- #176
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Going back a bit in this thread...
I think I have learned a bit more about QFT from some of the great posts here. Especially learning some of the situations in which QFT would be helpful for application. Specifically, it seems as if QFT is best to apply when scattering is being discussed and the results might include any of a variety of particles. On the other hand: while QFT might include elements that describe entanglement, apparently that is a weaker/less useful side of things. My sense is that explains why entanglement experiments don't require the deeper theory of QFT - the basics of entanglement are well described by QM/QED without the need for any relativistic considerations (I don't consider descriptions of entangled photons as being relativistic although others might).
And as to some of the discussions about "microcausality": As I now understand it, there are 2 key (and somewhat opposing) elements at play. Both relate to the act of performing a measurement on entangled Alice and considering what happens to remote Bob (the previously entangled partner):
1) No signaling theorem being that the marginal probability of an outcome for Bob does NOT change due to Alice's choice of measurement. In short, Bob's outcomes are always random.
2) The experimentally demonstrated quantum nonlocality being that the state of Bob DOES change due to Alice's choice of measurement. In short, Bob is cast into a pure state relative to Alice.
I realize some of the posters here may not agree with my assessments, no problem there. But hopefully I am a little further along than before.
I think I have learned a bit more about QFT from some of the great posts here. Especially learning some of the situations in which QFT would be helpful for application. Specifically, it seems as if QFT is best to apply when scattering is being discussed and the results might include any of a variety of particles. On the other hand: while QFT might include elements that describe entanglement, apparently that is a weaker/less useful side of things. My sense is that explains why entanglement experiments don't require the deeper theory of QFT - the basics of entanglement are well described by QM/QED without the need for any relativistic considerations (I don't consider descriptions of entangled photons as being relativistic although others might).
And as to some of the discussions about "microcausality": As I now understand it, there are 2 key (and somewhat opposing) elements at play. Both relate to the act of performing a measurement on entangled Alice and considering what happens to remote Bob (the previously entangled partner):
1) No signaling theorem being that the marginal probability of an outcome for Bob does NOT change due to Alice's choice of measurement. In short, Bob's outcomes are always random.
2) The experimentally demonstrated quantum nonlocality being that the state of Bob DOES change due to Alice's choice of measurement. In short, Bob is cast into a pure state relative to Alice.
I realize some of the posters here may not agree with my assessments, no problem there. But hopefully I am a little further along than before.