Still the best video I've ever found that describes the phenomenon of the double-slit experiment.
Cartoon by "Dr Quantum"
Cartoon by "Dr Quantum"
For starters it depicts photons as balls, when it would be much less confusing and more intuitive to instead think of them as waves with discreet energy amounts. If you think about it as a wave, what's happening is a wave with a photon-amount of energy passes through both slits which causes an interference pattern. When it hits the wall it coalesces into a single particle/dot.
Also, it talks about 'observer' and strongly indicates the observer needs to be a conscious entity. Instead of observer, just use the word "detector", and bear in mind that detector interacts with the photon (whereas at the classical level you can watch or observe something without affecting the system).
The difficulty is most video are either way to technical or way too high-level.
I’ve also always wondered if it matters what side of the slits the detector is on? The experiment as depicted in that video has the detector on the gun side of the slits. Would you get the same thing if you moved it to the wall side of the slits? Also, does the wall itself count as a detector/observer?
Everything has a de Broglie wavelength, but the more massive it is the shorter the wavelength, so you'd need closer slits and higher-resolution detectors to notice anything. I guess if you used a really big particle then you'd reach a point where it would be bigger than its own wavelength and you couldn't observe any wave behaviour.
> I’ve also always wondered if it matters what side of the slits the detector is on?
No, the important thing is observing which path it takes
> Also, does the wall itself count as a detector/observer?
Not unless there's a way for you to tell when and where it hits the wall.
A finitely bounded wave is better described as a wavelet.
https://en.wikipedia.org/wiki/Wavelet
Particles are the wavelets that when summed, give us the field as a whole, ie, particles are the wavelet transform of a field.
I'm a layperson who reads a bit so I could be misinterpreting. I was always partial to the idea of probabilistic squeezing rather than collapse. In the absence of quantum gravity, probabilities can propagate only as far as their gravitational effects allow. As particles interact the compatible possible positions reduces to eventually squeeze the location to an infinitesimal size. It may be utterly wrong as an idea but it would negate the need for observers, detectors, or many worlds which makes it a bit compelling.
- It shows the single-slit case as a vertical band. Actually, the single slit case is also a smear[1][2]. A smear just a wide as the double slit pattern (but less rippled). Photons don't switch between moving like bullets and moving like waves, they consistently move like waves and consistently hit like bullets.
- It shows the photon detector as an eye off to the side of the experiment. You gotta stick it in the beam path for it to interact with the photon. You can't see photon flying by in front of you, you can only see photons bounced into your eye. Note that I'm not saying the detector has to absorb the photon, but it does have to interact with the photon and it can't interact with the photon if it's way off to the side like that.
Ultimately, it's playing into the common misunderstanding that a human glancing towards a quantum experiment has some profound effect upon it.
1: https://www.youtube.com/watch?v=h53PCmEMAGo
2: http://backreaction.blogspot.com/2021/10/the-delayed-choice-...
In an experimental setup, you might have many different levels of interaction: the photon either hits one sensor or another, that results in one or another message being sent to your recording device, which records one or the other result on your harddrive, etc. As the scale goes up, more and more stuff gets dependent on the result of your measurement, until eventually everything is, yourself included. And if everything is dependent on the result of your experiment, they must all be consistent with a given result of your experiment. Thus, you end up with exactly one answer.
Since the slit edge isn't changed by the diffraction of light, there is no inconsistency between whether the photon passed through its slit or the other.
(And if you observe it, but nobody else observes you, then you are in a superposition as far as the rest of the world is concerned.)
You can think of the barrier with two slits as a device that measures (a) whether the photon hit the barrier or missed barrier and additionally (b) when the photon hits the barrier, where did it hit the barrier. Notably, if the photon misses the barrier, it doesn't tell you where it missed. This is why, when the photon doesn't hit the barrier, it can end up in a superposition of passing through both slits.
There's some classic thought experiment, I think it's [1], thinking about an atom decaying into a superposition expanding in a spherical shape, and how you can make barriers to shape the outgoing superposition. For example, to make an expanding half sphere, block off the other half sphere and focus on the times the decay didn't hit the barrier.
1: https://en.wikipedia.org/wiki/Renninger_negative-result_expe...
I still believe the video I linked to is the best for a general audience.
I'm not sure someone without prior knowledge would follow that video.
Someone who watched the Dr. Quantum video has learned a bunch of keywords and phrases associated with quantum mechanics. They've now heard of waves and particles and detectors and whatnot. But they have been actively misled with respect to how those things behave. I bet it's possible to put together a reasonable looking test where watching the Dr Quantum video caused scores to go down.
She never discusses the detector portion of the experiment and how it's been observed to make light switch from "wave" to "particle".
Is that not accurate in the video I linked?