Talk:Double-slit experiment/Archive 7

Archive 1

←

Archive 5

Archive 6

Archive 7

Archive 8

Archive 9

Archive 10

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

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

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 $p_{y}d/\hbar$ varies by 2π. We calculate the angle α_fsubtended by the fringes as follows:

$p_{y}d/\hbar =(h/\lambda )\sin(\alpha _{f})d/\hbar ={\frac {h\sin \alpha _{f}}{\lambda }}{\frac {2\pi d}{h}}={\frac {2\pi d\sin \alpha _{f}}{\lambda }}=2\pi$

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)

Scale Question

Does all matter behave this way in the Double-slit when reduced to its smallest state? Many of the experiments I've seen compare the behavior of grouped objects to the behavior of individual objects, like a single photon compared to a body of water. Would a single water molecule behave in the same manner as the photon? --IronMaidenRocks (talk) 04:52, 2 April 2012 (UTC)

Water molecules are smaller than buckyballs, and buckyballs will interfere with themselves, so presumably if one could fire a single water molecule at an appropriate double-slit apparatus it would behave in such a way that it would contribute to a wet interference fringe on a detection screen. The problem, I would guess, is that it is more difficult to control a water molecule than it is to control a buckyball. Another problem might be that unless you are operating in a vacuum water molecules are all over the place. If you found a water molecule on a detection screen it might be difficult to show that it wasn't just a stray. On the other hand, buckyballs are not very common.

Generally speaking, the problem with doing an experiment with larger things is how to keep them from interacting with the environment before they interfere with themselves at a detection screen. An electron moving through a CRT, from cathode to screen, is unlikely to hit one of the oxygen molecules that did not get evacuated while they were making the CRT. But a tiny pith ball falling from the top of the inside of the CRT to the bottom might easily hit (or be hit by) some of the molecules of gas that were not successfully evacuated when making the tube. A sparrow in its own special shielded space ship on the way to the moon would still get hit by all sorts of cosmic rays along the way. What I am trying to get at is the idea that the larger something is the more likely it is to get "measured."

When the double-slit experiment is done with light there is no guarantee that every photon will avoid getting "measured" after it is emitted by the laser or whatever the experimenters are using to provide themselves with photons heading in the right direction. You can actually confirm this fact for yourself if you have access to a little laser pointer based double-slit apparatus. The laser will light up the whole region around where the double slits are located, including the tiny vertical patch between the two slits. So some of the photons that the experimenters hoped would go through both slits went through neither. Instead, those photons got "measured" by converting to elevated electron orbits in the atoms of whatever the double-slit board was made of. (I wonder how I would feel if I were put in a space suit and aimed at two narrow slits in a steel wall, and the technicians in charge said that I might interfere with myself and show up at a number of places, most of which were covered by space ships in waiting, but that it was perhaps more likely that I would splat on the double-slit barrier.)

The experimenter doesn't have to worry that not all the photons get through. After all, photons are cheap to produce, and losing a few along the way doesn't ruin the experiment. But I suspect that the bigger the particle being used, the more are lost by their running into the wrong thing and getting "measured." If a buckyball is "measured" by being hit by a stray ray of light that reveals that the buckyball was where it got hit and not somewhere else, then it is no longer in a state where it has two superimposed psi functions. The psi-functions have collapsed. I suspect that experimenters have to fire many more buckyballs in an experiment to get enough to go through to produce satisfactory results.

I think there has to be a law of diminishing returns. How many .22 caliber bullets would you have to fire dead center at an appropriate double-slit apparatus to get one that would succeed in going through both slits? If one bullet ever made it to the detection screen the suspicion would surely be that the gun barrel was wearing out and shooting to the side occasionally, or that a bullet was imperfect and veered to one side or the other, or...

Back to your original question, it isn't really a question of aggregation (since buckyballs will self-interfere). It is a question of "size" as measured by how hard it is to keep the particle being fired at a double-slit apparatus from interacting with something that will spoil that run of the experiment. So any 0 rest mass particles should work. Any single atoms should work. And any molecules that aren't "too big" to escape detection should work. I think that about covers everything. Matter,energy, and what else? Anything like a body of water, even as small as a test tube full of water, is going to be too big to miss. Something will hit it and decohere it before it gets from the double slit apparatus to wherever the detection screen is. But I can't help thinking of science-fictional situations. What would it be like to be fired into some kind of trajectory that would have equal chances of going around both sides of a black hole and therefore actually going around both sides of it only to emerge into ordinary reality when the psi-functions associated with both of me would merge, interfere, and make me show up at one place or another depending on where the wave function collapsed. Clearly it is late at night or I wouldn't be thinking such nonsense.P0M (talk) 06:05, 12 April 2012 (UTC)

It feels, to me, like scientists are quick to assume what's actually happening. If we say the reason for canceling the wave effect is that the observer can only see from one dimension of time, we would assume that he would not be able to see the wave pattern at all. Does the act of not observing the passage of the photon pass the observer into a dimension where both things happened at once? We would assume that, as in your experiment where we are the photon, we would not feel that we had been in two places at once. We would experience having gone through one or the other.

It would seem to me that there's some more reasonable underlying reason for the perceived 'self-reactive' pattern. Perhaps a minor nature of matter that we don't yet know about and cannot yet measure. Something so delicate that it might interfere with one single particle of matter, but having the effect lost when paths are attempted measurement. --IronMaidenRocks (talk) 09:07, 14 April 2012 (UTC)

{obligatory qualification that this page is not a general discussion forum for the topic, but}

I personally think that any attempt to generalize on "what's really real" in the material world, such as what's happening to such-and-such photons, comes down to interpreting the information we get from the world and the inevitable pitfalls of doing so (see Blind men and an elephant). This is because everything that is observed ultimately derives from interacting sets of information, new information entering into relations with existing information, etc. That's the direction physics is going, relational information theory (see Holographic principle and Relational quantum mechanics).

Features of the world such as time, spatial separation, particles, measured properties of matter, etc., emerge from this informational realm, as formalized by conscious analytical brains with a highly developed symbolic language. Even consciousness -- what is consciousness if not a sequence of comparisons between sets of information in the information-rich context of the brain? But, by stopping at the level of particles, fields, and forces, there is a limit to the useful conclusions we can draw about how the world is put together, and progress in physics ceases. But hey, what do I know.... -Jordgette [talk] 23:04, 14 April 2012 (UTC)

I don't know whether the article can be any clearer on the universality of quantum mechanics. Maybe the article needs to say that our current understanding is that all effects (waves at the beach, etc.) are grounded in the way nature is, as described at the quantum level. It might be possible to predict how mobs of people would behave if we knew enough about the psychology of individual humans, but if we had to begin with the behavior of mobs and use that knowledge to try to learn about the psychology of individual humans we would be faced with a daunting task. Physics started with the mass behavior of things in the universe that we experience as "rigid rods," "beams of light," etc. All our thinking, all our direct experience, involves things that are on that scale.

It would be difficult for scientists not to think in terms of what is "really" going on, because that is where they came into this movie. They were looking at things that they perceived as really happening, and they were trying to explain why they happened. Neils Bohr insisted over and over again that scientists should not go beyond assertions about what they could see to make assertions about things that they could not see. If you do a double-slit experiment you input a certain minimum amount of energy into a cleverly devised laser device that only emits one quantum of energy at a time, and you receive the same set amount of energy at the detection screen. You know where it started out and you know where it ended up. It seems perfectly natural to assert that it must have been someplace at any time between the aforesaid two events. According to the way Bohr thought about things, when some people asserted that there was some "minor nature of matter that we don't yet know about and cannot yet measure" that accounts for where the photon shows up, they were stating thing for which they had no evidence. Your idea is the same idea that Einstein had, and it is generally called the idea of "hidden variables" (i.e., things that we would like to know the value of, the measure of, but that are still hidden to us, and perhaps are always going to be hidden to us). Bohr thought that Einstein was "quick to assume what's actually happening." For a long time people thought that there would never be a way to be sure that there really wasn't something that a photon carried along with it from the minute it left the laser, or maybe from the minute that it encountered the double-slit apparatus, that would determine exactly where it was going to show up. But Bell showed that the "hidden variable" people were wrong.

This story is long, complicated, and has a weird plot. So it is difficult to take it all in at one time. Nevertheless, it would not give proper respect to the scientists who have tried to be responsible about working things out to call them hasty. Einstein tried more than once to show Bohr that he was wrong, and Bohr defeated Einstein with logic and mathematics. Bohr didn't call Einstein an idiot when Einstein challenged his new quantum mechanics, and Einstein didn't call Bohr a fool when Bohr defeated him. Einstein just went back and figured out another challenge. And so it went until they both died. Their followers carried forth with variations of those two basic contentions until Bell came along. Even now, some people still look for loopholes in Bell's proof. Things should be that way. But nobody is irresponsibly jumping to conclusions or holding up his/her own view as dogma. P0M (talk) 05:33, 16 April 2012 (UTC)

But why would the photons ever interact with each other over these two separate realities? In every thought experiment I've conducted, two realities intersecting is inconceivable. The observer is always locked into the one, its a self defeating mind game. The very reason why we can't measure the path of the photon is because, purportedly, we can't intersect these realities. Why, then, is such dual-reality activity being observed on the impact end? Why is the path nature and the impact nature of the photon so different in ability to be measured? --IronMaidenRocks (talk) 03:45, 19 April 2012 (UTC)

I don't understand what you mean by "the photons" "interact[ing] over these two separate realities." In the purest form of the experiment there is only one photon going through the apparatus during one time interval.

I think I understand the part where you say: "The very reason why we can't measure the path of the photon is because, purportedly, we can't intersect these realities. Why, then, is such dual-reality activity being observed on the impact end? Why is the path nature and the impact nature of the photon so different in ability to be measured?" You need to take out the "purportedly, and then you will have what the quantum mechanics people have been trying to tell us. Take out "purportedly" because you can't shine a photon on a photon and gather up in your retina the reflected photon you directed toward the target photon and so "see" the target photon.

I had a friend in Singapore who wrote to me that his apartment complex was being invaded by red flying things that showed up out of nowhere on the walls and other surfaces, that could move very fast, and evidently they moved too fast for the eye to follow them because he never really saw them flying from one place to another. I finally convinced him that there was some joker with a laser pointer at work. He would not have been fooled for very long by a regular flashlight because part of the light come out toward the observer even if the main focus of the light is on a wall nearby, so the observer of a spot on the wall could always easily find the source of the light. The thing about photons is that a whole intense beam of them can go past you an inch in front of your nose and you will not see anything. (If the beam is intense enough, enough dust in the air may reflect a tiny part of the beam out toward someone standing to the side, but usually only barns or other very dusty places have enough dust in the air to let that happen.)

The photon is a little like the ghost Quaspar. When Quaspar is on the move s/he has dematerialized and does not exist on this plane of existence. So you cannot find Quaspar in his/her dematerialized state in the mundane world. The only way you can see this ghost is to put a ghost catcher out and hope that Quaspar will get caught in it. The ghost catcher can be a piece of photographic film, a sheet of white paper, a CCD camera, etc. Wherever Quaspar materializes, s/he will do so at a single point. But from then on Quaspar ceases to haunt the universe. If anybody sees a scintillation at the point Quaspar met his/her end, that must be because another (phoenix) photon has been generated where Quaspar terminated. We don't know whether, while still dematerialized, Quaspar goes through one slit, the other slit, or both slits. All that we know is that the width and separation of these slits makes a mathematically definable difference in where Quaspar might show up, and that if one slit is closed off then the whole experience will change.

What you call the "path nature" (and what I call the part of the total event that pertains to "being out of touch with this universe") and what you call the "impact nature" (and what I call the part of the total event that pertains to "materializing at a definite time and place") Whenever you attempt to determine something about the "path nature" (e.g., what Quaspar is doing between laser and detection screen), you will inevitably "measure" Quaspar and make him/her have an "impact nature." The answer to any "path nature" attempted question is always an "impact nature" answer.

The main kicker in your questions is the repeated word "why." There are probably quite a lot of "why" questions that cannot be given an immediate answer. Why does π ＝ 1.14159...? Why isn't it equal to 1.1400000 or 1.1500000? There may be an answer to that question, but it won't be found in the realm of regular mathematics or geometry. We have to invent non-Euclidean geometry to even make sense of the idea that π might have some other value. And then we have to figure out some explanation for the form of geometry that our universe corresponds to, for why the universe is that way and not some other way. Trying to understand why photons have a dual and complementry wave-particle nature is trying to understand why the universe is the way it is and not some other way.

There has been a great deal of interest in "string theory" because it appears to be an entryway into some kind of physics that will supply some answers to these "why" questions on a deeper level than just, "because that is the one and only way that things work." Briane Green has a recent book on the subject of "strings" and "branes." But, before you try to tackle that book, I would recommend (on the basis of my efforts to bring clarity to my own thoughts) that you let yourself become accustomed to the concrete results of empirical physics such as the double-slit experiment. You are already aware of the questions that bug the physicists. Just be aware that they (generally) did not reject the evidence of their senses because of the preconceptions they brought with them from the macro world. So they had to say, "Well, if that's really the way photons behave in this universe, I guess I'd better get used to it and try to figure out the implications for other parts of my understanding of the universe." Starting with Neils Bohr, the great masters have all said something like, "If you think any of this makes sense, then you obviously have not even gotten to first base in understanding what we are seeing in the physics lab. If it isn't weird it isn't quantum." I've noticed that physicists like George Greenstein are pretty good at following the via negativa, and telling readers of their books what we are not justified in asserting about what is "really" going on.P0M (talk) 06:51, 19 April 2012 (UTC)

So, the photon has a different nature until it's measured. This doesn't necessarily mean there are alternate realities, but simply that we don't know how the photon behaves until something measures it? If that's the case, I feel significantly less confused. Maybe I understand it less now, because it makes sense. --IronMaidenRocks (talk) 19:04, 19 April 2012 (UTC)

"we don't know how the photon behaves until something measures it?" -- That's basically it, yes. John Wheeler was fond of saying that a photon doesn't even exist (in the "particle" sense anyway) until it interacts with something. Although that is a metaphysical position -- it is an assertion that goes beyond present empirical experiment -- it's as good a way of confronting the issue as any. -Jordgette [talk] 22:19, 19 April 2012 (UTC)

Now I'm even more intrigued. The photon is presumably still under the effects of standard mechanics to some extent; its not everywhere, its behaving quite reasonably with the guidelines of our natural universe as we understand them. Still, I can't figure out why it would appear to be interfering with itself; nothing outside the 'many worlds' theory seems to come close to being an explanation. Here's a crazy idea I came up with relating the problem to computer science, I came up with it while trying to rationalize why the particle doesn't appear just anywhere, but only in relation to variables applied to it (velocity, mass, etc):

The photon isn't really traveling. Its being placed by a physics processing computer running all scenarios, which places the photon, when measured, according to the most logical path. The 50/50 split at the slit causes a paradox in the pathing logic of the program, because both paths are equally likely. This causes it to run scenarios where the photon is going through both holes at once. The program chooses the 'both holes' scenario because this is the only situation which doesn't cause a processing deadlock. Interfering with either slit will change the perfect split scenario, causing the physics engine to behave normally. --IronMaidenRocks (talk) 07:43, 21 April 2012 (UTC)

Leibniz was ahead of you by several centuries. All individuals (which he called "monads") are totally isolated from all other monads. They have no real relationships. All relations among monads are mediated by God and occur outside of what we imagine to be space and time. The acts of will (I will hit the letter "a" on my keyboard) of each monad are perceived (read) by God. God then updates the states of all monads who need to be updated (the fruit fly sitting on the "a" key sees a finger approaching), and so forth and so on. (If this account reminds you of the movie Matrix, there is probably a reasonable explanation.)

The physics model speaks of psi-wave fronts emerging from both slits and propagating toward the detection screen. They overlap. Their potential results are either computable (or, by your model, computed), and when they reach the detection screen they are ordinarily resolved by delivering the photon of energy to some electron. There has to be an electron ready to have its energy state changed or nothing will happen. That's why a photon doesn't scintillate in a pure vacuum. (We would miss seeing the stars if this rule changed.) When electrons are available, the choice of which place to show up is determinate only in the sense that the photon won't show up where there is a 0 probability of its showing up. Where it does show up is a random selection among all of the possibilities. For instance, there might be a spot well away from the center of the detection screen for which there is only a 0,01% probability of a photon showing up. But one must show up there if you wait a while. By your model there would have to be another part of the "physics processing computer" (or Leibniz's God) that would pick at random one of the possible positions for that individual photon to show up. But the computer would have to have a true random number generator and also some way to jigger the percentages of "payout." The problem is that algorithms do not produce true randomness, and the mind of God is presumably not randomly fluctuating in some way. When you start with certainty and try to use it to introduce uncertainty, then you get paradoxes or infinite regression. When you start with uncertainty, then you need to look at ways in which uncertainties can generate something that looks like certainty. In the case of physics, the certainty can be explained by "arrow of time" arguments that show how the probability that an egg balanced on the tip of a broken off cane of bamboo will fall and break is very high, but that the probability is very low that the broken egg being hit by forces generated somehow in the ground in which the bamboo is rooted will be reassembled and then the egg will be catapulted back to its position atop the bamboo stalk. So it is, I think, always going to be easier to deal with a system that simply observes the regular rules of probabilities in things like photon self-interference and computes those probabilities for individual events and for very many runs of the same experiment. (You won't see interference fringes at once in a double-slit experiment involving single photon deliveries stretched out over some extended period of time, and you will never know where a photon will show up next. At best you will know where a photon will not show up.)

Imagine that you had your physics processing computer, and that it laid out a CGI "movie" of a double-slit experiment. The CGI movie would show the laser being set up, the barrier screen being set up, the detection screen being set up, etc. Then it would show a virtual physicist pushing a virtual button that allowed the virtual laser to have just enough energy to deliver one virtual photon. Then it would show a virtual photon appearing on the virtual detection screen. Nothing needs to "happen" between the virtual laser and the virtual detection screen. They are only lighted pixels of a computer screen anyway. All that has to happen is that the computer follows its own rules for how light should be transmitted when two slits are involved. There is no real energy, only virtual energy. The virtual energy cannot go anywhere, but the software calculates where it would probably show up. Unfortunately, this model would be determinate because a computer works on algorithms. Even the so-called "chaos" math works out exactly the same way every time you work the math providing that you start with exactly the same numbers. To get a truly random number we need to go to quantum processes. The computer would show a w% chance of a photon showing up in the central band of an interference fringe, x% of it showing up on the adjacent left-side band, y% of it showing up on the adjacent right-side band, z% probability of a photon showing up on the next band out from the center on the left side, and so forth. But then for this run of the virtual experiment, which band would the virtual photon be made to show up at? To get a real random choice I think you need to get out of the computer and into a real-world quantum event generator. On top of that your computer would have to keep track of how many virtual photons where made to appear on each band, and avoid any band getting too many or too few virtual hits. Where is this information kept if the universe we believe we inhabit is nothing but a CGI picture made of floating pixels on some non-real computer screen? Why did Leibniz need his monads anyway? Why did not God just keep a memory records for each monad and work out its story the way a human author might imagine an entire novel on the scale of Crime and Punishment before ever writing it down? Why do we need a "physical world" if there is a computer to compute every change? On the other hand, in what sense does the computer exist if it is not a part of what we perceive to be the physical universe?

Your model has explanatory power in the sense that many models do. It says, essentially, "Forget about the supposed physical location of the photon in this experiment. Forget that humans conceive of a photon as a tiny particle. Just calculate what happens to a wave front of a certain frequency that emerges from the snout end of a laser, approaches double slits of certain dimensions, passes one component through each of the two slits, combines these two wavefronts by superposition as they approach the detection screen and then hits the screen, which forces the photon to show up somewhere. What bugs people like Einstein is that there is no way to decide which "selection" of fringe band any given photon makes. They believe that it cannot be due to no determinate cause. "There has to be a reason why it came here to this fringe rather than going to some other fringe." P0M (talk) 19:22, 21 April 2012 (UTC)

Thanks for the well thought out reply, Patrick; especially the part about Leibniz. It does sound quite similar. However, my idea is not that there is no physical relationships, but that physical reactions are being calculated and performed by this 'physics computer'. Its not selecting random outcomes, but rather, selecting the most logical scenarios based on the 'loaded physics program'.

For example, in my thought experiment, a photon with mass 0, velocity 0, etc, is illogical and will be read anywhere that is measured - or, perhaps nowhere. Would this particle register only once or engulf the whole universe? Introduce some variables to the equation. Mass and velocity are determinables, so the physics engine knows logically where photons with such variables will go. A photon with such hard-set variables will not 'ping' off every other photon and interfere, because they all have set variables which make such random collisions unlikely - the double-slit scenario is an exception, because the computer is doing something different to work around a paradox.

I start to stretch for 'whys', because it looks like I'm fooling myself by perspective and becoming too deterministic in my thinking. But why do physics happen? The phenomenon seen in the double-slit experiment might give us a unique window there. It will certainly tell us more accurately how light works. How important it could be to keep considering this, where others would push it aside and say "we can't know".

Something else I've been considering is time relative to the experiment. It would seem that when anything measures the photon, it is measured relative to time. For example, a photon is registered when measured no matter if a sentient observer is looking at it. We might be able to check and observe how much time had passed from when the photon was registered, to when we read the measurement. That is, all of this exchange of photons occurs whether anyone is there to see it or not. Any deterministic process is unreasonable, for otherwise that force would have simply picked between one of the two 50/50 scenarios. The computer in my experiment would have to be an inanimate force, not capable of making its own moral judgement. However, I would still reason that the 'logical evolution' of taking the 'both paths' scenario is a deterministic way of avoiding a paradox of some sort, whether in my scenario or not, otherwise a paradox simply would have occurred.

But back onto time and the experiment: working on this macro level, one is drawn closer to the idea that time might be, in some way, relative and perhaps a vector of mass. But I guess that's getting off-topic. --IronMaidenRocks (talk) 00:48, 22 April 2012 (UTC)

Leibniz and his ideas about what space and time are led by way of Kant to Einstein's ideas about space and time. I do not believe that Leibniz was right. I am not even sure that I am right about Leibniz. But here is one of the truths that emerged from thinking about thinking during the time between Leibniz and the present: Nature does its own thing, and humans try to impose their own conceptual schemes, theories, models—call them what you will—on nature to explain nature in some way that gives us the ability to predict things better. "We control nature by obeying here," as Bacon said. So we have to be able to understand what nature is really up to, not what we would like nature to be doing. Richard Feynman said that the double-slit experiment is a sort of prime example or central nugget of all of the mystery of quantum mechanics. Anybody with a pocket laser and something to make little parallel slits in a sheet of thin metal can observe the phenomenon. We can watch nature doing its own thing, and we can sort of slow it down by reducing the rate of photon production until only one photon is going onto the detection screen at a time. (Doing so will take somewhat greater resources.) But all we get out of experience can be reduced to some simple equations that tell us what but do not tell us why.

Theories can be "confirmed" in the sense that we do more and more experiments and keep getting good results from some theory, but theories cannot be proven to be correct because there is always the next run of the experiment, the next test of the theory. Swan number one is white, so is number two, so is the millionth, and then somebody goes to Australia and the theory that all swans are white falls apart.

Progress comes when a theory fails to be confirmed and people have to scramble to account for the instances that do not fit the old theory. But the result is not a "true theory." Instead it is another "convenient fiction," that is, something that came out of human creativity and that is provisionally reliable enough to let us build MRI machines or whatever else we want to do.

The models that we build (mental or physical) have utility, but they do not promise to be anything other than convenient fictions. Ideas about what might be happening but that pertain to things for which we cannot gain evidence are sometimes valued because they make us feel better, or maybe because they suggest other experiments that we could be doing, but they are all speculation. Einstein's speculation was that there are "hidden variables" that account for where the photon will ultimately show up, and that will account for other quantum events, but it could not be proven because by Einstein's own admission/construction they were "hidden," i.e., we have no empirical information whatsoever about them. He presumed them to exist. Then Jonathan Bell came along and proved that even though nobody knows what is "really" going on, Einstein could not be right.

Try to get more context for understanding this experiment. You might start with the Introduction to quantum mechanics where some of the history of things that forced people to drop old ideas is given. In the dawn years of the 20th century, people learned that position and velocity are indeterminate, i.e., the closer you get to pinning one of this pair of measurements down for, e.g., an electron, the farther off the mark you will be on what the other one should be. The group of physicists around Neils Bohr maintained that a particle has neither position nor momentum (mass times velocity) until they are measured and you can't measure them at the same time. The best you can do is to measure one and then measure the other as soon as possible thereafter. But measuring the first will always affect the results of measuring the other. So mass and velocity are not determinate. In Relativity theory it was discovered that while light is energy and therefore does not have mass, energy can be converted into mass, and mass can be converted into energy. What time is, and what space is, are issues that go back at least as far as St. Augustine. (And I've mentioned already the contributions of Leibniz and Kant.) Einstein brought them together in the idea of space-time, another part of the context that deserves to be studied without, at first, bringing in the complications of quantum theory (or complicating quantum theory by bringing in relativistic effects and how to account for their influences). The presence of mass affects the "passage" of time, i.e., clocks close to a huge mass like a sun or a black hole will tick at a different rate from clocks of the same design stuck out in interstellar space somewhere. But to understand that stuff you would have to learn about Einstein's General Relativity.

This discussion page is not really the appropriate place to discuss all of these ins and outs. An article on a single topic such as the double-slit experiment is more complete than it needs to be if it were presented in a general treatment of quantum mechanics for the beginning reader on the subject, but it only offers indirect guidance to related topics. To understand this article thoroughly one would have to follow all the linked articles and maybe all the articles linked to those articles. You might find it very helpful to read Introducing Quantum Theory by J.P. McEvor and Oscar Zarate. There are lots of other good books, but this one has the advantage of being reasonably short and yet reasonably complete, so it is easier to get an overview of the entire field in which the double-slit experiment is embedded. That way many of the assertions in this article that may appear dogmatic or unreasonable would be shown to have been arrived at by generations of responsible physicists as the result of having had some sense beaten into them by Mother Nature, who does not always like their "convenient fictions," especially when considered by humans to be "truth." P0M (talk) 06:11, 22 April 2012 (UTC)

Might this solve it ?

I just watched another video about it then it occurred to me, that these videos might be wrong. The videos are true for what ever happens after the split, interference yes, bright spots based based on probability yes no problem. But before we hit the split light (not even from a laser) light wont behave like a straight line (how its often simplified shown). Before it enters the split we also have these same radial waves of probability, as a result a single photon doesnt choose a side of a split, its a probability that passes both splits. It also doesnt need to "know" if the other split is open, thats just its situation; (for example it also doesnt need to know where the wall is still it doesnt pass trough.) At a single split, the same radial waves of probability 'like a drawn circle', on part hits first probability collapses in a single point. With a single slit, it wont pass like a straight line (but we like to think of it that way sure, but its not our mind that runs physics, its natures work) — Preceding unsigned comment added by 84.107.185.152 (talk) 07:47, 20 April 2012 (UTC)

The way the situation is modeled in mathematics, a probability wave emerges from the laser as a wave front that does not curve around. (The other way to get this kind of wave is to pick a wave whose center of radiation is so far away that the circumference of the wave that reaches the observer is so huge that any small part of it is almost perfectly a straight line.) That wave reaches both of the slits and is still essentially flat. When it goes through a single slit it is diffracted and so you will see a sort of three part fringe pattern just from going through one slit. When there are two slits there are two such patterns. They interfere, i.e., the probabilities of where a photon will show up are determined by the interaction of the two probability waves.

So in one sense light does not behave like a straight line because, at least in the model, what leaves from the laser is a surface moving away from the laser. Take the barrier with its slits away for the moment and ask why the laser puts a tiny spot of light on the screen even when the laser and the screen are feet or yards apart. The probability that the photons will hit the spot diametrically opposite to the laser is extremely high, and the probability that it will hit elsewhere falls off rapidly on all sides. When a single slit is put in the center, then the wave is affected by the way it propages through that narrow place. (Huygens had this figured out a long time ago.) But the probability for the photon to show up at the center of the target is still highest, and there are also fairly high probabilities for two side bands to show up. So where the light shows up appears to be at the end of a straight line when there is not any barrier to its passage, and still appears nearly like a straight line when there is a single slit in its way.

Where the probability wave hits first does not determine where the photon shows up. Otherwise, the diffraction effect would not show up.P0M (talk) 21:38, 20 April 2012 (UTC)

At or on the screen

The "on the screen" .... "at the screen" language in the first paragraph is confusing (at least to me). It seems impossible that the two different patterns are occurring simultaneously "on" the screen; and yet, what could "at" mean if not "on" ?

Greg P. Hodes, Ph.D. ghodesQjuno.com — Preceding unsigned comment added by 69.76.228.125 (talk) 22:34, 26 April 2012 (UTC)

I've changed "at the screen" to "on the screen" -- meaning "on" in the sense of "spilled coffee on the table," i.e., it's a real physical position.

There are two patterns superimposed on the screen (as well as elsewhere), but they are patterns of probabilities, so they are not visible. They produce a single visible patern as a result of their interaction.P0M (talk) 00:42, 27 April 2012 (UTC)

Slits to blame for interference pattern.

There is no mention of the possibility of the slit device it's self causing the interference. It is possible, and highly probable that the particles are bouncing off the edges of the inner walls of the slit, and so mathematically according to the size, shape and depth of the slits, causing the pattern to show up. If you toss a ball towards a double slit repeatedly, some balls will bounce off the inner walls of the slit, and be sent flying to the left, some to the right, and some to the central area. It is my theory that the slit it's self is causing the interference and that a particle is not in two places at once, and that it is not interfering with it's self. If someone credible could confirm what I am talking about, or refute it then please do. Freegen (talk) 05:44, 20 June 2012 (UTC)

If what you suggest were happening, then people would have noticed that the interference patterns were changing depending on how thick the barrier was made. If you have straight-line "bullets" bouncing off the sort of window frame, you have to imagine a "rifle" that shoots inaccurately, sometimes veering left, sometimes veering right, sometimes managing to go straight and then hitting the middle ground between slits. Then you would get some bullets going straight through and some being reflected in one direction (e.g., going from heading left into the left slit to going right coming out of it). So you ought to get something like this: ||| ||||||| |||.

I'm sure that people have been aware of the possibility you suggest going all the way back to Young and the people who were discussing his experiments in his own time. The math would not support the regular bands and predictable distances that depend on slit width and slit spearation, anyway.P0M (talk) 16:21, 20 June 2012 (UTC)

Another demonstration that that is not the explanation: if you block one slit, eliminating the interference pattern, the intensity of light (number of bullets) reaching the screen will decrease in some areas and increase in others. This is the proof that the light waves from the two slits are interacting. If it was only "bullets" bouncing off the edges of the slits, closing one slit could only decrease the number of bullets reaching a given area of screen, not increase it. --Chetvorno^TALK 20:00, 20 June 2012 (UTC)

You don't have to have slits to get two beam interference - a single light beam can be split into two beams travelling in different directions by beam-splitters - they will then produce interference fringes if they overlap, e.g. Michelson, Mach Zender interferometers, Fresnel Biprism etc etc. If you block off one path, the interference fringes disappear just as when you block off one of the double-slits. The geometry of the fringes follows the same rules as two overlapping beams generated by a double slit. This sort of interferometer can be set up so that there is only one photon travelling through it at any time, and fringes will still be observed. This cannot be explained by slit edge effects. Epzcaw (talk) 19:55, 15 August 2012 (UTC)

Interpretations

Shouldn't a mention be made of Everett and DeWitt's "many worlds interpretation?" — Preceding unsigned comment added by 98.170.215.104 (talk) 03:54, 1 August 2012 (UTC)

I'm not sure how useful it would be, as many worlds doesn't offer a unique elucidation of wave–particle duality, as far as I know. The only thing I can think of is that in other worlds, one or both slits may be closed, and in those worlds there is no interference. -Jordgette [talk] 22:20, 1 August 2012 (UTC)

Figure showing double slit fringes

Double slit fringes with sodium light illumination

I suggest that this would illustrate (maybe even illuminate) double slit interference a lot more clearly than the current figure which shows a combination of interference and diffraction.

Or this one,, which is a modified version of the existing one. Epzcaw (talk) 19:40, 15 August 2012 (UTC)

The original purpose of the double image was to head off the frequent confusion between "diffraction pattern" and "interference pattern" by making the difference concrete. I would therefore prefer the modified version of the existing one. Originally I used a picture of a cruder pair of patterns made the traditional way, and in a way I preferred that pair because it showed readers a pattern that they could reproduce for themselves. The first new photo is so artifact free that it begins to look manufactured in Inkscape or something. It's too beautiful. P0M (talk) 15:45, 18 August 2012 (UTC)

Substituted second figure. I have modified the text to take the change into account Epzcaw (talk) 19:45, 23 August 2012 (UTC)

Slow GIF animation

There's a big and slow GIF animation of a double slit simulation, causing longer load time and a bit laggy when scrolling pass. Weaktofu (talk) 03:22, 16 February 2013 (UTC)

The GIF animantionn is my own work an it is no very performant. If it would be accepted I can publish two static PNGs and a hyperlink to a YOUTUBE or a WIKI video source. 88.68.119.120 (talk) 23:16, 22 February 2013 (UTC)

I'm a bit curious about the simulation: How is it constructed? (i.e. what equations describe it) ...is the wave packet demonstrated a solution to the Klein-Gordon equation or how does it work? I assume the walls are chosen to be completely reflective? ----ChrisLHC (talk) 14:46, 29 May 2013 (UTC)

Dropping "s/he" construct

When this block quote was added to the article, the pronouns were modified to "he/she". Later on, another editor changed them to "s/he". But as this passage is a direct quote, I am changing the pronouns back to their original masculine form, as originally published by Časlav Brukner and Anton Zeilinger in their 2002 paper. Link to the full paper. The quoted passage is on page 3, second paragraph starting "Just to follow our example". — Preceding unsigned comment added by Ryanrs (talk • contribs) 08:53, 16 April 2013 (UTC)

No-one else sees the obvious invalidities presented by observations from these experiments?

I mean come on. It's very clear that the observer, which in these cases always does something to truthfully interact with the experiment, doesn't collapse the wave functions "just by observing" as the leaps in logic presented by the scientists running these experiments would have us believe. This is a major issue with scientists. They get stumped by often very obvious things, like the fact that the interaction of physical (electromagnetism included) properties of the so called "observers" themselves could very easily cancel a wave function property just by bombarding the experiment with interference. Where's my nobel prize? No thanks. Could scientists just stop overlooking these simple things in an attempt to, oh I dunno, try and look cool?

And no, I'm not even saying that there are cases where the simple act of observing without interference (you let me know when thats truly possible) might actually cause completely different outcomes from when the experiment is not observed. All I'm really saying is that for the most part, from what I know, this kind of true experiment hasn't happened yet. And when it does, all these people who believe that the simple act of observing was just a simple act of observing will realise that there was probably no way to even do this kind of experiment truthfully until that point in time. I would look forward to the results of that experiment there. As our understanding increases however, the double slit experiment, atleast, will be one of the first supposed quantum mechanical demonstrations to show, via true interfernceless observation, a wave pattern not collapsing so easily.

Our brains alone amplify our computer logic rendered thoughts to do things like cause our body to move. There's obviously alot of detection going on here. And at somepoint there's an electromagnetic charge generated. So its no wonder, even focused thoughts have shown interference on double slits. Essentially double slits are just our most sensitive detectors. Quantum unexplainable collapse of wave function my foot! Get back to work! (previously unsigned) Zoele (talk) 20:37, 2 May 2013 (UTC) (edited) Zoele (talk) 20:54, 2 May 2013 (UTC)

When you say bombarding the experiment with interference, I think what you mean is bombarding the experiment with environmental photons. They've already thought of that; it's called decoherence. -Jordgette [talk] 22:33, 2 May 2013 (UTC)

That's a nice long read, I'll get to that eventually but I have a concern with the title of it and the relevance of what you've said to what I've written. Thanks for your points, it is great to know that they may have thought about what I'm talking about but clearly you don't even know exactly what I'm talking about because I said exactly what I was talking about and the assumption that any photons generated from even the process of thinking would actually interfere with this experiment directly are what you are implying and that is not what I am implying at all. There are however, other forms of radiation (after all it must be some form of radiation) that is interacting with the experiment to cause a change. And the source doesn't have to be human thought but could easily be it (and has been proven to be an effector of the double slit phenomenon) and the other obvious candidate is the "observer". There are more than enough sources of interference present in all that can be considered the observer, and one would have to create an observer that doesn't interfere with such a highly sensitive experiment before getting close to saying that there is actually a quantum phenomenon taking place here. Afterall, this is a one major hole, and you don't need to be a quantum physicist to see it. Logic, also a science that many are familiar with (said many void here, except myself as far as I can tell), can easily shed photons on this massive hole for all to see.208.97.104.82 (talk) 23:39, 29 May 2013 (UTC)

I think the "change" you speak of is caused simply by the setup of the experiment. Set it up a different way, with a different slit separation for example, and the wave function will "collapse" in a different manner such that the interactions are consistent with the laws of physics. That aspect of QM isn't controversial or interesting. And, there are experiments called weak measurements that do what you describe, and no results have been found that are inconsistent with the predictions of QM. -Jordgette [talk] 18:19, 30 May 2013 (UTC)

I suppose I wasn't clear enough. I will describe what I'm talking about again. There is an experiment in which a beam of "particles" (electrons but usually a laser) is fired from the source emitter at a plate with 2 tiny slits in it. Now the experiment reports 2 different finds when "observed" and not when observed. This is specifically what I am referring to. Yes, I understand weak measurements have been tested but I don't know what theory of quantum mechanics "predicts" that when we observe phenomenons such as this, they will collapse the wave function. It doesn't matter because, and I know it has a name and whatever name it has, it simply does not take into account what I have stated above. That being that if we observe the results of the experiment without "observers" to run tests on the beam mid experiment and then run the test again with the "observers" and see different results after at the collector/deteciton screen behind, then yes we can say that the observer is obviously affecting the experiment.

The quantum leap being made here is that we are assuming there is no interference being caused by the observers, and that what is therefore happening is a quantum collapse of the wave function that is a given property of the particles fired. Anyway, it is perfectly fine that we make these leaps so long as the word "theory" is tagged on. There are still so many possible forms for interference. Even if one were to "unplug" the observer having left it in its position and then the results again show us the wave function having not collapse, then the PROPER assumption would be to see how the ELECTRICAL CURRENT is affecting the experiment. Obviously. As I said earlier, there are many forms of radiation that can be to blame. And it could even be a complex feedback or discharge effect caused by the moving electrons in the area creating magnetic fields. Do you understand what I am saying?Zoele (talk) 15:46, 31 May 2013 (UTC)

I'm sorry, I don't. What is this electrical current or other forms of radiation you are proposing? Sounds like speculation or original research. There's no place in Wikipedia for that. -Jordgette [talk] 18:08, 31 May 2013 (UTC)

You may be misinterpreting the language, Zoele. In QM, "observation" means "interaction". In your double slit example, in order to "observe" the electron to determine which slit it went through, something has to interact (collide) with the electron. For example, light photons have to scatter off the electron to determine its position. The momentum change caused by the collision destroys the coherence of the wavefunction ("collapsing" it) so the interference pattern is lost. --Chetvorno^TALK 19:59, 31 May 2013 (UTC)

Chetvorno understands. He also clarified it for me. Jordgette you are a bit too defensive of Wikipedia here. Nothing I spoke about was speculation. The only thing I didn't realise was that they consider any observation an interaction in Quantum physics. Light having to impact an electron to figure out where its going. However, there are still many other methods of observation that you yourself Jordgette linked to under weak measurements. These are also observations of a sort and their electromagnetic signatures are almost non existent. We can observe the wavefunction almost as it happens with such methods. Again, the broad issue is the generality of stating that simply observing is enough to collapse a wave function, when in truth, observations are inherently removed from subjects happenings. For example, if you watch a car crash happening before you, your photons shouldn't be affecting the carcrash anymore than the photons reflected off of anything else in the area. Now, at the quantum level, due to Heisenberg, yeah, we can't actually see an electron (well we can see the path it took) or a photon (we can't determine its position), which is infact what this whole experiment is truthfully reminding us. The way that it is still erroneously presented is that general observations, which therefore is a generality and can allude to any observation, including the type that would not have the following effect, collapse wave functions. This is simply invalid to state like this. Thanks for the clarification Chetvorno. Jordgette, open your mind. This isn't speculation, this is questioning scientific report. Something Wikipedians try to assume they're often immune from due to their propietary standards and organization. And just for you Jordgette, the observers they would be using that WOULD affect these experiments often have power supplies running through them which, by nature, being close to the experiment, could affect the experiment near the observation. A magnetic detector that can sense electrons moving through a slit will be proejecting a magnetic field which will have to be altered for it to know something has passed through. This might be a strong enough effect to actually collapse the wave function. Call it speculation, but theory is just as speculative, and its all over Wikipedia. You don't know what you're talking about Jordgette.Zoele (talk) 09:36, 4 June 2013 (UTC)

Do you have any suggestions for improving this article, or are you going to just continue giving your personal opinion of quantum mechanics and various Wikipedia editors? The standard for Wikipedia is verifiability. If you state "theories" that are not in the literature, then it's speculative original research on your part. I'm sorry but that is unambiguous. -Jordgette [talk] 20:37, 4 June 2013 (UTC)

Not to be rude but, I feared I might get such overly defensive responses. "just continue giving your personal opinion of quantum mechanics and various Wikipedia editors?" Yes. I might JUST be giving my personal opinion of an error I see here. Are you going to sit there and point this out or do something about it? Or are you OK with the error and lack of clarity remaining? Are you going to tell me you realised all along that there was interference from the special observers used to detect where photons and electrons would be traveling before and or after the plate with the 2 slits? Are you going to tell me you knew this all along? Because I would assume, that unless you were a quantum physicist, anyone else who actually understood what was being said here (myself) would realise that the part about this phenomenon IS NOT clear. Now, seeing as how you have the time to colour your name and give so many stool samples about how to use Wikipedia and this article in its so called "verifiable" (as if published articles have NEVER included utter BS or pure personal theory before) state, then how about you realise how important this might be for ALL THOSE INTERESTED WHO ARE NOT QUANTUM PHYSICISTS NOR PEOPLE WHO JUST HAPPENS TO REALISE THAT THE SPECIFIC OBSERVATION METHODS AT THE SUB ATOMIC LEVEL CAUSE SO MUCH INTERFERENCE THAT THEY REGISTER AS MAJOR DISTURBANCES IN THE FORCES GOVERNING HAPPENINGS AT THAT LEVEL AND SUBSEQUENTLY RESULT IN DIFFERENT OBSERVABLE (IN TERMS OF OBSERVATIONS AT THE OPTICAL LEVEL) OUTCOMES OF EXPERIMENTS AT THE OPTICAL LEVEL. Might just be important. Since this your baby, what are YOU gonna do about it Jordgette?Zoele (talk) 01:19, 5 June 2013 (UTC)

Zoele, the standard for Wikipedia is Verifiability: "Wikipedia does not publish original research. Its content is determined by previously published information rather than the beliefs or experiences of its editors. Even if you're sure something is true, it must be verifiable before you can add it." I haven't seen any links to previously published sources, that would back up your definition of interference, so it is difficult to know how to go about improving the article. If you don't like the verifiability aspect of Wikipedia, consider starting a blog on the topic. -Jordgette [talk] 02:41, 5 June 2013 (UTC)

Jordgette is right, Zoele. As far as I know there is no WP:RS that says the current theory of the double slit experiment is in error, as you imply above. But this is not the place to talk about that. This talk page is for discussing changes to the article (see WP:TALK). Do you have any specific changes you'd like to suggest? This is not the venue for discussing anything else. And the abuse of other editors has to stop (WP:TALKNO). --Chetvorno^TALK 02:54, 5 June 2013 (UTC)

What about undeniable biased favouratism? I'll be more careful henceforth but it was Jordgette who crossed the line first here anyway. It can be argued that my statements are not speculation and that not everything in this article is verifiable. Improper interpretations are clear throughout this article. In terms of the exact experiment the point of it truthfully, should be to show or explain the phenomenon demonstrated in its trials using sourced information. Some understanding of what is happening should be made rather than the leap that is : "it just collapses the wave function" - or something as simple as that, featured in the article. Assuming I am suddenly not allowed to point out obvious invalidities is just as rude. "You must first backflip before you can say what you are saying". The point of me saying this here was to bring it to attention. You have both now sadly made it clear you are biased against this discussion topic in terms of what it is bringing to light. Continue to defend the mistake. You could champion it on your own and even take all the credit (I really could care less) but I will not submit to the concept of having to visit my local physicist, get him to create an article, just so I can have proof that there is an obvious oversight in the grammar and word choice in certain key areas in this article.

Ctrl-F the following:

"That aspect of QM isn't controversial or interesting"

"Sounds like speculation or original research. There's no place in Wikipedia for that"

I'm not perfect but if I can't free-speech in a talk page on topic, I guess no one can right guys? Let it be known that Chetvorno's most recent reply applies directly to the both of us for I too feel abused by the quotes above, and I quote "And the abuse of other editors has to stop (WP:TALKNO)." Fine by me. Chetvorno, can you do the leg work for the fix I'm implying here? You seem to be a great wiki user. Thx in advanceZoele (talk) 21:49, 5 June 2013 (UTC)

It's not going to happen. There is no leg work to be done, because no such articles exist, and for good reason: all "intuitive" interpretations of quantum mechanisms that have ever been put forward disagree with experiment. In science, that means they are wrong. Therefore your initial premise, that physicists ignore "obvious" or intuitive interpretations of quantum mechanics merely to "look cool," is just incorrect. -Jordgette [talk] 22:02, 6 June 2013 (UTC)

Was talking to Chetvorno at the end but whatever. What I'm saying is, run an experiment with a test that does not interfere with the electrons yet is able to somehow detect where they're going and the result will not show a quantum collapse. Looks like you were right afterall Jordgette. Much earlier you linked towards articles talking about weak measurements. And it was my fault, I didn't realise that you were right on with your reference. They have thought of "it" and the issue now would be, to alter the conclusion presented on Wikipedia or, if wikipedia is just referencing (which it is to an extent), the original articles should have their contents updated to reflect that the simple act of observering isn't enough. I'm not saying all articles or even specific articles. But I know some do and the proliferation on Wikipedia and beyond of this incorrect wording is depressing. Is it wrong for me to feel like someone being put to death for a valid concept that the current masses are so opposed to?Zoele (talk) 03:10, 17 June 2013 (UTC)

Zoele, you can't address anyone exclusively on this page; anyone is free to comment on what you write, just as you are free to comment. --Chetvorno^TALK 11:30, 17 June 2013 (UTC)

There is no way to do what you have been so egregiously asking people to do: to "detect where they're going" without "interfering" with the particles. In QM, "interfering" is necessary to "detect where they're going". However, there are experiments that interfere "less". That's what the 'weak measurement' experiments you mentioned do. There are experiments that only give partial information about which slit the particle went through: "that particle went through the lefthand slit with 75% probability"; or "20 of the last 100 particles went through the left slit but we don't know which ones". In that case, the interference pattern 'partially' disappears! It's not either-or: in between perfect knowledge and no knowledge of which slit it went through there is a range of partial knowlege specified by probabilities. As the experiment produces more and more accurate information on "which slit", the interference pattern slowly fades from view, until an experiment that can determine with no error "which slit" the particle went through produces no interference pattern at all. But you can see that the tradeoff between particles and waves cannot be escaped. There is no free lunch. Every bit of additional information about the particle's trajectory is paid for by less visibility of the interference fringes. This has all been worked out by mainstream physicists and is specified by the Englert–Greenberger duality relation, and is at least mentioned in the article, although it is not very clearly described. Did you read the full article? --Chetvorno^TALK 11:30, 17 June 2013 (UTC)

3 times. Like I said I partially agree but there are still ways to detect without interference. We just need new methods of doing so without interference that would result in such findings, the wording is poor but the article is sufficient. It can't be that hard anyway. You could even use impact vectors. Going to read this article for the 4th time. I'll check out that Englert-Greenberger duality relation. In general this article makes less leaps than the general talk surrounding this "phenomenom" of sorts. Anyway peaceZoele (talk) 20:09, 23 June 2013 (UTC)