How do mirrors reflect single photons?

[confused2]

Yes.
I'm not sure about this but..
Take a potato. Look at the potato in a mirror. Now look at the potato - it looks the same. The rules for seeing potatoes in mirrors should also apply to looking straight at them - the mirror is somewhere between a complication and a way of demonstrating something about something. Can you think of a way of demonstrating quantum paths without the mirror as a distraction? Then kind of spread your demonstration over a mirror with the same effect/result?

[confused2]

OK. No takers. Imagine a box with holes on either side. You shine a laser beam through the holes and attempt to make the laser beam visible within the box by doing 'things' to the surfaces inside the box - this is effectively what Casper was trying to do but with a mirror (is it ????). Arguably (by me now) photons individually and collectively have no particular interest in anything other than the most probable (classical) path. Looking at the problem like this .. I don't think it will be possible to make any perceptible change to the beam or the path of the beam by modifying the surfaces in the box. By extension I don't think Casper was seeing what he thought he was seeing. I'd be pleased to be proven (or argued that I am) wrong . I suspect lasers might be a 'special case' but I can't see why. They (lasers) are already the product of many reflections within the source .. could that be it?

[Secular Sanity]

I'm not sure what you mean, C2.

[C C]

[...] Arguably (by me now) photons individually and collectively have no particular interest in anything other than the most probable (classical) path. [...] By extension I don't think Casper was seeing what he thought he was seeing. [...]

Is this about skepticism on your part? You don't believe all paths are literally taken, and that some interference type reduction delivers the most efficient, observed survivor path? (Light instead just lawfully or brutely wants to pursue the latter, rather than it being weeded down to that result?)

If going by Rennie (below) these experimental setups (involving mirrors, etc) are illustrative substitutes for abstraction description ("In QM, configuration space can be even more exotic."). Even Mithuna Yoganathan (in the Looking Glass video) expressed retrospective frustration that these conceptual models that they are figurative for are for outputting answers or predictions, rather than direct apprehension of what's ultimately going on. And rotsa ruck with that: "I think having both of those mental models [particle/wave] will help me just get closer to the truth..."

Any experiments demonstrating a single photon taking all paths -- the majority likewise eradicated by interference cancellation -- would be better (but just not possible at the homemade level?). We already know that bulk light sources -- both conventional and laser -- are dispensing multiple photons or waves everywhere.
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Discussion over Veritasium YouTube video
https://physics.stackexchange.com/questi...er-pointer

John Rennie: There is a sense in which the experiment does show the light is travelling by multiple paths, but we need to be careful here, as the light does not take multiple trajectories in real space - it takes multiple trajectories in an abstract space called configuration space.

[...] indeed, Feynman (allegedly) came up with his idea by considering light passing through a diffraction grating...

[...] The experiment is a nice way of explaining the basic idea, but you are quite correct that it does not show that the light takes multiple trajectories in real space; i.e. the 3D space in which the experiment is being done. It shows that light takes multiple trajectories in configuration space.
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Looking Glass: Does this experiment *actually* prove light is a particle?
https://youtu.be/W3Egv6iO3dI

VIDEO EXCERPTS: So in this book, he [Feynmann] insists that all the experiments in here, including this very experiment, can only be explained by his particle theory of light. But it's, it's honestly hilarious because I know that these experiments can be explained by waves just as well, and he does too, because they're very clearly equivalent.

[...] So is light a particle or a wave? I think the answer is that it's neither, but both of these pictures can be different and helpful ways to see the same thing. And it all comes down to the mental model that you use to understand something like light.

[...] I remember reading that when I was straight outta school and really, really enthusiastic about physics. And I hated it. I mean, I believed it, of course, but I found it extremely disheartening because I came to physics 'cause I wanted to understand how things worked, and this just seemed like a horrible, prescriptive formula for getting the right answer, but not understanding anything at all. Whereas for me, the wave picture has really helped me have some sort of like feeling of understanding light.

But my view on the particle theory of light has softened a bit recently because I think that that theory of light is quite helpful when it comes to thinking about light being absorbed by matter, which I don't feel like I understand anywhere near enough. [...] Light is just more nuanced than being a particle or a wave, and I think having both of those mental models will help me just get closer to the truth...

[confused2]

^^ Wow CC! (as usual).

The OP starts with a mirror .. Feynman talks about mirrors. Casper and Mithuna are looking at mirrors.

In the Youtubes..
A laser is pointed at black card on a mirror .. creating a bright spot because the 'black' isn't 100 % 'black'. We aren't interested in that spot .. only how the beam got there. Ideally we'd make a hole in the mirror so the spurious light from the bright spot it isn't a problem. We'd be left with all paths SOME of which include the mirror .. but many don't .. and we can check the laser beam is still a beam by (having gone through the hole in the mirror) by looking at it some distance away. I think we can replace the entire mirror (except for the hole) by vanta black card and the laser beam would still be fine .. it doesn't need Feynman's odd angle reflections in the mirror. The other point confusing the issue is the laser source which isn't perfect - it still spreads light in all directions .. if we are to analyse a beam we need a beam .. nothing more. We can get (pretty much) a beam by using a box with two holes .. beam in and beam out. Everything that allows, makes up, influences or whatever .. the beam passing through the box has to happen within the box. If all the faces inside the box are perfect reflectors or perfect absorbers .. will it affect the beam?

[C C]

[...] The other point confusing the issue is the laser source which isn't perfect - it still spreads light in all directions .. if we are to analyse a beam we need a beam .. nothing more. We can get (pretty much) a beam by using a box with two holes .. beam in and beam out. Everything that allows, makes up, influences or whatever .. the beam passing through the box has to happen within the box. If all the faces inside the box are perfect reflectors or perfect absorbers .. will it affect the beam?

Wouldn't perfect absorbers (or reflectors) on the internal walls, and a perfect beam, be introducing a different universe (and thereby whatever resulted is inutile for those of us existing in this one)? Similar to the "mirror box" experiment below that stipulates a world where QM effects do not apply.

Aside from (at the very least slightly) imperfect absorbers and reflectors of this imperfect realm, the air inside the box will minutely impact the conventional imperfect beam (maybe even the Casimir effect if there was a vacuum).

In addition to lack of QM and a wholly different goal, the other deficiency below is that the mirror box is missing a second (exit) opening...

Capture a laser beam
https://puzzling.stackexchange.com/quest...laser-beam