I read an interesting question here in the forum (Will a football (soccer) diffract?) and came up with the following doubt: even though its diffraction angle is too small to be detected, if we had the possibility to detect it, what would the diffraction of a soccer ball through a pair of posts look like? I mean, in the case of electrons, there is a screen in which the diffraction pattern can be appreciated. But what about this case? Would we see lots of soccer balls in different places or what?
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The diffraction pattern is overlaid by thermal motion and it would take extremely low temperatures to detect it for macroscopic object. For a correct treatment you need to take a density matrix approach which contains both quantum and classical statistics. In effect the quantum effect is wiped out by the classical statistics for macroscopic objects. Fortunately this is not always the case, quantum systems with energy gap are resilient against this averaging. If they weren't, then magnetism and superconductivity and not even matter would exist. – CuriousOne Mar 26 '16 at 18:29
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Each soccer ball would end up at one place, and the probability of landing in a particular place will be a function of position. Only if you kick many soccer balls would the diffraction pattern emerge. In that sense, it is no different than photon or electron diffraction: the actual pattern on the screen is actually made up of many millions of individual "hits". In fact, people have gone to great lengths to lower the flux of photons / electrons in such experiments to prove that a single photon "interferes with itself".
I wrote an earlier answer that goes into a little more detail. You can consider each dot in that answer "one place where the soccer ball hits", but recognize that, given the mass of the ball, the "fringe spacing" would be minuscule and you would not be able to discern fringes in any real world experiment like this.
But you asked for the "in principle" answer...
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During the total solar eclipse of 10 May 1994, in Michigan, when you looked at the ground under a nice bushy maple tree you could see a crescent shaped image of nearly eclipsed sun on the ground -- lots of them, corresponding to where the rays of light passed through the holes in the leaves. It had become dark enough to provide the required contrast. So this is the case of many holes.
This is an example of multiple pin-hole cameras, and can be explained with ray optics. I include it here because it illustrates one method of generating multiple images.
For football to diffract from the goalposts, the size must match that of the de Broglie wavelength of the football; they've done this with molecules, including buckyballs. However, unlike the scenario above, there is only one football, and your detector will only click at one spot for each kick. Many repetitions are required before the diffraction pattern would appear.
But you only get to detect each football in one place.
Peter Diehr
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1That's not diffraction, just pinhole imaging, see https://en.wikipedia.org/wiki/Camera_obscura. The actual diffraction pattern along the edges of these images is not easily visible. – CuriousOne Mar 26 '16 at 18:24
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The first part of this answer is not relevant to the question, and only confuses. The second part actually begins to address the question. – Floris Mar 26 '16 at 23:50
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@Floris: you want I should delete my answer? The first part illustrates how one might see many images, though not BT diffraction. The second part says the same as yours. – Peter Diehr Mar 27 '16 at 00:05
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1@PeterDiehr I think the first part detracts from the second. If you don't spend more time explaining what (not diffraction) is causing the multiple images you are just confusing the issue. What you do with your answer is entirely up to you... I would recommend you edit, not delete. But it is your answer so you can do with it as you see fit. – Floris Mar 27 '16 at 01:52
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