• The apparent (gravitational) horizon in cosmology

      Melia, Fulvio; Univ Arizona, Dept Phys, Appl Math Program; Univ Arizona, Dept Astron (AMER ASSOC PHYSICS TEACHERS, 2018-08)
      In general relativity, a gravitational horizon (more commonly known as the "apparent horizon") an imaginary surface beyond which all null geodesics recede from the observer. The Universe has an apparent (gravitational) horizon, but unlike its counterpart in the Schwarzschild and Kerr metrics, it is not static. It may eventually turn into an event horizon-an asymptotically defined membrane that forever separates causally connected events from those that are not-depending on the equation of state of the cosmic fluid. In this paper, we examine how and why an apparent (gravitational) horizon is manifested in the Friedmann-Robertson-Walker metric, and why it is becoming so pivotal to our correct interpretation of the cosmological data. We discuss its observational signature and demonstrate how it alone defines the proper size of our visible Universe. In so doing, we affirm its physical reality and its impact on cosmological models. (C) 2018 American Association of Physics Teachers.
    • The apparent (gravitational) horizon in cosmology

      Melia, Fulvio; Univ Arizona, Dept Phys, Appl Math Program; Univ Arizona, Dept Astron (AMER ASSOC PHYSICS TEACHERS, 2018-08)
      In general relativity, a gravitational horizon (more commonly known as the "apparent horizon") an imaginary surface beyond which all null geodesics recede from the observer. The Universe has an apparent (gravitational) horizon, but unlike its counterpart in the Schwarzschild and Kerr metrics, it is not static. It may eventually turn into an event horizon-an asymptotically defined membrane that forever separates causally connected events from those that are not-depending on the equation of state of the cosmic fluid. In this paper, we examine how and why an apparent (gravitational) horizon is manifested in the Friedmann-Robertson-Walker metric, and why it is becoming so pivotal to our correct interpretation of the cosmological data. We discuss its observational signature and demonstrate how it alone defines the proper size of our visible Universe. In so doing, we affirm its physical reality and its impact on cosmological models. (C) 2018 American Association of Physics Teachers.
    • Applicability of the Newtonian gravity concept inventory to introductory college physics classes

      Williamson, Kathryn; Prather, Edward E.; Willoughby, Shannon; Univ Arizona, Steward Observ, Ctr Astron Educ; West Virginia University, Morgantown, West Virginia 26501; Center for Astronomy Education (CAE), Steward Observatory, University of Arizona, Tucson, Arizona 85721; Montana State University, Bozeman, Montana 59717 (AMER ASSOC PHYSICS TEACHERS, 2016-06)
      The study described here extends the applicability of the Newtonian Gravity Concept Inventory (NGCI) to college algebra-based physics classes, beyond the general education astronomy courses for which it was originally developed. The four conceptual domains probed by the NGCI (Directionality, Force Law, Independence of Other Forces, and Threshold) are well suited for investigating students' reasoning about gravity in both populations, making the NGCI a highly versatile instrument. Classical test theory statistical analysis with physics student responses pre-instruction (N = 1,392) and post-instruction (N = 929) from eight colleges and universities across the United States indicate that the NGCI is composed of items with appropriate difficulty and discrimination and is reliable for this population. Also, expert review and student interviews support the NGCI's validity for the physics population. Emergent similarities and differences in how physics students reason about gravity compared to astronomy students are discussed, as well as future directions for analyzing the instrument's item parameters across both populations. (C) 2016 American Association of Physics Teachers.
    • Evaluation Methodology and Results for the New Faculty Workshops

      Chasteen, Stephanie V.; Chattergoon, Rajendra; Prather, Edward E.; Hilborn, Robert; Univ Arizona, Dept Astron (AMER ASSOC PHYSICS TEACHERS, 2016-12-29)
      This paper describes the current evaluation of the Physics and Astronomy New Faculty Workshop (NFW) as a case-study in evaluation of professional development workshops. We describe a The-ory of Action (ToA) for the workshop, and the evaluation methods and measures. The evaluation suggests that the ToA of the workshop is only partially fulfilled: workshop experiences are posi-tive, and participants gain knowledge of active learning, but participants have room for additional growth in skill, self-efficacy and social support in their use of active learning. We discuss the im-plications of these results for the NFW program and evaluation.