Gravitational polarization and the phenomenology of MOND

The modified Newtonian dynamics (MOND) has been proposed as an alternative to the dark matter paradigm; the philosophy behind is that there is no dark matter and we witness a violation of the Newtonian law of dynamics. In this article, we interpret differently the phenomenology sustaining MOND, as resulting from an effect of "gravitational polarization", of some cosmic fluid made of dipole moments, aligned in the gravitational field, and representing a new form of dark matter. We invoke an internal force, of non-gravitational origin, in order to hold together the microscopic constituents of the dipole. The dipolar particles are weakly influenced by the distribution of ordinary matter; they are accelerated not by the gravitational field, but by its gradient, or tidal gravitational field.Comment: 14 pages, 1 figure, to appear in Classical and Quantum Gravit

Does an atom interferometer test the gravitational redshift at the Compton frequency ?

Atom interferometers allow the measurement of the acceleration of freely falling atoms with respect to an experimental platform at rest on Earth's surface. Such experiments have been used to test the universality of free fall by comparing the acceleration of the atoms to that of a classical freely falling object. In a recent paper, M\"uller, Peters and Chu [Nature {\bf 463}, 926-929 (2010)] argued that atom interferometers also provide a very accurate test of the gravitational redshift when considering the atom as a clock operating at the Compton frequency associated with the rest mass. We analyze this claim in the frame of general relativity and of different alternative theories. We show that the difference of "Compton phases" between the two paths of the interferometer is actually zero in a large class of theories, including general relativity, all metric theories of gravity, most non-metric theories and most theoretical frameworks used to interpret the violations of the equivalence principle. Therefore, in most plausible theoretical frameworks, there is no redshift effect and atom interferometers only test the universality of free fall. We also show that frameworks in which atom interferometers would test the redshift pose serious problems, such as (i) violation of the Schiff conjecture, (ii) violation of the Feynman path integral formulation of quantum mechanics and of the principle of least action for matter waves, (iii) violation of energy conservation, and more generally (iv) violation of the particle-wave duality in quantum mechanics. Standard quantum mechanics is no longer valid in such frameworks, so that a consistent interpretation of the experiment would require an alternative formulation of quantum mechanics. As such an alternative has not been proposed to date, we conclude that the interpretation of atom interferometers as testing the gravitational redshift is unsound.Comment: 26 pages. Modified version to appear in Classical and Quantum Gravit

Atom interferometry and the Einstein equivalence principle

The computation of the phase shift in a symmetric atom interferometer in the presence of a gravitational field is reviewed. The difference of action-phase integrals between the two paths of the interferometer is zero for any Lagrangian which is at most quadratic in position and velocity. We emphasize that in a large class of theories of gravity the atom interferometer permits a test of the weak version of the equivalence principle (or universality of free fall) by comparing the acceleration of atoms with that of ordinary bodies, but is insensitive to that aspect of the equivalence principle known as the gravitational redshift or universality of clock rates.Comment: 5 pages, to appear in the proceedings of the "46th Rencontres de Moriond and GPhyS Colloquium on Gravitational Waves and Experimental Gravity", la Thuile, March 20-27, 201

Event Horizon Deformations in Extreme Mass-Ratio Black Hole Mergers

We study the geometry of the event horizon of a spacetime in which a small compact object plunges into a large Schwarzschild black hole. We first use the Regge-Wheeler and Zerilli formalisms to calculate the metric perturbations induced by this small compact object, then find the new event horizon by propagating null geodesics near the unperturbed horizon. A caustic is shown to exist before the merger. Focusing on the geometry near the caustic, we show that it is determined predominantly by large-l perturbations, which in turn have simple asymptotic forms near the point at which the particle plunges into the horizon. It is therefore possible to obtain an analytic characterization of the geometry that is independent of the details of the plunge. We compute the invariant length of the caustic. We further show that among the leading-order horizon area increase, half arises from generators that enter the horizon through the caustic, and the rest arises from area increase near the caustic, induced by the gravitational field of the compact object.Comment: 23 pages, 14 figure

Making youth engagement a reality in YouthScape

Meeting: Celebrating Dialogue : An International SAS2 Forum, November 3, 2008, Carleton University, Ottawa, ON, CASAS reports are made available in order to provide timely access to the information by interested researchers. This report has been subject to an internal review process to ensure accuracy and quality

Seeking Culturally Safe Developmental Evaluation: Supporting the Shift in Services for Indigenous Children

Background: Evaluation methods based on western frameworks that disregard Indigenous peoples’ worldviews and are imposed and implemented by outsiders are problematic for Indigenous communities.   Purpose: The article presents the experience of using developmental evaluation (DE) in supporting a shift in pre- and post-natal care programming for Indigenous mothers and their young children.   Setting: Indigenous peoples living in urban areas in Quebec often feel unwelcome mainstream services, resulting in under-use. A history of colonization in Canada has resulted in a loss of Indigenous child-rearing practices   Intervention: The study was carried out in the context of a three-year initiative aimed at strengthening the abilities of pregnant women, mothers, fathers, extended family, community, and practitioners to create conditions for the holistic development of themselves and their children. The goal was to create new knowledge through activities focused on promoting perinatal care and psychosocial adaptability. Cultural safety, an ecosystemic view of child development, and social innovation guided the approach to the intervention.   Research Design:  A case study approach was used to make sense of and describe the “how to” of the DE.   Data Collection and Analysis: Multiple methods of data collection informed the case study, including observation, field notes, interviews, and participatory evaluation activities.   Findings: The article sheds light on DE as a culturally safe and participatory practice that is compatible with Indigenous perspectives and contributes to supporting the transformation in services provided to Indigenous communities. We present building relationships, creating safe spaces for reflection and dialogue, questioning fundamentals, and co-creation as critical components of culturally safe DE, enabling development and a paradigm shift.   Keywords: developmental evaluation; indigenous; child-rearing; case study; cultural safety

The Transformative Power of Youth Grants: Sparks and Ripples of Change Affecting Marginalised Youth and their Communities

This study, based on research into a youth empowerment initiative in Canada, examines the transformational power of youth grants for marginalised youth and their communities. The positive changes on individual youth included increased confidence and skills, as well as strengthened social interactions between youth, and involved adults and organisations. To leverage grant impact, we identify the critical role of creating accountability at multiple levels, promoting sharing among grantees, and fostering allies and system thinkers. The evaluation points to the potential of grants for changing community's perception that youth are incapable of fostering community youth development. In the field of human development, attention is increasingly given to the role cash transfers and grants can play in reducing poverty and boosting the resilience of communities facing adversity (Hanlon and others, 2010). Interestingly, little of the discussion about this simple yet powerful tool has spilled over into either the child rights or community youth development sectors. Many programmes for vulnerable youth living in disadvantaged communities still apply a ‘charity’ approach that downplays the active role young people can assume in strengthening their own well-being and the resilience of their communities. This article examines cash transfers through youth grants as a mechanism for marginalised young people to act upon ideas and issues of importance to them. The study draws on an analysis of YouthScape (YS): a youth empowerment initiative in which almost 200 youth grants were allocated in four Canadian cities over a three-year period. With increasing interest in youth-granting in North America, this evaluation on the impacts and enabling conditions of the grants advances understanding of cash transfers as an entry point for reconnecting socially excluded young people with key adults, and as a tool for building important life skills and reinforcing aspects of community resilience

Young Children and Educators Engagement and Learning Outdoors: A Basis for Rights-Based Programming

This article reports on a study undertaken with 4 early childhood programs in a medium-size city in Canada investigating young children's and educators' perspectives on engagement and learning possibilities outdoors. A rights-based methodology including participant observations and interactive activities with children as well as focus groups and discussion groups with educators reveals the diversity and richness of young children's learning opportunities in the natural outdoor space. Educators also talk about forming more egalitarian and fulfilling relationships with children in outdoor activities. The value educators placed on play in natural spaces led to the creation of opportunities for play outside and motivated educators to support children's interactions outdoors by mediating policy and societal fear of the risk of outdoor play. Practice or Policy: The results of the study highlight the value of a learning community for early childhood educators so that they might support children's full use of outdoor space and the critical role of adult allies in advocating for rights-based programming

Immigrant children promoting environmental care: Enhancing learning, agency and integration through culturally-responsive environmental education

This paper examines the potential of culturally-responsive environmental education to engage immigrant early adolescents. Our study suggests that environmental involvement can become a means and an end for children to bridge their school and home in agential ways. Drawing from a multi-phase study involving focus groups with children, parents, and teachers from three culturally-diverse schools in Montreal, as well as a green action research project, we examine children’s role as environmental educators and ambassadors. The role of environmental ambassador allowed children to take on positions that departed from conventional parent-child social scripts, and enhanced the communication between school-student-home, between generations, and spoke to their sense of place. We contend that culturally-responsive environmental education offers a unique space for enacting democracy, knowledge creation and integration, but this opportunity is often squandered. Bi-directional, responsive, and consistent home-school-community-place relations need to be actively supported