# What's the reason double-slit experiment can't be explained by edge effects rather than quantum interference? [closed]

But instead, it was a PING PONG GUN (imagine as table tennis players use to train),

throwing out PING PONG BALLS. The two slits are say 20 cm wide, and the observing screen is say 5m distant.

If the ball goes through the EXACT MIDDLE of a 20cm slit, it will travel in a perfectly straight line and make a "dot" on the observing screen.

If the ball travels nearer and nearer to the left or right edge of a slit, the flight path will bend slightly towards that side. For example, due to electrostatic force (rather like how a vertical pour of water from a faucet will bend slightly as your hand approaches).

Note that this is not some sort of fantasy; you could very easily organise for the ball path to bend slightly when near an edge, using either electrostatic force, magnetic force, aerodynamic factors or other forces, with the correct material of balls and slits (substitute small metal balls and slits of magnetic material .. whatever).

Indeed, you could trivial arrange so that precisely this famous image

is the outcome.

This is the "trivial mechanical bending" explanation of "all this interference pattern stuff".

Can you help me understand in a clear way, What is the explanation of why this is not at all the explanation?

## closed as unclear what you're asking by Norbert Schuch, Daniel Griscom, ACuriousMind♦, user36790, GertJan 16 '16 at 2:52

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• Your claim "Indeed, you could trivial arrange so that precisely this famous image is the outcome." is just wrong. Even if we grant that things that are closer to an edge deviate into the direction of that edge, that doesn't produce the interference patterns observed. It would produce patterns highly dependent on what the spread of your beam onto the slit it, and it certainly would not show patterns of destructive interference. – ACuriousMind Jan 15 '16 at 21:58
• Anyone who closed this because it is "unclear" is, no offense, silly. The question is spectacularly clear, as every reader and answerer perfectly understood it, and indeed was able to answer it clearly. – Fattie Jan 16 '16 at 16:28
• Hi ACurious: Hmm, you presumably accept that one could arbitrarily specify the "bending function" of the edges, so that, literally in the exact experiment given, we could in fact produce the exact photo achieved. Right? Or is something wrong with that step? – Fattie Jan 16 '16 at 16:30
• Secondly, you presumably accept that for any given experiment, one could arbitrarily specify the "bending function" of the edges, so that, in that particular experiment, we could in fact produce the exact photo achieved using the "conventional" electron-gun experiment. Right? – Fattie Jan 16 '16 at 16:31
• The question is clear to me, it could be stated as: "Could double slit experiment be explained by the edge effects rather than quantum interference?". therefore, I will vote to reopen; although it might be off-topic due to other reasons like duplication. – Ali Jan 16 '16 at 17:44

Nope. The important thing about the double slit experiment isn't that you find a wavy pattern on the screen, it's that the output on the screen is not equal to the output you get with only one slit open, plus the output you get with only the other slit open. The particular pattern that one slit makes by itself doesn't matter.

• Ah - I guess you've hit the nail on the head, that's what I "forgot" in that naive explanation. I feel this line of thinking offers good insights in to the phenomenon! – Fattie Jan 16 '16 at 16:43

We can't explain it like you want, because try closing one of the slits first. Then do the experiment. Then do the same for the other and do the experiment. Classically, you'd expect, that both slits will function independently, hence you won't receive an interference pattern but instead a summation of intensities from each slit individually. But this isn't what is seen in the experiment.

So, it is pretty safe to say physicists have thought this through.

To add more, you could seperate the slits from each other.

Also, try answering why a region(of minimum intereference) that was receiving tennis balls when one slit was open, would stop receiving tennis ball if the second slit got opened.

• right, thanks to yourself and knzhou for pointing out the flaw. – Fattie Jan 16 '16 at 16:50

Your explanation makes no sense. To see why, suppose you have two slits and you record a particular interference pattern as a result: a series of light and dark bars. If you then cut an additional pair of slits half way between the first pair of slits, the resulting pattern may have some dark bars where formerly there were light bars. The only way this can be explained is if there is something going through the additional slits that deflects the light that would have hit the bars that were light in the two slit experiment. A full explanation of this point can be found in "The Fabric of Reality" by David Deutsch, Chapter 2.

• "The only way this can be explained..." not really. You can trivially explain it by simply asserting that: physical topology has a bizarre property where, the "bending function" of a hole is in fact bizarrely affected by the nearby presence of other holes. I find this exactly no more or less mystic and sensational than the idea that, the Things moving have a bizarre affect on themselves at a distance backwards in time, etc. – Fattie Jan 16 '16 at 16:57
• @JoeBlow: An explanation is an account of what is happening in reality to bring about a particular event. There is no explanation of interference experiments along the line you have indicated. You say that nearby other holes affect the outcome, but this is false. I could cut another slit nearby that has no effect at all on the outcome of the experiment provided that it is not in the path of the laser beam. – alanf Jan 16 '16 at 20:44

Your explanation has a tennis ball that is a body and you are influencing it with forces , but in reality particles like electrons , photons even complete atoms show this behavior because everything behaves like a wave of some wavelength , it is just that as the particles become macroscopic , the effect is minimized . The "famous photo" when you notice is just like a wave where the white regions being crest and the dark being the trough