Talk:Double-slit experiment/Archive 5

This is an archive of past discussions about Double-slit experiment. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.

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Please put new communications at the bottom of this talk page. If you put new stuff up here with the stuff from 2004 it is likely to get ignored.

(Please archive anything else not needed to archive 3. The others are full. P0M (talk) 01:46, 21 November 2007 (UTC)}

Composition question

Could the following sentence be reworded somehow?

As experimentally demonstrated for the first time in 1987[7] and since then found in many similar experiments[8], the Copenhagen interpretation deals only with measurements corresponding to the two extremes of a continuous range of parameter values, thus ignoring the possibility of a slight change of the interference pattern if the parameter is changed only slightly.

I had to read this sentence several times to be sure that "as experimentally demonstrated for the first time in 1987 and since then found in many similar experiments," was not describing the Copenhagen interpretation. It would be impossible to perform experiments on a point of view, no? And also, the Copenhagen interpretation per se is not something that "deals with measurements corresponding to the two extremes of a continuous range of parameter values" either, is it? How about something like the following: "An experiment performed in 1987 produced results, since confirmed by many similar experiments, that controverted assertions made by physicists who generally adhered to the Copenhagen interpretation and who had concluded that which-path information could never be obtained without destroying the possibility of interference. They were familiar only with measurements corresponding to the two extremes of a continuous range of parameter values, and did not take cognizance of the possibility of measurements that disturbed the particles in transit to a lesser degree and thereby influenced the interference pattern only to a comparable extent." P0M (talk) 02:23, 1 April 2009 (UTC)

Thank you for this rewording. I think it expresses perfectly what I wanted to convey. The critical issue, indeed, is not the Copenhagen interpretation, but the standard formalism of quantum mechanics (which formalism, however, is developed in close relationship with the development of the Copenhagen interpretation). My statement was a result of the observation that many of the Copenhagen ideas have to be given up when taking into account measurements that can only be described by the generalized (POVM) formalism.WMdeMuynck (talk) 11:08, 1 April 2009 (UTC)

I had another question left over from above: "Are you affirming that which-path information can be obtained for single photons, electrons, etc., and yet they will contribute to an interference pattern?" P0M (talk) 17:22, 9 April 2009 (UTC)

Quantum mechanical information is information on ensembles. For instance, an interference pattern is a property of an ensemble. What has been demonstrated is that by changing the measurement arrangement in a certain way statistical information can be obtained on both interference and path observables. We studied measurement procedures in which a parameter could be changed in a continuous way so as to have the measurement results change continuously from the results of an interference measurement into the results of a which-way measurement.WMdeMuynck (talk) 21:17, 9 April 2009 (UTC)

Thank you.P0M (talk) 02:59, 10 April 2009 (UTC)

Contradiction in article?

In the introductory section of this article it says

It is a widespread misunderstanding, originating with the Copenhagen interpretation, that any modification of the apparatus that can determine which slit a photon passes through destroys the interference pattern, thus illustrating the complementarity principle in the sense of particle-wave complementarity. An experiment performed in 1987 produced results, since confirmed by many similar experiments, that controverted assertions made by physicists who generally adhered to the Copenhagen interpretation and who had concluded that which-path information could never be obtained without destroying the possibility of interference.

But then in the next section titled Overview, the article says:

When two slits are open but a detector is added to the experiment to determine which slit a photon has passed through, then the interference pattern no longer forms and the experimental apparatus yields two simple patterns, one from each slit. This counter-intuitive result confounds everyday expectations yet is easy to demonstrate.

Those two paragraphs seem to be contradicting one another, with the first saying it's possible to detect which path photons follow without destroying the interference pattern and the second paragraph saying the opposite.

Not being an expert on the subject, though, I'm not sure how to resolve the contradiction in the article. 63.95.36.13 (talk) 19:10, 23 April 2009 (UTC)

You are correct. Your reasoning led to the conversation above. Something needs to be done to qualify the statements in the article. P0M (talk) 22:01, 23 April 2009 (UTC)

I do not think it to be a contradiction, although the statement is misleading because it takes into account only ideal interference and ideal which-way measurements, ignoring all intermediate possibilities yielding information on both interference and which-way observables.WMdeMuynck (talk) 07:30, 24 April 2009 (UTC)

Today I tried to change the text so as to look more consistent. Hope this will do.WMdeMuynck (talk) 23:01, 24 April 2009 (UTC)

If I followed the earlier discussion correctly, if individual photons are generated and sent through the apparatus as modified to lead to the results described above, then each photon will individually either interfere with itself (and contribute to the eventual formation of an interference pattern), or it will not interfere with itself (and contribute to the eventual formation of a diffraction pattern). Or have I got that wrong and experimenters have managed to get a photon to partially interfere with itself? P0M (talk) 01:52, 26 April 2009 (UTC)

You might put it this way: In a double-slit experiment the object passes through either one slit or the other, additional information (represented by the wave function) passes both slits. Quantum mechanics does not tell you anything about the ontological meaning of this information. Hidden variables theories can be more specific about that, for instance, de Broglie's guiding wave stearing the object so as to be found more often at certain places than at others. It is not unreasonable to assume that the guiding wave will be influenced differently if different things are happening at the slits. The two extremes are `no interference of the guiding wave when one slit is closed', `maximal interference when both slits are open and no further things happen at the slits'. In the Summhammer, Rauch, Tuppinger experiment I referred to, one slit is only partly open, in this way possibly influencing the guiding wave so as to let it deviate from the pure interference case more as the slit is less open. Note, however, that it is possible to calculate the quantum mechanical probabilities in these experiments without invoking hidden variables (we did so in a Phys. Rev. paper that can be downloaded here [[1]] (nr. 27). Quantum mechanics does not yield explanations in the way hidden variables theories can do, but often we do not need such explanations and can be satisfied with `just calculating measurement probabilities'. Most problems with quantum mechanics are a result of attempts to ask from quantum mechanics explanations it cannot give. That's what people tend to do who are not content with an instrumentalist interpretation of quantum mechanics: they confound the quantum mechanical wave function and de Broglie's guiding wave (or analogous constructions).WMdeMuynck (talk) 21:32, 26 April 2009 (UTC)

"The object passes through either one slit or the other." What evidence is there for this statement? P0M (talk) 00:31, 27 April 2009 (UTC)

That is a question not easy to answer. Remember that quantum mechanics does not tell us much about individual objects, it just tells us about the results of measurements. So, what we can tell about what an individual object is, must be derived either from our observations or from rational ideas we have about what is science (like, for instance, the ideas of substance and causality). It also depends on your definition of `object': do you consider the object as consisting of a particle-like core having also a wavelike part (as is suggested by the electron model of quantum electrodynamics, the wavelike part being associated with vacuum fluctuations) or do you consider only the particle-like core as the object. In the first case the object passes through both slits, even if its particle-like core is passing through one slit.

Note also that no theory can be proven by experiment (it can only be falsified). But there is sufficient experimental evidence that objects do not satisfy particle-wave complementarity (the object allegedly behaving as a particle in a which-way experiment and as a wave in an interference experiment): in all experiments there can be observed both particle-like and wave-like phenomena, the latter being responsible for the interference pattern (which is not a property of an individual object but of an ensemble), the pattern being built up by particle-like impacts of individual objects. This strongly suggests that the object, if it started as a particle and ended as a particle, probably has been a particle all the time. This, at least, is not contradicted by any experiment in which a detector is placed inside the interferometer (which is the kind of experiments we extensively studied). It is true, however, that to be tested these ideas have to await theories and experiments referring to individual objects rather than ensembles.WMdeMuynck (talk) 11:16, 27 April 2009 (UTC)

Thank you. That response seems quite rational to me. (I am probably too agnostic about everything. ;-) P0M (talk) 16:25, 27 April 2009 (UTC)

I think the quality of this article is much better than what it was about a year ago when I translated it into Chinese. Recently, I spent a few days updating the Chinese version. My suggestion is to separate the new results into a separate section under the heading Newest findings right before the Overview section. When the readers encounter this section, they know for sure that they are reading something which is very important if they plan to pursue advanced study in QM. Please let me know if this is a good idea or not. Thanks. —老陳 (留言) 06:14, 30 April 2009 (UTC)

After thinking about it for 2 weeks, I have concluded that this suggestion is not such a good idea. So, I would not act upon what I suggested and withdraw my suggestion. —老陳 (留言) 00:55, 15 May 2009 (UTC)

The role of observer

Why do the particles act the way they do when the are observed? They must think they can do whatever the hell they want. Well not when im watchin. Its obvious that these guys will just mess around unless you force them to behave accordingly. I did a double split experiment today, i used an A4 sheet of paper, taped to the window with two slits cut in it. When observed they acted like expected, but sure enough when i looked away they started acting erratical again. Basically i would like to hear some methods on how to control the particles, i propose building a quantum scarecrow that would trick them into behaving how i want. Would this work? If not why not? Any other ideas?

Any particle can suffer an acute identity crisis, and just as often exhibit multiple personalities. They are passive aggressive and invariably respond to questions in compliance with the expectations of the questioner. The next questioner can get a contradictory answer. They lack a self identity, and the tighter external controls are applied to manage one symptom the more erratic are their substitute symptoms.

Experimenters often suffer from transference due to hypnotic entanglement. It is difficult for a normal human to perform the splits. Success in doing a double split is inevitably fatal. 152.17.53.85 (talk) 18:53, 23 May 2009 (UTC)

Nothing like a good ol' switch to keep those particle hooligans in line. Gotta LAY DOWN THE LAW! - Drlight11 (talk) 10:40, 20 March 2010 (UTC)

Multiverse

I think having particles bounce to eachother to create this patern, beeing the particles themselves from 'parallel' universes. As a valid explanation should be mentioned. Because this whole principle is the foundation of quantum computing, which is kind of a child of this experiment.

But if you do i think it might lead to discusions which i my self cannot address either. For the philosophers of quantum mechanics, why is it that multiple univesers leaf their fingerprint as we see the patern?. De multiverse seams to be not that disconnected if so, .. as they merge into this pattern. Or like is it a multiverse where the universe constantly splits / or just one more dimension we cannt see?

Anyway i'm not such a good writer but this articles should deal with these kind of questions. —Preceding unsigned comment added by 82.217.115.160 (talk) 11:13, 6 April 2010 (UTC)

A fundamental question

It just occurred to me that one of the common ways of talking about the double-slit experiment is to assert that the photon is actually at one slit or the other, and that what experimenters lack is simply "which path" information, but that making such an assertion is in effect claiming there to be a hidden variable denoting position. If that were true it would violate the EPR paradox, no? The Bell inequalities claim that there cannot be such hidden variables, so if there were indeed a discoverable "where" to the photon then that would disprove Bell. [[User::|P0M]] (talk) 06:51, 19 July 2009 (UTC)

For some reason I missed your questions up till now. Let me try to answer them briefly.

With respect to EPR it is important to remember that Einstein's elements of physical reality correspond to quantum mechanical measurement results. This implies that, as hidden variables, these EPR elements are of a very restricted kind, it being reasonable to assume that in general a hidden variable should correspond to a microscopic property of the microscopic object rather than to a macroscopic measurement phenomenon. So, more general hidden variables theories than Einstein's are not excluded by the Kochen-Specker theorem (which finally proved beyond doubt that Einstein's assumptions were impossible).

With respect to the Bell inequality one issue is that only local hidden variables theories allegedly are excluded, thus boosting the idea that nonlocal hidden variables would still be possible. Personally, I even believe to have reasons for a thesis that even certain local contextual hidden variables theories are not excluded if the influence of quantum measurement is duly taken into account (see [[2]]).WMdeMuynck (talk) 13:25, 30 August 2009 (UTC)

Thank you very much. That is all very good information. I am back chained to the desk in the monk's cell, so it may take quite some time for me to process all of this. P0M (talk) 17:33, 30 August 2009 (UTC)

Sources

There seems to be a lot of references to animations and books, but are any of the books peer reviewed? Are there any references from studies using particle accelerators? I'm not for or against string theory, but I'd like to be able to rely on this article, which, unfortunately, I can not do, given the state of your references. —Preceding unsigned comment added by 75.36.160.141 (talk) 12:31, 29 August 2009 (UTC)

What does string theory have to do with anything? It's only even mentioned in one book title, and that part of that book that has to do with string theory does not have anything foundational to do with the author's explications of double-slit experiments.

Do you mean peer-review of books published by companies like Addison-Wesley, W.W. Norton, Princeton University Press, Prentice-Hall..., and by authors like Feynman, Cassidy, Greene, de Broglie, Philipp Frank, Einstein, Francis Weston Sears...?

To get anything published by any reputable publisher means that the book has been thoroughly checked out beforehand, because the reputations of these major publications depend on it, and it means that every physicist in the world with a sharp pencil will jump on anything that is questionable. Of the authors I've listed above, Sears is probably the least well known in the present day, but he was a professor at MIT and the author of an entire series of physics textbooks that form the basis for the physics textbook now generally known as "Sears and Zemansky." Physics departments in major universities have been ordering his books year after year for the last half century. When you get as good as any of the people on the list above, the number of your true peers is limited, everybody would be happy to be able to prove you wrong because that would mean a notch on their pistol grip, and you generally have answered their objections in advance because you have seen them coming. None of them would claim, "I am absolutely correct." They would all say, "I have evidence and argument. Where do you see something I need to fix?"P0M (talk) 18:30, 29 August 2009 (UTC)

The Electron Version of the Experiment

On this page is says: "A Young double slit experiment was not performed with anything other than light until 1961, when Clauss Jönsson of the University of Tübingen performed it with electrons[16][17]"

On page 186 of the textbook "Modern Physics" by Paul A. Tipler and Ralph A Llewellyn it says: "In 1927, C. J. Davisson and L. H. Germer verified the de Broglie hypothesis directly by observing interference patterns, a characteristic of waves, with electron beams." On page 36 of "The New Quantum Universe" by Tony Hey and Patrick Walters it says: "Only a few years later, in 1927, wavelike behavior of electrons was convincingly demonstrated - by Davisson and Germer in the USA, and G. P. Thompson in Scotland..."

I think this should be fixed. —Preceding unsigned comment added by Amichai22 (talk • contribs) 06:12, 9 December 2009 (UTC)

The Davisson-Germer experiment used Bragg diffraction, not a double-slit setup.

Andejons (talk) 07:15, 9 December 2009 (UTC)

Since the Bragg diffraction seems to be a variation on the double slit experiment it probably belongs on this page as well —Preceding unsigned comment added by 129.98.152.194 (talk) 20:43, 9 December 2009 (UTC)

What other experiments have been performed?

The conclusions of these two experiments (the original one by Young and using single photon emission) are

• Light is either wave like or particle like but not both simultaneously. • If we observe which slit the particle went through then the interference pattern is lost. • The photon passes through both slits.

There has been no reference made (so it is not clear whether such experiments have been tried or their results) to placing the screen between the double slits but before the plane where the interference pattern begins to form, or placing the screen immediately behind the double slits. With single photon emission these three configurations (the original and two suggested) are valid equivalents since, in the photon’s frame of reference, the apparatus approaches it at the speed of light; therefore the distance (in the photon’s frame of reference) between the double slits and screen is zero. The suggested configurations would show whether a single photon passes through only one slit.

Historically the analysis of what is happening in Young’s experiment (and its single photon derivative) has used the analogy of a wave in water. This analogy is a weak (since electromagnetic waves require no medium for propagation) so it can be modified without loss of rigour. Consider adding another component to the water wave analogy; a surfer riding the wave. The surfer travels with the wave and also transverses the wave front depending on his angle of attack. The surfer passes through one of the slits in the barrier, emerges on the other side of the barrier and will eventually reach a region where interference from the two slits is active. The surfer will continue to progress by moving where the interference patter is additive. The surfer is travelling on a wave which came from the slit he passed through and meets a wave that came from the other slit. Depending on the surfer’s angle of attack, he can switch from one wave to the other. Hence having come through slit one, he appears to have come through slit two.

With the above analogy in mind, is it valid to consider that the energy creating a single photon of light actually creates both a wave and a photon whereby the wave determines where the photon can travel?

Norman Sheldon (talk) 14:47, 24 December 2009 (UTC)

I think it is more accurate to say that a photon is neither a wave nor a particle. It is whatever it is, and humans try to conceptualize it according to concepts they can form on the basis of their macro world experiences. Dirac is said to have a mathematical description that conceptualizes all we know about the photon and one that can deliver "wave" conclusions about the photon or "particle" conclusions about the photon depending on how one evaluates the equation.

When trying to say something in ordinary English about what is going on in the double-slit experiment and in other situations that involve the wave-particle complementarity, some people have spoken of a particle plus its "guide wave." That sounds like your surfer and wave.

What happens when an electron falls from a higher orbital to a lower orbital? It has to lose energy to go into the lower energy orbital. Nobody can actually see the electron, and the whole deal is really a black box experiment. The physicist drops something in one end of the black box and something comes out the other end, and then we make models that try to explain/predict that kind of event. But it is only our model. The neatest thing the physicists can do is to think of an experiment that wrecks a model.

If the wave has a particle and the particle has a wave, what distinguishes the wave from the particle? Conceptually they are different, no? But does that prove that "in reality" they are different? Maybe it's like a "wolf note" produced when two open strings on a guitar, tuned in a certain way, are plucked at the same time. The musician hates the wolf note and even invents equal tempered tuning to try to get rid of such unwanted phenomena when playing the piano or other musical instruments, but does the wolf note exist as a separate, discrete, entity? Put your thumb on either of the two strings and the wolf note disappears. The wolf note never comes out of nowhere. So could you expect to get a wave without a particle or get a particle without a wave in your scheme? If they are two aspects of the same thing, you could only say that the fall of an electron creates two aspects of the same thing. And how would you ever know if you had a particle that did not have a wave, or had a wave that did not have a particle?

Interferometer experiments can be constructed that work like the double-slit experiment. Ordinarily one says that a photon hits a beam splitter and either gets reflected in a direction perpendicular to the original direction of travel, or else the photon goes straight. But the funny thing is that the experiment only makes sense if you assume that something wavelike gets deflected and also goes straight. Otherwise, at the far end of the experimental apparatus there could be no interference. So is there any way to prove that a particle goes through only one channel in the apparatus whereas a wave gets split and goes both ways? If they did the experiment with electrons, then there might be subtle gravity effects if one arm of the experiment went up, hit a mirror, and then went down to the fourth corner of the apparatus, whereas the other arm went down (to a high gravity region) and then back up.P0M (talk) 21:10, 24 December 2009 (UTC)

I'm a fan of relational quantum mechanics, and in that interpretation, particles such as photons and electrons are observer-specific manifestations of waves. If we consider a block universe model, a quantum of light can be thought of as a nearly horizontal line connecting events, such as "quantum emitted" and "quantum absorbed," with the vertical axis representing evolutionary time. If an observer tried to precisely determine the quantum's position at some point in time, it would appear as a single spot -- a photon. It's as if you held a laser pointer at a nearly horizontal angle, and then moved a horizontal plane vertically through this beam: An observer on the plane would see a spot, analogous to a photon, racing past. Its speed would be a function of the slope of the beam (which in the block universe model represents the speed of light, the speed of light in special relativity being a conversion factor between distance and time -- one second per 300,000 kilometers). The particle is just an observer-created "snapshot" of the wave that occurs when we extract information about the wave. This should apply equally to waves for electrons and other particles.

If that is the case, then both the wave and its associated particle would be split by a beamsplitter -- there is no distinction to be made between them, except that the particle is the wave after being observed. The beamsplitter merely cuts the probability of observing a particle at a particular place in half. PorkHeart (talk) 22:29, 10 February 2010 (UTC)

Perhaps we should transcend quantum mechanical descriptions analogously to our transcending classical rigid body theory when we want to describe atomic vibrations in rigid bodies like billiard balls. For quantum mechanics this could imply that we have to follow Louis de Broglie in his idea that a microscopic particle is accompanied by a guiding wave (this wave being different from the quantum mechanical wave function!) like a ship is accompanied by its bow wave. In this analogy the particle passes through one slit while its accompanying wave passes through both slits, interference being caused by the action on the particle by the superposition of the partial guiding waves passing the two slits. Such ideas have been developed further by de Broglie in his later publications. In this view quantum mechanics is only yielding a phenomenological description of the phenomena, the quantum mechanical wave function only yielding a description of a phenomenon without any explanation (like classical rigid body theory does not yield any explanation of the rigidity of a billiard ball, the latter having to be provided by a theory about the interaction between atoms).WMdeMuynck (talk) 11:03, 11 February 2010 (UTC)

New photo of screen patterns

I took a photograph [3] of double-slit and single-slit patterns. I think it's clearer than the existing photo and is more representative of what is likely to be seen in classroom situations. Please sound off on whether you think it should be the new photograph for this article. -Jordgette (talk) 07:57, 5 February 2010 (UTC)

Comparing your photographs with the existing ones demonstates that one should be very careful when interpreting empirical data: the features interpreted in the existing photographs as an interference pattern (because they are present only in the double-slit case) are present also in the new single-slit case. Although in the new double-slit photograph there is another feature that could be interpreted as the interference pattern, the question then arises where the additional stucture comes from. Only a more detailed discussion, relating the wavelength of the laser light with the widths and mutual distance of the slits can yield a more reliable choice. As it is now, the existing pictures are more "convincing" than the new ones, even though this might be unjustified.WMdeMuynck (talk) 13:29, 5 February 2010 (UTC)

Fair enough:

{\frac {n\lambda }{d}}={\frac {x}{L}}\quad \Leftrightarrow \quad {x}={\frac {n\lambda L}{d}}\;

In my case, wavelength = 740nm; L = 2m; d = 1.2mm

distance between fringes

={\frac {1(740nm)(2m)}{1.2mm}}={\frac {(.000740mm)(2000mm)}{1.2mm}}=1.23mm\;

The width of the area that I photographed was approx. 80mm. Recreating the setup just now, I measure the distances between the fringes to be slightly more than 1mm. Unless my math is faulty, it should be safe to say that the larger "fringes" are not the result of interference, as they are ~8mm apart.

I think the earlier example was just photographed badly. You can't see much of anything in the single-slit case. -Jordgette (talk) 22:43, 5 February 2010 (UTC)

Are you still linking to your original photos? I've done this experiment with several different physical setups and have never seen anything like your interference results. Your diffraction results look about right except that I think I can see unexplained striations within each of the seven bands I can make out. (They seem to be out-of-focus versions of the bands below them in the second picture.) If you will take a look at any of several photos of interference patterns produced by people who have very nicely equipped physics labs you will see something that is mathematically reproduced in simulations that work from math to a visualization, e.g.:

http://www.colorado.edu/physics/2000/schroedinger/two-slit2.html

In no case do you get something that looks like your interference photo, sort of like:

_|||_____||||||||_____||||__ (Why the big gaps?)

instead of more like:

_|_|_|_|_|_|_|_|_|_|_|_| (Should be the math-calc gaps.)

The electron version of the experiment shown in the Wikipedia article has particularly helpful photographs. There is also a diagram that has a vertical depiction of the interference pattern that is seen in physics laboratories.

I tried a number of ways to get a good physical apparatus. It wasn't as easy for me as some writers would make it seem. Recently I saw photos of someone who used mechanical pencil leads held at appropriate distances from each other. The results were remarkably good. I used a fairly strong laser from a cheap carpenter's "draw a really straight line" device, so the metal pins I used were a little too shiny for my comfort. I spray painted them dead black and glued them to a black plastic frame. The resulting device is mechanically stable and not fragile. I could not photograph the full width of the interference pattern produced. At around 3 meters from the double-slit device the full pattern was more than half a meter wide if I remember correctly -- and that was just the fringes that were bright enough to be noticeable as reflected light.

How thick was the plate through which your slits were made? When dealing with real objects rather than two-dimensional diagrams it is possible to get reflections from surfaces that "aren't there" in the diagrams. P0M (talk) 10:40, 6 February 2010 (UTC)

I wonder whether in the experiment of the new photographs a Rayleigh grating is used instead of a double slit. As far as I remember (but I must confess that my memories date from before the advent of the laser), the large number of fringes is characteristic of such a grating, a double slit only producing a few ones. The large-scale pattern might indeed be a spurious result of reflectionsWMdeMuynck (talk) 15:53, 6 February 2010 (UTC)

Interesting...thanks for all of the feedback. I used two single-edge razor blades, separated by a strip of sheet aluminum whose edges I sanded smooth. I'll try spray-painting the setup black, and I'll also try a different laser. I'd still like to get better photographs on the article, so I'll keep trying. -Jordgette (talk) 20:18, 6 February 2010 (UTC)

Only two blades? That would give you a single slit, and a diffraction pattern rather than an interference pattern. You need three elements, a center "post" and two side "walls.' Razor blades were the first things I tried.I found they were more useful for cutting fingers than anything else. ;-0

From the laser side it should look like XXXXXX| | |XXXXXXX with the |s being the edges of your blades and XXXXX being wall material abutting the two outside blades. One problem is that it is devilishly difficult to get everything lined up perfectly with the laser even if you manage to get the blades perfectly parallel to each other.

Sears, Optics, 1949, has some very nice photos facing page 222. He doesn't discuss how his lab technicians did these photos. The key element is the thickness. I imagine him using watchmaker's tools to fabricate a triangular cross-section center post (flat surface facing laser). The two side walls could be black electrician's tape or some kind of metal foil (assuming you could keep the edge straight and avoid crumpling it. I'm pretty sure they made something more substantial than that in his lab. Anyway, if you want to see what students would have seen in his lab, try to get the book out of a library somewhere. He also shows photos made with as many as 5 slits -- which look more like your photos. 5 slits starts to sound like a grating to me.

Can you think of anything that come pre-fabricated that would serve as a better center post than a brad? I think one of the reasons my photos are not ideal is that an ordinary brad may well not be entirely straight and of constant diameter. The circular cross-section should not be a problem because any reflections would not go through the slits but be directed back toward the plane behind the laser somewhere. Pencil lead is nice because it is already black and its diameter and straightness ought to be very well controlled. Maybe you could make a shock-mounted carrier of some kind so that if the double-slit apparatus ever got dropped it would be less likely to snap off the leads.

I wanted a fairly powerful laser so that I could project the pattern at a distance of a few meters. That way it would be large enough that I could get my camera fairly close to the beam, close enough to not need a view camera, and yet not block the beam with the camera. A couple years before that I had made a similar apparatus for classroom use that just used a $20 laser pointer. It worked o.k., but students had to walk up close to the white board to see the pattern.

Remember that except for the cheapest laser pointers all of even the red lasers carry warnings against looking into the beam. A beam reflected by a mirror surface (unlike a matte surface) can still be dangerous. That reminds me that when computers first had CD-ROM readers in them something in mine malfunctioned and the CD stopped spinning but the laser didn't go off. The result was a CD-ROM with a circular see-through portion where the laser had vaporized the metal in the sandwich. P0M (talk) 01:19, 7 February 2010 (UTC)

Thank you for all of the help. Here is my latest photograph [4]. This time, I used a brighter laser and an all-new new double-slit assemblage. This consisted of two razor blades, spray-painted flat black, with a .7mm pencil lead between them (as one editor suggested); these were clamped to a flat surface and epoxied at the top and bottom on both sides. The distances between the striations/fringes were predictably greater, with the smaller slit separation (d above). The slits were also much narrower this time, which I think improved the diffraction pattern.

As you can see, there is still a diffraction pattern in the double-slit case. However, is this not simply the superposition of both slits' diffraction patterns, plus the resulting interference (the striations)? By the way, although it can't quite be seen in the photo, the double-slit striations/fringes did continue in a regularly spaced fashion through the diffraction minima. -Jordgette (talk) 11:21, 7 February 2010 (UTC)

I think these photos are probably o.k. First, the diffraction pattern looks very good. Second, comparing your second photo with the one Sears made, there is a pretty good match. The intensities of each band do not uniformly decrease with distance from the center. In the Sears photo there are five bright vertical bands in the center, then a muddy grey band on each side, then a band that is almost invisible, followed by a couple brighter bands, and then there is a broad expanse where there must be fringe bands but they really don't show up in the photo. This is in a "plate" in a nicely printed book, but even so the photographs must have been clearer and may well have shown dim bands in these regions. If you have good measures of the slit widths, then you could compute the locations where the bright bands should show up, just to make sure. P0M (talk) 16:26, 7 February 2010 (UTC)

Thanks. I replaced the linked photo with an even better version [5]. The band distances are within 10% of the predicted values, but I don't have exact values for all of the contributing parameters. -Jordgette (talk) 08:55, 8 February 2010 (UTC)

To avoid confusion it might be good to point out in the article that in the photos two different effects can be seen, viz. the interference effect and the diffraction effect.WMdeMuynck (talk) 10:34, 8 February 2010 (UTC)

The original mathematical treatments (and the diagrams of today that I have seen) assume that a spherical wavefront propagates from each slit. This is a simplistic distortion since the wavefronts are both such that individually they produce not the predicted even wash of photons across the detection screen but the diffraction pattern seen in the top photo. Then the superposition that occurs is of two diffraction patterns slightly out of alignment. Is this not the basic description that we need to add to the article to explain the photos? P0M (talk) 14:01, 10 February 2010 (UTC)

The idea of `two diffraction patterns slightly out of alignment being superposed' is not what interference is like. That would amount to addition of intensities. Interference refers to addition of amplitudes of waves originating from different slits. The point is that the spherical waves we learned about in high school are just a first approximation. When the edge effects that cause refraction are taken into account we need higher approximations (described by higher harmonics). These higher harmonics are responsible for the additional structure on which the interference is superposed.WMdeMuynck (talk) 16:27, 10 February 2010 (UTC)

I moved the photo over and captioned as suggested. Thanks for all of the feedback. -Jordgette (talk) 23:53, 20 February 2010 (UTC)

This is indeed a very nice photo. Could you please move it to Wikimedia Commons? I would like to show it in the Chinese wikipedia also. Thanks! — 老陳 (talk) 07:05, 21 February 2010 (UTC)

Done Thank you. -Jordgette (talk) 09:45, 21 February 2010 (UTC)

Hi. For some reason the double slit page is in direct opposition to http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser "Unexpectedly, the results discovered were that: if anything is done to permit determination of which path the photon takes, then, the interference pattern disappears: there is no interference pattern. Each photon simply hits the detector by going through one of the two slits. Each slit yields a simple single pile of hits: there is no interference pattern." The opposition come from the statement " "It is a widespread misunderstanding that, when two slits are open but a detector is added to the experiment to determine which slit a photon has passed through, then the interference pattern no longer forms and the experimental apparatus yields two simple patterns, one from each slit, superposed without interference. Such a result would be obtained only if the results of two experiments were superposed in which either one or the other slit is closed." 75.168.207.151 (talk) 15:56, 7 March 2010 (UTC) strickjh2005

The above discussion was inserted into the middle of an earlier discussion above, where it was not likely to get noticed. I have moved it here so that it can receive some attention. It is related to the previous discussion, but the earlier discussion does not seem to have satisfied this reader. The statement from the delayed choice article is not written in a clear style. I cannot tell for sure what the writer was trying to say. Does anyone understand what the writer involved with the other article was actually trying to say? P0M (talk) 20:58, 7 March 2010 (UTC)

Several questions

Hello, I'm not a physicist, but I like physics, and I love Sheldon Cooper and am trying to understand some of the things he says. With this in mind, I have a few questions.

In the photos at the top of the article, it appears that the patterns of light form a long shape. It is "full" when there is one slit and it appears "striped" when there are two slits. But that long shape seems to be orthogonal to the slits. In all the other illustrations, the slits are shown as vertical, and in that photo, the long shape is shown as horizontal. Are the slits placed horizontally in that experiment? Are the slits parallel to the shape or orthogonal? This, to the amateur that I am, is very puzzling: how come light would be more likely to spread out towards the edge of the slid than into the slits' length?
In the Wikipedia article about 2001: A Space Odyssey (film), in the section "Scientific accuracy", it says, "The appearance of outer space is problematic [...] in terms of lighting. With no atmosphere in outer space, [...] light does not spread out to become ambient. The side of the Discovery spacecraft unlit by the sun would be virtually pitch-black." If this is true, does this mean that the double slit experiment need an atmosphere to work? If so, will any clear gas do? The double slit experiment does require light to spread, doesn't it?
The double slit experiment is often mentioned as the introductory experiment into quantum mechanics, but, apart from a brief mention, this article does not say much about the relation. Energy is measured in discrete, indivisible units called quanta. A photon has the ability to go through one slit as a particle and through both as a wave, and thus interfere with itself. What is the relation? Shouldn't it be mentioned?
About the sentence debated above in this discussion page: "Any modification of the apparatus that can determine which slit a photon passes through destroys the interference pattern", what kind of measurement does this refer to? Does the beam of light or photon have to go through an extra machine? Is that machine placed before or after the slits? Whether it's placed before or after the slits changes the meaning of the ability of the photon to "know" that it's been measured. (Doesn't it?) What does the measuring apparatus consist of? Is it possible to direct a photon to one slit rather than the other and therefore "know" which one it will go through without measuring it? Does this count as determining which slit a photon passes through and therefore stops the interference pattern from occurring? The sentence in the article is very vague in that regard.
How come the size of the slits that work for this experiment matches what is convenient for humans to manipulate? Would the double slit experiment work if the size of the apparatus were measured in nanometers, or miles? The article says, "Slits that are very wide in comparison to the frequency of the photons involved (e.g., two ordinary windows in a single wall) will permit light to appear to go 'straight through.'" But could that limitation be overcome if one were not limited to visible light but also tried the experiment with other types of electromagnetic waves? In short, is it a lucky coincidence that the experiment happens to work with apparatus that's just the right size to fit on a desk, or is there more to it than that?
The very first line of The Big Bang Theory is:

So if a photon is directed through a plane with two slits in it and either slit is observed it will not go through both slits. If it's unobserved, it will. However, if it's observed after it's left the plane but before it hits its target, it will not have gone through both slits.

(Please, please, PLEASE tell me this qualifies as fair use! Chuck Lorre, I love you. Don't sue me.) This sentence, which is the main reason I've read this article, does not seem to be covered by the article at all. The article is all about observing the photons, not the slits. How can one observe the slits with one photon? By the position of the photon on the target? How can an unobserved photon mean that it went through both slits? Couldn't the photon just have landed on the area between the slits? Or outside the slits in general? And as for the final part, how can one ever observe the photon after it leaves the plane but before it leaves its target? You can't "look" at a photon, can you? As far as I understand, one needs photons to see.

This is very confusing. I understand that as far as the sitcom is concerned, confusion is the point, but I was hoping to be less confused after reading this article. The line from the Big Bang Theory is illustrated at Think Geek, but this illustration still baffles me: Think Geek. How come the photon in the middle image is less observed than the one in the top image? The one in the middle image is still going towards the target, so how come it's unobserved? And the photon in the last image, where does it even come from? And how, how, HOW can one know it is between the plane and the target? How can one "look" at a photon and see it partway through its course?

According to its style guidelines, Wikipedia encourages contributors to make technical articles understandable. Most of these questions are asked with this in mind. It may be obvious for a physicist why the slits are always shown as vertical, but the light pattern in the picture at the top of the article is shown as horizontal, and it may be obvious to said physicist what is meant by a "modification of the apparatus that can determine which slit a photon passes through", but is is very confusing to the rest of us. So if anyone can help, maybe many people, not just me, would be grateful. And even Sheldon tried to teach physics to Penny. (The ungrateful ditz.)

Thanks.

Eje211 (talk) 11:55, 24 April 2010 (UTC)

As the guy who took the picture, I'll try to answer a few of your questions. I agree that there are some points in the article that could use clarification.

The single-slit band is, indeed, perpendicular to the direction of the slit. We use a laser beam for the experiment, which, without a slit in the way, produces a small spot on the screen. Limiting that spot by bringing in two vertical barriers on either side, causes the light to diffract horizontally (the waves spread out) as they pass each barrier. The result is a broad horizontal band. If the laser passed through a small hole instead of a slit, the result would be a large round spot, and the diffraction pattern (as seen in the photo) would take the form of concentric rings. You can see this going on inside your eyeball if you look at a bright screen or a bright sky. You may see specks floating about, debris that is in your eye fluid. You'll notice they create a bullseye pattern around them. This is from the light diffracting around the debris specks, which are like the inverse of tiny holes.

The "2001" article was just talking about ambient light. You don't need ambient light for the slit experiment; you just need the laser light. The spreading is done by the slits, not the atmosphere. The double-slit experiment would work in a vacuum.

The experiment would work for slits that were far apart, but the farther apart the slits, the smaller the interference fringes (stripes). However if you used light with a longer wavelength, such as infrared or microwave (not really light), the fringes would be that much larger. It just so happens that with visible light such as a red laser, a slit separation of 0.5-1.0mm produces nice, distinct fringes.

When the other article mentioned "observing the slits," that was referring to monitoring the slits to learn whether or not a photon could be detected going through. If the experiment is set up such that the passage of a photon through one of the two slits can be detected (through any method), then that photon will not interfere with itself and will not contribute to an interference pattern. -Jordgette (talk) 21:46, 24 April 2010 (UTC)

Thank you! Thank you! Thank you, Jordgette, for answering me so quickly. It actually feels good to know that the light is actually perpendicular to the slits, rather than just appearing that way. The article does not say much about the experiment being done with a laser; it's only mentioned in the caption of an illustration. I would have thought (wrongly) that not using a laser made some sense as the "randomness" of the non-laser light would add to the likelihood of the photons going through either slits. Maybe the article should mention the usefulness of laser light inside its actual body, not just in a caption. I'm not sure if I should make such changes myself. I'm REALLY not a physicist, and I'd be terrified to write something that's false. Particularly given that one of the main attributes of this experiment and of quantum mechanics in general is that they are completely counter-intuitive. (You cannot add light by opening a second slit and find darker patterns close to the middle of the pattern. It's not possible. It does not make sense. This is actually very exciting.)

Great picture, by the way.

Thanks again for your quick answer.

Eje211 (talk) 00:02, 25 April 2010 (UTC)

A laser is a coherent light source, as mentioned in the first sentence, but I just added "e.g., laser" to clarify that. BTW the original experiment, by Young, was done using regular, non-coherent light; coherent light just works better. But whether coherent or not, quantum mechanics says that every photon would not only go through both slits, but also take every other possible path, even through a distant galaxy (although the probability of finding that photon, if you looked for it there, would be extremely low). Now that's counterintuitive! -Jordgette (talk) 01:16, 25 April 2010 (UTC)

I just understood a part of Sheldon's line! When Sheldon says, "if it's unobserved, it will", the first "it" refers to the slits and the second to the photon! I thought both referred to the photon. So "if either slit is observed" means that the apparatus has been modified to test which slit the photon went through and "if it's unobserved" means that the apparatus has not been modified in such a way, right? So in the first case, "if either slit is observed", there is on interference pattern, and "if it's unobserved", there is. I still wonder what the last part, "if it's observed after it's left the plane but before it hits its target", means.

I think the last sentence is referring to the delayed choice experiment. If you allow a photon to pass through either/both slits, and then you check (past the plane of the slits) either or both paths, you will likely find a photon in one or the other path, but not both. In other words, in the experiment, a choice one makes in the present (to check the paths) can appear to affect what happened in the past (which slit the photon went through). There have been various attempts to explain this "retrocausality" — for example, this [6] — with varying success. -Jordgette (talk) 20:03, 25 April 2010 (UTC)

We will be obliged to keep living with such notions as retrocausality as long as we keep thinking about the wave function as a description of an individual object rather than of an ensemble of such objects, even though experiment is corroborating the latter interpretation. An ensemble interpretation allows to explain delayed choice experiments by means of selection of a subensemble. I think that even today the influence of the Copenhagen interpretation is responsible for this conundrum.WMdeMuynck (talk) 07:52, 26 April 2010 (UTC)

Merging the observer into the main article

Hello all, This is my first time entering anything into wikipedia, and I'm quite sure I'll make a formatting mistake, so if anyone wants to fix this up somehow, I'd appreciate it.

Anyway, the role of the observer barely gets a mention in the main article despite the fact that it has been one of the single most controversial aspects of Physics in the last eighty years or so. Most times I've heard the double slit experiment being referred to it's usually to do with the inherent questions caused by the role of the observer, yet anyone who comes to this wikipedia entry will only come away with info on wave/particle duality unless they're very diligent.

I'm guessing this subject has been largely left out due to the inherent controversy surrounding it, but it should really be included in the opening paragraph(s) with neutral comments explaining that there are differing opinions on the role of the observer, and what the perceived implications of the observer may be from different camps (although that should really only be touched on lightly initially and expanded upon later in the article). --Anarchisttomato (talk) 07:21, 3 May 2010 (UTC)

The influence of the observer is an important point for understanding the history of quantum mechanics. It is usually discussed within the context of quantum measurement, Schroedinger's cat paradox being the paradigmatic example. So, I agree that it should be discussed. It actually is discussed in several pages dealing with quantum mechanics and its interpretation. It is true that the influence of the observer has played a certain role in trying to understand the double slit experiment. However, the importance of the double-slit experiment is its exhibiting interference, and the experimental possibility to change the interference pattern by changing the measurement setup. Nowadays the human observer has been replaced by the human experimenter, whose observing does not have any influence after he has set up the experimental arrangement. So, it would be my advice to deal with the observer in a page on the History and/or interpretation of quantum mechanics, and not burden the important physical issue of interference with irrelevant historical information.WMdeMuynck (talk) 15:35, 3 May 2010 (UTC)

I agree. The early physicists who worked with quantum mechanics were not inclined to "mystify" it by making it seem that somebody's conscious awareness was the determining factor -- rather than there just being a measurement taken that people could access or not, as they choose. P0M (talk) 00:00, 5 May 2010 (UTC)

As an absolute non-expert on this topic I read this article to find out more about the effect of observation on the experiment. As I understood it, when a single photon is sent, it shows the interference pattern as long as there is no observation of which slit it went through. But if the photon is seen to go through one of the two slits, it does not show the interference pattern. Is that correct? If so, this is extremely profound and, I agreed with Anarchisttomato, it should definitely be a part of the article. I'd add it myself, but I'm confident it would be undone in minutes... --Robinson weijman (talk) 14:06, 13 May 2010 (UTC)

I disagree with User Robinson weijman. He wrongly understood that when a single photon is sent, it shows the interference pattern as long as there is no observation of which slit it went through. In fact a single photon does not show interference at all. Interference only shows up after many photons have passed the slit system. Please have a look at Tonomura's Video referred to in ref. 17 of the article. There the build-up of the interference pattern is demonstrated very clearly for the case of electrons. This happens independently of any observation.WMdeMuynck (talk) 23:36, 14 May 2010 (UTC)

Thanks for the reply, WMdeMuynck. I'm not an expert - my knowledge is limited to what I see e.g. on doubleslitexperiment.com but there the video clearly backs up what I wrote (see especially last 90 seconds or so). --Robinson weijman (talk) 13:14, 15 May 2010 (UTC)

Please try to distinguish popularized nonsense from the hard scientific evidence given in Tonomura's Video referred to in ref. 17 of the article.WMdeMuynck (talk) 11:27, 16 May 2010 (UTC)

I don't think you need to be rude! Please explain the problem rather than talk like that. I clearly stated I am not an expert. If this is source is not accurate (and I have heard the same thing in other places) then please specify the problem in the video. --Robinson weijman (talk) 16:53, 16 May 2010 (UTC)

There were three contradictions identified in the film mentioned by me (but dismissed by WMdeMuynck as popularised nonsense!) were:

Electrons behave like particles with one slide but like waves through two.
When one electron at a time is sent, the electrons still show an interference pattern, even though there is nothing with which to interfere.
When the slits are observed (to see which slit the electron passes through), the interference pattern collapses - the electrons behave again like particles.

The reference that WMdeMuynck mentions certainly confirms the second contradiction. It does not appear to discuss the other two (though it does mention electrons as particles and confirms the wave interference). --Robinson weijman (talk) 18:46, 16 May 2010 (UTC)

Sorry, it was not my intention to be rude. Since it seems to me that this discussion transcends the Wikipedia rules for this page (since it is not about editing the page but about understanding the subject) I will answer your questions on my Talk page.WMdeMuynck (talk) 22:33, 16 May 2010 (UTC)

Trying again - vital parts (popular (mis?)conceptions) missing from this article

In the conversation above I highlighted what I thought were three paradoxes which are either true but not stated clearly in the article or false (as user WMdeMuynck implies) but popular misconceptions.

Either way I think that they should be address in the article. Is anyone willing to take up the challenge? It needs someone with a good understanding of this topic who can communicate it in laymans terms - which rules me out. (BTW - I think the whole article is pretty impenetrable.) --Robinson weijman (talk) 22:03, 17 May 2010 (UTC)

I'm not sure I understand your confusion. I can see how the individual-particle version could be confusing (there is an interference pattern, even though with a single particle there is nothing to interfere), however the article clearly states, "The most baffling part of this experiment comes when only one photon at a time is fired at the barrier with both slits open. The pattern of interference remains the same, as can be seen if many photons are emitted one at a time and recorded on the same sheet of photographic film." In other words, with single particles, interference is seen only after a lot of particles have been allowed to build up on the photographic plate.

As for the other two items, I think your confusion may just be a result of the experiment producing results that seem counterintuitive to the lay person. Am I wrong? -Jordgette (talk) 22:45, 17 May 2010 (UTC)

Thanks for the reply. Regarding the single particle, it looks like the photon then behaves like a wave, right? Regarding the other two points (and the "paradoxes" in general), I just do not see them clearly in the article. The fact that observing an electron influences its behaviour is profound - and I miss that in the article. --Robinson weijman (talk) 08:32, 19 May 2010 (UTC)

Actually a single electron, by itself, acts like a particle regardless: It creates a definite spot on the screen, which would only be possible for a particle having a well-defined location. However with both slits open, and many electrons sent through the apparatus, the collection of particles, together, exhibit wave behavior by the way they are distributed on the screen. It's probably easiest to consider that with both slits open, the electron has a well-defined position when it hits the screen — where it manifests as a particle — but as it is going through the slits, it does not have a well-defined position and therefore acts as a wave, at that point. This wave nature influences the statistical probability of where it will show up on the screen, which is why after many "data points" (i.e., particles) have built up, you see the interference pattern. Perhaps this isn't adequately explained in the article.

As for the profundity of observation in this case, it might not be as profound as you imagine. The standard explanation is that the behavior of the electron is a result merely of how the experiment is set up. If you physically arrange things so as to see particle behavior, you will see particles, and if you arrange it to see waves, you see waves. This applies whether you are closing off one of the slits, or leaving both open and adding detectors; in both cases the wave nature is weakened or eliminated. Now, if you look at variations on the experiment, such as the quantum eraser and the delayed choice experiment, it does get more interesting and perhaps more profound, but this experiment is fairly straightforward.

So if you still think that the article is missing something, please try (again) to spell it out and we'll see what we can do. -Jordgette (talk) 20:59, 19 May 2010 (UTC)

Let me make one point, and see whether I can get that to stick, before I go any farther. In Atomic Physics and Human Knowledge," p. 11, Niels Bohr says,

I should like to emphasize that considerations of the kind here mentioned are entirely opposed to any attempt of seeking new possibilities for a spiritual influence on the behaviour of matter in the statistical description of atomic phenomena. For instance, it is impossible, from our standpoint, to attach an unambiguous meaning to the view sometimes expressed that the probability of the occurrence of certain atomic processes in the body might be under the direct influence of the will.

Bohr was making one kind of interpretation of the results of quantum physics, and he was contrasting his interpretation to that of other people who believe that the mind (whatever that is) has a determinative impact on the behavior of matter when quantum phenomena are involved. Interpretations are not physics. Interpretations are about physics (or about something else).

One kind of article can be about experiments. Another kind of article can be about interpretations of experiments. P0M (talk) 03:44, 21 May 2010 (UTC)

The article on the EPR paradox attributes this view to the Copenhagen physicists:

There exists no objective physical reality other than that which is revealed through measurement and observation.

I would be hesitant to call this statement an interpretation. To me is seems to be a belief. To it would be opposed other beliefs, among them the belief that there is an objective physical reality that cannot be revealed through measurement and observation. The second belief seems to me to assert that there is some foundation for assertions about objective physical reality other than measurement and observation. Such beliefs are explored in thought experiments involving the "black box," i.e., some device into which inputs can be fed and from which outputs can be collected, but which is impenetrable to the experimenter. The only way to attempt to explain the function of the black box would be to propose various models for the interior structure of the box. In common with the general understanding of science, it would be undependable to assert the presence of a real device internal to the black box that would duplicate the external model, since the next run of the experiment could produce results inconsistent with the behavior of the external model. On the other hand, it would seem audacious to deny that the black box has any real contents. If the black box contained a pure vacuum, then it would at least produce decompression effects on anything that passed through the box, but it would not be understandable if some other substantial effects were to occur. To make that idea a little less abstract, suppose one has a black box through which one shoots a beam of light. The light emerging from the opposite end of the black box is polarized. The experimenter might create many models to account for the observed output of polarized light. Possibly some people would be content to say: "It just happens." Possibly some people would counter: "Things don't 'just happen'. Look at that other black box. It does not yield polarized light. It does something else. So there has to be something in each box that is real and is different."

So one kind of article can be about experiments, another kind of article can be about interpretations of experiments. The "objective physical reality" of aspects of a class of experiments can be difficult to pin down because it seems wrong to speak of something being "objective" when it is in a black box or analogous situation and is not subject then to measurement and observations, and it also seems wrong to speak of the black box contents (including whatever was input into the black box) as being "unreal." Articles about experiments can discuss the ontological status of such things as "the photon in flight," and those questions of ontological status can have an impact on the interpretations of these experiments.

I hope that you will all be patient with me, and explain calmly if there are problems with my reasoning above. P0M (talk) 18:40, 22 May 2010 (UTC)

Thanks for the replies above. P0M - just for clarification, I'm not talking about anything spiritual or meta-physical. Rather it seems that there are some weird things in this experiment which the article misses. There are (from my above conversation):

1 Electrons behave like particles with one slide but like waves through two.

•Let me respond point by point. First, if a photon or an electron goes through a single slit it will show diffraction. Diffraction is a wave phenomenon. The photo of the single slit and double slit red laser light shows a diffraction pattern clearly occurring when there is one slit.

2 When one electron at a time is sent, the electrons still show an interference pattern, even though there is nothing with which to interfere.

•Experimenters have fairly clear information on what goes on at the laser end of the experiment. I.e., they can control when power is applied to the laser, they know a great deal about the operating parameters of the laser. Also, they can time the arrival of the photons at the detection screen. It's a little bit like manufacturing a gun, making bullets and loading them in the gun, pulling the trigger a large number of times, etc. After a short period of experimentation humans form a reliable picture of what will happen when someone pulls the trigger of a loaded gun. Likewise, experimenters also have fairly clear information on what goes on at the detection screen. The detection screen may be the same kind of apparatus that serves as "film" in digital cameras. So the arrival of a photon can be narrowed down to the pixel and to the accuracy of a clock attached to the digital detection device. I think there is nothing remarkable about these two observations. The firing of a laser and the detection of a scintillation on a detection screen are both interpersonal events, and people have done experiments so many times that they have a high degree of confidence in the accuracy of their observations.

•Experimenters have no information about what the electron or photon does while it is "in flight." All that experimenters can say for sure is that it makes a big difference whether there are two slits or there is only one slit, and that the dimensions of the slits and the distance they are separated are also significant factors in determining what will be observed at the detection screen. Experimenters can model what happens as the passage of a wave that gets divided because it passes through two slits, propagates by the manner appropriate to wave propagation figured out fairly clearly by Huygens and Fresnel. Or, in other words, it is as if the single photon or electron passes through both of the slits and then the resulting two waves interfere with each other. Your saying that "there is nothing with which to interfere" is a belief. My saying that the electron goes through both slits and interferes with itself is a belief. But there is no evidence for which way the electron or the photon has traveled.

3 When the slits are observed (to see which slit the electron passes through), the interference pattern collapses - the electrons behave again like particles.

•The only way that a photon can be observed is to make it get absorbed in changing the energy state of an electron. So an experimenter may put a barrier on the other side of the double slits, but very close to the median wall. Then if the photon or electron is observed on that near detection screen one might conclude that the photon had traveled through the slit that is in line with it, whereas if the electron or photon were to be observed on the distant detection screen it must have traveled through the other slit. There is no possibility of interference simply because the two paths are no longer what they were before. There is one path that terminates just beyond the median screen, and another path that terminates at the distant detection screen. And the only thing we seem to know for sure is that for interference phenomena to occur there must be two merging paths at the point that the photon is detected else there will be no interference.

Jordgette - thank you also for your detailed reply (which partially address the first two items). The links you gave were interesting but don't really address the issue, for me. OK - here's my issue:

Those three items I mention above come from this video. But I don't read them (at least not clearly) in the article. Are they wrong (like bumblebees cannot fly or you can see the Great Wall of China from space) or is the article incomplete?

Finally, I'd like to make a general comment: as a layman I find the article quite hard to read. I've got a science education so I should but able to get it but I don't. Not sure if that says more about me or the article (clue: the video I do understand!). --Robinson weijman (talk) 09:29, 25 May 2010 (UTC)

The video presents the double-slit experiment in a simplified, rather than rigorous, manner. It is not really accurate to say electrons change their behavior according to, or in response to, what slits we make them go through. It's more that, how they manifest in terms of our observations depends on the physical setup. It's more rigorous to say they appear to behave a certain way. Likewise, you may find the article difficult because the editors have chosen rigor over simplicity. That said, I'm sure there are parts that can be clarified, and it could probably use a once-over. -Jordgette (talk) 05:30, 26 May 2010 (UTC)

• Let me sum up too:

• Point 1 (from above): Photons and electrons behave like particles when they are coming out of a laser (and when the experimenters can make them go through a tiny aperture). We believe we know that photons are emitted from a very highly localized action -- the movement of an electron from one orbital to another orbital around an atom. Logically the photon at inception is not necessarily "particle-like" in any other way than that it seems to have been highly localized (a "point") at birth. So that understanding tends to fit our ideas about particles. The fact that they photon shows up at the other end of the experiment, on the detection screen, at another very tiny point, and is not spread out all over the screen, also makes the idea of a "particle" of light attractive. It is hard to understand how a wave would at one time be spread all across the detection screen and a tiny fraction of a second later would have shrunk and concentrated itself into a tiny blip smaller than a pin point. What is most significant, perhaps, is that energy is loaded into one tiny volume of space in the laser, and energy is delivered to one tiny volume of space on the detection screen. Energy does not get spread across the screen.

• Point 2: The only way that either the single slit or the double slit behavior can be explained is to deal mathematically with the idea of something wave-like passing through one or two (or more) slits.

• Point 3: Anything that assures that there is only one path from laser to detection screen will destroy the possibility of interference, i.e., interference fringes will not build up, and only a diffraction pattern will be seen. But the diffraction pattern is still a wave phenomenon, not a particle phenomenon.

• To use Jordgette's term, when an electron or a photon is made to manifest itself, i.e., when it "shows up" on the far detection screen, or when it shows up on a scrap of paper just to the far side of one slit or the other, then that electron or photon is no longer available to interfere with anything. That is the essence of what is meant by "measurement" or "observation."

• I agree that the article is hard to understand -- and in saying that I have to take the responsibility for not making it any clearer yet. But if you will read the history of the early years of quantum mechanics, you will see that Bohr, Heisenberg, and the other people in their school were in very uncomfortable (or perhaps equally uncomfortable and exhilarating) mental states. A great deal of the trouble comes from our trying to apply concepts that make good sense at "macro" levels to things that happen at extremely small scales. For one thing, we firmly believe that a silver dollar is either in somebody's left pocket or right pocket. It is not supposed to have a superposition of positions. It is not supposed to be half in either position. And it is not supposed to suddenly decide where it really is when somebody pulls the pockets out. Magicians do tricks with real coins that may look like that, but really coins are not supposed to trick magicians.

• If you will find Feynman's discussion on the double-slit experiment, he makes it very clear that a detected, measured, observed photon is one that ceases to travel. He also makes it clear that in his way of thinking about things, a photon travels in all possible paths from any point A to any point B. Maybe that is just his way of thinking about things, but it provides a model that works for him and works quite well. And models are all we get because the photon in flight is a photon in a black box. P0M (talk) 07:18, 26 May 2010 (UTC)

Thanks for the responses, both of you. I'm not able to put any more time into this discussion in the next few weeks. However, the comments you've made have helped clarify many of the issues that I had. Could you ensure this can find its way into the article? --Robinson weijman (talk) 21:14, 28 May 2010 (UTC)

New source

This could be included: http://physicsworld.com/cws/article/news/21623 MoZo1 (talk) 01:36, 19 June 2010 (UTC)

I think this idea could best be covered in a separate article. P0M (talk) 05:20, 19 June 2010 (UTC)

I think it certainly deserves a mention in this article, although not a lot of space. --Chetvorno^TALK 09:01, 20 June 2010 (UTC)

This experiment is not a new discovery. Is there no Wikipedia article on it? P0M (talk) 11:33, 21 June 2010 (UTC)

I can't find any, and I just regret not knowing it in the last 5 years. It's not new discovery, but a new source. I think it is to this experiment like the orbiting space station version of twin paradox to the traditional one. That has got a separated section in the original article. --MoZo1 (talk) 11:00, 22 June 2010 (UTC)

The traditional double-slit paradox comes about because what goes through the two slits is a superposition of probabilities with the spread occurring (primarily?) in space. The new paradox comes about because what is going forward toward a detection screen is a superposition of probabilities with the spread occurring (primarily) in time. As far as I can tell, the question, "Where is the photon/electron/atom" at the time when we figure it should be at the double-slit apparatus?" is a meaningless one, and it is precisely because it is meaningless that it makes for the paradox. Now this experiment comes along and says, "When does the photon/electron/atom do such-and-such?" -- and it is also a meaningless question. It is a meaningless question because it assumes that the particle has a definite position in time, when in fact there is no determinate position in time.

I'm going from memory, but if the above assessment is essentially correct then it ought to be possible to form the general picture that if somethings position in space-time is uncertain so that it is "in" different space-time positions while doing something that might sort it out in a "which path" way, then a paradoxical picture may develop at the detection screen.

If that generalization holds, the it mayt be possible to state the nub of the situation in the present article without going over limits. But if I also remember correctly, the time situation can be summed up in a description consisting of no more than a paragraph, and such a summation can have nothing untruthful or inaccurate in it, yet such a concise statement may need considerable explication to make it meaningful for the average well-informed reader.

The problem with trying to do both space- and time-indeterminacy at the same time is that it is too abstract to be useful for most people. The beauty of the double-slit experiment is that a description of its physical construction and of how to operate it is dead simple, yet the consequences are profound. It wouldn't be helpful to start out being too abstract. So maybe we need to have a separate section, note the space-time indeterminacy is a more broad formulation of space indeterminacy, and then give the specifics. If the specifics needed to really lead the reader through the experiment turn out to bloat the article too much, then that part could be exported to another article.P0M (talk) 14:49, 22 June 2010 (UTC)

Ok, no more reply, so let's go on: Since I don't feel safe editing this article yet, here is my proposal:
title: Another quantum version of the experiment
Gerhard Paulus of Texas A&M University and co-workers in Berlin, Munich, Sarajevo and Vienna have observed an interference pattern with electrons that pass through a double slit in time, not space, as a result of being ejected from an atom at one of two possible times by a laser pulse. The work was performed at the Technical University of Vienna in collaboration with physicists from the Max Born Institute in Berlin, the Max Planck Institute for Quantum Optics in Munich and the University of Sarajevo.
This experiment is different because the slits exist in time not space, and because the interference pattern appears when the number of electrons at the detector is plotted as a function of their energy rather than their position on a screen. The team was able to control the output of the laser so that all the pulses were identical. The researchers could, for example, ensure that each pulse contained two maxima of the electric field (that is, two peaks with large positive values) and one minimum (a peak with a large negative value). There was a small probability that an atom would be ionized by one or other of the maxima, which therefore played the role of the slits, with the resulting electron being accelerated towards a detector. If the atom was ionized by the minimum, the electron traveled in the opposite direction towards a second detector.
The team registered the arrival times of the electrons at both detectors and then plotted the number of electrons as a function of energy. The researchers observed interference fringes at the first detector because it was impossible to know if an electron counted by the detector was produced during the first or second maximum. There was no interference pattern at the second detector because all the electrons were produced at the same time at the minimum.
However,when the phase of the laser was changed so that there was one maximum and two minima, interference fringes were seen at the second detector but not at the first.
Source should be visible somehow: http://physicsworld.com/cws/article/news/21623
Thanks for helping! —Preceding unsigned comment added by MoZo1 (talk • contribs) 11:41, 2 July 2010 (UTC)

This strikes me as an overly detailed and technical description of a single variation of the classic experiment. I think it can effectively be covered in one sentence: Interference patterns have also been seen in a variation of the experiment in which electrons pass through a "double slit" in time, not space, as a result of being ejected from an atom at one of two possible times by a laser pulse.[reference] -Jordgette (talk) 18:58, 2 July 2010 (UTC)

Isn't the essence of the situation that the time location of the ejection is indeterminate? ~~It is not a case in which an electron might have been ejected at T₁ or at T₂, but nobody happens to know when the event actually occurred.~~ Reword: It is not a case in which an electron might have been ejected at T₁ or at T₂. It is not that nobody happens to know when the event actually occurred. Instead, the event is indeterminate with regard to time.P0M (talk) 13:32, 3 July 2010 (UTC) revised P0M (talk) 03:36, 13 July 2010 (UTC)

I think electrons and photons are not influenced by what you know or not know. But what you know will be influenced by the way you are measuring. If your time resolution is too small you are not able to determine the exact time of ejection. This is the case in interference experiments. This does not imply that these ejection times T₁ and T₂ would not exist. It just means that the experiment does not distinguish between them.WMdeMuynck (talk) 15:19, 4 July 2010 (UTC)

Here is the abstract of one article:

We study a temporal version of Young’s interference experiment by attosecond soft-x-ray pulses. The photoelectron energy spectra by attosecond double pulses exhibit an interference pattern, since we have no information on which pulse has generated the electron. We can re-establish the “which-way” information and control the interference visibility by changing the electron’s momentum with phase-stabilized laser pulses, by an amount depending on the time of ionization. Moreover, if we use a triple pulse, we can realize a situation where the electron passes through a single and a double slit simultaneously to the same direction and is observed by the same detector.

The URL is: http://ishiken.free.fr/Publication/DoubleSlit2006PRA.pdf

The statement suggested above, "Interference patterns have also been seen in a variation of the experiment in which electrons pass through a "double slit" in time, not space, as a result of being ejected from an atom at one of two possible times by a laser pulse," by User:Jordgette is not, I think, putting the situation correctly. There is a superposition of the time positions that are proper to the two pulses and that drive emission of an electron. If the electron were indeed being ejected at one time, it could not interfere with itself. P0M (talk) 03:30, 13 July 2010 (UTC)

You're right; perhaps a better wording would be, "...as a result of being ejected from an atom at two superposed times by a laser pulse." -Jordgette (talk) 03:50, 13 July 2010 (UTC)

To a certain extent the above wording would indeed be better, because it is defining the problem away. A problem would remain, however, with respect to the meaning of a phrase like `two superposed times'. This is equally concealing as a phrase like `two superposed positions'. The Copenhagen interpretation solves this problem by simply saying that the electrons do not have well-defined positions at all (which is another way of evading a problem). I think that the most physical way of approaching the problem is by taking into account measurement resolution, distinguishing between measurements having sufficient resolution to be able to register electrons at different positions or at different times, and measurements that have not. Only in the latter case there is interference.WMdeMuynck (talk) 12:50, 13 July 2010 (UTC)

The electrons are not being "registered."

What they are doing in the experiment is to create a situation in which an electron is "ejected from an atom at one of two possible times," and the trick is that in a single run of the experiment energy is produced in the scope of a single cycle as schematically indicated by the red and blue components diagrammed below:

Sorry for the crude image. The star represents the laser, and the green circle represents the atom. When the phase is such that the maximum (red) is split, then a self-interfering electron shoots off to the detection screen diagrammed on the left side. The physical measurements that can actually be made pertain to the time of excitation of the laser. That measurement can be made more or less precise without, I think, affecting the split-in-time maximum (the red quarter-circle images). If the minimum (blue) happens to be what sets off the electron, since it is not split in time, a non-interfering electron will show up on the detection screen at the opposite end. The emission of an electron depends on the total energy involved, so just one "quarter circle" part of it won't do anything. It has to be both parts, and they are not simultaneous. So when, exactly, does the electron get set off? That is indeterminate.

To me, the idea that measurements having one resolution would produce interference whereas measurements having greater resolution would rule out interference sounds more revolutionary than the way that the article authors describe things. An analogous situation would seem to be one in which a tiny organism were bisexual when seen under a low power microscope but unambiguously either male or female when seen under a high power microscope. I don't think "solipsistic" is the right word for that view, but it's something like that. P0M (talk) 02:47, 14 July 2010 (UTC)

The role of observation

It seems like this misleading assertion pops up anytime QM is discussed: "It is perhaps not so astounding that one knows nothing about what a light particle is doing between the time it is emitted from the sun and the time it triggers a reaction in one's body, butthe remarkable consequence discovered by this experiment is that anything that one does to try to locate a photon between the emitter and the detection screen will change the results of the experiment in a way that everyday experience would not lead one to expect. If, for instance, any device is used in any way that can determine whether a particle has passed through one slit or the other, the interference pattern formerly produced will then disappear. [citation needed]" Clearly if any kind of measurement is done on a particle, it will disrupt the particle's path (because in the quantum world, unlike the classical world, no kind of measurement can be performed in an even remotely passive, non-interfering way). The above seems to be inferring a common misconception, that observation alone or consciousness is doing something to these physical systems. Sorry if I'm repeating anything that's been previously discussed, this particular topic has just come up for me several times recently. Paxfeline (talk) 05:42, 10 July 2010 (UTC)

The article is clearly talking about "any device," and has no implication that anybody has to be consciously aware of what the device did. P0M (talk) 21:53, 12 July 2010 (UTC)

"Zero-slit experiment"

Regarding recent edits about the "zero-slit experiment": First, I could find no mention of the "zero slit experiment" in a reliable source, so this term would be considered a neologism by WP standards. Second, to say that the effect with a single hair and no slits is called "diffraction" is confusing to readers who may think that diffraction doesn't occur in either the double-slit or single-slit experiment -- it absolutely does. So I recommend not calling out diffraction here. Finally, there was a new paragraph about the "zero-slit experiment" and single photons. Citing no references, this appears to be original research and is therefore inappropriate for the article. If the editor knows of a reliable source which states this position, please add the reference. Thank you. -Jordgette (talk) 22:33, 4 August 2010 (UTC)

Understood regarding avoiding confusion on the term "diffraction".

The zero slit experiment was performed by Thomas Young, although it is commonly misreported that his research involved double slit experiments. The term "zero slit experiment" is invoked as the shortest, most easily identifiable, and descriptive term to refer to the experiments of Thomas Young. The most accessible resource I know of that describes these parts of Young's work is "Great Experiments in Physics" published by Holt, Reinhart & Winston / NY (January 1, 1960). Fortunately the relevant sections are available online in google books:

Great Experiments in Physics

Starting around page 96.

My goal is to clarify to the general public that Young did not perform the first double slit experiment, but rather he performed the first zero slit experiment, and researchers have employed a double (or sometimes single) slit setup since.

Young performed the experiment with things like cards and thin wires. Young reports on Newton's data when he originally performed the zero slit experiment with a human hair. Young's successors generally employed slits cut/etched into a material. I know of no unique experiments since Young that follow his setup, i.e. I do not know of any zero slit experiment involving fermions, much less single fermions, nor single bosons. This is important because the physical situations are different. Physical interpretations of the 2-slit setup focus on the potential trajectories through the slits whereas no such physical interpretation is possible when there are no slits. This is not so much "original research" as it is a simple fact. Thank you for your cogent point about avoiding confusing regarding diffraction, and thank you for taking your time to read and evaluate this material. -c9h13no3hcl

c9h13no3hcl -- Some of your edits are good and I'm glad you're working on this article with great interest. But I'm sorry, the paragraph about single photons is original research, or at best, synthesis -- please familiarize yourself with these core Wikipedia principles. It's a new and not uncontroversial assertion that apparently has not been advanced in a reliable secondary source, so it can't go in here. "Physical interpretations of the 2-slit setup focus on the potential trajectories through the slits whereas no such physical interpretation is possible when there are no slits." -- That's not true. Whether the outer walls are there or not, the photons take trajectories through space, on one side of the hair/wire or the other (or both). A different interpretation (barring specific reliable sources) would appear to fall under fringe theory.

If there are no slits but rather only a single post (in the form of a wire/needle/hair/etc.) then all of the possible particle trajectories are directed outward, away from the post. This is in contrast to the slit situation, wherein the hypothesized photon particles may be deflected inwards. That is why it's important to distinguish apart the "0 slit" experiment. C9h13no3hcl (talk) 17:58, 9 August 2010 (UTC)

Let's not call "Young's experiment" a misnomer unless a reliable source advances this position; that's a personal opinion. Also let's not say that he observed the patterns in his paper, unless he physically used that paper as the screen in the experiment :-).

Finally, I've taken a few minutes to revert specific edits (rather than doing the easy thing of reverting them all), so in exchange may I ask that you not re-revert them until consensus with other editors has been achieved on this talk page. Thank you. -Jordgette (talk) 19:12, 5 August 2010 (UTC)

Jordgette, I must strongly disagree with you on the practice of continuing to call the double slit experiment "Young's experiment". This is not a personal opinion. Young did not use 2 slits. This is a verifiable and reliably sourced fact.

Specific theories may consider the two setups identical in essential features and so researchers interpreting their data in terms of these theories will refer to the setups identically. However, this sloppy language is unwarranted, the effort to distinguish between the two setups in communication is minimal. Furthermore, referring to them identically is misleading to the layperson or the person who does not read the original source themselves. These categories comprise the majority of readers. We should strive for accurate communication in reporting the facts in an easily readable form. Where possible we should keep the text as easily readable as possible, employing terms in their most common and mainstream usage, but not at the loss of accuracy.

It's not me who's calling it "Young's experiment" -- this is a commonly used term seen in much of the literature, and that's what Wikipedia reflects. It isn't sloppy language any more than "gauge theories" have nothing to do with the width of railroad tracks (for which they were initially named). If you find it important, perhaps add a sentence, with a proper citation, mentioning that Young never used actual slits. However, I believe it's irrelevant. Pasteur is known for an experiment disproving spontaneous generation, and he used glass flasks, but if we did the same general experiment in a modern lab it would still be Pasteur's experiment even if we used different methods of containment and exclusion. In a similar vein, nobody that I have read would say that the presence or absence of the side walls has any bearing on the experiment's outcome, except perhaps that they make the interference fringes clearer than they would be otherwise. But again, if you have a secondary source stating otherwise, cite it!

I'm hoping that others will weigh in on this so we have a variety of perspectives. -Jordgette (talk) 22:38, 5 August 2010 (UTC)

Your analogy to gauge theories is incorrect. Like most words, it has multiple definitions, and the relevant one has to be inferred on context, it can be ambiguous. This is not the case here. "double slit" or "2 slit" is unambiguous. It means 2 vertical spaces in an object. Since Young's experiment lacked this feature, Young did not perform a 2-slit experiment. Additionally your analogy to Pasteur is a false comparison because the point of the experiment is to have a sealed vessel. The experiment isn't named after anything particular in the setup, it's just a demonstration that a sealed vessel cannot spontaneously generate new matter.C9h13no3hcl (talk) 17:30, 6 August 2010 (UTC)

I agree with Jordgette.

Young discovered a very important phenomenon, so the experiments that illustrate the phenomenon are appropriately named after him.

Young interpreted a phenomenon previously observed by Newton, and probably observed by many others, namely the interference patterns of light. He did not discover it originally, he references Newton's data in his paper. He replicated the experiment, as a good experimentalist, and confirmed the observation of interference fringes. What is most notable is that he was the first person (that I know of) to understand just how significant these observations were, how well they demolished the corpuscular hypothesis. He put forth very convincing arguments in favor of the wave theory and thus was very influential in shifting thinking among light researchers away from the particle.C9h13no3hcl (talk) 17:30, 6 August 2010 (UTC)

For ease in communicating with people first coming into contact with the phenomenon, the common practice in textbooks is to call speak of the "double slit." The almost canonical physics text, Optics, by Francis Weston Sears, p. 214, start the section on this subject by writing:

8-7 Double slit interference. Young's experiment.

It's more respectful to speak of Young's experiment, but more practical for interesting people and letting people identify what the experiment is to speak of the double-slit experiment.

A "zero slit experiment" would imply, to me, a solid wall, and the experiment as Young originally performed it could be reached by a series of intermediate steps in which the central barrier (the part of the wall between the slits) is kept constant, but the width of the slits is increased. In Young's version, the width of the slits would have been determined by the distance to the two walls of the room. Technically, you could think of a double-slit experiment in which the width of the slits would be infinite. So the name would be "infinite width double slit experiment." Let's avoid that complication. P0M (talk) 03:00, 6 August 2010 (UTC)

I understand that, if one is accustomed to picturing a wall with 2 slits etched in, then "0 slits" would imply a solid wall. However this interpretation of the term wouldn't make sense, shining light at a solid wall isn't much of an experiment and certainly isn't remotely relevant to investigating the debate of wave vs. particle. The lay person, however, may not realize this. So, we just need to make the distinction clear by stating that Young's experiment involved passing light over a thin wire. We can call it the "thin wire" experiment or, if you want to honor Newton for performing it first, the "Newton's hair" experiment. I'm not overly concerned with the label, I threw out "0 slit" because it made the most sense to me. Anyone here is free to put in their $0.02 on the most reasonable name. Some people give priority to the 2 slit experiment and see the 0 slit experiment as a limiting case of the former wherein the slits are steadily widened. Others give priority to the 0 slit case because it is ultimately simpler and was performed first, so they see the 2 slit experiment as an extension of the 0 slit wherein 2 vertical columns of matter are steadily brought in closer to the needle/wire/hair.C9h13no3hcl (talk) 17:30, 6 August 2010 (UTC)

You can see how the math works out using one of the simulations given in the resources for our article. Check this URL out to see how I set it up:

http://www.wfu.edu/~moran/z_GIF_images/Young_one%20wire_experiment.gif

P0M (talk) 04:49, 6 August 2010 (UTC)

Thank you for that link.C9h13no3hcl (talk) 17:30, 6 August 2010 (UTC)

It would be useful to have citations showing the history of the experiment from Newton to Young. The idea of re-naming the experiment is, in my opinion, ill-advised. Check Google to see which term is used the most. There are reasons that experimenters refined the experiment to the version in which there are slits of known dimensions. The name "double-slit experiment" reminds readers of the basic nature of the phenomenon being studied. P0M (talk) 15:19, 7 August 2010 (UTC)

In Young's already-cited paper he specifically references Newton on page 4:

"The second- Table contains the results of a similar calculation, from Newton's observations on the shadow of a hair; and the third, from some experiments of my own, of the same nature..."

Emphasis mine. —Preceding unsigned comment added by C9h13no3hcl (talk • contribs) 12:05, 9 August 2010 (UTC)

It's rather to be expected that someone of that period would not be careful to cite where Newton published his results, but we should, if we can find the material. P0M (talk) 13:35, 9 August 2010 (UTC)

Even earlier than Newton: http://www.faculty.fairfield.edu/jmac/sj/scientists/grimaldi.htm

P0M (talk) 13:52, 9 August 2010 (UTC)

C9h13no3hcl--Please respect the normal editing process, and do not reintroduce materials without citation -- especially after others have explained to you why your actions are not acceptable. There are rules for editing in Wikipedia, and what you are doing by reintroducing previously reverted content verges on what is called edit warring. Edit wars are immensely destructive to the collaborative process through which Wikipedia is maintained.P0M (talk) 20:31, 12 August 2010 (UTC)