The many-worlds interpretation of quantum cosmology.

Frank J. Tipler

Daniel Parrochia

Since the 1970s, the Everett-Wheeler many-worlds interpretation (MWI) of Quantum Mechanics (1955) has been much in the news. One wonders about the worlds in question, their branches, their splittings, their number. It is most often ignored that this language is not that of Everett, whom Wheeler very quickly stopped supporting. Moreover, for some interpreters, the real meaning of Everett ideas is not the coexistence of many worlds, but the existence of a single quantum one. In this context, what should we think of attempts to verify Everett thesis? What about the connexion between MWI and the cosmological multiverse? How to understand the links between the quantum world and the classical one? This article tries to answer some of these questions.

Flávio Gimenes Alvarenga, A. B. Batista, J. C. Fabris +1 more

In the isotropic quantum cosmological perfect fluid model, the initial singularity can be avoided, while the classical behaviour is recovered asymptotically. We verify if initial anisotropies can also be suppressed in a quantum version of a classical anisotropic model where gravity is coupled to a perfect fluid. Employing a Bianchi I cosmological model, we obtain a "Schrödinger-like" equation where the matter variables play de role of time. This equation has a hyperbolic signature. It can be explicitly solved and a wave packet is constructed. The expectation value of the scale factor, evaluated in the spirit of the many-worlds interpretation, reveals an isotropic Universe. On the other hand, the bohmian trajectories indicate the existence of anisotropies. This is an example where the Bohm-de Broglie and the many-worlds interpretations are not equivalent. It is argued that this inequivalence is due to the hyperbolic structure of the "Schrödinger-like" equation.

M. P. Ryan

Andrei Olegovich Barvinsky, Alexander Yu. Kamenshchik

The authors revive an old proposal of Zeh (1986) for the preferred basis in the many-worlds interpretation of quantum mechanics. The algorithm for this basis reduces to the eigenvalue problems for density matrices of subsystems splitting the quantum system into the observer and the observable counterpart. A semiclassical calculational method for these eigenvalue problems is developed and the dynamical properties of the preferred basis are investigated. Applications of this proposal to quantum cosmology are discussed.

James B. Hartle