Gravitational wave astronomy involves people from around the world, all with their our own stories. Dr. Corey Gray, Caltech, is a member of the Siksika Nation (Northern Blackfoot tribe of Alberta) and Scottish. He is the lead operator at the Hanford Observatory of the Laser Interferometer Gravitational wave Observatory. In this hour-long public lecture, Dr. Gray presents a behind-the-scenes look at what it’s been like working at a land-based gravitational wave detector since 1998. He will share a “Top 3” list of his favorite detections as well as the experience of a son having the opportunity to recruit his mother to work with him because of language—the language of spacetime and the Blackfoot people.

The LIGO Scientific Collaboration made big news in 2016 by announcing what has been hailed as “the scientific breakthrough of the century:” the first direct detection of gravitational waves. This was a monumental discovery because it proved a prediction made 100 years earlier by Albert Einstein. LIGO has made many more detections over the years. These detections mark the beginning of a completely new field of science: gravitational wave astronomy.

Dr. Corey received his Bachelor of Science degrees in physics and applied mathematics from Humboldt State University in northern California. After graduation, he was hired as a detector operator by the California Institute of Technology to work for the LIGO Hanford Observatory in Washington state. As a member of the LIGO team, Corey’s work has included working with groups to help build the gravitational wave detector and also operating the detector as a member of the operator team.

He also enjoys outreach & science communication. Over the years he has given keynotes, plenary talks, public colloquia, conference panel sessions, and also a TEDx talk. His speaking engagements have taken him from Banff to Orlando, Montreal to Honolulu and many points in between. He especially loves to share the science of Einstein with Indigenous youth and other underrepresented groups.

]]>Faraz Mehdi, Kiran M. Kolwankar

In this paper, we demonstrate a low-cost method to measure the speed of light. It uses instruments which are readily available in any undergraduate laboratory in a developing country and some components which are inexpensive. The method is direct as it measures the time of flight of the LASER beam and easy to implement. It will allow students to verify the finite value of the speed of light first hand. It can be part of the undergraduate syllabus as a regular experiment or a demonstration experiment.

read more at https://arxiv.org/abs/2108.06773

]]>**Paul Quincey**

The specialised uses of solid angles mean that they are quite unfamiliar quantities. This article, apart from making solid angles a little more familiar, brings out several topics of general interest, such as how units are interrelated and how equations depend on the choice of units. Although the steradian is commonly used as the unit for solid angle, another unit, the square degree, is used in astronomy, and a unit introduced here, the solid degree (with 360 solid degrees in a hemisphere) could be used with benefits that are similar to those of the degree when it is used as the unit for plane angle. The article, which is suitable for students at A-level and introductory undergraduate level, also shows how solid angles can provide a gentle introduction to crystal structure, spherical trigonometry and non-Euclidean geometry.

read more at arxiv.org/abs/2108.05226

]]>**Gregory McGowan, Jeffrey Feaster, Andy Jones, Lucas Agricola, Matthew Goodson, William Timms, Mesbah Uddin**

We present in this paper a model of the transport of human respiratory particles on a Charlotte Area Transit System (CATS) bus to examine the efficacy of interventions to limit exposure to SARS-CoV-2, the virus that causes COVID-19. The methods discussed here utilize a commercial Navier-Stokes flow solver, RavenCFD, run using a massively parallel supercomputer to model the flow of air through the bus under varying conditions, such as windows being open or the HVAC flow settings. Lagrangian particles are injected into the RavenCFD predicted flow fields to simulate the respiratory droplets from speaking, coughing, or sneezing. These particles are then traced over time and space until they interact with a surface or are removed via the HVAC system. Finally, a volumetric Viral Mean Exposure Time (VMET) is computed to quantify the risk of exposure to the SARS-CoV-2 under various environmental and occupancy scenarios. Comparing the VMET under varying conditions should help identify viable methods to reduce the risk of viral exposure of CATS bus passengers during the COVID-19 pandemic.

read more at

]]>William J. Herrera, Herbert Vinck-Posada, Shirley Gomez Paez

Green’s functions in Physics have proven to be a valuable tool for understanding fundamental concepts in different branches, such as electrodynamics, solid-state and many -body problems. In quantum mechanics advanced courses, Green’s functions usually are explained in the context of the scattering problem by a central force. However, their use for more basic problems is not often implemented. The present work introduces Green’s Function in quantum mechanics courses with some examples that can be solved with essential tools. For this, the general aspects of the theory are shown, emphasizing the solution of different fundamental issues of quantum mechanics from this approach. In particular, we introduce the time-independent Green’s functions and the Dyson equation to solve problems with an external potential. As examples, we show the scattering by a Dirac delta barrier, where the reflection and transmission coefficients are found. In addition, the infinite square potential well energy levels, and the local density of states, are calculated.

read more at https://arxiv.org/abs/2107.14104

]]>abstract : Humans tend to be better at physics than at mathematics. When an apple falls from a tree, there are more people who can catch it—we know physically how the apple moves—than people who can compute its trajectory from a differential equation. Applying physical ideas to discover and establish mathematical results is therefore natural, even if it has seldom been tried in the history of science. (The exceptions include Archimedes, some old Russian sources, a recent book by Mark Levi, as well as my articles and lectures.) This TMC Distinguished Lecture presents a diversity of examples, and tries to make them easy for imaginative beginners and difficult for seasoned researchers.

]]>The Muon g-2 experiment announced one of the most tantalizing physics measurements in over a decade. It is possible that the measurement tells us that our theoretical calculation is missing some new physical phenomena. It is also possible that a new theoretical prediction points to the possibility that measurement and prediction basically agree. In this exciting video, Fermilab’s Dr. Don Lincoln gives you an insider’s perspective.

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