Bulletin of the American Physical Society
APS April Meeting 2015
Volume 60, Number 4
Saturday–Tuesday, April 11–14, 2015; Baltimore, Maryland
Session Q1: Kavli Foundation Plenary Session II: Our Changing View of the Universe |
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Sponsoring Units: APS Chair: Ian Shipsey, Oxford University Room: Holiday 4-6 |
Monday, April 13, 2015 8:30AM - 9:06AM |
Q1.00001: 50 Years of the CMB Invited Speaker: John Mather The cosmic microwave background radiation, measured with CN molecules but unrecognized by 1941, predicted in 1948, detected in 1964, and published in 1965, is now the basis for precision cosmology, a phrase that would once have been an oxymoron. With confirmation of its blackbody spectrum, and the statistics of its hot and cold spots and polarization, the CMB tells us that the expanding universe can be described very simply. With just 6 parameters, we match the measured statistics and enjoy the ``standard model'' of cosmology with percent-level accuracy, but we require two mysterious substances that only astronomers have detected: dark matter and dark energy. Gravity alone, acting on the primordial perturbations, explains the growth of cosmic structures, though we argue about the detailed properties of the dark matter. And the idea of cosmic inflation, propelled by a hypothetical field, fits the measurements and explains why the universe is flat and uniform, and filled with nearly scale-invariant primordial fluctuations. The development of instruments and theory has been spectacular, and I will summarize the breakthrough concepts. But after 50 years the job is not done: new equipment could measure the spectrum, anisotropy, and polarization even better. At long wavelengths, the spectrum could be different from a blackbody, due to electrons or redshifted hydrogen 21 cm emission, and it could be either hotter than the CMB (from energy release) or colder (from adiabatic cooling). At intermediate wavelengths, the spectrum could show traces of the hydrogen recombination lines, and we know that recombination was delayed by trapping of Lyman $\alpha $ photons. Moreover, the statistics of the polarization tell us about the nature of the forces during the first moments of the universe, and whether there were propagating gravitational waves in equipartition with other fluctuations. Discoveries await! [Preview Abstract] |
Monday, April 13, 2015 9:06AM - 9:42AM |
Q1.00002: Was Einstein Right? A Centennial Assessment Invited Speaker: Clifford Will A century after Einstein's formulation of general relativity, a remarkably diverse set of precision experiments has established it as the ``standard model'' for gravitational physics. Yet it might not be the final word. We review the array of measurements that have verified general relativity in the laboratory, in the solar system and in binary pulsars. We then describe some of the opportunities and challenges involved in testing Einstein's great theory in strong-field regimes, in gravitational waves, and in cosmology. [Preview Abstract] |
Monday, April 13, 2015 9:42AM - 10:18AM |
Q1.00003: Compact Binary Mergers as Multimessenger Sources of Gravitational Waves Invited Speaker: Stuart Shapiro On the centennial anniversary of Einstein's theory of general relativity, we are on the verge of directly detecting one of its most remarkable predictions -- gravitational waves (GWs). The inspiral and merger of compact binaries -- binaries with black hole, neutron star or white dwarf companions -- are among the most promising sources of GWs. Many of these sources are likely to generate observable electromagnetic (EM) and/or neutrino counterparts to the GWs, constituting a major advance in multimessenger astronomy. By way of illustration, we describe recent magnetohydrodynamic simulations in general relativity (GRMHD) that show how black hole-neutron star mergers can launch jets, lending support to the idea that such mergers could be the engines that power short-hard gamma-ray bursts. We also discuss other recent GRMHD simulations that show how an inspiraling, supermassive binary black hole in a galaxy core stirs and accretes magnetized plasma that orbits the holes in a circumbinary disk. This process can generate ``precursor'' and ``aftermath'' EM radiation with respect to the peak GW emission at merger. Computer-generated movies highlighting some of these simulations will be shown. [Preview Abstract] |
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