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Spring 2019 Colloquium Series

Date:  Thursday, June 6th, 2019
Speaker: Marilena LoVerde, Stony Brook University

Title: Neutrino Properties from Cosmology

Abstract: Cosmic background neutrinos are nearly as abundant as cosmic microwave background photons, but their mass, which determines the strength of their gravitational clustering, is unknown. Even if the neutrino masses are the minimum required by oscillation data, their gravitational effects on cosmological structure will nevertheless be detectable in — and in fact required to explain — data within the next decade. This presents the opportunity to detect the neutrino mass scale and test our standard cosmological model, but also to test for new physics in the dark sector. I will discuss the physical effects of neutrinos, or other hot dark matter, on structure formation, and prospects for learning about the physics these particles with future galaxy surveys and cosmic microwave background experiments.

Host: Tien-Tien Yu

 

Date:  Thursday, May 30th, 2019
Speaker: Nima Arkani-Hamed, Institute for Advanced Study

Title:  Spacetime, Quantum Mechanics and Positive Geometry

Abstract: Spacetime and Quantum Mechanics form the pillars of our understanding of modern physics, but there are several indications that these concepts are approximate and must emerge from deeper principles, undoubtedly involving new mathematics. In this talk, I will describe some emerging ideas along these lines, and present a new formulation of some very basic physics– fundamental to particle scattering and to cosmology–not following from quantum evolution in space-time, but associated with simple new mathematical structures in “positive geometry”.

The simplest examples of positive geometries are polytopes old and new, from cyclic polytopes and Associahedra to “cosmological” polytopes. Others, such as the “Amplituhedron”, involve generalizations of polytopes into the Grassmannian. In these examples, we can concretely see how the usual rules of space-time and quantum mechanics can arise, joined at the hip, from fundamentally geometric and combinatorial origins”.

Host: Graham Kribs

 

Date:  Thursday, May 23rd, 2019
Speaker: David Hogg, New York University and Flatiron Institute

Title:  Data-driven models and machine learning for the physical sciences

Abstract: There is immense hype, and immense promise, in machine learning for physics and astronomy. I use the case of stellar astrophysics as an example area in which to explore these ideas, but my points will be general and apply to any physics area where there are substantial data sets and good but not perfect physical models. When the information in the data is good enough to consistently rule out (in a statistical goodness-of-fit sense) the physical models, can we benefit from the data quality in ways that deliver new insights about fundamental physics? One of the main themes is that we want to pick and choose the parts of machine learning we do and don’t want to be using, because our objectives are very different from those of Amazon and Facebook. I’ll put a lot of emphasis on generalizability and causal structure. (Oh and by the way, data-driven models currently produce more precise measurements of stellar properties and compositions than any physical models.)

Host: Ben Farr

 

Date:  Thursday, May 16th, 2019
Speaker: Stanley J. Micklavzina, University of Oregon

Title: Physics Demonstrations in formal and informal education: 37 years to a doctorate!

Abstract: I started working with physics demonstrations 37 years ago while pursuing my undergraduate degree in Physics. I became enamored with the approaches of displaying and teaching the poetry of Physics, with eloquent demonstrations delineating the stanzas.

This colloquium will discuss the methods of utilizing Physics Demonstrations in presentations and the background of developing shows for the public and demos for the classroom.  Included will be demonstration examples created and implemented into formal classroom physics lessons as well as informal public presentations and performances and the differences in the methods for each.

What is the role and value of Physics Demonstrations for the future? This question will be asked with current budgets, developments in physics teaching, and the highly active role of media for students in this time frame. My perspective will be interwoven within the presentation.

 

Date:  Thursday, May 9th, 2019
Speaker: Javier Tiffenberg, Fermilab

Title:  SENSEI: First results, status, and plans

Abstract: I’ll present the status and prospects of the Sub-Electron Noise Skipper Experimental Instrument (SENSEI) that uses a non-destructive readout technique to achieve stable readout for thick fully depleted silicon CCD in the far sub-electron regime (∼ 0.05 e- rms/pix). This is the first instrument to achieve discrete sub-electron counting that is stable over millions of pixels on a large-area detector. This low threshold allows for unprecedented sensitivity to the largely unexplored, but theoretically well-motivated, area of sub-GeV dark matter models. We’ll discuss the reach and prospects of the SENSEI experiment currently under construction, which will use 100 grams of Skipper CCDs.  I’ll also present recent results from an engineering surface run and the lessons learned from a small scale prototype currently operating in the MINOS cavern at Fermilab.

Host: Tien-Tien Yu

 

Date:  Thursday, May 2nd, 2019
Speaker: Nicolas Treps, Laboratoire Kastler Brossel, Sorbonne Universite

Title:  Quantum Optics, at the heart of quantum metrology and quantum information

Abstract: Light has always been an invaluable tool for high precision measurements, and the corresponding sensitivity limits a very active research field. These limits arise from a complex interplay between light fundamental properties, such as its wave nature for the Rayleigh criteria, and the detection systems, delivering an intensity map. But quantitative limits can be set only when one consider noise, whatever its origin, and thus ultimately it is the quantum nature of light that governs the fundamental limits to sensitivity.

Quantum Optics emerged when experimentally it became possible to operate optical non-linearities acting directly on the quantum fluctuations, and thus on the spatio-temporal distribution of the photons. It was then demonstrated that the use of non-classical light light fields can improve the sensitivity of interferometers, for instance. But the possibility to master exotic light quantum state expend applicability beyond quantum metrology. Information carried by quantum light can be utilised for quantum communications of even quantum computing. Hence, in the same way that light was used to demonstrate the basic principle of quantum mechanics, we expect that it will be a cornerstone of quantum technologies.

During this talk, I will review the main concepts that make light such an invaluable tool for quantum technologies. I will then focus on the continuous variable approach and optical frequency combs, where the measurement of the electric field on its many frequency degrees of freedom allow for the multiplexing of quantum information and an interplay between quantum and classical application.

Host: Brian Smith

 

Date:  Thursday, April 25th, 2019
Speaker: Peter Yunker, Georgia Tech

Title:  Soft matter physics of the evolution of multicellularity

Abstract: The evolution of multicellularity set the stage for an incredible increase in the diversity and complexity of life on Earth. The increase in biological complexity associated with multicellularity required parallel innovation in the mechanical properties of multicellular bodies. Though a cursory review of any multicellular organism provides an appreciation of this intertwining of biological and mechanical complexity, little is known about how such mechanical properties may have evolved. We hypothesize that prior to the evolution of genetically-regulated development, physics played a key role in initiating simple multicellular development. Through a combination of experimental evolution (which allows us to observe the evolution of multicellularity in the lab, as it occurs), and the tools of soft matter (microscopy, mechanical testing, and more), we show that physics likely played a fundamental role in the evolution of complex multicellularity.

Host: Tristan Ursell

 

Date:  Thursday, April 18th, 2019
Speaker: Julien Tailleur, CNRS-Universite Paris Diderot

Title:  Statistical physics of active matter: pushing, walking and jamming together

Abstract: Active materials are driven out of thermal equilibrium at the microscopic scale, where individual units dissipate energy stored in the environment to inject momentum into the system. These energetical and mechanical drives endow active systems which a rich phenomenology, unmatched in passive systems. In this colloquium, I will review how statistical mechanics approaches account for the emerging properties of active materials, focusing in particular on their anomalous mechanical properties, as well as on their collective behaviors.

Host: John Toner

 

Date:  Thursday, April 11th, 2019
Speaker: David Sivak, Simon Fraser University

Title:  Design principles of molecular machines: efficient control and functional coupling

Abstract: Biomolecular machines are central actors in a myriad of major cell biological process. Their successful function requires effective energy conversion among diverse mechanical components, and time-reversal symmetry-breaking to achieve directed transport. It seems plausible that evolution has sculpted these machines to effectively transduce free energy in their natural contexts, where stochastic fluctuations are large, nonequilibrium driving forces are strong, and biological imperatives require rapid turnover. But what are the physical limits on such nonequilibrium effectiveness, and what machine designs actually achieve these limits? In this talk, I discuss how to rapidly and efficiently drive such noisy systems from one state to another, and how to allocate nonequilibrium driving forces among the steps of a machine cycle to maximize its throughput. These theoretical results find confirmation in experiments and provide nontrivial yet intuitive implications for the design principles of molecular-scale free energy transduction.

Host: Tristan Ursell

 

Date:  Thursday, April 4, 2019
Speaker: Suzanne White Brahmia, University of Washington

Title:  A new assessment of mathematical reasoning development in physics instruction

Abstract:  Mathematical reasoning flexibility across physics contexts is a desirable learning outcome of introductory physics, where the “math world” and “physical world” meet, yet research on upper division physics students reveals that majors continue to struggle making sense of the sophisticated ways that physics uses simple mathematics.  Physics Quantitative Literacy (PQL) is a set of interconnected skills and habits of mind that support quantitative reasoning about the physical world. We present the PIQL, Physics Inventory of Quantitative Literacy, which is currently under development in a multi-institution collaboration. PIQL assesses students’ proportional reasoning, co-variational reasoning, and reasoning with signed quantities as they are used in physics. Unlike concept inventories, which assess conceptual mastery of specific physics ideas, PIQL is a reasoning inventory that can provide snapshots of student ideas that are continuously developing. Item distractors are constructed based on the different established natures of the mathematical objects in physics contexts (e.g. the negative sign as a descriptor of charge type and the negative sign as indicator of opposition in Hooke’s law). An analysis of student responses on PIQL will allow for assessment of hierarchical reasoning patterns, and thereby potentially map the emergence of mathematical reasoning flexibility throughout the introductory sequence, and beyond. NSF DUE-IUSE # 1832836

Host:  Stanley Micklavzina