Observer effect
Some state a misunderstanding of the term refers to quantum mechanics, where, if the outcome of an event has not been observed, it exists in a state of 'superposition', which is something like being in all possible states at once. In the famous thought experiment known as Schrödinger's cat, the cat is empirically neither alive nor dead until observed – until that time, the cat is theoretically both alive and dead (technically half-alive and half-dead in probability terms). However, most quantum physicists, in resolving Schrödinger's seeming paradox, now understand that the acts of 'observation' and 'measurement' must also be defined in quantum terms before the question makes sense. From this point of view, there is no 'observer effect', only one vastly entangled quantum system. A significant minority still find the equations point to an observer; John Archibald Wheeler, who probably worked more deeply on this subject than any physicist thus far, devised a graphic in which the universe was represented by a "U" with an eye on one end, turned around and viewing itself, to describe his understanding.