Platforms, scales and networks: meshing a local sustainable sharing economy

The “sharing economy” has promised more sustainable use of the world’s finite resources, exploiting latency and promoting renting rather than ownership through digital networks. But do the digital brokers that use networks at global scale offer the same care for the planet as more traditional forms of sharing? We contrast the sustainability of managing idle capacity with the merits of collective local agency bred by caring-based sharing in a locality. Drawing on two studies of neighbourhood sharing in London and analysis of the meshing of local sharing initiatives, we ask how ‘relational assets’ form and build up over time in a neighbourhood, and how a platform of platforms might act as local socio-technical infrastructure to sustain alternative economies and different models of trust to those found in the scaling sharing economy. We close by proposing digital networks of support for local solidarity and resourcefulness, showing how CSCW knowledge on coordination and collaboration has a role in achieving these ends

Algebraic description of spacetime foam

A mathematical formalism for treating spacetime topology as a quantum observable is provided. We describe spacetime foam entirely in algebraic terms. To implement the correspondence principle we express the classical spacetime manifold of general relativity and the commutative coordinates of its events by means of appropriate limit constructions.Comment: 34 pages, LaTeX2e, the section concerning classical spacetimes in the limit essentially correcte

A Characterization Theorem for a Modal Description Logic

Modal description logics feature modalities that capture dependence of knowledge on parameters such as time, place, or the information state of agents. E.g., the logic S5-ALC combines the standard description logic ALC with an S5-modality that can be understood as an epistemic operator or as representing (undirected) change. This logic embeds into a corresponding modal first-order logic S5-FOL. We prove a modal characterization theorem for this embedding, in analogy to results by van Benthem and Rosen relating ALC to standard first-order logic: We show that S5-ALC with only local roles is, both over finite and over unrestricted models, precisely the bisimulation invariant fragment of S5-FOL, thus giving an exact description of the expressive power of S5-ALC with only local roles

Black holes, quantum information, and unitary evolution

The unitary crisis for black holes indicates an apparent need to modify local quantum field theory. This paper explores the idea that quantum mechanics and in particular unitarity are fundamental principles, but at the price of familiar locality. Thus, one should seek to parameterize unitary evolution, extending the field theory description of black holes, such that their quantum information is transferred to the external state. This discussion is set in a broader framework of unitary evolution acting on Hilbert spaces comprising subsystems. Here, various constraints can be placed on the dynamics, based on quantum information-theoretic and other general physical considerations, and one can seek to describe dynamics with "minimal" departure from field theory. While usual spacetime locality may not be a precise concept in quantum gravity, approximate locality seems an important ingredient in physics. In such a Hilbert space approach an apparently "coarser" form of localization can be described in terms of tensor decompositions of the Hilbert space of the complete system. This suggests a general framework in which to seek a consistent description of quantum gravity, and approximate emergence of spacetime. Other possible aspects of such a framework -- in particular symmetries -- are briefly discussed.Comment: 39 pages, 5 figures. v2: refs added, very minor clarifications v3: few small changes to agree with published version v4: corrected sign in eq. 3.3

Lieb-Robinson Bounds and Quasi-locality for the Dynamics of Many-Body Quantum Systems

We review a recently proven Lieb-Robinson bound for general, many-body quantum systems with bounded interactions. Several basic examples are discussed as well as the connection between commutator estimates and quasi-locality.Comment: contribution to the proceedings of the conference QMath 11 (Hradec Kralove, September 2010