Colloquium Archives (before June 2017)

More recent colloquia are posted on the Physics & Astronomy Colloquia page.

Anil Seth, Harvard-Smithsonian Center for Astrophysics

Topic: "The Formation of Galaxy Nuclei"  (Video)

ABSTRACT: Compact, massive nuclear star clusters are found at the centers of most elliptical and spiral galaxies. They are among the densest stellar systems in the universe, and often coexist with massive black holes. The mass of both the black holes and nuclear star clusters correlates with the mass of their host galaxies, suggesting a link between the accretion of material into the central parsecs of a galaxy and its overall evolution. My work focuses on understanding this link and the connection between nuclear star clusters and black holes. I will present results on how galaxy nuclei acquire their mass using cutting-edge observations of the closest nuclear star clusters. These nearby nuclei also represent the best targets for dynamically detecting the lowest mass (<10^6 Msol) central black holes, which are key to understanding the initial formation of black holes in the early universe.

Mark Dykman, Michigan State University

Topic: Topic: "Quantum Activation and quantum Measurements With NonLinear Oscillators"  (Video)

ABSTRACT: We study metastable decay in systems far from thermal equilibrium. Interest in the problem has spiked recently in the context of quantum measurements, nanomechanical systems, Josephson junctions, and cavity electrodynamics. The familiar decay mechanisms are tunneling and thermal activation. We show that periodically modulated systems display a different mechanism, which we call quantum activation. The decay rate shows scaling behavior near critical parameter values where metastable vibrational states disappear. The power spectra of modulated oscillators have specific features that allow measuring the effective oscillator temperature imposed by quantum fluctuations. In the talk, a comparison with the experimental observations will be made.

Steven Gubser, Princeton University

Topic: "Applied String Theory for the Impatient"  (Video)

ABSTRACT: The main application of string theory is to explain all of the fundamental physics in a single framework. Impatient theorists do not want to wait upon this program's full fruition to extract some useful information about experiment from string theory. I will discuss efforts to apply string theory to relativistic collisions of heavy nuclei and to high-temperature superconductors. I will emphasize apparent successes, such as shear viscosity, heavy-quark drag force, conductivity calculations, and ARPES spectra, but I will not entirely neglect reasons for skepticism about the string theory approaches.

Kevin Short, Department of Mathematics, University of New Hampshire

Topic: "A Mathematical Physicist at the Grammies?"  (Video)

Abstract: This talk will look at the mathematics underlying the analysis of music signals, and how ideas like the uncertainty principle, convolution, partitions of unity, and the (fast) Fourier transform naturally arise in the analysis. Applications to music decomposition, compression and repair will be considered. Some examples will be shown of work on restoring music tracks, including a 1949 Woody Guthrie wire recording that resulted in a Grammy award in 2008. Other examples may include real-time playback of layered decompositions of music, tracks from a compressed chaotic music synthesizer, and image and video compression. The underlying mathematical concepts will primarily be presented through diagrams and graphics, with technical details if time allows.

Roger Springett, Dartmouth Medical School

Topic: "Biophysics of Mitochondrial Function"  (Video)

ABSTRACT: Mitochondria are subcellular organelles of eukaryotes (cells containing a nucleus of which the human body is composed). They are approximately 1 micron in diameter, they contain their own DNA, divide and multiply like bacteria, and are believed to originate from a symbiotic relationship between bacteria and early eukaryotes. Their primary role is to consume oxygen and generate energy for the cell but they also contain proteins that trigger programmed cell death (apoptosis) when released from the mitochondria. I have developed optical spectroscopy instrumentation that can follow energy production and protein release in real time and this colloquium describes the thermodynamics of energy transduction and biophysics of protein release.

Michael Kesden, New York University

Topic: "A Maximum Spin from Black Hole Mergers"  (Video)

ABSTRACT: The famous "no hair" theorem implies that astrophysical black holes are fully described by their mass M and spin angular momentum S. However, if S grows above GM^2/c the black hole becomes a naked singularity unclothed by an event horizon. The cosmic censorship conjecture postulates that such naked singularities cannot occur in nature, but has never been proven to hold for the black holes produced in finite mass-ratio black-hole mergers. Understanding black-hole spins is also important for astrophysics. Supermassive black holes grow through two channels: continuous gas accretion and discrete binary mergers. The distribution of black-hole spins may help us determine the relative importance of these two channels in different environments. I will discuss the spins black holes acquire through both gas accretion and binary mergers, and present a new limit to black-hole spins in test-particle mergers.

Daniel Eisenstein, University of Arizona

Topic: "Dark Energy and Cosmic Sound"  (Video)

ABSTRACT: I will discuss how the acoustic oscillations that propagate in the photon-baryon fluid during the first million years of the Universe provide a robust methods for measuring the cosmological distance scale. The distance that the sound can travel can be computed to high precision and creates a signature in the late-time clustering of matter that serves as a standard ruler. Galaxy clustering results from the Sloan Digital Sky Survey reveal this feature, giving a geometric distance to a redshift of 0.3 and an accurate measurement of Omega_matter. I will review our recent work on the theoretical modeling of the shifts and scatter of the acoustic scale in N-body simulations. I will then present SDSS-lll, which will use the acoustic method to produce 1% distance measurements in order to map the curvature and expansion history of the Universe and measure the evolution of dark energy.

Fran Bagenal, University of Colorado

Topic: "Exploration of the Giant Magnetosphere of Jupiter"  (Video)

ABSTRACT: Jupiter is a planet of superlatives: the most massive planet in the solar system, rotates the fastest, has the strongest magnetic field, and has the most massive satellite system of any planet. These unique properties lead to volcanoes on Io and a population of energetic plasma trapped in the magnetic field that provides a physical link between the satellites, particularly Io, and the planet Jupiter. There are strong differences between the magnetospheres of Earth and Jupiter but there are also underlying basic physical principles that all magnetospheres share in common. This presentation provides a rough sketch of the magnetosphere of Jupiter based on previous space missions, briefly describes the current understanding and lists outstanding issues. We will also discuss how measurements to be made by NASA's Juno mission will address these issues.