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The whole point of entanglement is that measuring one of the pair affects the outcome for the other one. Whether the influence "travels" between the particles i

The whole point of entanglement is that measuring one of the pair affects the outcome for the other one. Whether the influence "travels" between the particles is subject to debate, but there is influence.

leephillips 5y ago
Sorry, no. There is no debate on this point. The confusion here may be merely linguistic, but there can be no instantaneous influence, in the sense of a causal effect or transmission of information, from one particle to a distant entangled particle. If there were, that would violate everything we know is true about causation, and therefore reality. Nonlocal entanglement does not, and can not, involve an instantaneous influence.
- yourenotsmart 5y ago
  You're arguing about something I'm not. The fact the waveform collapse appears instant doesn't violate causality at all. To break causality the collapse should be usable for communication, but it isn't. Yet it does appear instant, from all data we have. And that is not explained at all by our current understanding of quantum physics. It's "explained" as in we observe it, and can calculate how it works. But it's not explained as in how come that collapse happens instantly regardless of the distance. Therefore spacetime is either non-local, or we need another interpretation like many worlds that avoids the collapse and replaced it with neverending waveform, or something else. To say there's nothing here left to explain to me says you don't understand the problem in the first place. Either that, or you know something that leading physicists don't know right now.
  - codethief 5y ago
    > Therefore spacetime is either non-local You might be interested in Travis Norsen's book "Foundations of Quantum Mechanics - An Exploration of the Physical Meaning of Quantum Theory" (2017) where he argues that quantum mechanics (in the orthodox Copenhagen interpretation) is not even non-local because the word doesn't even make sense in quantum mechanics.
- snarkypixel 5y ago
  > there can be no instantaneous influence, in the sense of a causal effect or transmission of information, from one particle to a distant entangled particle Didn't the Bell's theorem prove that wrong though? I.e. that there needs to be some sort of "hidden variables" for it to work?
  - leephillips 5y ago
    More like the opposite of that. Bell’s theorem tells us that there are two choices: either QM is inherently non-local, or there are influences (hidden variables) that can operate faster than light. Although both choices are in a sense disturbing, most people realize that we have to accept the non-local option. If we do, everything still works, even if we might feel uncomfortable. If, however, we accept faster-than-light influences, nothing works.
    - snarkypixel 5y ago
      Makes sense. And unless I'm mistaken, to be entangled, they have to be very close to each others at some point, right? And then we can send one of the pair far away and they'd still be entangled. I can imagine some sort of more fundamental link connecting the two, but it's still not breaking ftl
      - leephillips 5y ago
        Yes, the particles are prepared together, then separated. Experiments on entangled particles have now managed to keep them entangled while separating them by huge distances—many kilometers. Of course there is a link connecting them, which we express by saying they are “entangled”. But we may never be able to connect this with concepts that are intuitive from our experience with the classical world.
        yourenotsmart 5y ago
        Non-locality is not just a problem of the classic world. There's no notion of it in the quantum mechanics world either. There's nothing in the math that suggests how can particles kilometers away can be connected "outside" space. And technically if they were, this would be apparent in many more ways than entanglement experiments, and it WOULD violate causality. General relativity also has no such concept as "simultaneous events" at distance. The very point of the theory is that event simultaneity is a meaningless concept at distance (any distance, but especially at large distance). So from scale cosmic to scale quantum, "non-local" is a meaningless concept, yet we have to just assume none of this matters and call the wave function collapse non-local, because that's the only way we decided the experiments make sense. So you're trying to handwave an issue away that's bigger than you admit. It implies space beyond space and time beyond time, where everything in the universe can happen simultaneously for two entangled particles regardless of where and when in that universe they happen to be. It's such an outrageous concept to introduce in this special case, with zero explanation, and without considering the larger implications it has, it honestly borders on The Avengers techno-babble about time travel in terms of how much sense it makes.
slowmovintarget 5y ago
Some work much more recent than 1997 with ADS/CFT correspondences shows that entanglement may manifest physically as wormholes. That is, there becomes a way for entangled particles to be local in spacetime despite them appearing to be distant in space. (ER = EPR conjecture).

leephillips 5y ago

Sorry, no. There is no debate on this point. The confusion here may be merely linguistic, but there can be no instantaneous influence, in the sense of a causal effect or transmission of information, from one particle to a distant entangled particle. If there were, that would violate everything we know is true about causation, and therefore reality. Nonlocal entanglement does not, and can not, involve an instantaneous influence.

yourenotsmart 5y ago
You're arguing about something I'm not. The fact the waveform collapse appears instant doesn't violate causality at all. To break causality the collapse should be usable for communication, but it isn't. Yet it does appear instant, from all data we have. And that is not explained at all by our current understanding of quantum physics. It's "explained" as in we observe it, and can calculate how it works. But it's not explained as in how come that collapse happens instantly regardless of the distance. Therefore spacetime is either non-local, or we need another interpretation like many worlds that avoids the collapse and replaced it with neverending waveform, or something else. To say there's nothing here left to explain to me says you don't understand the problem in the first place. Either that, or you know something that leading physicists don't know right now.
- codethief 5y ago
  > Therefore spacetime is either non-local You might be interested in Travis Norsen's book "Foundations of Quantum Mechanics - An Exploration of the Physical Meaning of Quantum Theory" (2017) where he argues that quantum mechanics (in the orthodox Copenhagen interpretation) is not even non-local because the word doesn't even make sense in quantum mechanics.
snarkypixel 5y ago
> there can be no instantaneous influence, in the sense of a causal effect or transmission of information, from one particle to a distant entangled particle Didn't the Bell's theorem prove that wrong though? I.e. that there needs to be some sort of "hidden variables" for it to work?
- leephillips 5y ago
  More like the opposite of that. Bell’s theorem tells us that there are two choices: either QM is inherently non-local, or there are influences (hidden variables) that can operate faster than light. Although both choices are in a sense disturbing, most people realize that we have to accept the non-local option. If we do, everything still works, even if we might feel uncomfortable. If, however, we accept faster-than-light influences, nothing works.
  - snarkypixel 5y ago
    Makes sense. And unless I'm mistaken, to be entangled, they have to be very close to each others at some point, right? And then we can send one of the pair far away and they'd still be entangled. I can imagine some sort of more fundamental link connecting the two, but it's still not breaking ftl
    - leephillips 5y ago
      Yes, the particles are prepared together, then separated. Experiments on entangled particles have now managed to keep them entangled while separating them by huge distances—many kilometers. Of course there is a link connecting them, which we express by saying they are “entangled”. But we may never be able to connect this with concepts that are intuitive from our experience with the classical world.
      - yourenotsmart 5y ago
        Non-locality is not just a problem of the classic world. There's no notion of it in the quantum mechanics world either. There's nothing in the math that suggests how can particles kilometers away can be connected "outside" space. And technically if they were, this would be apparent in many more ways than entanglement experiments, and it WOULD violate causality. General relativity also has no such concept as "simultaneous events" at distance. The very point of the theory is that event simultaneity is a meaningless concept at distance (any distance, but especially at large distance). So from scale cosmic to scale quantum, "non-local" is a meaningless concept, yet we have to just assume none of this matters and call the wave function collapse non-local, because that's the only way we decided the experiments make sense. So you're trying to handwave an issue away that's bigger than you admit. It implies space beyond space and time beyond time, where everything in the universe can happen simultaneously for two entangled particles regardless of where and when in that universe they happen to be. It's such an outrageous concept to introduce in this special case, with zero explanation, and without considering the larger implications it has, it honestly borders on The Avengers techno-babble about time travel in terms of how much sense it makes.

slowmovintarget 5y ago

Some work much more recent than 1997 with ADS/CFT correspondences shows that entanglement may manifest physically as wormholes. That is, there becomes a way for entangled particles to be local in spacetime despite them appearing to be distant in space. (ER = EPR conjecture).