Tuesday, February 27, 2018

Given entanglement, why is it permissible to consider the quantum state of subsystems?


Quantum entanglement is the norm, is it not? All that exists in reality is the wave function of the whole universe, true? So how come we can blithely talk about the quantum state of subsystems if everything is entangled? How is it even possible to consider subsystems in isolation? Anything less than the quantum state of the whole universe at once. Enlighten me.





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classical mechanics - Moment of a force about a given axis (Torque) - Scalar or vectorial?

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