4 ms·

This is something you can experimentally test. First you should know that "red ball or blue ball" is a simplification. Staying with the metaphor, if you open on

This is something you can experimentally test. First you should know that "red ball or blue ball" is a simplification. Staying with the metaphor, if you open one envelope differently you might get a purple ball and so know the other envelope contains a green ball. What we're actually dealing with are vectors on the complex unit sphere instead of ball colors, and opening the envelope is choosing two perpendicular axes along which to measure the state, causing probabilistic collapse to one or the other axis. Since you can choose which axes you measure, there are all sorts of tricky experiments you can do (called Bell tests) to test the theory that you're just discovering a pre-existing value vs. causing collapse to those values. The pre-existing value idea is called a local hidden variable, the existence of which has been conclusively experimentally disproven. I wrote a post on this you might find useful, explaining a Bell test called the CHSH game that computer scientists will find intuitive. All you need is your rememberance of the unit circle from high school path! https://ahelwer.ca/post/2018-12-07-chsh/ https://ahelwer.ca/post/2018-12-07-chsh/

zelphirkalt 5y ago
Thanks for the link. It seems to involve quite a bit more than unit circles though ;) I have one note, which I hope you don't take the wrong way: I think it would be great, if you could put the slides as PDF on your page (viewable with browser's PDF.js for example), rather than on slideshare.). Then the slides you link to for understanding the braket notation would be as accessible as the original page you link to.
- ahelwer 5y ago
  Oh sure I'll do that.
PoignardAzur 5y ago
I've read your article, and it helped me understand the shape of the proof, but I still don't understand it. If no information is transmitted between the people observing the quantum particles, how is it that you can improve their "performance" at the CHSH game above 75%? Like, what is the fundamental unit of "information"/coordination the players are extracting from their particles/qbits? Actually, while I'm being confused, what even is a qbit? From the descriptions, it sounds like it's not just an information, where two qbits with the same vector representation are equivalent, and it's more like a physical concept. Is it a particle? Or, like, it it some sort of global variable of the universe that stores some information that is undetermined until you "collapse" the global variable?
- ahelwer 5y ago
  A qbit is a mathematical model of some quantum phenomena that exhibits superposition & entanglement, like particle spin. The model seems to match the behavior rules of spin (and other quantum phenomena) as far as measurement and manipulation are concerned. Physicists generally avoid the question of whether nature really internally keeps track of the spin of a single particle with a complex 2-vector; instead we just say the model matches the experimental behavior as far as we have actually found, so the model is useful as a reasoning tool. Sorry for the sort of abstract answer. When we talk about information being communicated we're talking about someone choosing a bit that is then somehow reproduced with some fidelity somewhere else. Quantum entanglement doesn't allow such straightfoward possibilities. Instead it offers correlations that are stronger than would be possible with purely classical means. If this answer is frustrating because it doesn't match your intuition of what communication is - welcome to quantum mechanics! You just kind of have to learn the rules of the systems and get used to them. What you can do with entanglement (quite a lot!) is more important than what is "actually" happening under the hood.

zelphirkalt 5y ago

Thanks for the link. It seems to involve quite a bit more than unit circles though ;) I have one note, which I hope you don't take the wrong way: I think it would be great, if you could put the slides as PDF on your page (viewable with browser's PDF.js for example), rather than on slideshare.). Then the slides you link to for understanding the braket notation would be as accessible as the original page you link to.

ahelwer 5y ago
Oh sure I'll do that.

PoignardAzur 5y ago

I've read your article, and it helped me understand the shape of the proof, but I still don't understand it. If no information is transmitted between the people observing the quantum particles, how is it that you can improve their "performance" at the CHSH game above 75%? Like, what is the fundamental unit of "information"/coordination the players are extracting from their particles/qbits? Actually, while I'm being confused, what even is a qbit? From the descriptions, it sounds like it's not just an information, where two qbits with the same vector representation are equivalent, and it's more like a physical concept. Is it a particle? Or, like, it it some sort of global variable of the universe that stores some information that is undetermined until you "collapse" the global variable?

ahelwer 5y ago
A qbit is a mathematical model of some quantum phenomena that exhibits superposition & entanglement, like particle spin. The model seems to match the behavior rules of spin (and other quantum phenomena) as far as measurement and manipulation are concerned. Physicists generally avoid the question of whether nature really internally keeps track of the spin of a single particle with a complex 2-vector; instead we just say the model matches the experimental behavior as far as we have actually found, so the model is useful as a reasoning tool. Sorry for the sort of abstract answer. When we talk about information being communicated we're talking about someone choosing a bit that is then somehow reproduced with some fidelity somewhere else. Quantum entanglement doesn't allow such straightfoward possibilities. Instead it offers correlations that are stronger than would be possible with purely classical means. If this answer is frustrating because it doesn't match your intuition of what communication is - welcome to quantum mechanics! You just kind of have to learn the rules of the systems and get used to them. What you can do with entanglement (quite a lot!) is more important than what is "actually" happening under the hood.