J.S. Bell's Concept of Local Causality

John Stewart Bell's famous 1964 theorem is widely regarded as one of the most important developments in the foundations of physics. It has even been described as "the most profound discovery of science." Yet even as we approach the 50th anniversary of Bell's discovery, its meaning and implications remain controversial. Many textbooks and commentators report that Bell's theorem refutes the possibility (suggested especially by Einstein, Podolsky, and Rosen in 1935) of supplementing ordinary quantum theory with additional ("hidden") variables that might restore determinism and/or some notion of an observer-independent reality. On this view, Bell's theorem supports the orthodox Copenhagen interpretation. Bell's own view of his theorem, however, was quite different. He instead took the theorem as establishing an "essential conflict" between the now well-tested empirical predictions of quantum theory and relativistic \emph{local causality}. The goal of the present paper is, in general, to make Bell's own views more widely known and, in particular, to explain in detail Bell's little-known mathematical formulation of the concept of relativistic local causality on which his theorem rests. We thus collect and organize many of Bell's crucial statements on these topics, which are scattered throughout his writings, into a self-contained, pedagogical discussion including elaborations of the concepts "beable", "completeness", and "causality" which figure in the formulation. We also show how local causality (as formulated by Bell) can be used to derive an empirically testable Bell-type inequality, and how it can be used to recapitulate the EPR argument.Comment: 19 pages, 4 figure

Identities Matter: Identity Politics, Coalition Possibilities, and Feminist Organizing

This dissertation examines the processes of identity construction and deployment among Uruguayan women and organized women’s groups. I employ narrative analysis and process tracing methodology to analyze the question of why attempts to create multi-racial gender coalitions are frequently unsuccessful among Uruguayan women’s groups. I find that identity is constructed differently for women along the lines of race and class, even in a South American setting where racial attributes are supposedly of little import. These competing identities result in conflicts among the gender-based organizations that women form; as a consequence there is a reduction in coalition possibilities for otherwise similarly oriented women’s groups. I find that each group has distinct ideological conceptions of the salience of race and class to gender mobilization and these divergent ideological conceptions have had a direct impact on each organization’s willingness to coalesce with other local women’s groups. My research contributes an important component to the identity and social movements literature. The literature on identity politics and coalition formation is largely theoretical in nature. Much of the empirical literature on coalition formation highlights political and structural variables such as threat, resources, and political opportunities, and considers identity differences tangentially or not at all. My research combines these two approaches to present an empirical case study that specifies the relationship between identity politics and coalition politics. I highlight ideology, which is a key understudied variable. I find that ideological differences often impede coalition formation, and that this relationship holds variety of issue areas and types. I also find that political strategy is of central importance to coalition formation. Specifically, it may function separately from, or in collusion with, ideological differences in constraining or fostering coalition formation

Quantum Cryptography using entangled photons in energy-time Bell states

We present a setup for quantum cryptography based on photon pairs in energy-time Bell states and show its feasability in a laboratory experiment. Our scheme combines the advantages of using photon pairs instead of faint laser pulses and the possibility to preserve energy-time entanglement over long distances. Moreover, using 4-dimensional energy-time states, no fast random change of bases is required in our setup : Nature itself decides whether to measure in the energy or in the time base.Comment: 4 pages including 2 figure

Purifying two-bit quantum gates and joint measurements in cavity QED

Using a cavity QED setup we show how to implement a particular joint measurement on two atoms in a fault tolerant way. Based on this scheme, we illustrate how to realize quantum communication over a noisy channel when local operations are subject to errors. We also present a scheme to perform and purify a universal two-bit gate.Comment: 4 pages RevTeX, 2 figures include

Organic farming: biodiversity impacts can depend on dispersal characteristics and landscape context

Organic farming, a low intensity system, may offer benefits for a range of taxa, but what affects the extent of those benefits is imperfectly understood. We explored the effects of organic farming and landscape on the activity density and species density of spiders and carabid beetles, using a large sample of paired organic and conventional farms in the UK. Spider activity density and species density were influenced by both farming system and surrounding landscape. Hunting spiders, which tend to have lower dispersal capabilities, had higher activity density, and more species were captured, on organic compared to conventional farms. There was also evidence for an interaction, as the farming system effect was particularly marked in the cropped area before harvest and was more pronounced in complex landscapes (those with little arable land). There was no evidence for any effect of farming system or landscape on web-building spiders (which include the linyphiids, many of which have high dispersal capabilities). For carabid beetles, the farming system effects were inconsistent. Before harvest, higher activity densities were observed in the crops on organic farms compared with conventional farms. After harvest, no difference was detected in the cropped area, but more carabids were captured on conventional compared to organic boundaries. Carabids were more species-dense in complex landscapes, and farming system did not affect this. There was little evidence that non-cropped habitat differences explained the farming system effects for either spiders or carabid beetles. For spiders, the farming system effects in the cropped area were probably largely attributable to differences in crop management; reduced inputs of pesticides (herbicides and insecticides) and fertilisers are possible influences, and there was some evidence for an effect of non-crop plant species richness on hunting spider activity density. The benefits of organic farming may be greatest for taxa with lower dispersal abilities generally. The evidence for interactions among landscape and farming system in their effects on spiders highlights the importance of developing strategies for managing farmland at the landscape-scale for most effective conservation of biodiversity

Salud, trabajo y nutrición. Irlanda antes de la Hambruna

Editada en la Universidad Carlos IIIEn vísperas de la Gran Hambruna (1846-50), los ingresos irlandeses eran bajos según los patrones europeos. Sin embargo, un análisis de las dietas en Irlanda nos sugirieron que la pobreza se hallaba mitigada por una ingestión de calorías que sobrepasaba a las de Inglaterra y Francia en los inicios del siglo XIX. Las demandas calóricas extras debidas al trabajo agrícola no explican esta desproporción. La impresión de una alimentación saludable queda corroborada por un análisis comparativo entre las estaturas irlandesas y británicas de finales del siglo XVIII y principios del XIX.On the eve of the Great Famine (1846-50) Irish incomes wete low by west European standards. However, an analysis of Irish diets at the time suggests that poverty was mitigated by a calorifíc intake that exceeded that of early nineteenth-century England and France. The added physical requirements of farm work in Ireland were not commensurate. The impression of healthy food is corroborated by a comparative analysis of Irish and British heights in the late eighteenth and early nineteenth centuries.Publicad

Quantum Gravity as a Dissipative Deterministic System

It is argued that the so-called holographic principle will obstruct attempts to produce physically realistic models for the unification of general relativity with quantum mechanics, unless determinism in the latter is restored. The notion of time in GR is so different from the usual one in elementary particle physics that we believe that certain versions of hidden variable theories can -- and must -- be revived. A completely natural procedure is proposed, in which the dissipation of information plays an essential role. Unlike earlier attempts, it allows us to use strictly continuous and differentiable classical field theories as a starting point (although discrete variables, leading to fermionic degrees of freedom, are also welcome), and we show how an effective Hilbert space of quantum states naturally emerges when one attempts to describe the solutions statistically. Our theory removes some of the mysteries of the holographic principle; apparently non-local features are to be expected when the quantum degrees of freedom of the world are projected onto a lower-dimensional black hole horizon. Various examples and models illustrate the points we wish to make, notably a model showing that massless, non interacting neutrinos are deterministic.Comment: 20 pages plain TeX, 2 figures PostScript. Added some further explanations, and the definitions of `beable' and `changeable'. A minor error correcte

Quantum Cryptography

Quantum cryptography could well be the first application of quantum mechanics at the individual quanta level. The very fast progress in both theory and experiments over the recent years are reviewed, with emphasis on open questions and technological issues.Comment: 55 pages, 32 figures; to appear in Reviews of Modern Physic