How does QFT address the problem of Locality in Quantum Entanglement?

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Discussion Overview

The discussion explores how Quantum Field Theory (QFT) addresses the issue of locality in the context of quantum entanglement, particularly focusing on the implications of instantaneous effects between entangled particles and the preservation of causality in relativistic frameworks.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants assert that while quantum entanglement allows for instantaneous effects between particles, no information can be transmitted faster than the speed of light, thus maintaining consistency with special relativity.
  • Others argue that the measurement of one entangled particle does have a causal influence on the other, raising questions about how this influence can occur without violating the speed limit of 'c'.
  • A participant suggests that faster-than-light causal influence is a possible explanation for the correlations observed in experiments, although they do not elaborate further.
  • Some participants propose that the relationship between measurements may not involve causality at all, suggesting instead that the correlation is a feature of reality inherent in a non-local quantum state.
  • It is noted that the order of measurements can be frame dependent, complicating the discussion of causality.
  • Another participant emphasizes the need for precise time measurements in experiments to define simultaneity, indicating that the phenomena observed may be complex and not easily categorized within traditional frameworks.

Areas of Agreement / Disagreement

Participants express differing views on the nature of causal influence in quantum entanglement, with some asserting that causality is involved while others reject this notion. The discussion remains unresolved, with multiple competing perspectives presented.

Contextual Notes

The discussion highlights the limitations in understanding the implications of quantum entanglement and locality, particularly regarding the dependence on definitions of causality and the frame-dependent nature of measurements.

Soumya_M
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Quantum Entanglement allows spatially separated entangled particles to have impact on each other instantly (overcoming the allowed speed-limit of causal influence which is 'c'). How does Quantum Field Theory address this problem (protecting causality and chronology)?
 
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No information can be transported at speeds greater than c using entanglement. This is stated clearly in nearly every authoritative treatment of the subject, yet we still get loads of people asking this same question.

There is no conflict with SR.
 
Mentz114 said:
No information can be transported at speeds greater than c using entanglement.

What you said about information transfer is allright. But what about the "causal influence". I mean, when one of the entangled particles is measured, it has an "effect" on the other particle (instantly). The measurement of the first particle, "causes" this impact. So the two events (1. measurement of the first particle and 2. impact on the second particle) can be said to be causaly related (event '1.' being the cause and event '2.' its effect). So although there is no instant transfer of information, the "causal influence" does seem overcome the speed limit of 'c'. This is what begs explanation.
 
Faster-than-light 'causal influence' is certainly one possible explanation for the correlations found in the Aspect and subsequent experiments.

I'm not qualified to say any more so I'll leave it there.
 
Soumya_M said:
What you said about information transfer is allright. But what about the "causal influence". I mean, when one of the entangled particles is measured, it has an "effect" on the other particle (instantly). The measurement of the first particle, "causes" this impact. So the two events (1. measurement of the first particle and 2. impact on the second particle) can be said to be causaly related (event '1.' being the cause and event '2.' its effect). So although there is no instant transfer of information, the "causal influence" does seem overcome the speed limit of 'c'. This is what begs explanation.

Two points:

1) If you call the measurements A and B, which occurred first is frame dependent.

2) I prefer to think that there is no causality involved at all. There is a feature of reality that two measurements will have a particular relationship with each other. Neither caused the other (you can't talk about which came first). As soon as you see one measurement you know about the result of the other, but there is no causal influence, just correlation built into a non-local quantum state.
 
PAllen said:
If you call the measurements A and B, which occurred first is frame dependent.
True.
Doing the Aspect experiment involves some very precise time measurement, in order to set up a frame in which simultaneity is well defined.

There seems no doubt that something strange is happening, but maybe it's not appropriate for this sub-forum.
 

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