3 ms·

This video is very misleading. - 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

This video is very misleading. - 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 https://www.youtube.com/watch?v=h53PCmEMAGo 2: http://backreaction.blogspot.com/2021/10/the-delayed-choice-quantum-eraser.html http://backreaction.blogspot.com/2021/10/the-delayed-choice-...

mensetmanusman 4y ago
Why isn’t the slit material edge itself a detector since it must be interacting with the photon?
- lazide 4y ago
  Photons that interact with the edge go through a different process of absorption and re-emission + scattering (or not). They aren't the original photon.
  - mensetmanusman 4y ago
    That’s true of the air the photon is traveling through though…
    - lazide 4y ago
      And many of these experiments are performed in vacuum for that reason.
      - mensetmanusman 4y ago
        The photon double slit is not usually in a vacuum…
        lazide 4y ago
        Photon true, but electron always. Photon also works the same in a vacuum though, and has been verified as such.
- OkayPhysicist 4y ago
  IMO, detection/observation is the wrong framing of the problem. A better approach is about consistency. All interactions in a system must be consistent: if you have two Schrodinger's cat-boxes being controlled by the same measurement, then either both cats will be dead, or both will be alive, you will never find one dead and the other alive. 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.
- int_19h 4y ago
  It is a detector, as is the wall. But you still don't know the state of that detector until you observe it, so now the photon+detector system is itself in superposition as far as you're concerned. (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.)
- Strilanc 4y ago
  Actually... it is! 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_experiment#Renninger's_negative-result_experiment https://en.wikipedia.org/wiki/Renninger_negative-result_expe...
alberth 4y ago
I really appreciate you linking to this video, and did enjoy it. 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.
- Strilanc 4y ago
  "Plays into common misconceptions" is one of the worst properties that a video targeted at general audiences can have. This even happens if your video is technically correct but sounds sorta like the common misconception [1]. 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. 1: https://www.youtube.com/watch?v=eVtCO84MDj8 https://www.youtube.com/watch?v=eVtCO84MDj8

mensetmanusman 4y ago

Why isn’t the slit material edge itself a detector since it must be interacting with the photon?

lazide 4y ago
Photons that interact with the edge go through a different process of absorption and re-emission + scattering (or not). They aren't the original photon.
- mensetmanusman 4y ago
  That’s true of the air the photon is traveling through though…
  - lazide 4y ago
    And many of these experiments are performed in vacuum for that reason.
    - mensetmanusman 4y ago
      The photon double slit is not usually in a vacuum…
      - lazide 4y ago
        Photon true, but electron always. Photon also works the same in a vacuum though, and has been verified as such.
OkayPhysicist 4y ago
IMO, detection/observation is the wrong framing of the problem. A better approach is about consistency. All interactions in a system must be consistent: if you have two Schrodinger's cat-boxes being controlled by the same measurement, then either both cats will be dead, or both will be alive, you will never find one dead and the other alive. 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.
int_19h 4y ago
It is a detector, as is the wall. But you still don't know the state of that detector until you observe it, so now the photon+detector system is itself in superposition as far as you're concerned. (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.)
Strilanc 4y ago
Actually... it is! 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_experiment#Renninger's_negative-result_experiment https://en.wikipedia.org/wiki/Renninger_negative-result_expe...

alberth 4y ago

I really appreciate you linking to this video, and did enjoy it. 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.

Strilanc 4y ago
"Plays into common misconceptions" is one of the worst properties that a video targeted at general audiences can have. This even happens if your video is technically correct but sounds sorta like the common misconception [1]. 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. 1: https://www.youtube.com/watch?v=eVtCO84MDj8 https://www.youtube.com/watch?v=eVtCO84MDj8