This is a list of this week’s papers on quantum foundations published in various journals or uploaded to preprint servers such as arxiv.org and PhilSci Archive.

Comment on decoherence by time dilation. (arXiv:1510.02239v1 [quant-ph])

on 2015-10-10 8:49am GMT

Authors: H. Dieter Zeh

Remarks regarding a novel decoherence mechanism [arXiv:1311.1095].

Generalized Second Law for Cosmology. (arXiv:1510.02099v1 [hep-th])

on 2015-10-10 8:49am GMT

Authors: Raphael Bousso, Netta Engelhardt

We conjecture a novel Generalized Second Law that can be applied in cosmology, regardless of whether an event horizon is present: the generalized entropy increases monotonically outside of certain hypersurfaces we call past Q-screens. A past Q-screen is foliated by surfaces whose generalized entropy (sum of area and entanglement entropy) is stationary along one future null direction and increasing along the other. We prove that our Generalized Second Law holds in spacetimes obeying the Quantum Focussing Conjecture. An analogous law applies to future Q-screens, which appear inside evaporating black holes and in collapsing regions.

A generalized definition of Bell’s local causality

on 2015-10-08 12:00am GMT

**Abstract**

This paper aims to implement Bell’s notion of local causality into a framework, called local physical theory, which is general enough to integrate both probabilistic and spatiotemporal concepts and also classical and quantum theories. Bell’s original idea of local causality will then arise as the classical case of our definition. First, we investigate what is needed for a local physical theory to be locally causal. Then we compare local causality with Reichenbach’s common cause principle and relate both to the Bell inequalities. We find a nice parallelism: both local causality and the common cause principle are more general notions than captured by the Bell inequalities. Namely, Bell inequalities cannot be derived neither from local causality nor from a common cause unless the local physical theory is classical or the common cause is commuting, respectively.

Nature – Issue – nature.com science feeds

on 2015-10-07 12:00am GMT

**Q&A: David Deutsch**

Author: Kristin Lynn Sainani

Physicist David Deutsch is considered the founding father of quantum computing. In his 2011 book, The Beginning of Infinity, Deutsch argues that there is such a thing as objective beauty.

A Complete Graphical Calculus for Spekkens’ Toy Bit Theory

Latest Results for Foundations of Physics

on 2015-10-07 12:00am GMT

**Abstract**

While quantum theory cannot be described by a local hidden variable model, it is nevertheless possible to construct such models that exhibit features commonly associated with quantum mechanics. These models are also used to explore the question of \(\psi \) -ontic versus \(\psi \) -epistemic theories for quantum mechanics. Spekkens’ toy theory is one such model. It arises from classical probabilistic mechanics via a limit on the knowledge an observer may have about the state of a system. The toy theory for the simplest possible underlying system closely resembles stabilizer quantum mechanics, a fragment of quantum theory which is efficiently classically simulable but also non-local. Further analysis of the similarities and differences between those two theories can thus yield new insights into what distinguishes quantum theory from classical theories, and \(\psi \) -ontic from \(\psi \) -epistemic theories. In this paper, we develop a graphical language for Spekkens’ toy theory. Graphical languages offer intuitive and rigorous formalisms for the analysis of quantum mechanics and similar theories. To compare quantum mechanics and a toy model, it is useful to have similar formalisms for both. We show that our language fully describes Spekkens’ toy theory and in particular, that it is complete: meaning any equality that can be derived using other formalisms can also be derived entirely graphically. Our language is inspired by a similar graphical language for quantum mechanics called the ZX-calculus. Thus Spekkens’ toy bit theory and stabilizer quantum mechanics can be analysed and compared using analogous graphical formalisms.

A Probabilistic Model of Spin and Spin Measurements

Latest Results for Foundations of Physics

on 2015-10-07 12:00am GMT

**Abstract**

Several theoretical publications on the Dirac equation published during the last decades have shown that, an interpretation is possible, which ascribes the origin of electron spin and magnetic moment to an autonomous circular motion of the point-like charged particle around a fixed centre. In more recent publications an extension of the original so called “Zitterbewegung Interpretation” of quantum mechanics was suggested, in which the spin results from an average of instantaneous spin vectors over a Zitterbewegung period. We argue that, the corresponding autonomous motion of the electron should, if it is real, determine non-relativistic spin measurements. Such a direct connection with the established formal quantum mechanical description of spin measurements, into which spin is introduced as a “non-classical” quantity has, to our knowledge, not been reported. In the present work we show that, under certain “model assumptions” concerning the proposed autonomous motion, results of spin measurements, including measurements of angular correlations in singlet systems, can indeed be correctly described using classical probabilities. The success of the model is evidence for the “reality” of the assumed autonomous motion. The resulting model violates the Bell—inequalities to the same extent as quantum mechanics.

PRL: General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

on 2015-10-06 2:00pm GMT

Author(s): Janne V. Kujala, Ehtibar N. Dzhafarov, and Jan-Åke Larsson

The notion of (non)contextuality pertains to sets of properties measured one subset (context) at a time. We extend this notion to include so-called inconsistently connected systems, in which the measurements of a given property in different contexts may have different distributions, due to contextua…

[Phys. Rev. Lett. 115, 150401] Published Tue Oct 06, 2015