Is the evidence for dark energy secure?

Several kinds of astronomical observations, interpreted in the framework of the standard Friedmann-Robertson-Walker cosmology, have indicated that our universe is dominated by a Cosmological Constant. The dimming of distant Type Ia supernovae suggests that the expansion rate is accelerating, as if driven by vacuum energy, and this has been indirectly substantiated through studies of angular anisotropies in the cosmic microwave background (CMB) and of spatial correlations in the large-scale structure (LSS) of galaxies. However there is no compelling direct evidence yet for (the dynamical effects of) dark energy. The precision CMB data can be equally well fitted without dark energy if the spectrum of primordial density fluctuations is not quite scale-free and if the Hubble constant is lower globally than its locally measured value. The LSS data can also be satisfactorily fitted if there is a small component of hot dark matter, as would be provided by neutrinos of mass 0.5 eV. Although such an Einstein-de Sitter model cannot explain the SNe Ia Hubble diagram or the position of the `baryon acoustic oscillation' peak in the autocorrelation function of galaxies, it may be possible to do so e.g. in an inhomogeneous Lemaitre-Tolman-Bondi cosmology where we are located in a void which is expanding faster than the average. Such alternatives may seem contrived but this must be weighed against our lack of any fundamental understanding of the inferred tiny energy scale of the dark energy. It may well be an artifact of an oversimplified cosmological model, rather than having physical reality.Comment: 12 pages, 5 figures; to appear in a special issue of General Relativity and Gravitation, eds. G.F.R. Ellis et al; Changes: references reformatted in journal style - text unchange

What Will You Do Next? A Cognitive Model for Understanding Others’ Intentions Based on Shared Representations

Goal-directed action selection is the problem of what to do next in order to progress towards goal achievement. This problem is computationally more complex in case of joint action settings where two or more agents coordinate their actions in space and time to bring about a common goal: actions performed by one agent influence the action possibilities of the other agents, and ultimately the goal achievement. While humans apparently effortlessly engage in complex joint actions, a number of questions remain to be solved to achieve similar performances in artificial agents: How agents represent and understand actions being performed by others? How this understanding influences the choice of agent’s own future actions? How is the interaction process biased by prior information about the task? What is the role of more abstract cues such as others’ beliefs or intentions? In the last few years, researchers in computational neuroscience have begun investigating how controltheoretic models of individual motor control can be extended to explain various complex social phenomena, including action and intention understanding, imitation and joint action. The two cornerstones of control-theoretic models of motor control are the goal-directed nature of action and a widespread use of internal modeling. Indeed, when the control-theoretic view is applied to the realm of social interactions, it is assumed that inverse and forward internal models used in individual action planning and control are re-enacted in simulation in order to understand others’ actions and to infer their intentions. This motor simulation view of social cognition has been adopted to explain a number of advanced mindreading abilities such as action, intention, and belief recognition, often in contrast with more classical cognitive theories - derived from rationality principles and conceptual theories of others’ minds - that emphasize the dichotomy between action and perception. Here we embrace the idea that implementing mindreading abilities is a necessary step towards a more natural collaboration between humans and robots in joint tasks. To efficiently collaborate, agents need to continuously estimate their teammates’ proximal goals and distal intentions in order to choose what to do next.We present a probabilistic hierarchical architecture for joint action which takes inspiration from the idea of motor simulation above. The architecture models the casual relations between observables (e.g., observed movements) and their hidden causes (e.g., action goals, intentions and beliefs) at two deeply intertwined levels: at the lowest level the same circuitry used to execute my own actions is re-enacted in simulation to infer and predict (proximal) actions performed by my interaction partner, while the highest level encodes more abstract task representations which govern each agent’s observable behavior. Here we assume that the decision of what to do next can be taken by knowing 1) what the current task is and 2) what my teammate is currently doing. While these could be inferred via a costly (and inaccurate) process of inverting the generative model above, given the observed data, we will show how our organization facilitates such an inferential process by allowing agents to share a subset of hidden variables alleviating the need of complex inferential processes, such as explicit task allocation, or sophisticated communication strategies

’What the Hell is That?’: Representations of Professional Service Markets in The Simpsons.

This paper makes productive connections between two forms of representation—formal scholarship on professional service workers and their depictions in The Simpsons cartoon series. In considering the show's representations of Attorney Lionel Hutz and Dr Nick Riviera, I ponder the ways in which the market-based behaviours of these 'expert' individuals are so repeatedly targeted for satire. Through a detailed dissection of The Simpsons' scripts, I demonstrate how, on the one hand, the show to a large degree reflects critical thinking on the nature of the 'professional project' yet, on the other, offers some rather more ambivalent, even sympathetic, notions of professional identity