Veritasium
9 HN recommenders · recommended in 10 months, 2015–2022
9:16 · 4.5M views · Jan 12, 2015
Veritasium explains quantum entanglement and spooky action at a distance, walking through Bell's inequality and the experiments that rule out hidden variables, in under ten minutes.
HN recommends it as one of the clearest layman explanations of Bell's theorem.
10 comments from Hacker News
I can't recommend Veritasium and CGP Grey enough. They are amazing YouTube Channels! Check out this video where Veritasium explains Quantum Entanglement. this video It amazes me how he explains something so difficult in less than 10 minutes!
Check out this video It's my favorite video for explaining how we know that the state is not determined until it has been measured. It's not just a decision we thought up on paper. It is real and well proven.
You understood correctly that quantum mechanics cannot be based on some hidden variable we haven't or cannot find. (Edit: oops, I re-read your comment and it seems you say the exact opposite thing? The point is that Bell's theorem rules hidden variables OUT. Here's an easily digestible video about this: this video ) About probability: no one knows. It might be that there is a "wave function collapse" that has a probabilistic outcome. But it might be that there is no such a thing. Quantum mechanics that remain in the "quantum" realm are not probabilistic, it's only when you cross over to the classical world. So it might be equally well, that the Everett interpretation (so-called "many worlds interpretation") is true, and the probability is something physicist Sean Carroll calls "self-locating uncertainty": [LINK] That is, there are multiple "yous" that experience different outcomes, and you don't know which branch of the wavefunction you find "yourself" in, which "you" you are.
> it's both simply because it hasn't been measured ... Meaning it's either one or the other A common misconception about quantum superposition is that the particle "has" some state, and we only use superposition to model that we "dont know". This is called the hidden-variable theory ( [LINK] ). It's been proven that this hidden variable theory can't be true because of [LINK] . This is completely non-intuitive. See this video for a laymen's explanation: [LINK] (you may also need to watch the prev. video about the EPR paradox [LINK] ). Edit: actually, this is a much better video this video - less technical and more visual.
I don't think that explanation is clear. It takes a bit more work to get something which proves the experimental difference. One of the better explanations I've seen is regarding measuring spin with three state detectors: this video This would give specific probabilities to certain outcomes (not just 50/50) IF there were a local hidden variable. (Note: the word local is important there. It means information encoded and carried by or with the particles themselves.)