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There's no spooky action at a distance. Let's imagine we have an entangled qubit system that consists of a superposition of the states (0,1) and (1,0), i.e. eit

There's no spooky action at a distance. Let's imagine we have an entangled qubit system that consists of a superposition of the states (0,1) and (1,0), i.e. either part A is in state 0 and part B in state 1 or vice versa. When we perform a measurement on the first part of the system and obtain 1, it simply means that we have "branched" into the (1,0) state of the system. This branching is usually irreversible because of the decoherence caused by the measurement (which itself is just an ordinary quantum process). There is no information exchange or any type of exchange between the two parts of the system going on, we simply branch into a part of the probability space defined for the system. The question whether the other branches still exist then leads to either the "classical" interpretation of quantum mechanics or the "many worlds" interpretation. The latter seems to be favored today as we know that there's nothing special about the measurement process that causes the collapse of a wave function (it's a quantum process in itself), but in the end there's not really a way to test this so it's really more of a philosophical question. Articles about "spooky action at a distance" should really mention this, as we have a much better understanding of the measurement process in quantum mechanics today than Einstein et. al. had when they wrote their paper.

virgil_disgr4ce 5y ago
If there's one single phrase I wish I could erase from history it's "Spooky action at a distance." Ugh. It bugs me a lot that Quanta made these misleading statements that just continue the confusion over what should be a more widely-understood core feature of the universe we live in. Tangentially, I wish "interaction" would come to replace "measurement," especially in the context of decoherence. The universe is branching *constantly* everywhere as various quantum systems interact.
joe_the_user 5y ago
What you're describing could be done with classical physics. Have one penny and two lockets. Place the penny blindly in one of the two lockets. Take one locket across the world. Opening it instantly lets you whether the other locket has contains the penny. And the point of this description is this is not what's weird about quantum entanglement. What's weird about quantum entanglement is you have two different measurement types that are non-orthogonal and they combine according to quantum logic rather than classical logic [1]. Having a particle in a state of this sort can't be explained by any analogy to discreet events occurring beforehand. [1] https://en.wikipedia.org/wiki/Quantum_logic#Quantum_logic_as_the_logic_of_observables https://en.wikipedia.org/wiki/Quantum_logic#Quantum_logic_as... Edit: Whether this is "spooky action at a distance" is in the eye of the beholder. One thing is isn't able to be is fully reducible to actions happening on something like a "classical time line" but another thing is isn't to able to do is transmit information.

virgil_disgr4ce 5y ago

If there's one single phrase I wish I could erase from history it's "Spooky action at a distance." Ugh. It bugs me a lot that Quanta made these misleading statements that just continue the confusion over what should be a more widely-understood core feature of the universe we live in. Tangentially, I wish "interaction" would come to replace "measurement," especially in the context of decoherence. The universe is branching *constantly* everywhere as various quantum systems interact.

joe_the_user 5y ago

What you're describing could be done with classical physics. Have one penny and two lockets. Place the penny blindly in one of the two lockets. Take one locket across the world. Opening it instantly lets you whether the other locket has contains the penny. And the point of this description is this is not what's weird about quantum entanglement. What's weird about quantum entanglement is you have two different measurement types that are non-orthogonal and they combine according to quantum logic rather than classical logic [1]. Having a particle in a state of this sort can't be explained by any analogy to discreet events occurring beforehand. [1] https://en.wikipedia.org/wiki/Quantum_logic#Quantum_logic_as_the_logic_of_observables https://en.wikipedia.org/wiki/Quantum_logic#Quantum_logic_as... Edit: Whether this is "spooky action at a distance" is in the eye of the beholder. One thing is isn't able to be is fully reducible to actions happening on something like a "classical time line" but another thing is isn't to able to do is transmit information.