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The concern that the article presents - that the middle filter influences the light and thus allows it to pass through the third filter - is actually addressed

The concern that the article presents - that the middle filter influences the light and thus allows it to pass through the third filter - is actually addressed in popular quantum mechanics explanations that use the 3 filter experiment. They say that if we use two entangled photons and let them fly far apart, then pass one of them through two filters, and the second photon through the middle filter, the first photon will be affected - it will get a chance to pass though the pair of filters. That they say is "spooky action at distance" - the second photon will influence behaviour of the first photon at the remote site of the experiment and the "influence" is faster then the speed of light. Example here by MinutePhysics and 3Blue1Brown: https://youtu.be/zcqZHYo7ONs https://youtu.be/zcqZHYo7ONs Explanation about entanglement starts at around 8:50. But even with that addressed, to me personally this video is not satisfying. If the spooky action at distance can be observed so trivially - choosing a filter at one site site affects what happens at the remote site - we don't need a mathematical inequality (the Bell's inequality), it's already so obviously spooky. There are also serious problems with clarity of their explanation, as I commented in https://www.youtube.com/watch?v=zcqZHYo7ONs&lc=Ugz3tzpDP_i1N5hwXVR4AaABAg.9E0Ji-B15oK9cUCejB5owm https://www.youtube.com/watch?v=zcqZHYo7ONs&lc=Ugz3tzpDP_i1N... and https://www.youtube.com/watch?v=zcqZHYo7ONs&lc=Ugz3tzpDP_i1N5hwXVR4AaABAg.9E0Ji-B15oK9cVOYU37sI6 https://www.youtube.com/watch?v=zcqZHYo7ONs&lc=Ugz3tzpDP_i1N... I am not sure the real Bell experiments are really done using 3 polarizing filters and will the effect really be observed in experiment with two remote sites. My conclusion, it's problematic to rely on "pupular science" explanations, even by good channels like MinutePhysics and 3Blue1Brown.

abbeyj 4y ago
> They say that if we use two entangled photons and let them fly far apart, then pass one of them through two filters, and the second photon through the middle filter, the first photon will be affected - it will get a chance to pass though the pair of filters. I don't think that can be correct. This would allow FTL communication of information. I could put the filter in the path of the second photon when I wanted to send a 1 and leave it out of the path of the second photon when I wanted to send a 0. In the 1 case the other side would sometimes see the photon pass both filters. In the 0 case the other side would never see the photon pass both filters. Combine this with a little error correction and you have a channel for transmitting arbitrary information faster than light which would violate the no-communication theorem. https://en.wikipedia.org/wiki/No-communication_theorem https://en.wikipedia.org/wiki/No-communication_theorem The MinutePhysics video you link describes a different setup with only one filter in the path of each photon. This gives you some information about the probability that other photon got past its filter but it doesn't let you transmit anything.
- avodonosov 4y ago
  Yes, thank you, in distributed setting they really use only two filters. But my main point is that the video addresses the issue from the article. The video lays out intuition for the Bell's theorem using the 3 filter experiment. And then, at 8:50 they say: "what if the act of passing through one filter changes how the photon will later interact with other filters? Then you can easily explain the results of the experiment" and continue explaining that the real spookiness can be proven in a distributed experiment.

abbeyj 4y ago

> They say that if we use two entangled photons and let them fly far apart, then pass one of them through two filters, and the second photon through the middle filter, the first photon will be affected - it will get a chance to pass though the pair of filters. I don't think that can be correct. This would allow FTL communication of information. I could put the filter in the path of the second photon when I wanted to send a 1 and leave it out of the path of the second photon when I wanted to send a 0. In the 1 case the other side would sometimes see the photon pass both filters. In the 0 case the other side would never see the photon pass both filters. Combine this with a little error correction and you have a channel for transmitting arbitrary information faster than light which would violate the no-communication theorem. https://en.wikipedia.org/wiki/No-communication_theorem https://en.wikipedia.org/wiki/No-communication_theorem The MinutePhysics video you link describes a different setup with only one filter in the path of each photon. This gives you some information about the probability that other photon got past its filter but it doesn't let you transmit anything.

avodonosov 4y ago
Yes, thank you, in distributed setting they really use only two filters. But my main point is that the video addresses the issue from the article. The video lays out intuition for the Bell's theorem using the 3 filter experiment. And then, at 8:50 they say: "what if the act of passing through one filter changes how the photon will later interact with other filters? Then you can easily explain the results of the experiment" and continue explaining that the real spookiness can be proven in a distributed experiment.