Main Question or Discussion Point
If you change the spin of an entangled particle without knowing its original spin, what happens to the other entangled particle?
An entangled pair share one wave function. So they are in a way one thing. If either one is projected into a different spin state the partner will have the same/opposite spin ( the '/' depends on the preparation).If you change the spin of an entangled particle without knowing its original spin, what happens to the other entangled particle?
Nothing. You will change the total wave function of the two particles, but you can't say that something has happen to the first particle.If you change the spin of an entangled particle without knowing its original spin, what happens to the other entangled particle?
I don't understand here. If by "all particles" you mean the two you have, then putting them both with spin-up doesn't corresponds to an entangled state.Assume you don't need to know its original state, can you impart up spin on all particles, would this break the entanglement or down spin all the entangled particles
You cannot learn quantum mechanics from videos on the internet. They're fun, they're interesting, some are better than others, but there is always something missing.I've recently seen the excellent youtube video on "Quantum Entanglement & Spooky Action at a Distance" by Veritasium - but either I'm not understanding something - or there seems to be something missing from the explanation.
The local operator can choose to measure the polarization on any axis they want; whatever result they get, a measurement of the other photon will produce the opposite result. Say the operator holds their polarizer at an angle of ##\theta## degrees. If their photon passes through the filter, they have just measured the photon to be polarized at that angle; if it doesn't pass they've just measured it to be polarized at 90 degrees to that angle. Either way, if we measure the other photon with a polarizer at the same angle, we will find the opposite polarization result.It seems that the operator can choose the ANGLE of polarisation of both entangled photons (+_180 degrees) - even if one photon is very far away - is this correct ??
regardless of the percentage which clear the filter of the local operator ? - or do you mean only in the case that half the photons clear the local operator filter and half are absorbed ? Thankyou for your detailed first reply (!)However, that doesn't mean that the operator has any control over the angle of the remote photon. No matter what anyone does and no matter which angles are chosen for the two measurements, the remote observer will always find that half the photons clear his filter and half are absorbed.
The percentage that clears the local operator’s filter is always 50%, no matter what the angle of the filter, just as with the remote filter.regardless of the percentage which clear the filter of the local operator ? - or do you mean only in the case that half the photons clear the local operator filter and half are absorbed ?
OK - so what would be a better experiment ? I am aware that someone thinks that a hidden variable determining whether any photon is detected at all, or whether no photon is detected by both local and remote operators, could give results that allow the probabilities actually detected but still be consistent with non-quantum phenomena (see Explained & Debunked_ Quantum Entanglement & Bell Test Experiments - YouTube). Do you think this is a possibility ? Many thanks in advance.(And I should add that there are serious practical difficulties in actually performing this experiment in exactly this form - this is a thought experiment as described)