New varying speed of light theories

We review recent work on the possibility of a varying speed of light (VSL). We start by discussing the physical meaning of a varying $c$, dispelling the myth that the constancy of $c$ is a matter of logical consistency. We then summarize the main VSL mechanisms proposed so far: hard breaking of Lorentz invariance; bimetric theories (where the speeds of gravity and light are not the same); locally Lorentz invariant VSL theories; theories exhibiting a color dependent speed of light; varying $c$ induced by extra dimensions (e.g. in the brane-world scenario); and field theories where VSL results from vacuum polarization or CPT violation. We show how VSL scenarios may solve the cosmological problems usually tackled by inflation, and also how they may produce a scale-invariant spectrum of Gaussian fluctuations, capable of explaining the WMAP data. We then review the connection between VSL and theories of quantum gravity, showing how ``doubly special'' relativity has emerged as a VSL effective model of quantum space-time, with observational implications for ultra high energy cosmic rays and gamma ray bursts. Some recent work on the physics of ``black'' holes and other compact objects in VSL theories is also described, highlighting phenomena associated with spatial (as opposed to temporal) variations in $c$. Finally we describe the observational status of the theory. The evidence is currently slim -- redshift dependence in the atomic fine structure, anomalies with ultra high energy cosmic rays, and (to a much lesser extent) the acceleration of the universe and the WMAP data. The constraints (e.g. those arising from nucleosynthesis or geological bounds) are tight, but not insurmountable. We conclude with the observational predictions of the theory, and the prospects for its refutation or vindication.Comment: Final versio

Feminist Dilemmas and the Agency of Veiled Muslim Women: Analysing Identities and Social Representations

This article addresses dilemmas of agency for feminism through reflections on social psychological research on the role of representations in the construction of identity by Muslim women. Engaging first with Saba Mahmood’s account of religious subjectivities in Politics of Piety (2005), the author argues that feminist research requires a social conception of agency that addresses dialogical dynamics of representation and identity. Drawing on research concerning veiling and identity among Muslim women in the UK and Denmark, the author shows how a social conception of agency may be elaborated through the analysis of how competing representations of gender are negotiated in the self–other encounter. The author argues that a dialogical approach to researching identity in context defies blunt political judgement while shedding light on the intersecting socio-cultural forces and relations of power that engage processes of resistance and re-presentation