The David and Edith Harris Physics Colloquium Series

FALL 2017 Schedule

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

NOVEMBER 9, 2017
ANDREA GHEZ
UCLA
Host: Deepto Chakrabarty

PAPPALARDO DISTINGUISHED LECTURE

"Our Galactic Center: A Unique Laboratory for the Physics & Astrophysics of Black Holes"

The proximity of our Galaxy's center presents a unique opportunity to study a galactic nucleus with orders of magnitude higher spatial resolution than can be brought to bear on any other galaxy. After more than a decade of diffraction-limited imaging on large ground-based telescopes, the case for a supermassive black hole at the Galactic center has gone from a possibility to a certainty, thanks to measurements of individual stellar orbits. The rapidity with which these stars move on small-scale orbits indicates a source of tremendous gravity and provides the best evidence that supermassive black holes, which confront and challenge our knowledge of fundamental physics, do exist in the Universe. This work was made possible through the use of speckle imaging techniques, which corrects for the blurring effects of the earth's atmosphere in post-processing and allowed the first diffraction-limited images to be produced with these large ground-based telescopes.

Further progress in high-angular resolution imaging techniques on large, ground- based telescopes has resulted the more sophisticated technology of adaptive optics, which corrects for these effects in real time. This has increased the power of imaging by an order of magnitude and permitted spectroscopic study at high resolution on these telescopes for the first time. With adaptive optics, high resolution studies of the Galactic center have shown that what happens near a supermassive black hole is quite different than what theoretical models have predicted, which changes many of our notions on how galaxies form and evolve over time. By continuing to push on the cutting-edge of high-resolution technology, we will be able to capture the orbital motions of stars with sufficient precision to test Einstein’s General theory of Relativity as well as theories of galaxy formation and evolution - all in regimes that have never been probed before.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

NOVEMBER 16, 2017
WEI LI
Rice University
Host: Yen-Jie Lee

“Nearly "Perfect" Quark-Gluon Droplet at the Smallest Scales”

In high energy collisions of large, heavy nuclei (e.g., Au or Pb), a new state of matter consisting of liberated quarks and gluons is formed at a temperature of a few trillion Kelvins. This "Quark-Gluon Plasma" (QGP), discovered at the Relativistic Heavy Ion Collider (BNL) and the Large Hadron Collider (CERN, Switzerland), is found to exhibit amazing collective behavior as a nearly "perfect" fluid, which flows with close-to-zero viscous dissipation. It was thought that elementary collision systems like proton-proton (pp) or proton-nucleus (pA) are too small and dilute to form a QGP fluid so they were often treated as a reference in understanding the emergence of perfect fluidity in large heavy ion systems. Surprisingly, in recent years, evidence for collective effects and QGP formation has also been revealed in those smallest collisions, when looking at a fraction of rare events releasing largest number of particles. In this talk, I will describe key findings related to the possible formation of the tiniest QGP fluid in pp and pA systems, and discuss their implications to the standard paradigm of heavy ion physics, as well as new opportunities opened up in studying emergent Quantum Chromodynamics phenomena under extreme conditions.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

NOVEMBER 30, 2017
XIANGDONG JI
Tsung-Dao Lee Institute, Shanghai and University of Maryland
Host: Tracy Slatyer

"Searching for Dark Matter"

Dark matter is among the most important mysteries in science today. There are compelling arguments that dark matter particles are a class of weakly-interacting massive particles, or WIMPs, that arise naturally in physics beyond the standard model. WIMP searches using various low-energy detectors have been conducted around the globe for nearly thirty years, with dramatic improvements in scale and sensitivity. After a brief overview of the field, I will focus on a Chinese dark matter experiment, PandaX-II, running in the Jinping Underground Lab, in Sichuan Province. The PandaX-II detector uses 580kg ultrapure liquid xenon as the detection target, and has a record sensitivity about ~0.1 events/ton×day. The most recent results with an exposure of 54 ton×day data will be shown and discussed. The future running and upgrading plan of the PandaX experiment will be presented, along with the prospect of building the world “ultimate WIMP dark matter detector” in the next decade. 

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

DECEMBER 7, 2017
STEVEN GUBSER
Princeton University
Host: MIT Society of Physics Students

“Number Theory and Spacetime”

Our description of spacetime relies on the real numbers and hence is wedded to arbitrarily small intervals of length and time.  But quantum theory hints at the existence of a smallest possible length, the Planck length.  Number theory provides an alternative to the real numbers known as the p-adic numbers.  Recent work has argued that quantum field theory defined over the p-adic numbers is holographically dual to a discrete spacetime.  Constructions related to p-adic numbers also have a surprisingly prominent role in the early development of the renormalization group.  I will explain what the p-adic numbers are and provide some intuition for what they are good for in string theory and beyond.  The ultimate aim of using them to understand quantum gravity is ambitious indeed, but I will explain some first steps that give hope for the future.

Time: 4:00 pm
Place: Room 34-101 *NOTE ROOM CHANGE
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

PAST FALL 2017 COLLOQUIUM SPEAKERS

SEPTEMBER 7, 2017
SAVAS DIMOPOULOS
Stanford University
Host: Jesse Thaler

"Searching for New Physics with Small Scale Experiments and LIGO"

I will talk about new physics and dark matter searches via "tabletop" experiments and gravitational wave detectors.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

SEPTEMBER 14, 2017
JEREMY ENGLAND
MIT
Host: Mehran Kardar

"No Turning Back: The Nonequilibrium Statistical Thermodynamics of becoming (and remaining) Life-Like"

There are certain, specific behaviors that are particularly distinctive of life.  For example, living things self-replicate, harvest energy from challenging environmental sources, and translate experiences of past and present into actions that accurately anticipate the predictable parts of their future.  What all of these activities have in common from a physics standpoint is that they generally take place in the far-from-equilibrium regime, where dissipation drives strong dynamical irreversibility.  We have therefore sought to understand the emergence and persistence of life-like phenomena in fluctuating, classical many-body systems by proving and applying general results in nonequilibrium statistical mechanics.  How fast are self-replicators allowed to grow, and when do they spontaneously emerge?  How much energy must a chemical network harvest to sustain itself away from equilibrium, and when can it learn to do so through self-organization? We report recent progress in tackling these questions and others using theory and simulation.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

SEPTEMBER 21, 2017
ERIC CORNELL
JILA, NIST, and the University of Colorado at Boulder
Host: Wolfgang Ketterle and David Pritchard

"Ultracold Bose Soup: Where Few-Body meets Many-Body Physics"

Degenerate bose gases were first created in labs about twenty years ago. These gases now come in many varieties and their microscopic properties may be probed with a diverse range of experimental tools. Degenerate bose liquid, on the other hand, is available in any element the customer wants, but only if that element is helium, and even a century after it was first realized, microscopic experimental probes are relatively limited. Can we make our ultracold bose gases more liquid-like? On the way, can we learn some interesting things at the interface between few- and many-body physics?

Time: 12:00 pm NOTE TIME CHANGE
Place: Room 54-100 NOTE ROOM CHANGE

SEPTEMBER 28, 2017
DMITRI BASOV
Columbia University
Host: Pablo Jarillo-Herrero and Nuh Gedik

"Quantum Materials: Insights from Near Field Nano-Optics"

In 1944 Hans Bethe reported on “the diffraction of electromagnetic radiation by a hole small compared with the wave-length” [Physical Review 66, 163 (1944)]. This seminal paper was among the early precursors to a new and vibrant area of research: near field nano-optics. I will discuss recent nano-optical experiments on quantum materials including: transition metal oxides undergoing the insulator to metal transition and graphene. Central to the nano-optical exploration of quantum materials is the notion of polaritons: hybrid light matter modes that are omnipresent in polarizable media. Infrared nano-optics allows one to directly image polaritonic standing waves [Science 343, 1125 (2014), Nature Materials 14, 1217 (2015)] yielding rich insights into the electronic phenomena of the host material supporting polaritons [Science 354, 195 (2016)]. I will give a progress report on the search for the role of the Berry phase in the properties of graphene via transient polaritonic imaging [Nature Photonics 10, 244 (2016)].  In a parallel development, we harnessed near field optics to uncover the elusive electronic and magnetic phases that occur only at the nano-scale in the vicinity of the insulator to metal transition in correlated oxides [Nature Physics 13, 80 (2017) and Nature Materials 15, 956 (2016)].

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

OCTOBER 5, 2017
ANDREW STROMINGER
Harvard University
Host: MIT Physics Graduate Student Council

"Soft Hair on Black Holes"

An overview will be given of recently discovered connection between asymptotic symmetries in general relativity and soft theorems in quantum field theory together with their implications for the black hole information paradox.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

OCTOBER 12, 2017
TULIKA BOSE
Boston University
Host: Graduate Women in Physics

"Unlocking the mysteries of the Universe with the CMS experiment at the Large Hadron Collider"

The discovery of the Higgs Boson at the Large Hadron Collider (LHC) in 2012 was a ground-breaking event in particle physics history. The LHC has restarted recently at an unprecedented center of mass energy of 13 TeV and the data collected by the CMS experiment is expected to help fully understand the nature of electroweak symmetry breaking and potentially discover new physics. In this talk, I will review recent results from the CMS experiment with special focus on searches for physics beyond the Standard Model.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

OCTOBER 19, 2017
THOMAS SUNN PEDERSEN
Max Planck Institute for Plasma Physics
Host: Nuno Loureiro

"Plans for Creation and Studies of Electron-Positron Plasmas in a Laboratory Magnetosphere"

The mass symmetry of the constituents of an electron-positron plasma makes it particularly amenable to theoretical and numerical analysis, and thus can be thought of as the “hydrogen atom of plasma physics”. Truly unique behavior is predicted, such as the absence of some fundamental waves and an associated absence of an important class of microscopic instabilities that otherwise lead to turbulence and fast transport for magnetically confined plasmas. In addition, these plasmas are believed to be present in various astrophysical scenarios often in combination with a confining dipolar magnetic field, such as black holes and neutron stars.

I will report on our efforts to create and study a laboratory magnetosphere - a levitated superconducting ring current - filled with electron-positron plasma, to test the often startling predictions from theory and simulations. Recent experimental progress includes demonstration of almost loss-less injection of a positron beam into the confining field of a magnetic dipole, radial compression in the dipole, and confinement of positrons in the dipole field for thousands of toroidal precession times. 

This work is supported by the European Research Council (ERC), the Germany Research Society (DFG), the Max Planck Institute for Plasma Physics, the NIFS Collaboration Research Program, Japan Society for the Promotion of Science (JSPS), and the UCSD Foundation.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

OCTOBER 26, 2017
ELIEZER RABINOVICI
Hebrew University of Jerusalem
Host: Daniel Harlow

"SESAME: Opening a Source of Light in the Middle East"

SESAME is a cooperative venture by scientists and governments of the Middle East set up on the model of CERN (European Organization for Nuclear Research).

Members of SESAME are Cyprus, Egypt, Iran, Israel, Jordan, Pakistan, the Palestinian Authority, and Turkey.

The Synchrotron Light source will be used by researchers to study a large variety of scientific questions. It is being constructed in Jordan and is now starting its preparations for doing science starting in 2017/2018.

I will describe from a very personal point of view of how this project has come into being starting from 1995. The story will move from the CERN cafeteria through the Sinai desert to the completion of a high quality scientific electron accelerator in Jordan.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

NOVEMBER 2, 2017
DOUGLAS FINKBEINER
Harvard University
Host: Tracy Slatyer

"What Astrophysicists Need to Know about Transdimensional Inference"

Many problems in astronomy and physics involve estimating parameters within some model framework, where the number of parameters itself may be unknown. We have all confronted situations like: "I know I want a polyomial, but what order?" or "How many blobs should I fit in this image?" It is possible to apply popular Markov chain Monte Carlo techniques in these situations, even though the problems are transdimensional, i.e, there are steps in the chain that change the number of parameters. This revelation has allowed us to take a more principled approach to a number of problems. I will show 3 examples of interest in astrophysics: (1) crowded-field stellar photometry, (2) the 3-D distribution of interstellar dust in the Milky Way, and (3) the population of DM subhalos in strongly lensed systems, even when no single halo is detectable. These techniques do require some CPU, but are far from being too slow or complicated to contemplate. Indeed, when properly understood, Bayesian transdimensional inference is straightforward to apply to a broad class of problems.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

 

 

Last updated on November 9, 2017 9:20 AM