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
Symmetry in quantum mechanics There are rotational matrices for each spin quantum number. Evaluating the exponential for a given "z"-projection spin quantum number "s" gives a (2"s" + 1)-dimensional spin matrix. This can be used to define a spinor as a column vector of 2"s" + 1 components which transforms to a rotated coordinate system according to the spin matrix at a fixed point in space. For the simplest non-trivial case of "s" = 1/2, the spin operator is given by where the Pauli matrices in the standard representation are: The total angular momentum operator is the sum of the orbital and spin and