arXiv:1002.3917v4 [quant-ph] 30 May 2011 Version 2.2 Consistent Histories of Systems and Measurements in Spacetime Ed Seidewitz ∗ 14000 Gulliver’s Trail, Bowie MD 20720 USA (Dated: 31 January 2011) Traditional interpretations of quantum theory in terms of wave function collapse are particularly unappealing when considering the universe as a whole, where there is no clean separation between classical observer and quantum system and where the description is inherently relativistic. As an alternative, the consistent histories approach provides an attractive “no collapse” interpretation of quantum physics. Consistent histories can also be linked to path-integral formulations that may be readily generalized to the relativistic case. A previous paper described how, in such a relativistic spacetime path formalism, the quantum history of the universe could be considered to be an eignestate of the measurements made within it. However, two important topics were not addressed in detail there: a model of measurement processes in the context of quantum histories in spacetime and a justification for why the probabilities for each possible cosmological eigenstate should follow Born’s rule. The present paper addresses these topics by showing how Zurek’s concepts of einselection and envariance can be applied in the context of relativistic spacetime and quantum histories. The result is a model of systems and subsystems within the universe and their interaction with each other and their environment. 1 ∗ Electronic address: seidewitz@mailaps.org Abstract PACS numbers: 03.65.Ca, 03.65.Ta, 03.65.Yz, 11.80.-m Keywords: path integrals; spacetime paths; relativistic quantum mechanics; relativistic dynamics; measure- ments; subsystems; Born’s rule; einselection; envariance