Colloquium Archives (before June 2017)

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

Rajamani Vijayaraghavan, University of California , Berkeley

Topic: "The Evolution of a Quantum Wave-function During Measurement: From Quantum Jumps to Feedback"  (Video)

Abstract: The textbook picture of measurement in quantum mechanics describes an instantaneous process that transforms a quantum superposition into probabilistic classical outcomes. Since any realistic measurement protocol takes a finite amount of time, it is natural to ask: How does the quantum wavefunction evolve during the process of measurement? The theory of weak continuous measurement addresses this question by evolving the quantum wavefunction based on the partial information available in a given measurement time. In this talk, I will discuss experiments using superconducting electrical circuits to implement real-time monitoring of the quantum wavefunction as it evolves during a measurement.

Laura Trouille, Northwestern University

Topic: "The Monster's Fiery Breath: Supermassive Black Holes at the Centers of Distant Galaxies"  (Video)

Abstract: Most, if not all, galaxies, including our own Milky Way, are host to a supermassive black hole (SMBH) at their center. Since the discovery of a tight empirical correlation between SMBH mass and host galaxy bulge mass, mounting observational evidence and advances in cosmological simulations suggest a link between galaxy evolution and central black hole growth. However, advances in this field are stymied by disagreement over accuracy of selection methods for accreting SMBHs and applicability of these selection methods to more distant galaxies. In this talk, I will discuss our resolution of the long-standing question with regards to the nature of BPT-composites and our new method for identifying distant active galactic nuclei (AGN). I will also present our recent results using the rare population of post-starburst galaxies as a probe to understanding the role of mergers and AGN in galaxy evolution.

Marc Kamionkowski

Topic: "The Cosmic Microwave Background: Beyond the Power Spectrum"  (Video)

Abstract: Virtually all the information we've obtained from the cosmic microwave background (CMB) about cosmological parameters and the early Universe comes from measurements of the temperature power spectrum or, equivalently, the temperature two-point correlation function. However, a variety of higher-order correlations, and the polarization, may encode a wealth of additional information on the early Universe, the physics of cosmic acceleration, and the distribution of matter at low redshifts. I will discuss some of these new signatures as well as the physical scenarios they probe.

Alex Pope, U. Mass Amherst

Topic: "Dust-obscured activity in high redshift galaxies"  (Video)

Abstract: We now know that the majority of the star formation activity at high redshift occurs behind dust. Building on the success of the first extragalactic submm surveys over a decade ago, I will discuss recent observations with Spitzer and Herschel that have advanced our understanding of dust emission in high redshift galaxies; these observations can help to determine how intense star formation and active galactic nuclei growth proceeds in the obscured galaxies that are orchestrating massive galaxy formation through major mergers and turbulent gas-rich disks. I will discuss whether there is evidence for evolution at high redshift. I’ll discuss how future large dish (sub)millimeter facilities, such as the Large Millimeter Teleschope (LMT), will directly detect the majority of the sources contributing to the infrared background allowing us to make a complete census of dust-obscured activity in the Universe.

Gavin Schmidt, NASA/Goddard Institute for Space Studies

Topic: "What are climate models good for?"  (Video)


"If we had observations of the future, we obviously would trust them more than models, but unfortunately observations of the future are not available at this time." (Knutson and Tuleya, 2005)

Climate change is ongoing, and trying to explain what is happening now, and what might happen in the future are key tasks that require large-scale complex climate models of the atmosphere, ocean, land surface and cryosphere. But how well do such models perform? Can they predict climate changes in the face of the chaotic dynamics of weather? How have they performed so far? I will discuss how the credibility of model results can be established and what are the current limitations. This involves assessing short term climate variability, the response of the climate system to external factors (such as variability of the sun or large volcanic eruptions), paleo-climate information and how model-data discrepancies get resolved. I will (hopefully) demonstrate that while climate models are by no means perfect, they can be very useful.

Christopher Fuchs, Perimeter Institute, Toronto

Topic: "Quantum Theory from Quantum Information? (What would Feynman say?)"  (Video)

Abstract: How did the field of quantum information begin? To my mind, it was when John Wheeler formed his group of students and postdocs at the University of Texas in the early 1980s. David Deutsch (quantum Turing machines, quantum speed up), Benjamin Schumacher (qubits, quantum channel capacities), William Wootters (no-cloning, quantum teleportation), Wojciech Zurek (no-cloning, decoherence). Even Richard Feynman visited once. Those names now ring out to our field like the names of Bedford, Exeter, Warwick, and Talbot in King Henry's famous Saint Crispin's Day Speech.