Wigner's friend and continuous time evolution of the state of a closed system and the probabilistic, discontinuous collapse of the state of a system upon measurement. Wigner's friend is therefore directly linked to the measurement problem in quantum mechanics with its famous Schrödinger's cat paradox. The thought experiment posits a friend of Wigner in a laboratory and lets him perform a quantum measurement on a physical system (this could be a spin system or also Schrödinger's cat). This system is assumed to be in a superposition of two distinct states, say, state 0 and state 1 (or "dead" and "alive", in the
Big Book (thought experiment) Big Book (thought experiment) The "Big Book" is a thought experiment developed by Ludwig Wittgenstein about the nature of ethics and the verifiability of ethical knowledge. This account is given by him in an early work, the 1929 "Lecture on Ethics", and it matches also his position given in the early "Tractatus Logico-Philosophicus" (Proposition 6.41). "No statement of fact can ever be, or imply, a judgment of absolute value. Suppose one of you were an omniscient person and therefore knew all the movements of all the bodies in the world dead or alive and that you also knew all the