Schrödinger's cat regard the "alive and dead" cat superposition as quite real. Intended as a critique of the Copenhagen interpretation (the prevailing orthodoxy in 1935), the Schrödinger's cat thought experiment remains a defining touchstone for modern interpretations of quantum mechanics. Physicists often use the way each interpretation deals with Schrödinger's cat as a way of illustrating and comparing the particular features, strengths, and weaknesses of each interpretation. Schrödinger wrote: Schrödinger's famous thought experiment poses the question, ""when" does a quantum system stop existing as a superposition of states and become one or the other?" (More technically, when does the actual quantum state
Sum rule in quantum mechanics to construct operator equalities, which are then applied to the particles or energy levels of a system. Assume that the Hamiltonian formula_1 has a complete set of eigenfunctions formula_2 with eigenvalues formula_3: For the Hermitian operator formula_5 we define the repeated commutator formula_6 iteratively by: The operator formula_8 is Hermitian since formula_5 is defined to be Hermitian. The operator formula_10 is anti-Hermitian: By induction one finds: and also For a Hermitian operator we have Using this relation we derive: The result can be written as For formula_17 this gives: See oscillator strength. Sum rule in quantum mechanics In quantum mechanics,