Internal measurement

In quantum mechanics, internal measurement refers to the measurement of a quantum system by an observer (referred to as an internal observer or endo-observer).

A quantum measurement represents the action of a measuring device on a quantum system. When the measuring device is a part of the measured quantum system, the measurement proceeds internally in relation to the whole system.

Internal measurement theory was first introduced by Koichiro Matsuno and developed by Yukio-Pegio Gunji. They expanded on the original ideas of Robert Rosen and Howard Pattee regarding quantum measurement in living systems viewed as natural internal observers that belong to the same scale of the observed objects. According to Matsuno, an internal measurement is accompanied by a redistribution of probabilities that leave them entangled in accordance with the many-worlds interpretation of quantum mechanics by Everett. However, this form of quantum entanglement does not survive in an external measurement, in which the mapping to real numbers takes place and the result is revealed in classical spacetime, as the Copenhagen interpretation suggests. This means that the internal measurement concept unifies the current alternative interpretations of quantum mechanics. Provided by Wikipedia