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For those thinking Star Trek, they literally address it a few paragraphs down :) The name quantum teleportation brings to mind a technology out of Star Trek, w

by smaili 7y ago

For those thinking Star Trek, they literally address it a few paragraphs down :) The name quantum teleportation brings to mind a technology out of Star Trek, where “transporters” can “beam” macroscale objects—even living humans—between far-distant points in space. Reality is less glamorous. In quantum teleportation, the states of two entangled particles are what is transported—for instance, the spin of an electron. Even when far apart, entangled particles share a mysterious connection; in the case of two entangled electrons, whatever happens to one’s spin influences that of the other, instantaneously.

lossolo 7y ago
Yes, this is interesting because it seems like information would travel faster than light in this case, but based on our current knowledge about universe this would break Einstein's Theory of Special Relativity, which could mean there is some other out of band channel of communication between entangled particles.
- roywiggins 7y ago
  Specifically, it violates the no-communication theorem. Not only can't you signal faster than light, you can't signal using measurement at all. https://en.m.wikipedia.org/wiki/No-communication_theorem?wprov=sfla1 https://en.m.wikipedia.org/wiki/No-communication_theorem?wpr...
  - kgwgk 7y ago
    What is “it”? Where is the violation?
    - roywiggins 7y ago
      Just that classical information cannot be sent faster than light using measurements of entangled particles. Of course, quantum teleportation works, it's just not FTL, and the spooky connection between entangled particles can't be used to send information either.
      - kgwgk 7y ago
        So there is no violation anywhere. We agree :-) Your parent thought that there could be one (“it seems like information would travel faster than light in this case”) and your response (“specifically, it violates ...”) was somewhat confusing.
- Diederich 7y ago
  https://www.quora.com/Does-quantum-entanglement-violate-special-relativity https://www.quora.com/Does-quantum-entanglement-violate-spec... was illuminating.
- smogcutter 7y ago
  I've heard it analogized something like this: You and I have a deck of two playing cards. We know which cards they are. We shuffle them, and each take one without looking. Then we can travel as far from each other as we want, and whenever I take a peek at my card I'll know instantaneously what card you have (and vice versa). We remain connected at a distance, but no information really traveled faster than c and you and I couldn't use our knowledge of the other's card to communicate.
  - perl4ever 7y ago
    Yeah, I've heard that analogy, and I've also read somewhere it's wrong, despite sounding good. But unfortunately I didn't absorb the explanation of why.
abdullahkhalids 7y ago
> in the case of two entangled electrons, whatever happens to one’s spin influences that of the other, instantaneously. This is a very lazy way of saying what happens in the experiment and what eventually leads to confusion. "influences" is the most problematic word here. A non-incorrect statement would be, "the outcome of measurements are found to be correlated when the two distant observers meet at a future time and compare notes." I think at our current understanding of the philosophy of physics, saying more is not something most people should be attempting.
- root_axis 7y ago
  I think most people can intuitively understand the observed behavior by thinking about the process as if the two particles had been "pre-programmed" to correlate with each other at the time of entanglement. With that explanation, things seem pretty mundane, then it can be explained that even though the behavior appears like the particles have been pre-programmed, the nitty gritty of Bell's Theorem shows us that this isn't the case, and that's why it is so fascinating to scientists.
dbqpdb 7y ago
This is correct, but this also doesn't really capture how significant and incredible of a feat quantum teleportation is. If we have a system in a quantum state A, it is 100% impossible to actually determine A with any precision. The best you can do is say that when you inspect A, you get will get this collection of classical outcomes with these probabilities. The state A itself, while arguably quite real, is fundamentally unknowable. However we can move this state A from particle to particle or system to system, with theoretically absolute fidelity. This is quantum teleportation. It really is quite incredible. This thing that you can't know can be moved around. This is kind of philosophically non-trivial. Theres a pretty solid philosophy of science argument which is basically if you can't actually know something via experiment then what claim does it have to being called real? At first glance this might seem to apply to quantum states, but being able to move them around exactly atomically even though you cant really glance under the hood kind, gives some serious weight to there being something "real" there.

by smaili 7y ago

lossolo 7y ago

Yes, this is interesting because it seems like information would travel faster than light in this case, but based on our current knowledge about universe this would break Einstein's Theory of Special Relativity, which could mean there is some other out of band channel of communication between entangled particles.

roywiggins 7y ago
Specifically, it violates the no-communication theorem. Not only can't you signal faster than light, you can't signal using measurement at all. https://en.m.wikipedia.org/wiki/No-communication_theorem?wprov=sfla1 https://en.m.wikipedia.org/wiki/No-communication_theorem?wpr...
- kgwgk 7y ago
  What is “it”? Where is the violation?
  - roywiggins 7y ago
    Just that classical information cannot be sent faster than light using measurements of entangled particles. Of course, quantum teleportation works, it's just not FTL, and the spooky connection between entangled particles can't be used to send information either.
    - kgwgk 7y ago
      So there is no violation anywhere. We agree :-) Your parent thought that there could be one (“it seems like information would travel faster than light in this case”) and your response (“specifically, it violates ...”) was somewhat confusing.
Diederich 7y ago
https://www.quora.com/Does-quantum-entanglement-violate-special-relativity https://www.quora.com/Does-quantum-entanglement-violate-spec... was illuminating.
smogcutter 7y ago
I've heard it analogized something like this: You and I have a deck of two playing cards. We know which cards they are. We shuffle them, and each take one without looking. Then we can travel as far from each other as we want, and whenever I take a peek at my card I'll know instantaneously what card you have (and vice versa). We remain connected at a distance, but no information really traveled faster than c and you and I couldn't use our knowledge of the other's card to communicate.
- perl4ever 7y ago
  Yeah, I've heard that analogy, and I've also read somewhere it's wrong, despite sounding good. But unfortunately I didn't absorb the explanation of why.

abdullahkhalids 7y ago

> in the case of two entangled electrons, whatever happens to one’s spin influences that of the other, instantaneously. This is a very lazy way of saying what happens in the experiment and what eventually leads to confusion. "influences" is the most problematic word here. A non-incorrect statement would be, "the outcome of measurements are found to be correlated when the two distant observers meet at a future time and compare notes." I think at our current understanding of the philosophy of physics, saying more is not something most people should be attempting.

root_axis 7y ago
I think most people can intuitively understand the observed behavior by thinking about the process as if the two particles had been "pre-programmed" to correlate with each other at the time of entanglement. With that explanation, things seem pretty mundane, then it can be explained that even though the behavior appears like the particles have been pre-programmed, the nitty gritty of Bell's Theorem shows us that this isn't the case, and that's why it is so fascinating to scientists.

dbqpdb 7y ago

This is correct, but this also doesn't really capture how significant and incredible of a feat quantum teleportation is. If we have a system in a quantum state A, it is 100% impossible to actually determine A with any precision. The best you can do is say that when you inspect A, you get will get this collection of classical outcomes with these probabilities. The state A itself, while arguably quite real, is fundamentally unknowable. However we can move this state A from particle to particle or system to system, with theoretically absolute fidelity. This is quantum teleportation. It really is quite incredible. This thing that you can't know can be moved around. This is kind of philosophically non-trivial. Theres a pretty solid philosophy of science argument which is basically if you can't actually know something via experiment then what claim does it have to being called real? At first glance this might seem to apply to quantum states, but being able to move them around exactly atomically even though you cant really glance under the hood kind, gives some serious weight to there being something "real" there.