refer to some other interference pattern -- but this sentence leaves the reader to depend on total guesswork.
# "Look at light in the background"??? Nobody can see light. One sees things of a certain magnitude by means of reflecting light off of them.  So what is the author really trying to say?  My guess is that s/he refers to looking at some lighted surface that stands at some distance from the observer. 
# Now we are instructed to look at this "light" through a single slit made by two pencils.  Pencils have become animate, and operate in pairs. They go around carving slits in things?  Probably not.  Probably the author is trying to say that one should hold two pencils close together so that there is a very narrow gap between the two pencils.  
# If all this guesswork, which should not be necessary, is correct then the author is describing a single slit experiment, and asserting that "the interference pattern... is evident to anyone."  According to normal English syntax, "the interference pattern" has to refer to an earlier mention interference pattern. (A little dog came walking over the hill. The dog was a Corgie.)  But the earlier interference pattern was produced by interference between light transmitted through two slits.
The existence of a diffraction pattern produced when light is passed through a narrow gap is well known. But that phenomenon is different from the interference pattern produced by two slits illuminated by coherent light.P0M 07:42, 29 August 2006 (UTC)
thread_title:  Does not convey a clear meaning 

message: The article currently reads:
"...Although the double-slit experiment is now often referred to in the context of quantum mechanics, it was originally performed by the English scientist Thomas Young some time around 1805..."
but the Thomas Young article says c. 1801, as does Tipler's "Physics" (as referenced in main article, page 1131).  It's a minor point, but if anyone can verify it, it probably should be changed for accuracy's sake! Dom 15:41, 12 January 2007 (UTC)
replies: text: Why not fix it then? P0M 07:06, 13 January 2007 (UTC)

text: ok 129.234.4.1 21:08, 13 January 2007 (UTC)
thread_title:  Check Dates