4 ms·

> similar to how entangled pairs seem to transmit information faster than light If your lover sends you a left-half heart locket through the postal service, wh

by zwkrt 8y ago

> similar to how entangled pairs seem to transmit information faster than light If your lover sends you a left-half heart locket through the postal service, when you get it you can assume he has the right-half of the locket "faster than the speed of light". However this is cheating because to know that he has the other half requires prior knowledge of the exchange--either he sent a previous letter where he stated his intent, or you just made an assumption about the state of the environment (namely, that your partner is the only one who would send you presents in the mail). In either case, no laws of physics need be broken.

ahelwer 8y ago
This is absolutely not how entanglement works. This analogy requires the locket half you receive to be defined at time of "entanglement" (when the locket halves are separated & sent). Half a century of Bell experiments have told us that the result of measuring an entangled system is defined at time of measurement, not at time of entanglement. If it were defined at time of entanglement, the particles would have to carry information with them to "remember" how they decided to collapse (a local hidden variable). Bell experiments disprove the existence of local hidden variables as a means to explain entanglement. I wish people would stop posting these third-hand metaphors about quantum entanglement being like finding a single right-handed glove in your pocket or whatever. They are irredeemably flawed and completely misrepresent how entanglement works.
- zwkrt 8y ago
  Yes my analogy had a hidden variable, but it is "less wrong" than saying that entanglement allows FTL communication, for reasons analogous to those that I provided at the end; entanglement can only convey information as fast as light because the two parties detecting the entangled particles aren't communicating they are just on the receiving end of a shared experience. I don't think I can explain entanglement to a lay person more succinctly than the locket/glove analogy, even though it does hand wave the most quantum-ey part of the experiment.
  - ahelwer 8y ago
    But I feel this harms more than it helps, like saying "quantum computers compute with every possible value simultaneously in superposition" which gives the audience a very flawed understanding of how QCs work (that they'll be able to solve NP-complete problems in polynomial time for example). By phrasing quantum phenomena in terms familiar to the classical audience, we do them a disservice; we are lying to them. In this case, the question "why doesn't quantum entanglement enable FTL communication?" is properly that the reduced density operator of an EPR half is the maximally mixed state. All we can do to simplify that is to tell them that quantum concepts exist outside of classical language, and in order to understand them they'll have to learn a new language - mathematics. The most you can say is quantum entanglement enables FTL "correlations" which are stronger than classical correlations but not strong enough to enable information transfer.
    - dwringer 8y ago
      Not encountering this for the first time, I've given much thought to your position over the years. But according to many mathematicians, mathematics is within the purview of natural language[1][2]. And wasn't it Feynman himself alleged to have said if we can't explain something in a lecture intended for undergraduate freshmen, we don't really understand it? [3, p19]. [1] https://en.wikipedia.org/wiki/Language_of_mathematics https://en.wikipedia.org/wiki/Language_of_mathematics [2] http://www.cut-the-knot.org/language/MathIsLanguage.shtml http://www.cut-the-knot.org/language/MathIsLanguage.shtml [3] http://calteches.library.caltech.edu/563/2/Goodstein.pdf http://calteches.library.caltech.edu/563/2/Goodstein.pdf EDIT: This is not to challenge your specific assertions on this topic - on which I cannot speak with any particular authority.
      - ahelwer 8y ago
        Undergraduate freshmen are perfectly capable of understanding basic linear algebra, and thus quantum entanglement. Regarding the nature of language and how it relates to mathematics, I don't think it's correct to say math is a "subset" of language; there is no satisfactory definition of language that encompasses all the way humans communicate with one another, and it makes more sense to restrict the definition of language to its use in specific interactions (the language of interacting with a cashier to buy an item from a store, and the different language of telling your team what you worked on during standup, for example). In this sense the use of mathematics to describe quantum mechanics is a language in itself.

by zwkrt 8y ago

ahelwer 8y ago

This is absolutely not how entanglement works. This analogy requires the locket half you receive to be defined at time of "entanglement" (when the locket halves are separated & sent). Half a century of Bell experiments have told us that the result of measuring an entangled system is defined at time of measurement, not at time of entanglement. If it were defined at time of entanglement, the particles would have to carry information with them to "remember" how they decided to collapse (a local hidden variable). Bell experiments disprove the existence of local hidden variables as a means to explain entanglement. I wish people would stop posting these third-hand metaphors about quantum entanglement being like finding a single right-handed glove in your pocket or whatever. They are irredeemably flawed and completely misrepresent how entanglement works.

zwkrt 8y ago
Yes my analogy had a hidden variable, but it is "less wrong" than saying that entanglement allows FTL communication, for reasons analogous to those that I provided at the end; entanglement can only convey information as fast as light because the two parties detecting the entangled particles aren't communicating they are just on the receiving end of a shared experience. I don't think I can explain entanglement to a lay person more succinctly than the locket/glove analogy, even though it does hand wave the most quantum-ey part of the experiment.
- ahelwer 8y ago
  But I feel this harms more than it helps, like saying "quantum computers compute with every possible value simultaneously in superposition" which gives the audience a very flawed understanding of how QCs work (that they'll be able to solve NP-complete problems in polynomial time for example). By phrasing quantum phenomena in terms familiar to the classical audience, we do them a disservice; we are lying to them. In this case, the question "why doesn't quantum entanglement enable FTL communication?" is properly that the reduced density operator of an EPR half is the maximally mixed state. All we can do to simplify that is to tell them that quantum concepts exist outside of classical language, and in order to understand them they'll have to learn a new language - mathematics. The most you can say is quantum entanglement enables FTL "correlations" which are stronger than classical correlations but not strong enough to enable information transfer.
  - dwringer 8y ago
    Not encountering this for the first time, I've given much thought to your position over the years. But according to many mathematicians, mathematics is within the purview of natural language[1][2]. And wasn't it Feynman himself alleged to have said if we can't explain something in a lecture intended for undergraduate freshmen, we don't really understand it? [3, p19]. [1] https://en.wikipedia.org/wiki/Language_of_mathematics https://en.wikipedia.org/wiki/Language_of_mathematics [2] http://www.cut-the-knot.org/language/MathIsLanguage.shtml http://www.cut-the-knot.org/language/MathIsLanguage.shtml [3] http://calteches.library.caltech.edu/563/2/Goodstein.pdf http://calteches.library.caltech.edu/563/2/Goodstein.pdf EDIT: This is not to challenge your specific assertions on this topic - on which I cannot speak with any particular authority.
    - ahelwer 8y ago
      Undergraduate freshmen are perfectly capable of understanding basic linear algebra, and thus quantum entanglement. Regarding the nature of language and how it relates to mathematics, I don't think it's correct to say math is a "subset" of language; there is no satisfactory definition of language that encompasses all the way humans communicate with one another, and it makes more sense to restrict the definition of language to its use in specific interactions (the language of interacting with a cashier to buy an item from a store, and the different language of telling your team what you worked on during standup, for example). In this sense the use of mathematics to describe quantum mechanics is a language in itself.