Quantum superposition the eigenvector corresponding to the measured eigenvalue. It is natural to ask why ordinary everyday objects and events do not seem to display quantum mechanical features such as superposition. Indeed, this is sometimes regarded as "mysterious", for instance by Richard Feynman. In 1935, Erwin Schrödinger devised a well-known thought experiment, now known as Schrödinger's cat, which highlighted this dissonance between quantum mechanics and classical physics. One modern view is that this mystery is explained by quantum decoherence. A macroscopic system (such as a cat) may evolve over time into a superposition of classically distinct quantum states (such as "alive" and
Two-body Dirac equations The four-vectors formula_120 and formula_121 have only three independent components since The similarity to the three-dimensional structure of the nonrelativistic Schrödinger equation can be made more explicit by writing the equation in the c.m. frame in which Comparison of the resultant form with the time independent Schr\"{o}dinger equation makes this similarity explicit. A plausible structure for the quasipotential formula_83 can be found by observing that the one-body Klein-Gordon equation formula_127 takes the form formula_128 when one introduces a scalar interaction and timelike vector interaction via formula_129and formula_130. In the two-body case, separate classical and quantum field theory arguments show that