Observation of the Final Boundary Condition: Extragalactic Background Radiation and the Time symmetry of the Universe

This paper examines an observable consequence for the diffuse extragalactic background radiation (EGBR) of the hypothesis that if closed, our universe possesses time symmetric boundary conditions. For simplicity, attention is focused on optical wavelengths. The universe is modeled as closed Friedmann- Roberston-Walker. It is shown that, over a wide range of frequencies, electromagnetic radiation can propagate largely unabsorbed from the present epoch into the recollapsing phase, confirming and demonstrating the generality of results of Davies and Twamley. As a consequence, time symmetric boundary conditions imply that the optical EGBR is at least twice that due to the galaxies on our past light cone, and possibly considerably more. It is therefore possible to test experimentally the notion that if our universe is closed, it may be in a certain sense time symmetric. The lower bound on the "excess" EGBR in a time symmetric universe is consistent with present observations. Nevertheless, better observations and modelling may soon rule it out entirely. In addition, many physical complications arise in attempting to reconcile a transparent future light cone with time symmetric boundary conditions, thereby providing further arguments against the possibility that our universe is time symmetric.Comment: latex 2.09, 30 pages, 1 figure. Figure added, errors corrected. Slight revision of published versio

Consistent probabilities in loop quantum cosmology

A fundamental issue for any quantum cosmological theory is to specify how probabilities can be assigned to various quantum events or sequences of events such as the occurrence of singularities or bounces. In previous work, we have demonstrated how this issue can be successfully addressed within the consistent histories approach to quantum theory for Wheeler-DeWitt-quantized cosmological models. In this work, we generalize that analysis to the exactly solvable loop quantization of a spatially flat, homogeneous and isotropic cosmology sourced with a massless, minimally coupled scalar field known as sLQC. We provide an explicit, rigorous and complete decoherent histories formulation for this model and compute the probabilities for the occurrence of a quantum bounce vs. a singularity. Using the scalar field as an emergent internal time, we show for generic states that the probability for a singularity to occur in this model is zero, and that of a bounce is unity, complementing earlier studies of the expectation values of the volume and matter density in this theory. We also show from the consistent histories point of view that all states in this model, whether quantum or classical, achieve arbitrarily large volume in the limit of infinite `past' or `future' scalar `time', in the sense that the wave function evaluated at any arbitrary fixed value of the volume vanishes in that limit. Finally, we briefly discuss certain misconceptions concerning the utility of the consistent histories approach in these models.Comment: 22 pages, 3 figures. Matches published versio

Consistent Probabilities in Wheeler-DeWitt Quantum Cosmology

We give an explicit, rigorous framework for calculating quantum probabilities in a model theory of quantum gravity. Specifically, we construct the decoherence functional for the Wheeler-DeWitt quantization of a flat Friedmann-Robertson-Walker cosmology with a free, massless, minimally coupled scalar field, thus providing a complete decoherent histories formulation for this quantum cosmological model. The decoherence functional is applied to study predictions concerning the model's Dirac (relational) observables; the behavior of semiclassical states and superpositions of such states; and to study the singular behavior of quantum Wheeler-DeWitt universes. Within this framework, rigorous formulae are given for calculating the corresponding probabilities from the wave function when those probabilities may be consistently defined, thus replacing earlier heuristics for interpreting the wave function of the universe with explicit constructions. It is shown according to a rigorously formulated standard, and in a quantum-mechanically consistent way, that in this quantization these models are generically singular. Independent of the choice of state we show that the probability for these Wheeler-DeWitt quantum universes to ever encounter a singularity is unity. In addition, the relation between histories formulations of quantum theory and relational Dirac observables is clarified.Comment: 27 pages, 4 figures. Minor revisions and updated references. Matches published versio

Literacy, Numeracy and Labour Market Outcomes in Canada

Most research on the contribution of human capital to economic growth and its role in the distribution of income uses indirect measures of human capital such as educational attainment and work experience. Such measures are arguably inputs into the production of human capital in the form of skills, competencies and knowledge. This study uses Canadian data from the international Adult Literacy Survey to analyse the role of directly observed skills -- specifically, prose, document and quantitative literacy -- on individual labour market earnings. The contributions of unobserved skills are taken into account using input measures (education and experience). We find that literacy skills have a large and statistically significant causal effect on earnings. As much as one-third of the return to education may be due to the combined effects of education on literacy and of literacy skills on earnings. In contrast, very little of the return to labour market experience is associated with the combined effects of experience on literacy and literacy skills on earnings.

Large Scale Baryon Isocurvature Inhomogeneities

Big bang nucleosynthesis constraints on baryon isocurvature perturbations are determined. A simple model ignoring the effects of the scale of the perturbations is first reviewed. This model is then extended to test the claim that large amplitude perturbations will collapse, forming compact objects and preventing their baryons from contributing to the observed baryon density. It is found that baryon isocurvature perturbations are constrained to provide only a slight increase in the density of baryons in the universe over the standard homogeneous model. In particular it is found that models which rely on power laws and the random phase approximation for the power spectrum are incompatible with big bang nucleosynthesis unless an {\em ad hoc}, small scale cutoff is included.Comment: 11pages + 8figures, LaTeX (2.09), postscript figures available via anonymous ftp from oddjob.uchicago.edu:/ftp/ibbn/fig?.ps where ?=1-8 or via email from [email protected], Fermilab-Pub-94/???-A and UMN-TH-1307/9

Ethical Language and Themes in News Coverage of Genetic Testing

Ethical theory is employed in this study to assess news coverage of genetic testing, a topic with widely acknowledged ethical implications for professions and society. Ethical language and themes were examined in thirty-one broadcast and print stories by major news organizations in 1995 and 1996. Concerns about consequences, especially avoidance of harm, were prominent in most stories; ethical duties received less attention. Ethical themes, sometimes emerging as direct questions to readers or viewers, underlined choices facing individuals and society. Some stories powerfully brought home ethical issues without directly mentioning ethics.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

The Promise and Peril of Anecdotes in News Coverage: An Ethical Analysis

This article assesses the use of anecdotes in news coverage on ethical grounds, pointing both to their promise and to their potential dangers. The analysis draws on Craig's framework for analyzing news coverage of ethics; on Christians, Ferre, and Fackler's communitarian ethic; and on Gilligan's relationship-oriented ethic of care. Cases from news stories illustrate the ethical complexity of anecdote use. This study suggests how journalists can choose anecdotes more critically and points to an adaptation of the anecdotal form that is ethically supportable.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Hearing in the Juvenile Green Sea Turtle (Chelonia mydas): A Comparison of Underwater and Aerial Hearing Using Auditory Evoked Potentials

Sea turtles spend much of their life in aquatic environments, but critical portions of their life cycle, such as nesting and hatching, occur in terrestrial environments, suggesting that it may be important for them to detect sounds in both air and water. In this study we compared underwater and aerial hearing sensitivities in five juvenile green sea turtles (Chelonia mydas) by measuring auditory evoked potential responses to tone pip stimuli. Green sea turtles detected acoustic stimuli in both media, responding to underwater stimuli between 50 and 1600 Hz and aerial stimuli between 50 and 800 Hz, with maximum sensitivity between 200 and 400 Hz underwater and 300 and 400 Hz in air. When underwater and aerial hearing sensitivities were compared in terms of pressure, green sea turtle aerial sound pressure thresholds were lower than underwater thresholds, however they detected a wider range of frequencies underwater. When thresholds were compared in terms of sound intensity, green sea turtle sound intensity level thresholds were 2–39 dB lower underwater particularly at frequencies below 400 Hz. Acoustic stimuli may provide important environmental cues for sea turtles. Further research is needed to determine how sea turtles behaviorally and physiologically respond to sounds in their environment