The way I've always thought of this is there are potentials for interactions and interactions.

Interactions act like point particles and potentials for interactions act like waves.

Arguing over the distinction is a bit like debating whether people are the things they do, or the thing that does things. There is some philosophical discussion to be had, but for the most part it doesn't really matter.

It does not. It shows that individual photons self interfere, so they cannot be idealized particles.

Are you getting confused with the photoelectric effect experiment?

Hmm? The double slit experiment definitely shows that particles are waves—weird quantum waves, but still waves.

what happens when you only send a single photon down the line though?

As the other comments have already mentioned, it interferes with itself, so you still observe the same interference patterns [0] [1]. Which admittedly seems impossible at first, but so does the rest of quantum physics.

[0]: https://www.feynmanlectures.caltech.edu/III_01.html#Ch1-S5

[1]: https://en.wikipedia.org/wiki/Wave%E2%80%93particle_duality#...

> Which admittedly seems impossible at first, but so does the rest of quantum physics.

AKA, miracles can happen, hehe.

I'm not trolling, this is a philosophical point I'm making.

Depends on the definition of miracle I guess. There's all sort of unintuitive shit going on in the quantum world, but we can make it happen so reliably that it's hardly a miracle anymore. Wikipedia defines a miracle as "an event that is inexplicable by natural or scientific laws and accordingly gets attributed to some supernatural or praeternatural cause". But we understand "how" quantum mechanics quite well, even if the behavior described by the equations is not very intuitive to humans.

It still interferes with itself, and that interference affects the pattern of detections. It's as if the photon were a wave right up until the moment of detection, at which points it's forced to “particalize” and pick a spot to be located at — but it's the amplitude of the wave it was just before detection that determines where on the detection screen the photon is likely to show up. If you send many photons through one at a time, the detections (each just a point on the screen) will fill out the expected double slit pattern.

It's worth reading about, but it's kind of wave-like even then: https://en.wikipedia.org/wiki/Double-slit_experiment#Interfe...

It would be going too far to say it's only a wave though. It's both wave and particle.

The way I read GGP was as contradicting the assertion that everything is just waves and not at all particles.

It's a wave of probability, that interferes through the slits and then collapses into a probability of one somewhere along the wavefront at the point of detection. Whatever that means :-)

I've always wondered what degree of confidence exists amongst the cogniscenti that a single photon event happened. I tend to think the criteria of measurement here would suggest the most likely outcome was a shitload more than 1 photon, and that all the "but we measured we can see one only" measurements are themselvs hedged by a bunch of belief.

That said, I do like the single photon experiment, when it's more than a thought experiment.

Double slit experiment has been done with electrons which are, afaik, much easier to detect and send single file. It's been done with molecules. It's not a thought experiment.

Quantum superposition is real. There's no doubt about that.

Not a physicist, just here to observe single photons weren't reliably emitted until the modern era. like the 1970s. The double slit experiment pre-dates this. it's from 1801. The one which confirms "self interaction" was 1974. I was in high school 1973-78 so the stuff we did, was comparatively "new" physics in that sense. Not a message I remember receiving at the time.

From the pop-sci history reading I do, "detecting" reliable generation of single photon STREAMS in the early days depended on using mechanisms which inherently would release a sequence of photons on a time base, over time, and then gating the time sufficiently accurately to have high confidence you know the time base, and can discriminate an "individual" from the herd.

I don't doubt quantum theory. I only observe it's mostly for young students (like almost all received wisdom) grounded in experiments which don't actually do what people think they do. The ones you run in the school lab are illustrative not probative.

What people do in places like the BIPM in Paris, or CERN, isn't the same as that experiment you did with a ticker-tape and a weighted trolleycar down a ramp. "it's been confirmed" is the unfortunate reality of received wisdom, and inherently depends on trust in science. I do trust science.

Now we have quantum dots, and processes which will depend on reliably emitting single photons and single electrons, the trust has moved beyond "because they did it in CERN" into "because it's implemented in the chipset attached to the system I am using" -QC will need massive amounts of reliably generated single instance signals.

> just here to observe single photons weren't reliably emitted until the modern era.

A dim light bulb from a few feet away emits on the order of 1k photons/sec, which is low enough that you can count individual emissions using fairly simple analog equipment [0] [1].

> The double slit experiment pre-dates this. it's from 1801. The one which confirms "self interaction" was 1974.

There's an experiment from 1909 that demonstrated the double-slit experiment with single(ish) photons [2].

> I only observe it's mostly for young students (like almost all received wisdom) grounded in experiments which don't actually do what people think they do. The ones you run in the school lab are illustrative not probative.

> What people do in places like the BIPM in Paris, or CERN, isn't the same as that experiment you did with a ticker-tape and a weighted trolleycar down a ramp. "it's been confirmed" is the unfortunate reality of received wisdom, and inherently depends on trust in science. I do trust science.

The double-slit experiment is actually fairly easy and cheap to run [3]. Certainly more complicated than ticker tape, but not by much.

[0]: https://en.wikipedia.org/wiki/Scintillation_counter

[1]: https://en.wikipedia.org/wiki/Photomultiplier_tube

[2]: https://www.biodiversitylibrary.org/page/31034247

[3]: https://www.teachspin.com/two-slit

do it once, it looks like one particle.

repeat the single photon launch many times, and you see a wavelike distribution of photon strikes

The two-slit experiment shows that photons behave like waves if you aren't looking at them, and that they fail to behave like waves if you are.

Everett reconciled that. They only appear to fail to behave like waves because the observer is waves as well.

Another interpretation of the double-slit posits a guiding 'Pilot Wave' separate from physical particles... aka DeBroglie-Bohm Theory or Bohmian Mechanics.

Apparently it's not popular among professional physicsts though John Bell investigated it a bit. Einstein had some unpublished notes in the 1920s about a "Gespensterfeld" (ghost field) that guided particles.

Born was influenced by this 'Ghost field' idea when he published his famous interpretation of the 'Wave Function' |Ψ|^2 as a probability rather than a physical field.

More info: Nonlocal and local ghost fields in quantum correlations. https://arxiv.org/abs/quant-ph/9502017

Veritasium did a video on this [1] with a surface of oil to replicate the effect on a petri dish.

[1] https://www.youtube.com/watch?v=WIyTZDHuarQ

Pilot wave is still my favorite - I don’t really believe it, but I like the image

It is indeed a great way to translate classical intuitions to the quantum domain.