In firing a single photon at the center divider of a double slit, does it ALWAYS go through the slits?

Question

If we think of a single photon approaching the slits as a wave function, and we fire the photons at the midpoint of the two slits, one at a time, then I would think the probability function is highest at this midpoint. That would mean that, depending on the separation of the two slits, some of the photons would impact the wall separating the slits. If I fire a photon at a thin piece of material, why would it not at least occasionally 'hit' the material, (with a possible photoelectric effect). How is it that ALL the photons avoid this 'wall' and pass through one slit or the other?

Most of the photons will hit the wall and not pass through the slits. They are simply not tallied into the final result. The most curious aspect is how to get the light-dark bands at the other side of the double slit, from the subset of photons that manage to pass through? There is actually a picturable model where each electron does pass through only 1 slit at a time, and yet the light-dark bands still appear statistically after many photons. It is called bohmian mechanics, a non mainstream model but mathematically equivalent to standard QM. See https://www.youtube.com/watch?v=WIyTZDHuarQ — James, Nov 19 '22 at 18:29
What a great way to visualize and think about the particle/wave duality - using pilot waves. First time I've ever heard or seen of such a model. — Vim Schrotnock, Nov 20 '22 at 02:23
as far as i understand it, pilot waves can offer a mechanistic explanation for how the statistical results come about in QM, except for entangled particles, which there seems no mechanistic explanation in any theories. The pair just is entangled. It cannot be via information in the wave, because those spread locally, and there are Bell-type experiments which can test that the information cannot have been encoded in the wave, but must spontaneously be passed between particles in the form of correlated behavior. — James, Nov 20 '22 at 03:33

score 2 · Answer 1 · answered Nov 20 '22 at 21:18

Short answer: When the photon hits the walls or the web of the double slit, obviously an interaction takes place. The photon is absorbed and finally EM radiation is re-emitted.

Long answer tl;dr: What happens at the boundary regions between the slit walls? The photon passes through unhindered? No, it also has an interaction. It gets polarized, the electric and magnetic field components are aligned. Clearly to prove by the fact, that, if one aligns two polarizers by 90° to each other, no more photons pass through. But if you place a third polarizer between them at 45°, then light passes through. And this is only possible if the field components of the photon are rotated by the polarizers.

The question whether photons are reflected at the center bar is understandable, but more interesting is what happens between the edge region and the photon. Instead of reflection, transmission occurs. And here the interaction has a direct influence on the intensity distribution on the observation screen. Instead of intensity distribution one could also speak of diffraction pattern. But not of interference pattern, because photons (almost) never interfere. The edges diffract the photon in such a way that it hits certain parts of the screen with higher probability and others rather not. It would be to investigate in how far phononic and other lattice oscillations produce the selective deflection of photons (as well as electrons). But of course it is easier to calculate with the wave property and interference of the particles in the double-slit experiment.

score 1 · Answer 2 · answered Nov 19 '22 at 17:40

Don't try to analyze a diffraction problem using particles: you'll just confuse the issues.

Thinking of waves, well, what happens when waves impinge on opaque material? You see this every day. Some of the energy is reflected, some is absorbed. There's nothing particularly profound beyond this that happens in the double slit experiment. For narrow slits, you may need to account for polarization, but classical electrodynamics is fine for that, no quanta needed.

score 1 · Accepted Answer · answered Nov 19 '22 at 17:46

You are correct. To the left of the "wall with slits" we typically approximate that we are illuminating the wall/slits with a plane wave. If the wall is much bigger than the diameter of the beam then what matters is the fraction $\eta$ of the slit area compared to the total beam area. It is only this fraction $\eta$ of photons that make it through the slits and allow us to perform an interference experiment. If you put a big power meter before and after the slits you will see a power reduction by an amount $\eta$. If you're performing an experiment where you try to send photon or electron waves through the slit if you have a flux of 1 photon or electron per second but $\eta$ is 0.01 then it will take on average 100 s for a single point to be detected on your detection screen.

@VimSchrotnock glad I was able to be helpful. If this answer was helpful then you can give it an upvote and if it answered your question you can mark it as the answer with the check mark. — Jagerber48, Nov 19 '22 at 18:10

In firing a single photon at the center divider of a double slit, does it ALWAYS go through the slits?

3 Answers3