# Has the double slit experiment with classical projectiles ever been performed?

I was wondering if the double slit experiment with mascroscopic objects has ever been tried. In any course of quantum mechanics, a way to introduce quantum effects is to introduce the double slit experiment. For example, in Feynman lectures, two examples are given, that of a quantum particle going through the slit (which behaves like standard double slit wave interference) and that of bullets which, according to classical intuition would do something else (either make two line patterns or not, but certainly not interference patterns).

My question is, has the classical version of experiment ever been tried with actual macroscopical projectiles? Can't we just set up a machine to throw bullets/golf balls (or if we want to avoid gravitational effects, maybe marbles on a floor) at two slits (in a vacuum)?

We know what would light do. If you use incoherent beams you would have two one slit patterns, but this beats the point, because you are still using waves.

What would the actual pattern be for classical projectiles?

Edit: To be clear, I am not looking to understand quantum mechanics, I was mostly looking for a controlled research experiment on a classical double slit experiment with macroscopical classical (non-wave-like) projectiles.

Edit2: I am not asking if we have observe the interference pattern of larger objects. I am just wondering if anybody has performed a scattering experiment with classical projectiles and two slits, regardless of the wavelength to slit size ratio condition.

Edit3: some users have suggested firearm industry experiments, anybody knows where I could find some examples of those?

• Comments are not for extended discussion; this conversation has been moved to chat. Commented Feb 11, 2021 at 20:22

Having read your edits, I will answer with reasonable confidence that nobody has ever done rigorously such an experiment because of how trivial it is. We already know what happens, there's no point in doing it. The interesting thing is finding where the line between classical and quantum is by performing the experiment on bigger and bigger objects.

EDIT: answering your comment, a double-slit experiment with, say, golf balls is a simple Newtonian mechanics problem, and you can predict the outcome yourself.

Balls, unlike waves, would always travel in one direction both before and after the slit. That means that if the shooting point is aligned with a slit, the ball passes and if it doesn't it will just bounce back. On the other side of the slit, the ball would always hit the same point and there's nothing preventing it from doing so. You could try this experiment yourself.

The thing is that the physical problem and the mathematics to describe it are straightforward and known. You've mention chaos but that doesn't arise in a framework such as this, you need much more complicated equations for chaos to arise.

The fundamental point behind the double-slit experiment is interference, and that is an inherently wave-like phenomenon. If you agree that golf balls do not behave like waves, then there's no reason to expect interference.

• I will leave the question open for now, but this is the closest I have gotten to an answer today. You say "We already know what happens", but I have not been able to find anybody performing the experiment or at least doing the full modelisation/calculation for a given set-up. Classical experiments are done every day, without looking necessarily for quantum effects, you have other interesting phenomena (like classical chaos). I wonder if a classical double slit experiment like that would be as predictable as we think. Commented Feb 11, 2021 at 17:24
• Thanks again. Why are you considering trivial? Are you considering some kind of ray tracing problem? I think you are missing out two things, these are not necessarily point particles and the interaction with the edges of the slit may not be as easy to predict. That’s why I wanted to see an experiment. Also I never expected to have any interference whatsoever. Commented Feb 11, 2021 at 19:19
• Even if balls aren't point particles you could stil expect a deterministic result assuming the object are fired always in the same way and path and that the firing happens when the system (the slits) gets back to equilibrium. Even if we allow for small disturbances these will be random in nature and we wouldn't have any physical process. But at this point I don't see what the double-slit experiment has to do with it all and what kind of physics you're looking for. Commented Feb 11, 2021 at 19:59
• I was considering more like looking at distributions depending on speed, angle, initial position and so on, plus looking at the difficulties of constructing such an experiment. Commented Feb 11, 2021 at 20:21

Yes but we had done double slit experiment and achieved interference pattern by bigger and bigger molecules like 'buckministerfullerene' or Buckyballs which is a ball shaped compund of 60 carbon atoms. We have even done for behemoth, complex organic molecules, consisiting of porphyrin rings.

Problem with subsistituting projectiles as bullets or balls is that their de broglie wavelength is very miniscule; $$\lambda_{matter} \propto \frac{1}{p}$$ where $$p$$ is momentum of object. So their interference pattern would be extremely hard if not impossible to precisely measure.

• Sure but this is not what I meant. I am not asking to observe the interference pattern of macroscopical objects. I am just wondering if anybody has performed an scattering experiment with classical projectiles and two slits, regardless of the wavelenght to slit size condition. Commented Feb 11, 2021 at 16:08
• @Mauricio Yes there are few such experiments conducted but still the objects are not as big as bullet or ball. One which I could find is:phys.org/news/2006-09-single-particle-macroscopic.amp Commented Feb 11, 2021 at 16:14
• yeah something more similar like that but without the liquid (which generates waves that can interfere). Commented Feb 11, 2021 at 16:25