7,445 research outputs found
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
Nuclear fallout: limiting the filibuster has led to more delays
This week is the two-year anniversary of the introduction of the ‘nuclear option’ into the US Senate by the then Majority Leader, Harry Reid. John D. Rackey and Lauren C. Bell reflect on the elimination of the filibuster for federal judicial nominations, writing that divided partisan control of the Senate and White House has made the former less efficient. Since the Republican Party retook the Senate in January, the number of civilian nominees has hit a five-year low, and nominees have had to wait much longer for confirmation. Gridlock in the chamber more generally has also increased
Experiences and perceptions of Spring Lane Sure Start Children's Centre
Spring Lane Sure Start Children’s Centre was designated in September 2007, and ‘officially opened’ in February 2009. The Centre is housed in refurbished premises within a nursery/school complex in the heart of Northampton and offers diverse health, childcare, early education and support services delivered by a multi-professional team. These services and activities are available to children aged 0-5 years old, and their parents/carers, residing within a catchment area comprising eight ‘Super Output Areas’ in the Castle and St. James ward of Northampton.
In April 2009, the Centre for Children and Youth (CCY) – a research centre based at The University of Northampton – was commissioned by Spring Lane Sure Start Children’s Centre to collate and gather evaluative data regarding experiences and perceptions of the Children’s Centre during its first year of activitie
Strategies for life in flow: tenacity, morphometry, and probability of dislodgment of two \u3cem\u3eMytilus\u3c/em\u3e species
The attachment strength of sessile intertidal organisms is continuously challenged by the hydrodynamic forces generated by breaking waves. This study explores mechanisms by which the attachment strength, or tenacity, can vary for one of the dominant competitors for space in this environment, the marine mussel. Tenacity was measured for 2 co-existing mussel species, Mytilus californianus and Mytilus trossulus, either solitary or within a bed (= bed mussels). The tenacity of M. californianus was higher than M. trossulus, due to increased byssal thread thickness, and the tenacity of solitary mussels was higher than bed mussels, due to the presence of more byssal threads per mussel. These tenacity measurements were coupled with modeled hydrodynamic forces to predict the probability of dislodgment due to wave action. For a given water velocity, the predicted probability of dislodgment of M. californianus was lower than that of M. trossulus because the latter produces relatively thinner threads (reducing tenacity) and a relatively more voluminous shell (increasing hydrodynamic loading). Compared to solitary mussels, bed mussels had a lower probability of dislodgment for a given water velocity (despite their lower tenacity) because they are subjected to relatively smaller hydrodynamic forces. These predictions are consistent with field observations that mussels typically form dense aggregations and that M. trossulus rarely inhabits highly wave-exposed shores
Trends and Regional Variation in Hip, Knee and Shoulder Replacement
Analyzes patterns in underuse or overuse of joint replacements among Medicare beneficiaries by geographic regions and race/ethnicity. Explores underlying factors and highlights the need for physician and patient education and shared decision making
Assumptions for a Market Share Theorem
Many marketing models use variants of the relationship: market share equals marketing effort divided by total marketing effort. Usually, share is defined within a customer group presumed to be reasonably homogeneous and overall share is obtained by weighting for the number in the group. Although the basic relationship can be assumed directly, certain insight is gained by deriving it from more fundamental assumptions as follows: For the given customer group, each competitive seller has a real-valued "attraction" with the following properties: (1) attraction is non-negative; (2) the attraction of a set of sellers is the sum of the attractions of the individual sellers; and (3) if the attractions of two sets of sellers are equal, the sellers have equal market shares in the customer groups. It is shown that, if the relation between share and attraction satisfies the above assumptions, is a continuous function, and is required to hold for arbitrary values of attraction and sets of sellers, then the relation is: Share equals attraction divided by total attraction. Insofar as various factors can be assembled into an attraction function that satisfies the assumptions of the theorem, the method for calculating share follows directly
Prolific pair production with high-power lasers
Prolific electron-positron pair production is possible at laser intensities
approaching 10^{24} W/cm^2 at a wavelength of 1 micron. An analysis of electron
trajectories and interactions at the nodes (B=0) of two counter-propagating,
circularly polarised laser beams shows that a cascade of gamma-rays and pairs
develops. The geometry is generalised qualitatively to linear polarisation and
laser beams incident on a solid target.Comment: 4 pages, 1 figure, minor revisions, accepted for publication in
Physical Review Letter
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