Talk:Double-slit experiment/Archive 2

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: 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: 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: 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 

message: Let's say that someone does the double slit experiment as follows:
The particle emitter being used is a photon gun. Each time a button is pressed, one and only one green photon is fired. The gun is aimed in such a way that the green photon goes through the middle of the left hand slit and strikes the detector screen at exactly the same spot every time. Since the gun is aimed through the middle of the left hand slit, what difference does it make if the right hand slit is open or closed? The width of the slit is much greater than the wavelength of the photon. All that happens is that you end up with many hits at a single point on the detector screen.
Please let me know what is wrong with this way of thinking about the double slit experiment.
By the way, what is the usual width of the slits in this experiment? Any slit visible to the naked eye would have to have a width many times the wavelength of any visible light photon. n5i124 Honeychurch 09:13, 30 August 2007 (UTC)
thread_title:  Questions about the double slit experiment