Is Everetts relative state formulation the same as many-worlds?
Yes, Everett’s formulation of the relative state metatheory is the same as many-worlds, but the language has evolved a lot from Everett’s original article [2] and some of his work has been extended, especially in the area of decoherence. (See “What is decoherence?”) This has confused some people into thinking that Everett’s “relative state metatheory” and DeWitt’s “many-worlds interpretation” are different theories. Everett [2] talked about the observer’s memory sequences splitting to form a “branching tree” structure or the state of the observer being split by a measurement. (See “What is a measurement?”) DeWitt introduced the term “world” for describing the split states of an observer, so that we now speak of the observer’s world splitting during the measuring process. The maths is the same, but the terminology is different. (See “What is a world?”) Everett tended to speak in terms of the measuring apparatus being split by the measurement, into non-interfering states, without present
