Colloquium Archives (before June 2017)

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

Dawn Meredith, University of New Hampshire

Topic: "Helping Students Connect Meaning and Mathematic"  (Video)

ABSTRACT:  Mathematics is the language of physics, yet mathematics may sometimes seem simply as a way to calculate numbers to our students. This talk will focus on several ways that students do use mathematics to do physics (some productive, others not as much), and how we can promote student use of the productive ways of using mathematics.

Adam Frank, University of Rochester

Topic: "Star Formation Feedback: Do Stars Practice Birth Control?"  (Video)

ABSTRACT:  The link between turbulence and feedback in star formatting environments and protostellar jets remains controversial. Star forming clouds are highly inefficient with only 10% to 30% of cloud  becoming stars.  In this talk I will present a general overview of how stars may control their own formation  efficiency by feeding energy back into the cloud which created them.

David Latham, Harvard-Smithsonian Center for Astrophysics

Topic: "Super Earths and Life"  (Video)

ABSTRACT:  Transiting planets are special.  The amount of light blocked by the planet as it passes in front of its host star sets the size of the planet (relative to the star).  If an orbit can be derived from Doppler spectroscopy of the host star, the light curve also provides the orientation of the orbit, leading to the mass of the planet (again relative to the star).  The resulting density for the planet can be used to constrain models for its structure and bulk properties. We are on the verge of using these techniques to characterize Super Earths, planets in the range 1 to 10 Earth masses that may prove to be rocky or water worlds.  NASA missions such as Kepler and TESS promise to play key roles (and I will report on the status of both).

William Oliver, MIT Lincoln Labs

Topic: "Amplitude Spectroscopy with a Superconducting Artificial Atom"  (Video)

ABSTRACT: Superconducting persistent-current qubits are quantum-coherent artificial atoms with multiple energy levels. In the presence of large-amplitude harmonic excitation, the qubit state can be driven through one or more of the energy-level avoided crossings. The resulting Landau-Zener-Stueckelberg (LZS) transitions mediate quantum-coherent phenomena as a function of the driving-field amplitude.  In this talk, we present our recent demonstration of amplitude spectroscopy, a spectroscopy approach based on LZS transitions that monitors the system response to amplitude rather than frequency. This allowed us to probe the energy spectra of our artificial atom over the bandwidth 0.01 - 120 GHz, while driving it at a fixed frequency of only 0.16 GHz. These experiments exhibit a remarkable agreement with theory, and are extensible to other solid-state qubit modalities. We anticipate they will find application to qubit control and state-preparation methods for quantum information science and technology.

Avi Loeb, Director, Institute for Theory and Computation, Harvard University

Topic: "Exploring New Physics in the Early Universe and Around Black Holes"  (Video)

ABSTRACT: The Universe offers environments with extreme physical conditions that cannot be realized in laboratories on Earth. These environments provide unprecedented tests for extensions of the Standard Model.  I will  describe two such "astrophysical laboratories", which are likely to represent new frontiers in observational astrophysics over the next decade. One  provides a novel probe of the initial conditions from inflation and the nature of the dark matter, based on 3D mapping of the distribution of cosmic hydrogen through its resonant 21cm line. The second allows to constrain the metric around supermassive black holes based on direct imaging or  the detection of gravitational waves. I will describe past and future observations of these environments and some related theoretical work.

Edward Kolb, Department of Astronomy and Astrophysics, University of Chicago

Topic: "Dark Matter, Dark Energy, and Inflation"  (Video)

ABSTRACT: The standard cosmological model seems to be able to account for all cosmological observations.  But its three basic ingredients, dark matter that holds together cosmic structures, dark energy that drives the universe in ever increasing expansion, and inflationary   perturbations that provide the seed perturbations for all we see   around us, are complete mysteries.  In the talk I will highlight  what we don't know about the cosmological standard model.

Mark Reid, Harvard-Smithsonian Center for Astrophysics

Topic: "Measuring the Cosmos"  (Video)

Abstract: Over 2000 years ago, Hipparcus measured the distance to the Moon by triangulation from two locations across the Mediterranean Sea. However, determining distances to stars proved much more difficult. Many of the best scientists of the 16th through 18th centuries attempted to measure stellar parallax, not only to determine the scale of the cosmos but also to test the Heliocentric cosmology.  While these efforts failed, along the way they lead to many discoveries, including atmospheric refraction, precession, nutation, and aberration of light. It was not until the 19th century that Bessel measured the first stellar parallax.

Warren Brown, Harvard-Smithsonian Center for Astrophysics

Topic: "Hypervelocity Stars and Massive Black Holes"  (Video)

ABSTRACT:  Hypervelocity stars ejected from the Galaxy at ~1000 km/s are a natural consequence of the massive black hole in the Galactic center.  We discovered the first hypervelocity star in 2005, and since then our targeted survey has discovered 14 unbound stars.  The distribution of hypervelocity stars is linked to the black hole ejection mechanism, and reveals the history of stars interacting with the black hole.  Measuring hypervelocity star trajectories also allows us to place unique constraints on the Galactic dark matter potential.

Angela Olinto, Department of Astronomy and Astrophysics Kavli Institute of Cosmological Physics University of Chicago

Topic: "The Highest Energy Cosmic Particles"  (Video)

ABSTRACT: After almost a century of observations, we still don't know the  origin of the highest energy cosmic rays but the possibilities have narrowed down with the discovery that the ultra-high energy sky displays an anisotropic distribution in arrival directions. A correlation between the arrival directions of ultra-high cosmic rays measured by the Pierre Auger Observatory and the distribution of nearby extragalactic objects signals the dawn of particle astronomy. We will discuss these historic results and their implications both for astrophysics and particle physics. Future projects on the field will also be addressed.

Robert Bluhm, Colby College

Topic: "Testing Lorentz Symmetry"  (Video)

ABSTRACT: Lorentz symmetry is a fundamental component of the standard model in particle physics and of general relativity.  However, in recent years, the idea that Lorentz symmetry might not hold exactly due to effects arising at the Planck scale in a quantum theory of gravity (such as string theory) has received much attention.  This talk will look at theoretical investigations of Lorentz tests, which use a framework known at the Standard-Model Extension. A variety of recent phenomenological tests of Lorentz symmetry will be examined.