The David and Edith Harris Physics Colloquium Series

fall 2014 Schedule

Thursdays - Socials: 3:30pm in 4-349 (The Pappalardo Room) // Talk: 4:00pm in 10-250 (unless otherwise noted)

David PritchardSEPTEMBER 4, 2014
DAVID PRITCHARD
MIT

Host: Peter Fisher

"What Do Students Learn, What From, What Should They Learn, An Example, Can MOOCs Help?"

Data from our MasteringPhysics.com online tutor showed tremendous learning, but little evidence that our students think like a physicist.  Further disquieting news comes from investigations of exactly what students learned, how much they remembered as seniors, the role of homework copying, the limitations of partial credit grading, and the great disparity between what physics teachers want to teach and what our students want to learn.  I shall present evidence that a blended on-campus course can teach physics expertise.  Then I’ll describe a vision of how research, development, online learning and MOOCs can be combined to spread better learning universally.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

Allan AdamsSEPTEMBER 11, 2014
ALLAN ADAMS
MIT
Host: Edward Farhi

“Quantum Liquids and Turbulent Black Holes"

The physics of black holes is amazingly rich, with deep connections to basic physical questions that nominally have nothing to do with gravity. For example, the response of a black hole to being kicked is intimately connected to the response of a quantum liquid to being stirred.  In this colloquium I will describe this "holographic" connection and use it to draw lessons about turbulent fluids, disordered quantum systems and black hole dynamics. For instance, a detailed study of gravitational dynamics reveals the surprising fact that superfluid turbulence in two dimensions can decay and dissipate energy like normal fluid turbulence in three dimensions.   Such gravitational analysis also leads to novel predictions for the effects of disorder on strongly-interacting systems.  Conversely, familiar facts about turbulent flows imply that the horizons of certain accreting black holes behave like fractals with dimension 10/3.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

Duncan BrownSEPTEMBER 18, 2014
DUNCAN BROWN
Syracuse University
Hosted by Matthew Evans

"Gravitational Waves: A New Frontier in 21st Century Astronomy and Astrophysics"

Gravitational waves are among the most remarkable predictions of Einstein’s theory of general relativity. These ripples in the curvature of spacetime carry information about the changing gravitational fields of distant objects. Almost a century after Einstein first predicted the existence of gravitational waves, scientists are on the brink of detecting them for the first time. Gravitational-wave astronomy will be a radically new tool for exploring the universe. I will describe the efforts of the Laser Interferometer Gravitational-wave Observatory (LIGO) to detect gravitational waves from astrophysical sources, including the inspiral and merger of black holes and neutron stars. I will explain how binary compact object coalescence provides a potentially transformative laboratory for fundamental physics and astrophysics.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

Steven JohnsonSEPTEMBER 25, 2014
STEVEN JOHNSON
MIT
Hosted by the MIT Society of Physics Students

"Hot Topics in Thermal Radiation"

"Do not all fix'd Bodies, when heated beyond a certain degree, emit Light and shine; and is not this Emission perform'd by the vibrating motions of their parts?" -- Sir Isaac Newton, The Third Book of Opticks, part I (1704).

Everyone knows that when an object gets hot enough, it glows. The quantitative mathematical theory of thermal radiation is over a century old, with the solution to the "ultraviolet catastrophe" of black-body radiation playing an important role in the origin of quantum mechanics. Well before Planck's law, Kirchhoff quantified the observation that a good absorber (a nearly black surface) is a good emitter, by presenting what is now known as "Kirchhoff's law" (of thermal radiation, not of circuits): the emissivity of a surface (the fraction of black-body radiation that it emits) is equal to its absorptivity (the fraction of incident light that it absorbs) at any given frequency.  This statement, which can be derived from detailed balance in thermodynamics or alternatively from the fluctuation-dissipation theorem combined with electromagnetic reciprocity, has taken on a new significance in the design of synthetic thermal emitters. For applications from spectroscopy to thermophotovoltaics, many researchers are exploiting photonic crystals, surface-plasmon resonances, and other optical effects in wavelength-scale media in order to design nano-patterned surfaces that radiate a tailored spectrum, for example to radiate primarily in a narrow frequency range.  At first glance, Kirchhoff's law also seems to impose a fundamental limitation on radiated power: since you can never absorb more than 100% of incident light, you can never emit more than a black body. It turns out that this is not the case, however. By the 1950's, it was realized that "near-field" heat transfer, between two surfaces separated on the wavelength scale or less, could exceed the black-body limit, but the problem proved surprisingly challenging to study: theoretical predictions were only possible for flat surfaces until developments (at MIT and elsewhere) in the last few years, when an explosion of new developments has appeared in the literature.  There has also been new work on thermal radiation from strongly nonlinear media, and we have recently shown that these can even exceed the black-body limit.   In this talk, we start with basic thermodynamics and work our way to these modern twists on the old notion of radiant heat.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

Alyssa GoodmanOCTOBER 2, 2014
PAPPALARDO DISTINGUISHED LECTURE IN PHYSICS
ALYSSA GOODMAN

Harvard University
Hosted by Jesse Thaler

"Seeing Stars Form in the Milky Way"

Stars like our Sun take millions of years to form.  Yet, by observing many thousands of sample systems, astrophysicists, working like demographers, have pieced together a sketchy but quantitative tale of how vast clouds of tenuous interstellar matter collapse under their own weight into the stars that comprise galaxies like our Milky Way.  This talk will focus on both new discoveries related to the physics of the star formation process, and on the new ways that observations and numerical simulations are combined, statistically analyzed, and visualized, in the quest for deeper understanding.  In particular, the talk will focus on new ways of combining large multi-wavelength surveys using new software tools like the WorldWide Telescope and Glue, both of which the speaker has helped to develop.  Case studies presented will include the story of a tremendous star-forming gas cloud (named "Nessie") that is helping us trace out the structure of the Milky Way, as well as the story of a relatively tiny star-forming region (called "Barnard 5") where incredibly detailed new observations are forcing astronomers to wonder whether analytic calculations can ever fully explain star formation.   The presentation will conclude with thoughts on where scholarly publishing is headed in the coming decade and century, and how we should best present and preserve purely digital information in the scholarly record.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

Nuh GedikOCTOBER 9, 2014
NUH GEDIK
MIT
Host: Marc Kastner

"Shining light on Topological Insulators"

Topological insulators are novel materials that do not conduct electricity in their bulk but possess exceptional conducting electronic states on their surface. These surface electrons have a number of highly unusual characteristics: (i) they behave like massless relativistic particles similar to photons (ii) their spin is locked perpendicular to their momentum and (iii) this state is robust against moderate disorder. Understanding and characterizing unique properties of these materials can lead to novel applications such as current induced magnetization or extremely robust quantum memory bits. In this talk, I will first give a brief introduction to these materials and then describe our recent experiments in which we used ultrashort laser pulses to probe and control properties of the topological surface states. Utilizing the short duration of these pulses, we succeeded in capturing femtosecond movies of the electronic energy bands in a three dimensional manner. These movies reveal an exotic hybrid state between electrons and light, which was predicted theoretically but has never been observed in solids before.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 8-329 (NOTE ROOM CHANGE)

Pablo Jarillo-HerreroOCTOBER 16, 2014
PABLO JARILLO-HERRERO
MIT
Host: Ray Ashoori

"Dirac Electrons – Living on the Edge”

Over the past decade, the physics of low dimensional electronic systems has been revolutionized by the discovery of materials with very unusual electronic properties where the behavior of the electrons is governed by the Dirac equation. Among these, graphene has taken center stage due to its ultrarelativistic-like electron dynamics and its potential applications in nanotechnology. Moreover, recent advances in the design and nanofabrication of heterostructures based on van der Waals materials have enabled a new generation of quantum electronic transport experiments in graphene. In this talk I will describe our recent experiments exploring electron-electron interaction driven quantum phenomena in ultra-high quality graphene-based van der Waals heterostructures. In particular I will show two novel realizations of a symmetry-protected topological insulator state, specifically a quantum spin Hall (QSH) state, characterized by an insulating bulk and conducting counterpropagating spin-polarized states at the system edges. Our experiments establish graphene-based heterostructures as highly tunable systems to study topological properties of condensed matter systems in the regime of strong e-e interactions and I will end my talk with an outlook of some of the exciting directions in the field.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

Beate HeinemannOCTOBER 23, 2014
BEATE HEINEMANN
University of California Berkeley
Hosted by Markus Klute

"LHC: The First Three Years And The Next Two Decades"

Following a design and construction phase of about 20 years, in summer 2012 the ATLAS and CMS experiments at Large Hadron Collider have discovered a Higgs boson. Following this discovery, more data were analyzed and first measurements of the properties have been made, suggesting that it indeed looks very much like the Higgs boson expected in the Standard Model of particle physics. The other major observation of the LHC is that no deviations from the Standard Model have been found, neither in precision measurements nor in direct searches for new particles. The presence of a Higgs boson and lack of other new particles puzzles in particular the theorists as it seems extremely unnatural. In 2015, after a 2-year shutdown, the LHC will start up again at nearly twice the previous energy, and will greatly increase the discovery potential for new particles. The collision rate will also continue to be increased in the future, further extending the discovery potential and enabling a precision measurement program for the Higgs boson. Throughout the talk I will focus in particular on the Higgs boson and the naturalness problem, what we have learned so far, and what we hope to learn from the future LHC data.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

Juan MaldacenaOCTOBER 30, 2014
JUAN MALDACENA
Institute for Advanced Study
Hosted by Jesse Thaler

"Quantum Mechanics and the Geometry of Spacetime"

Quantum mechanics is important for determining the geometry of spacetime. We will review the role of quantum fluctuations that determine the large scale structure of the universe. In some model universes we can give an alternative description of the physics in terms of a theory of particles that lives on its boundary. This implies that the geometry is an emergent property. Furthermore, entanglement plays a crucial role in the emergence of geometry. Large amounts of entanglement are conjectured to give rise to geometric connections, or wormholes, between distant and non-interacting systems.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

Steven BlockNOVEMBER 6, 2014
STEVEN BLOCK
Stanford University
Hosted by Ibrahim Cissé

“Optical Tweezers:  Gene Regulation, Studied One Molecule at a Time"

Technical advances have led to the birth a new field, dubbed single molecule biophysics. Single-molecule methods can record characteristics that are otherwise obscured by traditional, ensemble-based approaches, revealing rich new behaviors in biomolecules. An entire arsenal of techniques with single-molecule sensitivity has been developed. Prominent among these technologies is the optical trap, or "optical tweezers," which is based upon radiation pressure. When combined with in vitro bioassays, optical trapping microscopes can measure molecular properties with unprecedented precision, right down the atomic level—currently achieving a resolution of ~1 angstrom over a bandwidth of ~100 Hz—all while exerting exquisitely controlled forces in the piconewton (pN) range. Ultrasensitive systems for measuring force and displacement permit the nano-mechanical properties of single molecules to be explored noninvasively. Among the notable successes for optical traps have been measurements of the fundamental steps generated by motor proteins (for example, kinesin and myosin) and by processive nucleic acid enzymes (for example, RNA polymerase), as well as the strengths of noncovalent bonds between proteins and the energetics and kinetics of folding in biopolymers, such as DNA and RNA. This talk will give special attention to our recent success in following the co-transcriptional folding of RNA in real time as it gets synthesized by RNA polymerase, and how that folding directly regulates genes.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

John MarkoNOVEMBER 13, 2014
JOHN MARKO
Northwestern University
Hosted by Leonid Mirny

“Micromechanical Studies of DNA-protein Interactions and Chromosome Organization"

The centimeter-long DNAs in our cells are folded up into micron-scale chromosomes through an array of protein-DNA interactions.  Our group uses single-DNA micromanipulation – stretching and twisting of the double helix – as a tool to analyze a variety of protein enzymes that act on DNA. I will describe a few different kinds of “magnetic tweezers” experiments our group is involved focused on enzymes that package DNA and which change its topology, based on piconewton-scale force measurements.  I will then discuss analogous but larger scale (nanonewton force scale) micromanipulation approaches to study the large-scale structure of chromosomes. I will discuss experiments that show us how chromosomes behave as gels of underlying protein-DNA "chromatin" fibers. Results of recent experiments studying condensin complexes - thought to be major "crosslinkers" of chromosomes - will be presented.  The role of condensins in the control of DNA entanglements will also be discussed.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

John PreskillNOVEMBER 20, 2014
JOHN PRESKILL
California Institute of Technology
Hosted by the MIT Physics Graduate Student Council

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)


NOVEMBER 27, 2014 - NO COLLOQUIUM DUE TO THANKSGIVING HOLIDAY

Omar HurricaneDECEMBER 4, 2014
OMAR HURRICANE
Lawrence Livermore National Laboratory
Hosted by Peter Fisher

“Progress Towards Ignition on the National Ignition Facility"

Ignition has been a long sought-after goal needed to make fusion energy a viable alternative energy source, but ignition has yet to be achieved. For an inertially confined fusion (ICF) plasma to ignite, the plasma must be very well confined and very hot to generate extremely high pressures needed for self-heating – achieving this state is not easy!

In this talk, we will discuss the technology, science, and progress towards ignition on the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) in Northern California. We will cover the some of the setbacks encountered during the progress of the research at NIF, but also cover the great advances that have been made.

In particular, we will cover the recent work using the new “high-foot” pulse-shape implosion that presently holds the record for fusion performance. High-foot implosions are the first facility based fusion experiments to generate more energy from fusion than was invested in the fusion fuel and demonstrate significant yield amplifications from alpha-particle self-heating.

Time: 4:00 pm
Place: Room 10-250

Refreshments @ 3:30 pm in 8-329 (NOTE ROOM CHANGE)

Last updated on September 26, 2014 3:24 PM