4 ms·

You state this as a fact, but there seems to be an interpretation of entanglement in what you wrote, so I will ask a question: Sticking to the metapher, how do

You state this as a fact, but there seems to be an interpretation of entanglement in what you wrote, so I will ask a question: Sticking to the metapher, how do you know, that looking at the content of one envelope will _affect_ the content of the other envelope, in contrast to you _discovering_ the other envelope's content to be the other color? Asked differently: Why do you necessitate that viewing one envelope's content _affects_ the other, rather than merely allowing to conclude the other, because some law of the universe makes it happen to be always the other color? To me this seems really an interpretation, rather than a fact, that one can simply put there without dispute.

simcop2387 6y ago
Part of this is because of tests like the ones involved with Bells theorem. Minute physics does a better job explaining it then I can. https://m.youtube.com/watch?v=zcqZHYo7ONs&vl=en https://m.youtube.com/watch?v=zcqZHYo7ONs&vl=en
ahelwer 6y ago
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 6y 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 6y ago
    Oh sure I'll do that.
- PoignardAzur 6y 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 6y 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.
emrah 6y ago
> Why do you necessitate that viewing one envelope's content _affects_ the other, rather than merely allowing to conclude the other, because some law of the universe makes it happen to be always the other color? Right, I'm not the one necessitating it. That's how quantum mechanics works for entangled particles. You can read more on this if you look up "EPR paradox".
- zelphirkalt 6y ago
  I read most of https://en.wikipedia.org/wiki/EPR_paradox https://en.wikipedia.org/wiki/EPR_paradox. To me it is still unclear, how all this proves, that it must be one particle or some observation of its attributes affecting the entangled other particle or observation of one of those attributes of it. The wiki article always says things like "X has shown in experiment Y, that Z.", but the details are what matters, if I am to really understand it. I guess without investing years for the mathematical background and physics background, it is hopeless, to try and understand it in an afternoon. My mind will always ask the next "but why?" question and I will be left with the feeling of not understanding it properly. Perhaps my idea how it might happen is too much of a metaphysical one? Here is what I think: I imagine entangled particles to be something like 2 sides of the same coin. Something we can observe in the known "world" (all the things we know about or can look at in a lab or experiments), but which has an actual character, somewhere/when, that we cannot grasp yet. Perhaps like an object in front of 2 light sources, throwing 2 shadows, and we observe the shadows, instead of the real object. But the shadows for us are all we currently can observe at our level of scientific understanding or with our technology. It is unclear to me, which definition of locality that object would be in or not in, reading that wiki page, so I am trying to not use that word. The problem is, how one could prove or disprove such a thing, because it is basically an "escape hatch", with which one can always say, that there is something, we do not yet see. From an "unknown object, whose shadow we can perceive" one also cannot draw many predictions, I think, so it might not be immediately useful to assume such. My guess is, that physicists stick to theories one can prove or disprove things about. Perhaps I will ask a knowledgeable coworker to explain to me, why my idea cannot be how it really is. Thanks for the pointers, I can also mention those in my questions.
  - 6y ago

simcop2387 6y ago

Part of this is because of tests like the ones involved with Bells theorem. Minute physics does a better job explaining it then I can. https://m.youtube.com/watch?v=zcqZHYo7ONs&vl=en https://m.youtube.com/watch?v=zcqZHYo7ONs&vl=en

ahelwer 6y ago

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 6y 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 6y ago
  Oh sure I'll do that.
PoignardAzur 6y 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 6y 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.

emrah 6y ago

> Why do you necessitate that viewing one envelope's content _affects_ the other, rather than merely allowing to conclude the other, because some law of the universe makes it happen to be always the other color? Right, I'm not the one necessitating it. That's how quantum mechanics works for entangled particles. You can read more on this if you look up "EPR paradox".

zelphirkalt 6y ago
I read most of https://en.wikipedia.org/wiki/EPR_paradox https://en.wikipedia.org/wiki/EPR_paradox. To me it is still unclear, how all this proves, that it must be one particle or some observation of its attributes affecting the entangled other particle or observation of one of those attributes of it. The wiki article always says things like "X has shown in experiment Y, that Z.", but the details are what matters, if I am to really understand it. I guess without investing years for the mathematical background and physics background, it is hopeless, to try and understand it in an afternoon. My mind will always ask the next "but why?" question and I will be left with the feeling of not understanding it properly. Perhaps my idea how it might happen is too much of a metaphysical one? Here is what I think: I imagine entangled particles to be something like 2 sides of the same coin. Something we can observe in the known "world" (all the things we know about or can look at in a lab or experiments), but which has an actual character, somewhere/when, that we cannot grasp yet. Perhaps like an object in front of 2 light sources, throwing 2 shadows, and we observe the shadows, instead of the real object. But the shadows for us are all we currently can observe at our level of scientific understanding or with our technology. It is unclear to me, which definition of locality that object would be in or not in, reading that wiki page, so I am trying to not use that word. The problem is, how one could prove or disprove such a thing, because it is basically an "escape hatch", with which one can always say, that there is something, we do not yet see. From an "unknown object, whose shadow we can perceive" one also cannot draw many predictions, I think, so it might not be immediately useful to assume such. My guess is, that physicists stick to theories one can prove or disprove things about. Perhaps I will ask a knowledgeable coworker to explain to me, why my idea cannot be how it really is. Thanks for the pointers, I can also mention those in my questions.
- 6y ago