The David and Edith Harris Physics Colloquium Archives

FALL 2012 Schedule

September 6, 2012
CERN and Princeton University
Hosted by Jesse Thaler

"Higgs and Beyond at the LHC, with a little help from QCD"

Recently, the two general-purpose experiments at CERN's Large Hadron Collider, ATLAS and CMS, announced the discovery of a particle with many of the characteristics of a Higgs boson, the crucial missing element of the standard model of particle physics. This talk will review the main elements of this discovery and examine the road ahead for the LHC. In doing so, it will include a discussion of the role being played by Quantum Chromodynamics (QCD) and in particular, the progress from the past few years in handling and understanding QCD objects known as "jets''.

September 20, 2012
University of California, Los Angeles
Hosted by Josh Winn

"Exploring the Universe with WISE"

The Wide-field Infrared Survey Explorer (WISE) is a NASA Medium Explorer (MIDEX) that surveyed the entire sky in 4 mid-infrared bands at 3.4, 4.6, 12 and 22 microns with vastly greater sensitivity than previous all-sky surveys at these wavelengths.  WISE observed everything that is further from the Sun than the Earth, and this includes minor planets, comets, nearby brown dwarfs and star forming regions both in the Milky Way and in distant galaxies.  The WISE long wavelength channels are very powerful for detecting Ultra-Luminous Infrared Galaxies, and WISE should detect the most luminous galaxies in the Universe. The WISE short wavelength channels are very powerful for detecting old cold brown dwarfs, and WISE should detect the nearest brown dwarfs to the Sun.  WISE has also measured the radiometric diameters of nearly 160,000 asteroids.  WISE has a 40 cm cryogenic telescope, 1024x1024 arrays, a scan mirror to freeze images on the arrays while the spacecraft scans continuously, and takes 47'x47' images every 11 seconds in all four bands from an IRAS/COBE style Sun-synchronous nearly polar low Earth orbit.  WISE launched from Vandenberg Air Force Base on Dec. 14, 2009, ejected its cover on Dec. 29, 2009, and entered routine survey operations on Jan. 14, 2010.  It completed fully sky coverage on July 17, 2010, and then starting warming up in early August.  WISE ran with its 3 shortest bands until the end of September, and then with its two shortest bands until Feb. 1, 2011.

September 27, 2012
Hosted by Eddie Farhi

"Strong Correlations with String Theory"

It turns out that string theory is useful: via the AdS/CFT correspondence, it provides a tractable description of certain quantum many-body systems, in terms of a gravitational theory in extra dimensions. This exotic-seeming viewpoint is most effective in regimes of strong interaction, where our standard theoretical picture of weakly-interacting particles flounders. The extra dimensions organize information by length scale, just as we are instructed to do by the renormalization group. I will motivate this so-called holographic duality, and explain our efforts to apply these ideas to real physical systems which have the common feature that interactions are important for determining their collective behavior. These include the quark-gluon plasma, cold atoms at unitarity, and the `strange metal' state of high-temperature superconductors.

OCTOBER 4, 2012
University of Pennsylvania
Hosted by Jeff Gore

"Inference in Biological Physics"

I'll discuss two recent experiments, in which knowing a little bit about probability goes a long way in helping us to extract the meaning from experiments. The first involves change-point detection in single-molecule studies of molecular motors. The second involves simultaneous activity measurements on intact mammalian retina.

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

Refreshments @ 3:30 pm in Marble Lounge, 8-329 *NOTE ROOM CHANGE

OCTOBER 11, 2012
Cornell University
Hosted by PGSC

"At a Physics/InfoSci Intersection"

Twenty-five years into the internet era, twenty years into the WorldWideWeb era, ten years into the Google era, and a few months past the Facebook era, we've yet to converge on a new long-term methodology for scholarly research communication.  I will provide a sociological overview of our current metastable state, and then a technical discussion of the practical implications of literature and usage data considered as computable objects, using arXiv as exemplar.

OCTOBER 18, 2012
Hosted by Deepto Chakrabarty

"Pollution of the Early Universe by the First Stars and Galaxies"

The elements heavier than hydrogen and helium are formed predominantly in stars, via either core fusion during their main lifetimes or explosive nucleosynthesis during their violent deaths.  Astronomical spectroscopy permits us to measure the universal abundance of these chemicals at very low concentrations, over most of cosmic history. Logic dictates that as one looks backward in time to the age of the very first stars, the heavy element concentration should decline, eventually to zero.  I will describe new efforts to extend the frontier of heavy element observations to ever earlier times using new instrumentation developed at MIT.  These measurements are providing early indications that light and chemicals began to emerge from the first galaxies when the universe was 750 million years old, or about 5% of its present age.

OCTOBER 25, 2012
Northwestern University
Hosted by Janet Conrad

"The Brave Nu World"

Neutrinos are the most elusive of the known fundamental particles. Nonetheless, over the last 15 years, heroic experimental efforts aimed at understanding neutrinos have discovered that neutrinos are more interesting than originally dictated by the standard model of particle physics. After introducing the neutrinos, I will discuss how we came to discover that they have tiny but nonzero masses, comment on the most recent observations, and try to explain why this is a big deal. I will then describe some of the fundamental questions related to neutrinos, and how we hope to answer some of them in the near future.

NOVEMBER 1, 2012
Hosted by The MIT Society of Physics Students

"Inflationary Cosmology, the Origin of Density Perturbations, and the Door to the Multiverse"

I will begin by reviewing how inflation works, emphasizing how inflation can account for the observed uniformity of the universe, its near-critical mass density, and the spectrum of primordial density perturbations.  These density perturbations can be seen today in the cosmic microwave background radiation, and they are also believed to have been the seeds for structure formation in the universe.  I will describe how the density perturbations arise from microscopic quantum fluctuations in the early universe, stretched by inflation to astronomical length scales.  At the end I will discuss briefly how the density perturbations at very long wavelengths, larger than the observed universe, can give rise to eternal inflation --- inflation that goes on forever producing an infinite number of "pocket universes".

NOVEMBER 8, 2012
Brandeis University
Hosted by Mehran Kardar

"Order through Disorder: Entropy Driven Self-Assembly"

Although the idea that entropy alone is sufficient to produce an ordered state is an old one, the notion remains counter-intuitive and it is often assumed that attractive interactions are necessary to generate phases with long-range order. In this talk I will describe how to rationally design the shape of particles with repulsive interactions in order to assemble equilibrium structures of ever increasing complexity, ranging from conventional three-dimensional crystals and liquid crystals to more exotic structures such as one-dimensional twisted ribbons and two-dimensional fluid membranes. Simple argument demonstrates that all these structures maximize the overall entropy of the system.   

NOVEMBER 15, 2012
Hosted by Nuh Gedik

“Molecular Electronics for Chemical Sensors”

This lecture will detail the creation of ultrasensitive sensors based on electronically active conjugated polymers (CPs) and carbon nanotubes (CNTs).  A central concept that a single nano- or molecular-wire spanning between two electrodes would create an exceptional sensor if binding of a molecule of interest to it would block all electronic transport.  The use of molecular electronic circuits to give signal gain is not limited to electrical transport and CP-based fluorescent sensors can provide untratrace detection of chemical vapors via amplification resulting from exciton migration. Nanowire networks of CNTs provide for a practical approximation to the single nanowire scheme.  New methods for fabrication using solventless deposition methods will be described that allow for economical flexible sensor fabrication.  These methods include abrasion deposition and selectivity is generated by covalent and/or non-covalent binding selectors/receptors to the carbon nanotubes.  Sensors for a variety of materials and cross-reactive sensor arrays will be described.  The use of carbon nanotube based gas sensors for the detection of ethylene and other gases relevant to agricultural and food production/storage/transportation are being specifically targeted and can be used to create systems that increase production, manage inventories, and minimize losses.

NOVEMBER 29, 2012
University of California, Berkeley
Hosted by Liang Fu

"Topological Insulators and Their Implications for Electronic Order"

Much of condensed matter physics is concerned with understanding how different kinds of order emerge from interactions between a large number of simple constituents. In ordered phases such as crystals, magnets, and superfluids, the order is understood through "symmetry breaking".  A major discovery of the 1980s was that electrons confined to two dimensions and in a strong magnetic field exhibit a completely different, "topological" order in the quantum Hall regime.  Topological order was recently discovered in some three-dimensional materials, dubbed "topological insulators", in zero magnetic field. Spin-orbit coupling, an intrinsic property of all solids, drives the formation of the topological state.  The first part of the talk will explain how topological insulators were predicted and discovered by building on the quantum Hall effect.  The second part will cover more recent work on connections between topological insulators, magnetoelectric effects ("axion electrodynamics"), and strong correlation effects.

DECEMBER 6, 2012

University of California, Berkeley
Hosted by Sara Seager

"ExoPlanets Just Larger than Earth: Densities, Chemical Composition, and Occurrence"

The Kepler Space Telescope has now discovered over 2300 exoplanets, with measured sizes and orbital distances from their host stars.   Most of the detected planets are 1-4 times the size of Earth, revealing a heretofore unknown large population of planets composed of rock, water, and gas.   We are measuring the occurrence planets as a function of their size, to estimate the number of Earth analogs. We are also measuring the masses and densities of planets, to provide information on the internal chemical composition of these planets just larger than Earth.