Book review: accelerating democracy: transforming governance through technology

John O. McGinnis demonstrates how new technologies combine to address a problem as old as democracy itself: how to help citizens better evaluate the consequences of their political choices. Ana Polo Alonso thinks we can support or dismiss McGinnis’s proposals, but we cannot deny that the author makes a major effort to bring forth ingenious measures to really ‘accelerate democracy.’ Accelerating Democracy: Transforming Governance through Technology. John O. McGinnis. Princeton University Press. December 2012

Book review: The violent image: insurgent propaganda and the new revolutionaries

"The Violent Image: Insurgent Propaganda and the New Revolutionaries." Neville Bolt. Hurst. May 2012. --- Fast-moving, self-propelled ‘violent images’ have radically changed the nature of insurgency in the modern world. The global media has revolutionised the way ideas, messages and images are disseminated, and the speed with which they travel. Neville Bolt investigates how today’s revolutionaries have rejuvenated the nineteenth century ‘propaganda of the deed’ so that terrorism no longer simply goads states into overreacting, thereby losing legitimacy. Ana Polo Alonso finds an elegantly-written and well-researched read, suitable for students of media studies and terrorism

Multi-partite analysis of average-subsystem entropies

So-called average subsystem entropies are defined by first taking partial traces over some pure state to define density matrices, then calculating the subsystem entropies, and finally averaging over the pure states to define the average subsystem entropies. These quantities are standard tools in quantum information theory, most typically applied in bipartite systems. We shall first present some extensions to the usual bipartite analysis, (including a calculation of the average tangle, and a bound on the average concurrence), follow this with some useful results for tripartite systems, and finally extend the discussion to arbitrary multi-partite systems. A particularly nice feature of tri-partite and multi-partite analyses is that this framework allows one to introduce an "environment" for small subsystems to couple to.Comment: Minor changes. 1 reference added. Published versio

Entropy budget for Hawking evaporation

Blackbody radiation, emitted from a furnace and described by a Planck spectrum, contains (on average) an entropy of $3.9\pm 2.5$ bits per photon. Since normal physical burning is a unitary process, this amount of entropy is compensated by the same amount of "hidden information" in correlations between the photons. The importance of this result lies in the posterior extension of this argument to the Hawking radiation from black holes, demonstrating that the assumption of unitarity leads to a perfectly reasonable entropy/information budget for the evaporation process. In order to carry out this calculation we adopt a variant of the "average subsystem" approach, but consider a tripartite pure system that includes the influence of the rest of the universe, and which allows "young" black holes to still have a non-zero entropy; which we identify with the standard Bekenstein entropy.Comment: Proceedings of the conference "VARCOSMOFUN'16" in Szczecin, Poland, 12-17 September, 2016. Accepted for publication in "Universe", belonging to the Special Issue "Varying Constants and Fundamental Cosmology