arXiv subjects

H. D. Zeh

Publications and source records attributed to H. D. Zeh.

21 records · Page 2Linked to original sources

arXiv1994

Arrow of time in a recollapsing quantum universe

We show that the Wheeler-DeWitt equation with a consistent boundary condition is only compatible with an arrow of time that formally reverses in a recollapsing universe. Consistency of these opposite arrows is facilitated by quantum effects in the region of the classical turning point. Since gravitational time dilation diverges at horizons, collapsing matter must then start re-expanding ``anticausally" (controlled by the reversed arrow) before horizons or singularities can form. We also discuss the meaning of the time-asymmetric expression used in the definition of ``consistent histories". We finally emphasize that there is no mass inflation nor any information loss paradox in this scenario.

gr-qc↗

arXiv1994

Symmetries, superselection rules, and decoherence

We discuss the applicability of the programme of decoherence -- emergence of approximate classical behaviour through interaction with the environment -- to cases where it was suggested that the presence of symmetries would lead to exact superselection rules. For this discussion it is useful to make a distinction between pure symmetries and redundancies, which results from an investigation into the constraint equations of the corresponding theories. We discuss, in particular, superpositions of states with different charges, as well as with different masses, and suggest how the corresponding interference terms, although they exist in principle, become inaccessible through decoherence.

gr-qc↗

arXiv1994

Time (a-)symmetry in a recollapsing quantum universe

It is argued that Hawking's `greatest mistake' may not have been a mistake at all. According to the canonical quantum theory of gravity for Friedmann type universes, any time arrows of general nature can only be correlated with that of the expansion. For recollapsing universes this seems to be facilitated in part by quantum effects close to their maximum size. Because of the resulting thermodynamical symmetry between expansion and (formal) collapse, black holes must formally become `white' during the collapse phase (while physically only expansion of the universe and black holes can be observed). It is conjectured that the quantum universe remains completely singularity-free in this way (except for the homogeneous singularity) if an appropriate boundary condition for the wave function is able to exclude {\it past} singularities (as is often assumed).

gr-qc↗