Colloquium Archives (before June 2017)

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

Joachim Ankerhold, University of Ulm

Topic: "The noise is the signal - and more news from classical and quantum environments"  (Video)

Abstract: Realistic systems are never completely isolated, but are embedded in fluctuating environments. This issue has become of particular relevance with the spectacular progress in tailoring superconducting devices of growing complexity. Integrated circuits can be operated in the classical as well as in the quantum regime and thus allow to study fundamental processes far from equilibrium with unprecedented accuracy. Recently, it has turned out that noise is not always an annoying side aspect, but can also carry information or even be used as a resource. In this talk I will discuss theoretical challenges and current experimental developments. Topical realizations include the detection of charge noise in mesoscopic conductors, quantum coherence in presence of strong dissipation, and cooperative effects of driving and dissipation in artificial atoms and ultra-cold atomic gases.

Bill Wootters, Williams College

Topic: "Why Does Nature Like the Square Root of Negative One?"  (Video)

Abstract: Abstract:This talk will not answer the question posed in the title. Instead, the question motivates an investigation into the differences between standard quantum theory, based on the complex numbers, and a closely analogous theory based on the real numbers. I focus particularly on three information-theoretic questions: (i) Is information transferred optimally from preparation to measurement? (ii) Is a quantum state locally accessible? (iii) Is entanglement “monogamous”? It turns out that the two theories give opposite answers to all three questions. Though the answers don’t tell us why nature prefers the complex theory, they do tell us that the choice between real and complex numbers has significant information-theoretic consequences.

Ryan Hickox, Dartmouth College

Topic: "The beauty of simplicity: Some insights on galaxy and black hole formation"  (Video)

Abstract: Astronomers now have a general picture for how galaxies and supermasive black hole form over cosmic time. However, these objects exhibit a rich and complex phenomenology that can make it challenging to build a clear physical intuition for how this process works in detail. I will give a brief introduction to galaxy and black hole formation, and show that some important aspects of this process can be explained remarkably well with extremely simple physical scenarios based on the underlying growth of dark matter structures and the characteristic timescales for variability. I will focus on the triggering of powerful starburst galaxies, the evolution of the specific star formation rate in galaxies, and the connection between star formation and the growth of black holes, and will present a simple intuitive pictures for these processes that can help us better understand the more complex relevant physics.

Martin Elvis, Harvard-Smithsonian Center for Astrophysics

Topic: "QUASARS ARE SIMPLE: how the 3 forms of radiation pressure determines quasar structure"  (Video)

Abstract: To a good approximation, all quasars are the same. Even over 13 Gyr of cosmic history and at power outputs that range of a factor of 10^6, the differences are subtle. This implies that there should be a simple underlying physical basis for all the many complicated-seeming forms of atomic emission and absorption that we see in quasar spectra. These features have been a mystery since quasar were discovered 50 years ago this month. I propose that ALL of this phenomenology is explained simply looking carefully at the three ways in which radiation can push on matter: electron scattering, atomic line driving, and solid state absorption in molecules and dust. The zones where each of these work, and fail, produce distinctive features. The sum of these features explains everything. Quasars are, in fact, simple.

Matthew Kleban, New York University

Topic: "Watching Worlds Collide: Testing the Multiverse with Observational Cosmology"  (Video)

Abstract: String theory predicts that our entire observable universe is a tiny part of an enormous cosmic landscape populated by bubbles containing highly exotic physics.. This picture, if correct, revolutionizes our understanding of the universe on both the largest and most microscopic length scales. Some have criticized the multiverse as untestable or non-scientific. In this talk, I will present a number of avenues by which the multiverse can be falsified or confirmed using current and near-future data from observational cosmology.

Jenny Greene, Princeton University

Topic: "Galaxy Nuclei, Galaxy Outskirts"  (Video)

Abstract: I will talk about two different aspects of massive galaxy evolution. First, I will discuss the assembly of ellipical galaxies based on high signal to noise spectra beyond the effective radius taken with an integral-field spectrograph. The stars in the outskirts of these galaxies are enriched in alpha elements but have low metallicity, similiar to thick disk stars in our galaxy. We suggest that thes stars were accreted from small galaxies that formed early and had a truncated star formation history. Second, I will discuss supermassive black hole scaling relations, and what they may tell us about the coevolution of black holes and galaxies. I will end with tantalizing new clues about the lifetimes of sub-pc supermassive black holes binaries.

Janet Luhmann, University of California, Berkeley

Topic: "The Coupling Between the Sun and the Heliosphere"  (Video)

Abstract: Although Eurgene Parker had many basic concepts of the Sun's non-radiative outputs figured out ~50 years ago, observations since then have revealed- as with many things in nature- 'the devil is in the details'. This colloquium reviews some of those details that impact the way we view the interplanetary medium and the solar cycle's effects on it. Available resources are used to demonstrate the current possibilities for understanding the sources of ecliptic plasma and field conditions that have consequences for the planets.

John Donoghue, University of Mass, Amherst

Topic: "The Quantum Correction to the Newtonian Potential"  (Video)

Abstract: While quantum mechanics and general relativity are commonly said to be incompatible, that is not really true. I use the quantum correction to the gravitational interaction as an example of the modern techniques (called Effective Field Theory) that allows quantum predictions in general relativity.