Title: Causal relationship | Article about Causal relationship by The Free Dictionary
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Causality
Causality
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Content: Second, the state variable &psgr; gives only probabilities that a given eigenstate will be found after the performance of a measurement, and such probabilities are also all that is calculable about a later state &psgr; ′
by the deterministic prediction. Despite its probabilistic character, the quantum state still evolves deterministically. However, which eigenvalue (say, of position) will actually be found in a measurement is unpredictable. See Determinism, Eigenvalue (quantum mechanics), Quantum mechanics, Quantum theory of measurement, Uncertainty principle
Nonrelativistic mechanics assumes that causal action can be propagated instantaneously, and thus that an absolute simultaneity is definable. This is not true in special relativity. While the state of a system can still be understood in terms of the positions and momenta of its particles, time order, as well as temporal and spatial length, becomes relative to the observer's frame, and there is no possible choice of simultaneous events in the universe that is the same in all reference frames. Only space-time intervals in a fused “spacetime” are invariant with respect to choice of reference frame. The theory of special relativity thus rejects the possibility of instantaneous causal action.