Talk:Double-slit experiment

Proposal to split this into two articles, one concerned with classical optics model, and the other the quantum mechancial one

At the moment, it seems to me that this article is a mish-mash of classical optics, and discussions of the quantum mechanical interpretation of the experiment. I propose to separate the two aspects, and to this end, will start work on the classical optics article. At the moment, this will be on my user page. Comments/views welcome. Epzcaw (talk) 16:01, 29 May 2011 (UTC)

the double-slit experiment proved classical optics wrong. a page on classical physics and double slit would be a page on the birth of quantum physics. Kevin Baas^talk 01:30, 30 May 2011 (UTC)

I don't understand your comment. Young's experiment was an important part of the evidence used to justify the use of wave theory to model the propagation of light starting in the early nineteenth century and continuing till today, as opposed to the particle theory originally advanced by Newton - see quotations below. It still works very well - I am sure that you will find the designers of lenses and other optical systems find it perfectly adequate in their work, and many current optics books still use it. I have to hand the 4th volume of Wiley-VCH's Encyclopaedia of Optics, 2004, and at least 10 of 19 articles use either ray or wave optics in their discussions. Surely this means that you cannot say that 'classic optics is wrong'.

See the following:

Heavens and Ditchburn, 'Insight into Optics', page 38:

"In the eighteenth century, the wave theory was neglected. It did not gain acceptance unitl the experiment of Young (1773-1829) together with the work of Fresnel (1788-1827) who applied the theory to a wide range of phenomena"

Born and Wolf, Principles of Optics, 1999, pages 287, and 290

"The prize (Paris Academy) was awarded to Jean Augustin Fresnel (1788-1827) whose treatment was based on the wave theory, and was the first of a series of investigations which, in the course of a few years, were to discredit the corpuscular theory completely. The substance of his memoir consisted of a synthesis of Huygen's envelope construction with Young's principle of interference" p xxvii

and

The earliest experimental arrangement for demonstrating the inteference of light is due to Young" page 290

Stephen Mason, A History of Science'

... Young performed an experiment in which two light waves were allowed to overlap and interfere, producing alternate light and dark bands..... Young instanced such phenomena as evidence for the wave theory of light" page 469

Penguin Dictionary of Physics

"Interference ..... These and similar fringes (Young's fringes) are readlily explicable on wave theory, and were used by Fresnel and Young as evidence to establish wave theory"

My suggestion is that an explanation of the double slit experiment using classical optics only would be useful, and should be separated from the discussion of the implications of the experiment considered from a quantum mechanical point of view.

Can you provide a reference source which says that Young's experiment proved that classical optics was wrong? Epzcaw (talk) 11:40, 30 May 2011 (UTC)

The wave theory of light _is_ the quantum mechanical view of light. It is only a matter of realizing certain repurcussions of this view that one discovers "quantum mechanis". Though it wasn't until a similiar experiment was done w/electrons that quantum physics really hit its prime. Kevin Baas^talk 14:56, 10 July 2011 (UTC)

Classical optics is no more wrong than Newtonian Mechanics. Both provide models of how the worlds works in certain conditions and are accurate enough to be used in designing many of the things we use: (cars, planes, bridges etc etc) are designed using Newtonian mechanics, and optical devices (cameras, spectrometers, laser scanners etc etc) are designed using classical optics. Of course, much of our world is also designed using QM (e.g. electronics) and relativity (satellites, particle colliders etc) so each model has its place. So I still don't understand what you mean!!Epzcaw (talk) 17:40, 10 July 2011 (UTC)

I don't understand how your statement about how classical physics is a useful approximation of more exact physics in any way relates to what i said, so i have no foothold on your confusion. Kevin Baas^talk 17:52, 10 July 2011 (UTC)

Classical physics is not "wrong" any more than quantum physics is "right". Both are models created by humans to try to represent what they observe in the world. They both work well in particular circumstances. What about the re-normalization problem in quantum mechanics? Does this make all quantum mechanics wrong?

I guess, like in many arguments, we are not really talking about the same thing Epzcaw (talk) 18:23, 10 July 2011 (UTC)

we seem to be talking past each other, by no fault of our own. i mean that historically the double-slit experiment was a big step on the road to our current quantum physics understanding of physics. hell, when they did an analogue of the experiment for electrons, that was ground-breaking. regarding renormalization in quantum mechanics; does it make it wrong - if so then our understanding of limits in regard to calculus and our understanding of probability are fatally flawed. so in short: no, there never was a problem with renormalization. the problem was in the thinking; with some misconceptions some people had due to a shallow understanding of the math and/or poor spatial reasoning. is there a problem with triangles in that angles can exceeded 180 degrees when put on a curved surface? no. Kevin Baas^talk 19:43, 11 July 2011 (UTC)

Truce? I'm sure we're on the same side really! But I love classical wave light theory, and used it a lot in my working life, so I guess I feel I must defend its honour!!

Must quantum particles go through one slit or another?

The article is concerned with "apparatus that can determine which slit a photon passes through." Is there any reliable reference that justifies the assumption that the photon must go through one slit or another rather than through both at once and portions of the "thin plate" along the edges of the slits besides? User:Fartherred from 207.224.85.91 (talk) 23:44, 6 July 2011 (UTC)

That's kind of the point. You only get interference if you let the photon propagate as a wave, as opposed to collapsing it onto one slit or the other as a particle. Dicklyon (talk) 23:53, 6 July 2011 (UTC)

I don't know what you mean by "thin plate."

There are three levels on which you can look at this kind of phenomena: (1) empirical experience, (2) equations, (3) interpretations in various human languages that talk about what the equations tell us about how the Universe really is.

The empirical experience is quite straightforward. You can easily build your own double-slit apparatus with some plastic railroad track, some automatic pencil lead, some black electician's tape, some glue, and a moderately inexpensive laser pointer. You will see what everybody sees. But, why does it happen?

On the empirical level you can demonstrate that closing off one slit or the other drastically changes the results. You can, if you want to take the trouble, make experiments with different slit widths, different distances between the slits, different distances between laser and double-slit barrier, and between double-slit barrier and the detection screen (white paper pinned to the wall). You can even, I guess, invest in some fancy darkroom and expensive electronic "photographic film," put neutral density filter after neutral density filter in front of the laser until you get the output so damped down that only one photon is getting registered at a time on the CCD "film." Again, you will reliably see what has been verified in lab after lab, time after time.

So, on the empirical level, you can get a very complete, consistent (as long as you do not get too much experimental error from things like jostling the laser), record that will agree with what other experimenters had found. If this were not the case, if somebody came up with credible results where an ordinary double-slit apparatus did not deliver the expected results, it would cause quite a stir.

So what you know about, empirically, is what you did to set up the experiment (most important factors being slit dimensions), and what came out. You can get very familiar with your apparatus, checking time laser was activated and time flash was detected on the screen (with the slit barrier out of the way, for instance). So you have empirical information about when and where a photon was emitted, and empirical information about when and where a photon was detected. You will also know the frequency of photons characteristic of your laser. As far as I know, that is all you can know about on an empirical level.

Everything else that anybody claims to know about the experiment is based on creations of human beings that we hope will be a very reliable predictive guide for us. Richard Feynman says that the photon goes from laser to detection screen by every possible path. Most people insist on their naive sense of how things in the universe work and say that the photon must be going through one slit or the other. Why does it matter, then, whether the other slit is open? Well, it is because quantum effects occur in a "non-local" universe, i.e., a universe in which things (such as slits) do not have to be in touch with each other to "know about" each other and to influence how "each of them" (which is really one of them in some sense) acts. Or it's because of "guide waves." Or it's because of .... It's easier to discount this theory and say that "light is a wave, it spreads out wide enough to encompass both slits, and it goes through both of them," but it is harder (for me at least) to say that about electrons. A single electron heads out from a cathode, comes to the electrical equivalent of a double slit, and goes through both slits. Really? An electron has mass. Does the mass split somehow? If we do the same experiment with a buckyball, which has 60 carbon atoms, you are saying that it is a wave that goes through both slits and all that mass also goes both ways? Incredible! But we are talking about quantum mechanics, so maybe that is exactly the best way to explain it. So we have, for starters, the idea of a particle that goes through the slit by one path, by two paths, by "all possible paths" (which I suspect must be infinite in number), or maybe the slits are in this universe and the photon or the electron in motion are not in this universe until they "materialize" at the far end of the experiment. Who knows?!

There are "slits in time" versions of this experiment in which a photon can be emitted at either the peak or the trough of a sine wave current applied to a photon emitting device. By some kind of experimental trickery that I can't remember at the moment, the experimenters can contrive to have one situation in which the experiment begins at the highest electrical potential (the peak) and goes through the descent, the zero potential point and then through further descent to the bottom of the trough, and back up to the first half of a peak, where it ends. So one of these peak values (for instance, +4v or +4v) touches off a photon. But it could be either one of them, and they are separated in time. Interference is produced because, as it were, the photon sent off at the peak of the electrical potential interferes with the photon sent off at the trough of the electrical potential and they are out of phase with each other so they interfere. Are we really talking about two photons, the possibilities of two photons, one photon and the mere fact that it could have been another photon a split second later, or what??? Again, we have no idea of what is really going on. (If they have the experiment start with zero volts and end at zero volts, there is only one 4v. point encountered in this one run, so the photon must be emitted at a single point in time. No interference will be noted.)

There have been different sets of equations used to describe/predict this experiment. Basically, there are pre-quantum and post-quantum theories. Before quantum mechanics, the theories treated light as a classical wave. Huygens had the basic math needed to account for the interference pattern in a highly accurate way. (If there were errors due to inadequacies of the equations, experimenters would have had to have exquisite lab instruments to sort these mistakes out from mere experimental error.) Equations that are derived on a quantum theoretical basis have slightly different predictions, if I remember correctly. But they don't tell us what the particle "does." They just tell us what to expect at the detection screen. If I remember correctly, Dirac had a set of equations that was created in such a way that the equations could be solved to deliver information about a particle that would be consistent with the data supplied, or, alternatively, could be solved to deliver information about the wave that would be consistent with the data supplied. You could get either kind of result, depending on how you set things up. But that reflects the experimental situation. You can get information about photons in terms of their wave characteristics, or in terms of their particle characteristics, but not at the same time.

The double-slit experiment is neat because it requires computing the results of wave characteristics of the laser-produced photons at the double slit apparatus, but it requires computing the results of particle characteristics at the detection screen -- yet it refuses to give us anything more than probabilities regarding where the particle impacts will be observed.

Back to your question regarding a "reliable reference that justifies the assumption that the photon must go through one slit or another," I think you could troll through Google and find assertions by people who "ought to know," but I don't think they can justify any such assertion. It would be a major coup if somebody could do that, and a hot topic of debate if anybody seriously tried to prove it. I'm pretty sure it's one of those "you can't get there from here" situations.

P.S. Here is something on a slightly different, but related, topic that you may find useful: http://www.china-learn.info/Science/Science%20lessons.html P0M (talk) 01:12, 7 July 2011 (UTC)

Thanks for the response.

It seems that there is some notion that photons and electrons can each one at a time go through both slits. This could be documented by a reference without eliminating the notion that people have of particles going through one slit or the other. Of course, the universe might be not only weirder than I imagine but also weirder than I can imagine. That is close to a quote but I don't know what article it would fit into if I could find the source.

The 80th &81st words of the article are "thin plate." It would be possible to provide more technical information about an example experimental set-up without turning the article into a forbidden how-to article. The fancy mathematical notation that can be used is good for some people, not me. Perhaps both sorts of information can be offered without one being dependent on on the other.

The way that physics labs with good budgets make things, I guess, was to take a thin sheet of brass and something like a tiny rotary saw for a Dremel drill set, and physically cut slits into the plate. Some people have advocated exposing a sheet of photographic film to light, developing it (yielding a sheet of plastic with a thin black layer on the emulsion side, and then scratching two parallel lines in the black layer. I tried lots of these methods and concluded that most likely the people who gave the advice for such "easy" methods had never tried to do the work themselves. My first successful attempt was done by gluing the smallest diameter brads I could find to a kind of plastic railing and then building side barriers on beyond those "slit walls" using black electrician's tape. The main problem with that method was that the brads may look straight to the naked eye, but when you look closely you will discover that they all bend a little.

Also, my brads were shiny, and could reflect damaging laser light directly into my eyes -- not good!

I think you may have in mind something that has bothered me a little -- that is the fact that the brass plate (or whatever substitute one may use) is not of zero thickness, so there may be some effects due to light bouncing off those very narrow "walls" to each of the slits. I would like to experiment with that idea, but it ignores the basic requirement (often not mentioned) for the ideal double-slit instrumentation which is that the "wave fronts" coming at the double slits should be parallel to the surface of the barrier with the slits in it. In the early days, sunlight was used, and because the distance from the lab to the sun was so great, the curvature of a circle drawn with the sun at its center and the earth at its circumference was so near to being flat that nobody could see that the actually curved line was not a straight line. So what hit the double slits was effectively "flat," and there was therefore no possibility of hitting the sides of the slits a glancing blow. (Imagine the difference between one machine gun on a tripod swinging back and forth a little as it shot bullets toward two open windows, and one hundred rifles with barrels welded together shooting one hundred bullets at toward the same two windows. No bullet with hit the window frames a glancing blow because all bullet trajectories would be perpendicular to the double-window barrier.

Stay tuned. It is not appropriate to make a "how to" article here, but I can make one elsewhere and post a URL here.

It seems that in the realm of electrons and photons there is no such thing as a sharp boundary with particle on one side and not on the other. So, how large must the electron be extended to slip some of its substance through both slits and the barrier between them? That barrier is mainly empty space with some electrons and nuclei holding each other at arm's length(see below) any way.

True it is that sheets of solid brass are mostly vacuum, but there are plenty of electrons whizzing around, and no straight-line paths through anything except the thinnest of gold leaf or something like it that is found to be translucent if not transparent. The slit width is significant in that it has to be greater than the wavelength of the light directed at the slit or else the light cannot pass. Examine the window in the door of a microwave oven. The microwaves are just photons of a frequency pretty far below that of the red light we can see and even below the infrared light that we use to heat things. That means that their wavelength is greater that visible light. So visible light can go through the metal screen in the microwave oven door, but microwaves cannot go through it -- which is good because it prevents sensitive parts of the cook from getting cooked from the inside out.

Electrons have extremely short wavelengths, which is why we use electron microscopes when we want to make well-defined images of very small things. So by ordinary, macro-world, logic, the wavelength of electrons ought to require very small slits positioned very close together. The things that are actually used for making "double-slits" are actually crystalline structures that have the "slits" built in as part of that crystalline structure. (I'm using my imagination a bit here because I don't think I've ever seen a very detailed explanation of how the lab apparatus is set up, what crystals are used, etc.) Anyway, the electron does not have to be "extended." It has its characteristic wavelength (remember that "wave" and "particle" are both analogies, and rather poor ones at that, made between things on atomic and sub-atomic levels and the bullets and ocean waves that we see in everyday life), so to make an apparatus that will produce interference the experimenters must make a device with "slits" that are tailored to the electron's wavelength.

On the internet I have found many explanations without numbers for the dual slit experiment; contradictory, interesting, clear, impenatrable and otherwise. Numbers for dimensions and voltages are less common. User:Fartherred from 207.224.85.91 (talk) 04:47, 7 July 2011 (UTC)

In the article there should be a sort of empirical formula relating wavelength, slit width, slit separation, etc. and the characteristics of the interference fringes produced. If one knows the dimensions of the slits and the distances between the slits and the detection screen along with the distances between fringes in the interference pattern, you can actually use that information to measure the wavelength of the light being used.

I can tell you that the most recent apparatus I used had a center "post" the width of a piece of mechanical pencil lead, I think it was 0.07 inch diameter lead, and the slits were on the order of 0.01 inch in width (about the thickness of a dollar bill). I got a nice bright interference pattern that was convenient to photograph at around ten feet from the barrier with the double slits in it, but I could project it on a wall twenty feet away where it would be much more spread out (greater distance between bright bands) but naturally also much dimmer.

The voltages I mentioned were just dummy numbers. My guess would be that voltages would be different depending on the kind of circuitry involved, just as you can buy computer chips that require 5 volts to operate, and other computer chips that do the same job but are differently fabricated and only require a lower voltage. It's a little like asking what voltage an electric blanket requires. If you buy one fabricated for the U.S. market, it will be designed to get warm when fed 120 volts AC. If you take that item to China or anywhere else where the household voltage is 240 volts, you will get a very hot blanket and hopefully one that burns itself out before it sets the bed on fire. P0M (talk) 09:15, 7 July 2011 (UTC)

After plowing through the article some more I find it better than I thought it was. I will need more time to be able to comment intelligently on the article, if ever. User:Fartherred from 207.224.85.91 (talk) 05:57, 7 July 2011 (UTC)

Following through the math of the classical physics model (the Huygens stuff) will help you understand what is going on. Graphing out where the wave fronts will be at different distances from the double slits will also help. You can see where the two "wave fronts" will reinforce each other and where they will cancel each other. There are good simulations on-line that let you use a virtual double-slit apparatus with which you can change slit widths and distances, light frequencies (light wavelengths), and then see how those figures will affect the interference pattern those settings would produce. Finally, you can build your own double-slit apparatus (but be sure not to stare into the laser because you might burn holes in your retinas if you did) and see the real thing instead of schematic diagrams of the apparatus and phenomena.P0M (talk) 09:15, 7 July 2011 (UTC)

Arm's length is a variable unit of measure in this case the length of the arm of an electon in an atom. The size of the 2s orbital or the 6s orbital for neutral atoms or ions can all be considered arm's length.

I do not do much experimenting. I need the details of experiments to interpret the results.

I learned of the wavefront explanation for refraction by prisms and for diffraction about 44 years ago. I could perhaps dust the cobwebs off of my memories, but I do not doubt the internal self-consistancy of the model. I never really used the matrix manipulations or differental equations that I learned for much of anything. Any notation beyond college sophmore calculus is likely to cause me to skip the section until I learn more (perhaps a long time). I would bet that if two state superposition has any use as an explanation of the universe that it should show up as a result of experiments that can be demonstrated to someone of my mathmatical sophistication. If more complex notation cannot be dispensed with, I suspect the situation that prevailed with Ptolemaic astronomy. People using ever more complex mathematical tricks to reconcile their pet theory with the real world. I have not made up my mind yet.

J.B.S. Haldane wrote: "My own suspicion is that the universe is not only queerer than we suppose, but queerer than we can suppose." (Possible Worlds: And Other Essays[1927], Chatto and Windus: London, 1932, reprint, p.286. Emphasis in the original) This shows that even a communist can sometimes do something worthwhile. User:Fartherred from 207.224.85.91 (talk) 00:41, 8 July 2011 (UTC)

See http://vsg.quasihome.com/interf.htm for a simulation of the experiments that you could perform for yourself with a little trouble.

The classical equation linking the slit separation s, wavelength of light λ, distance from the slits to the screen D, and fringe width (the distance between the centers of the observed bands of light -- x) is:

λ / s = x / D

Note that the math doesn't say anything about "the wave" or "the particle" or "the anything" going through one slit or the other or the two of them. The math and the simulations represent what you will see under various conditions. Everything else is a sort of narrative that humans impose on the situation to make it appear to make sense to them. P0M (talk) 01:52, 8 July 2011 (UTC)

The same result is obtained (not surprisingly) when you use Englert–Greenberger duality relation which is a detailed treatment of the mathematics of double-slit interference in the context of quantum mechanics.

"We have in particular $D=0$ for two symmetric holes and $D=1$ for a single aperture (perfect distinguishability). In the far-field of the two pinholes the two waves interfere and produce fringes. The intensity of the interference pattern at a point y in the focal plane is given by

$I(y)\propto 1+V\cos{(p_yd/\hbar+\phi)}$

where $p_y= h/\lambda\cdot \sin(\alpha)$ is the momentum of the particle along the y direction, $\phi=\text{Arg}(C_A)-\text{Arg}(C_B)$ is a fixed phase shift, and $d$ is the separation between the two pinholes. The angle α from the horizontal is given by $\sin(\alpha)\simeq \tan(\alpha)=y/L$ where $L$ is the distance between the aperture screen and the far field analysis plane."

Fringes occur each time $p_yd/\hbar$ varies by 2π. We calculate the angle α_fsubtended by the fringes as follows:

$p_yd/\hbar = (h/\lambda )\sin(\alpha_f) d/\hbar = \frac{h\sin\alpha_f}{\lambda} \frac {2 \pi d} {h} = \frac{2 \pi d\sin\alpha_f}{\lambda} = 2 \pi$

giving

$\sin {\alpha_f} = \frac {\lambda}{d}$

The fringe spacing, y_f is then given by

$y_f= \frac {dL}{\lambda}$

which is the same expression as above, just in different notation.

I have been able to see double slit fringes by cutting two slits in a piece of cardboard with a Stanley knife (separation a bit less than a mm but I haven't measured it exactly), illuminating with a laser pointer and viewing at about 2m. You need to have fairly dim lighting, but not total darkness to see them. Epzcaw (talk) 08:55, 8 July 2011 (UTC)

If you are still interested, you can find a "how I did it" article on constructing a double-slit apparatus here: http://www.china-learn.info/Science/Double-slit_experiment/Made%20my%20own%20double-slit%20apparatus.html

There is a trick I had not thought of that will enable an experimenter to make parallel scratches in flashed photographic negatives: just sandwich a sheet or two of paper between two razor blades and guide your cut with a straight edge.P0M (talk) 08:59, 6 August 2011 (UTC)

P0M (talk) 06:36, 9 July 2011 (UTC)

POM and Epzcaw have been more helpful than I could expect. Profound concepts are touched and useful details included in the discussion. I still have hope of making comments related to the article when I have digested this material and that left at [[User_talk:207.224.85.91]]. Fartherred (talk) 11:40, 20 July 2011 (UTC)

There is one more thing that may be of interest to you. Some people have done experiments in which two lasers are used, one for each slit. The result is that most of the time there is no interference, but occasionally two wave-functions reach the detection screen at closely enough to the same time that they interfere. Dirac thought that a photon could only interfere with itself, but it appears that he was wrong. (It's a little like two marksmen shooting at the same bullseye and having their bullets collide just as their noses touch the paper, I guess. It would not happen very often.

If you decide to do your own double-slit experiment, be sure to follow the regulations for laser use posted on your laser. Some people have published stuff about using green lasers, which might be a mistake since the shorter the wavelength the more damaging power each photon packs. I would stick with red lasers of low power. Anyway, I can only tell you how I did it. Following safety precautions is entirely your responsibility. P0M (talk) 03:03, 21 July 2011 (UTC)

Remove "Three slit experiment" section

I have now read this paper, and it does not say

"In 1926 Max Born proposed that as a consequence of the quantum mechanics, only two slits would produce the familiar results of the double-slit experiment, while three or more slits would not".

What it does say is

"Therefore, by Born’s rule and its square exponent, interference always occurs in pairs of possibilities and is defined as the deviation from the classical additivity of the probabilities of mutually exclusive events (2)."

The authors are not just referring to Born, but to the conventional interpretation of quantum mechanics, i.e. that the probabilty is the sum of the square of the wave functions, and the only interference terms are cross terms between individual waves, just as in classical wave theory.

What the authors of this paper were looking for was second order interference terms, where the probability includes terms which are multiples of three terms. Such terms would not, of course, occur, in a two slit experiment, because there are only two terms, and this is the reason for doing a three slit experiment.

I don't think this is therefore relevant to the double slit experiment (it might merit an article of its own), and will certainly confuse readers who are new to the subject, so I propose to remove it, unless someone can persuade me otherwiseEpzcaw (talk) 17:06, 2 August 2011 (UTC)

I have now done this as no-one has objectedEpzcaw (talk) 09:19, 5 August 2011 (UTC)

I think this is a good idea. Maybe someone can start a new article on three slit experiment.--LaoChen (talk)06:44, 6 August 2011 (UTC)

Dear editors, whether I can add section ===Copenhagen interpretation=== following sentence?:

Event-probability interpretation of quantum theory specifies this interpretation, considering a particle to be an ensemble of dot events connected by probabilities.

Gqu (talk) 08:51, 7 August 2011 (UTC)

Are you saying that you want to add the above sentence to the Copenhagen interpretation section? If so, I think the word "specifies" in the sentence needs to be changed. "Specifies" ordinarily would make the sentence mean that there is something in the Copenhagen interpretation that specifically refers to the event-probability interpretation and requires it or insists on it. "The divorce decree specified that the antique horseshoe should remain nailed to the house that became the sole property of the wife."

It sounds like you are actually trying to indicate that the EPI makes more specific the Copenhagen interpretation, i.e., adds specifications to it. P0M (talk) 14:27, 7 August 2011 (UTC)

Thank you. It is very expressive example.

But EPI really develops the Copenhagen interpretation, because:

1. in the Copenhagen interpretation the concept of continuously existing particle remains. Hence, there is a question, through which slit the particle has passed? EPI considers a particle to be an ensemble of dot events connected by probabilities. And at an interference there probability of the event defining this particle passes through slits, but not the particle.

2. some variants of the Copenhagen interpretation consider wave function to be a certain physical essence. The Copenhagen interpretation postulates that this function submits to the equations of the quantum theory. In EPI this function represents a characteristic of the 4-vector of density of probability of dot event (http://arxiv.org/abs/1002.3425 ,pp. 1-3). It is proved (G. Quznetsov, Progress in Physics, v.2, (2009), pp.96-106) that this function submits to such equations. Thus, In EPI there is no division of Universe on quantum and classical parts, as in the Copenhagen interpretation. And there is no problem of the collapse of wave function.

Then, maybe that:

"EPI develops this interpretation, considering a particle to be an ensemble of dot events connected by probabilities."? Gqu (talk) 08:27, 8 August 2011 (UTC)

I find the above material to be beyond the scope of this article. It may be a useful addition to the Copenhagen interpretation article, but this article hardly offers a comprehensive run-down of the many interpretations. Even the Interpretations of quantum mechanics article doesn't cover every sub-interpretation. I feel like this one is too new to the literature to be included, certainly in this article. -Jordgette (talk) 19:10, 8 August 2011 (UTC)

Maybe the best thing to do is to put a link to the article on EPI down below this article in the "see also" slot.P0M (talk) 20:37, 8 August 2011 (UTC)

Clarification

I have added a template regarding the double slit experiment with electrons. Such section does not explain with clarity why in despite of firing one electron there is an interference pattern. Thanks --Camilo Sanchez (talk) 20:44, 17 September 2011 (UTC)

I've added something that may fulfill your request.P0M (talk) 02:37, 18 September 2011 (UTC)

This template has returned, despite two clarifying changes being made. Let's try to determine what is still unclear about the section. The probability of any point on the screen being hit by an individual electron depends on the point's distances to the the two slits. If the point is equidistant to the two slits, that point has the highest probability of being hit by any individual electron, and therefore corresponds to a maximum, whereas slightly to the left or right that probability is lower and may correspond to a minimum. These probability relationships repeat across the screen, with the greatest maximum at the center. This is why an interference pattern eventually develops when many individual electrons are built up on the screen. Should that be spelled out as such in the section? -Jordgette [talk] 22:47, 9 October 2011 (UTC)

I suspect that spelling it out will not help. The problem is not with the idea of additions of probabilities, but with the idea that there are probabilities involved at all.

Before it was removed, the template complained that there is, "no explanation on why there is an interference pattern when one electron is fired." It appears that Camilo Sanchez is somehow getting the wrong information out of what we have written because there is no interference pattern when only one electron is fired. The interference pattern gradually builds up, as is well shown by the video on the lab experiment performed in Japan. Any one electron will appear somewhere on the screen, and most of the time any electron will show up on what will become one of the bright bands. Of course it doesn't "make sense" that this should happen since something with mass must presumably be somewhere at any time during its trip from the emitter to the target screen, and so it looks like it ought to be going through one slit or the other (or on one side or another of a charged wire). So it doesn't "make sense" that the presence of the other possible path could have any effect on the trajectory of the electron since the electron "was never there" and consequently "the other path cannot be a causal factor" (at least in a universe that believes in no action at a distance). Nevertheless, the universe does not seem to give an electrical panel punch-out for what we think. Maybe the electron goes by two paths, or by all possible paths, or maybe there are not really two paths in a non-local universe.

It seems that there is another kind of complementarity involved in attempts to explain what happens between observable events (the brief pulsing of some apparatus that kicks out an electron, and some change at a highly localized spot on the detection screen). Either we talk as though there is an electron that takes one path and a "something" that carries a copy of the probabilities that takes the other path, or we get rid of the ghostly and probably entangled twin of the electron and talk about one electron -- but then we have a non-local connection such that what we ordinarily regard as two slits are in effect a single slit the passage through which has a bizarre effect on the single electron. The treatment by Gunn Quznetsov offers a way around those equally unappealing alternatives, but it involves the infinite regress of saying that a "wave" that is nothing other than the probabilities for mass, momentum, position, etc., etc. itself has a trajectory (i.e., it must itself have a position), and yet if the position where the electron shows up is a function of a probability, the position (or the trajectory, if you prefer) of the "wave" ought to itself be governed by a probability. If I'm right, then any model that humans make to explain things like electron interference patterns will not be a complete and satisfying account of what happens. No Tinkertoy model will be a fully satisfactory substitute for the real thing.

There is in fact no explanation for why an interference pattern will eventually form when enough single electrons have been fired at a detection screen. So Camilo Sanchez is asking for the impossible. Or maybe there really is some way that the Schrödinger equation can be deduced from some kind of string theory??? But I don't think that there is a "reason" for why string theory is true, even if it is true. At the level of investigation represented in the Double-slit experiment Wikipedia article, all we can really say is that we can make statistically valid predictions of what will happen, but we cannot explain why it happens. Weird though it is, it's just the way the universe works.

I don't know whether the Double-slit experiment article is the right place to discuss "scientific theory," "models," "useful fictions," etc. However, an understanding of these issues would certainly be useful in a society that seems more and more to vilify science and also to want to give orders to people about what they ought to believe.P0M (talk) 06:53, 10 October 2011 (UTC)

Ok, I understand that is a difficult question. So maybe the reader should be told that there is no explanation?. I mean, for the most part if we are talking about one particle being fired at a time and then over time forming the bands that are visible when the light waves go through the slit the reader is going to want to know the reason why one particle behaves as a wave, after all, is the electron going through one slit of through both? Basically what I am trying to get here is, can we tell the reader why the particle is behaving like a wave, or is it a wave? I mean, maybe you guys know about quantum theory but that is a basic question that is not being answered in the article. I think it's just responsible to answer it. --Camilo Sanchez (talk) 05:59, 11 October 2011 (UTC)

The reader has certainly been told that there is no explanation in other articles (e.g., Introduction to quantum mechanics), Maybe you are right that the issue needs to be brought up again in this article. Understanding quantum mechanics is like drinking from a fire hose. I've just this moment turned from reading The Quantum Challenge by George Greenstein and Arthur Zajonc. "Is the electron going through one slit or through both?" Either way you answer, you will find evidence to show that you are wrong. It amounts to the basic question, "Is light a particle, or is it a wave?" The only answer that even begins to be satisfactory is to say that it is something other than either one of those familiar things, and that if we do one kind of experiment we can get it to show up behaving like a particle (the photons always hit the detection screen in one spot for each one, and they don't "wash across the screen"), but if we do another kind of experiment we can get it to show up behaving like a wave. By doing the double-slit experiment we get a "two for the price of one." The experiment would not work if each single photon did not behave like a wave at the double-slit barrier, and the experiment would not work if each single photon did not behave like a particle when it hit the detection screen. But do not believe me. Get The Quantum Challenge and let that book hammer out the result.

You might also be helped by Fritjof Capra's book, The Tao of Physics. He is a physicist who has studied Eastern philosophies and Buddhism. His main point is that in learning Buddhism we have to give up lots of ideas that seem perfectly reasonable to us, and replace them with ideas that sound like nonsense. In the Prajnaparamita Sutras there are several places where the Buddha is quoted as starting a sentence with ordinary human notions such as the idea that each human is a discrete entity, and then ending the sentence is a way that destroys the ordinary notion and replaces it with a correct Buddhist understanding. For instance, since there are not really any discrete entities called "human beings," the Buddha says, "As no beings have I brought salvation to millions of human beings over the course of time." (That's not an exact quotation, or even an exact quotation of one English translation, but i think you can get the idea.)

Maybe reading Flatland would help. The author imagined a two dimensional world with inhabitants like people drawn in a comic strip. They can only be aware of things on the surface of their two-dimensional world. Then somebody in our world comes upon them and starts casting shadows on the two-dimensional world. They can see the shadows. The man starts to use his hand to make various shadow forms. One looks like a fox that is opening and closing his mouth. Then the man turns his hand another way and the same hand looks like something entirely different to the Flatlanders. We are a little like that when trying to look at light, electrons, etc. They "turn" one way and look like a particle, then they "turn" another way and look like a wave. And, one thing which we tend to forget, most of the time they are not "throwing a shadow on our world" at all. Maybe in some sense humans would need to be able to grow into another dimension to really perceive photons, electrons, etc., as they really are.

In the Dao De Jing and the Zhuang Zi we are introduced to the idea that although the universe is real, the way humans experience and understand that universe is severely limited. We work by imposing things that we build on small volumes of the Universe. For instance, we have the equivalent of a plaster cast we made of something. We label that hunk of plaster "starfish," and carry it around with us. If we pick up a snail it will not fit into the plaster cast. But if we find another starfish it may fit well enough that we say, "I think I just found another starfish." But we constantly get into trouble because our plaster cast of a horse will also fit a zebra pretty well. If we get used to tractable horses and identify a zebra as a horse then we may get ourselves killed when we try to ride it. So from the Daoist point of view we have one "plaster cast" that we have labeled "wave," and another "plaster cast" that we have labeled "particle." Nobody would ever mistake one of these casts for the other. But we grab a photon and we find that it fits right into the "particle" cast, but also that it fits right into the "wave" cast. Now we are really in trouble. We have to understand that the cast is not the starfish, horse, zebra, particle, wave, etc. It's just something we cobbled together. Jill Bolte Taylor wrote a book called My Stroke of Insight about what happened to her when she had a stroke and lost the ability to use concepts. She prefers to talk about "language" instead of concepts, but that's just a choice of words issue. Anyway, on a radio interview she once said, "Language is the tool by which we construct our world, and by which we understand our world." Quantum mechanics seems to me to do a good job of reminding us that concepts are only as good as we make them. As somebody once said, "The map is not the territory." So if you believe the map that says there is a bridge across a chasm and the bridge has recently fallen down, you may drive your car over the edge. P0M (talk) 07:36, 11 October 2011 (UTC)

Needs addition of University of Toronto experiment

All I have to say is wow. No mention of the somewhat recent monumental experiment that shows how they can know which slit it traveled through without destroying the pattern. — Preceding unsigned comment added by 72.25.65.147 (talk) 23:16, 9 March 2012 (UTC)

See http://physicsworld.com/cws/article/news/46193 for a report and a link. This is not the only experiment that shows that one can get partial information about quantum events by doing things that make particles partially "show up" in the real world. Has anyone published on an experiment that does the calcite crystal kind of trick on single particles? P0M (talk) 03:25, 10 March 2012 (UTC)