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
Dead or Alive 2 remake of "DOA" and "DOA2" for the Xbox with a greatly improved graphics engine. As it was created after "Dead or Alive 3", it takes elements and mechanics from both its original iteration and successor. The action of 3D-axis movement is as free-formatted as "DOA3", and Hitomi, as well as Tengu are now playable characters (albeit outside story mode), but other elements have been kept intact from "DOA2". The biggest set of changes instituted in "Dead or Alive Ultimate" are online play over Xbox Live and the inclusion of slopes, which are a type of environmental hazard. Dead or Alive