Multiple worlds

Mohammad H. Ansari, Yuli V. Nazarov

We present a compact and self-contained review of the recently developed Keldysh formalism for multiple parallel worlds. The formalism has been applied to consistent quantum evaluation of the flows of informational quantities, in particular, to the evaluation of Renyi and Shannon entropy flows. We start with the formulation of the standard and extended Keldysh techniques in a single world in a form convenient for our presentation. We explain the use of Keldysh contours encompassing multiple parallel worlds. In the end, we briefly summarize the concrete results obtained with the method.

Kohei Morita, Kohei Morita

One of the problems of the many worlds interpretation (MWI) of quantum mechanics is about the ontological status of multiple worlds. In the MWI, the multiple worlds are quasi-classical, and the quasi-classical worlds are considered as emergence and pattern. However, the ontological understanding about the quasi-classical realms remains ambiguous. This article aims to clarify the ontological status of the quasi-classicality in the MWI. In particular, the notion of emergence and pattern has been investigated in the philosophy of science. The investigation about these notions provides a refined ontology of many worlds interpretation.

Mariette DiChristina

Howard Barnum

This unpublished 1990 preprint argues that a crucial distinction in discussions of the many-worlds interpretation of quantum mechanics (MWI) is that between versions of the interpretation positing a physical multiplicity of worlds, and those in which the multiplicity is merely psychological, and due to the splitting of consciousness upon interaction with amplified quantum superpositions. It is argued that Everett's original version of the MWI belongs to the latter class, and that most of the criticisms leveled against the MWI, in particular that it is illogical or incoherent, are not valid against such "psychological-multiplicity" versions. Attempts to derive the quantum-mechanical probabilities from the many-worlds interpretation are reviewed, and Everett's initial derivation is extended in an attempt to show that these are the unique possible probabilities. But there remains a challenge for proponents of the MWI: to show that their interpretation requires probabilities, rather than merely nonprobabilistic indeterminacy. A 2002 preface, revised in 2004, briefly discusses the extent to which I still agree with the claims in the paper. While its derivation of probabilities used, and failed to justify, noncontextuality, I still agree with the paper's general interpretation of the MWI, though not with the MWI itself.

Dan Gilhooley, Frank Toich