Why would entangled particles light years away need to be able to cancel?

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Discussion Overview

The discussion revolves around the nature of entangled particles in quantum mechanics, particularly in the context of the EPR experiment and the implications of their states when separated by large distances. Participants explore concepts of cancellation, conservation laws, and the interpretation of wavefunctions, while questioning the necessity of entangled particles being able to "cancel" their states without direct interaction.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions why entangled particles need to be able to cancel their spins if they are light years apart, suggesting that their states should not matter until they interact.
  • Another participant discusses different interpretations of the wavefunction, arguing that it represents probabilities rather than a physical reality, which could imply that the EPR scenario is not as troubling as it seems.
  • A participant mentions that particles typically need to cancel due to conservation laws, using the example of photons produced from an atom with no angular momentum.
  • Some participants argue that as long as particles can cancel when they interact, their states while apart should not matter, drawing analogies to energy conservation in a roller coaster scenario.
  • One participant expresses uncertainty about the necessity of cancellation when particles are not touching, indicating a lack of clarity on the topic.
  • Another participant asserts that entangled particles behave as if they remain in contact, despite the lack of understanding of the underlying mechanism, and notes that experimental results contradict the idea that their states can be arbitrary when separated.
  • Clarification is provided that "touching" is not a relevant concept in quantum physics, with "interacting" being the appropriate term.

Areas of Agreement / Disagreement

Participants express differing views on the necessity and implications of entangled particles being able to cancel their states. There is no consensus on the interpretation of these phenomena or the relevance of their states when separated by distance.

Contextual Notes

Participants highlight limitations in understanding the nature of entanglement and the implications of measurement settings on the results, indicating that the discussion is complex and nuanced.

Green Zach
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Ok, here's my problem... In the EPR experiment it is described that if entangled particles are required to be able to cancel each others spin's then no mater how far apart these particles are, if one is measured you can instantly infer the state of the other particle. Why would the other particle's state matter if it is thousands of light years away? The particles need to be ABLE to cancel but they can't cancel if they don't come in contact with each other so the state of the particles doesn't really mater until they touch so their states should be able to be whatever they want until they touch. Am i missing something?
 
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Some people think of the wavefunction as a mathematical representation of the properties of the system, and some think of it as a mathematical representation of our knowledge about the system. I don't think either of those "interpretations" make much sense.

What everyone agrees on is that we can think about the wavefunction as a measure of the probability that a measurement will have a certain result. The never ending debate is about whether it should, or could, be interpreted as something more than that. As I said, I don't think it can.

If it's just a measure of the probabilities of possible results of experiments, then there's nothing truly disturbing about the EPR scenario, except perhaps that this would imply that QM doesn't actually describe the world.
 
Usually, the particles are required to "cancel" each other as you say because of some conservation law. If you created 2 photons from an atom that had no angular momentum and they had angular momenta which didn't add up to 0 then you've just violated conservation of angular momentum.
 
Matterwave said:
Usually, the particles are required to "cancel" each other as you say because of some conservation law. If you created 2 photons from an atom that had no angular momentum and they had angular momenta which didn't add up to 0 then you've just violated conservation of angular momentum.

As long as when the two particles touch they can cancel, i don't see how what they do when they don't touch really maters as long as the resulting differences in their states doesn't allow energy to be created or destroyed somewhere else. Its like saying that because a roller coaster speeds up as it goes down a track that energy is being created... no because once it reaches the height it fell from again (as long as there is no friction involved) it will be going the same speed that it was when it left that height initially. The coaster's state changed but as long as when it goes back to the height it fell from it is going the same speed as it was before it's initial drop, Newton is happy. This is like the particles... as long as they CAN cancel they should be able to do whatever they want and because they can't cancel unless they are touching... their states don't mater as long as they are able to cancel by the time they touch. This means that even if you measure one of the particles, the other can still be in a state of superposition... in fact... the only time information about one of the particles must travel instantly is when the two are touching but there would be no distance between them anyways!
 
I'm not developing some crazy idea... I'm actually fairly confident that I'm missing something but i just don't see why the particles would need to be able to cancel even if they couldn't cancel because they aren't touching.
 
Green Zach said:
I'm not developing some crazy idea... I'm actually fairly confident that I'm missing something but i just don't see why the particles would need to be able to cancel even if they couldn't cancel because they aren't touching.

Entangled particles act "as if" they remain in contact with each other. No one knows exactly what happens or how it is done. However, the general scenario you describe is ruled out experimentally.

Please keep in mind that in the particular example you provide, there does not appear to be any obvious problem. If you measure the 2 entangled photons at the same angle setting, say 0 degrees, they will in fact cancel (in terms of conservation). But if you measure at certain other settings - say one at 0 degrees and the other at 22.5 degrees - you get results that make no sense in conventional (classical) terms.

The best place to start is to learn about EPR and Bell's Theorem. You can learn about this from one of my web pages on the subject: Bell's Theorem with Easy Math which also provides some relevant background. You can also see the original references.
 
Green Zach said:
This is like the particles... as long as they CAN cancel they should be able to do whatever they want and because they can't cancel unless they are touching... their states don't mater as long as they are able to cancel by the time they touch. This means that even if you measure one of the particles, the other can still be in a state of superposition... in fact... the only time information about one of the particles must travel instantly is when the two are touching but there would be no distance between them anyways!
"Touching" isn't a concept that's used in quantum physics. The term "interacting" is used, but what we're talking about here isn't an interaction.
 

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