Experimental Studies of Black Holes: Status & Prospects

More than a century ago, Albert Einstein presented his general theory of gravitation. One of the predictions of this theory is that not only particles and objects with mass, but also the quanta of light, photons, are tied to the curvature of space-time, and thus to gravity. There must be a critical mass density, above which photons cannot escape. These are black holes. It took fifty years before possible candidate objects were identified by observational astronomy. Another fifty years have passed, until we finally can present detailed and credible experimental evidence that black holes of 10 to 10¹⁰ times the mass of the Sun exist in the Universe. Three very different experimental techniques have enabled these critical experimental breakthroughs. It has become possible to investigate the space-time structure in the vicinity of the event horizons of black holes. I will summarize these interferometric techniques, and discuss the spectacular recent improvements achieved with all three techniques. In conclusion, I will sketch where the path of exploration and inquiry may lead to in the next decades.

Reinhard Genzel, born 1952 in Bad Homburg v. d. H., Germany, is one of the Directors of Max Planck Institute for Extraterrestrial Physics, Professor in the Graduate School of the University of California, Berkeley and an Honorary Professor at the Ludwig Maximilian University, Munich. He is a Scientific Member of the Max Planck Society and a member of the US National Academy of Sciences. His research interests include astrophysics of galactic nuclei, star formation, kinematics and cosmic evolution of galaxies, massive black holes and experimental infrared, submillimeter and millimeter astronomy. He has received numerous honours and awards, including the Shaw Prize of The Shaw Prize Foundation and the Crafoord Prize in Astronomy. In 2020, he received the Nobel Prize in Physics, jointly with Andrea Ghez, for the discovery of a supermassive compact object at the centre of our galaxy.

https://science.umd.edu/events/genzel.html

Relativistic optics and laser-driven particle accelerators

The remarkable increase in peak laser intensity over the past 30+ years –over 6 orders of magnitude--has spurred new and exciting advances in laser-driven sources of relativistic charged particles and light, along with the new field of indestructible plasma optics. I will start with our recent results demonstrating acceleration of electrons up to 10 GeV in just 30 cm—a distance 5,000 times smaller than required using conventional technology, and then work backward to highlight the physics building blocks that made such a result possible.

Jonathan Bagger, American Physical Society

This year, 2024, marks the 125th anniversary of the founding of APS.  To recognize the occasion, the APS Board refreshed the Society’s mission, vision, and core values.  It also endorsed a strategic framework to guide APS in the years ahead.  In this talk, I will introduce the Society.  I will explain what it is, where it is going, and most importantly, why we should care.

Challenges and Opportunities in Communicating STEM

This talk aims to explore twin universal concerns in communicating scientific work, for any audience. For one, we will describe and demonstrate elements of craft: distilled, actionable lessons from professional writers translated and applied to the unique challenges we face in relaying complex technical projects. These elements include familiar obstacles like jargon but also less familiar opportunities like basic narrative tension. For another, we will explore calibration: research from cognitive science and human brain evolution can serve us well in considering our audiences with savvy compassion. In sum, the talk seeks to improve the clarity, impact, and persuasive power of our work, with hopes of benefiting scientists and engineers at any stage of their careers.

Scaffold and Arch: From Dispersion Theory to Matrix Mechanics*

Students of quantum mechanics interested in the history of their field are likely to be baffled by the Umdeutung (= reinterpretation) paper with which Heisenberg laid the basis for matrix mechanics in the summer of 1925. In Dreams of a Final Theory, Steven Weinberg confessed that he had never understood this paper. In an interview in the 1960s, Alfred Landé, a contemporary of Heisenberg, put it more bluntly: “Heisenberg stammered something, Born made sense of it.” And, indeed, the so-called Dreimännerarbeit (= Three Man Paper) of late 1925/early 1926, in which Born, Heisenberg and Jordan gave the first systematic exposition of matrix mechanics poses no particular difficulties for those familiar with the basics of quantum mechanics. In this talk, I will argue that the reason the Umdeutung paper, by contrast, looks so mysterious to modern eyes is that it still shows many traces of the scaffold on which it was built, a lengthy paper on the Kramers dispersion theory that Heisenberg co-authored with Kramers in late 1924/early 1925. Since the dispersion-theory scaffold is no longer visible today, admirers of the matrix-mechanics arch built on top of it are left wondering how this arch was originally erected.

*Based on joint work with Anthony Duncan (Department of Physics and Astronomy, University of Pittsburgh)

The Next Generation of Neutrino Astrophysics with PUEO

Neutrinos provide a unique window into the highest energy accelerators in the Universe. Due to only interacting weakly, they are capable of traveling directly from their sources to detectors built on Earth. They are ideal candidates for unraveling the mysteries of the ultra high energy cosmic ray flux and understanding particle physics at energies beyond the capabilities of detectors on Earth.

In this talk, I will provide an overview of past, present, and future astrophysical neutrino detectors, with specific focus on the Payload for Ultrahigh Energy Observations (PUEO), a new experimental effort that will fly out of Antarctica in December 2025. I will discuss how updates to the trigger and instrument make PUEO a discovery instrument. And finally, I will talk about how PUEO fits into the larger field of neutrino astrophysics

The Quantum Reform of the Modern Metric System:  Mass becomes quantum, and electrical measurements become honest

The modern metric system, officially known as the International System of Units (SI), has recently undergone its most revolutionary change since the inception of the metric system at the time of the French revolution.  The kilogram, ampere, kelvin, and mole all have new definitions, based on fixing the values of fundamental constants of nature.  Famously, the reform eliminates the artifact International Prototype Kilogram as the foundation of the unit of mass.  This lecture will explain why this was necessary and how it was accomplished.  Less famously, the century-old practice of having two separate unit systems for electrical metrology —“legal” and “scientific”— has disappeared with the reformed SI.    

https://ireap.umd.edu/events/paint-branch-distinguished-lecture-applied-physics-2024

Asymptomatic: The Silent Spread of COVID-19 and the Future of Pandemics

This talk explores an idea and its consequences. The first part leverages dynamical principles and public health data to explain how COVID-19's ability to silently spread between individuals often without causing illness is precisely what made it catastrophic for society as a whole. The second part looks ahead and identifies model-informed public health approaches that can effectively reduce asymptomatic transmission so as to prevent and control future pandemics.

PRX: What Kind of Papers We are Looking for?

PRX is published by the American Physical Society, a nonprofit membership society of scientists.  Its mission goal is to select around 250 *landmark* papers a year from all fields of physics and showcase them to a broad and multidisciplinary readership.  Is your paper a good match for PRX?  Or asked differently, what papers qualify as *landmark* papers?  How do the PRX editors actually select such papers?  Are such selections always accurate?How can you, as an author, navigate PRX’s editorial and peer-review process effectively and get the most out of your interactions with the editors and referees? I will use the talk to discuss with you how to answer these questions.  Many of these questions do not have a black-and-white answer in the case of a single paper.  Open-minded, reasoned, and constructive dialogues amongst the authors, the editors, and the referees are key to making each concrete process a meaningful and productive experience, and sometimes even a pleasure, for everyone.

Neutrino Astronomy: Viewing the High Energy Sky Through the South Pole Glacial Ice

This talk will summarize recent advances in the ongoing quest to view the universe at higher energies to identify the sources of the highest energy cosmic rays and to elucidate the astrophysical mechanisms at work in these extreme objects. I explain why neutrinos, nearly massless neutral elementary particles, are the perfect “messenger” particles, which enable us to both extend the energy range at which we can view the distant universe and to unambiguously identify sources of high energy cosmic rays. While the concept of a neutrino telescope is many decades old, the means to build such a telescope at the needed 1 cubic-kilometer scale remained technically elusive until the international IceCube collaboration successfully deployed the first such instrument in the glacial ice located at the Antarctic South Pole station. The IceCube Neutrino Observatory is comprised of over 5,000 highly sensitive photodetectors imbedded to a depth of 2.5 kilometers instrumenting a cubic kilometer of optically clear ice and began full operations in 2011. The IceCube detector has recorded neutrinos at energies over 1 PeV or about 10 15 times the energy of visible light photons, opening a new window into the high energy extreme universe for the first time. This new glimpse of the universe at these extreme energies has revealed the first ever neutrino sources, and our first unambiguous detection of high energy cosmic ray sources outside our galaxy. Recently the IceCube neutrino telescope has also given us our first view of the galactic plane in neutrinos. This talk will present an overview of these results. I will close with a brief description of what these first measurements tell us about the neutrino sky, and the
plans to build a next generation telescope with higher sensitivity.

The Mathematics of Human Population Growth and CO2 Emissions

In a paper published in the Science magazine in 1960, von Foerster et al. argued that human population growth follows a hyperbolic pattern with a singularity in 2026. Using current empirical data from 10,000 BCE to 2023 CE, we re-examine this claim. We find that human population initially grew exponentially as N(t)~exp(t/T) with T=3050 years. This growth then gradually evolved to be super-exponential with a form similar to the Bose function in statistical physics. Population growth further accelerated around 1700, entering the hyperbolic regime N(t)=C/(ts-t) with the projected singularity year ts=2030, which essentially confirms the prediction by von Foerster et al. We attribute the switch from the super-exponential to the hyperbolic regime to the onset of the Industrial Revolution and the transition to massive use of fossil fuels. This claim is supported by a linear relation that we find between population and the increase in the atmospheric level of CO2 from 1700 to 2000. But in the 21st century, the inverse population curve 1/N(t) deviates from a straight line and avoids crossing zero, thus escaping a literal singularity. We find that N(t) is well fitted by the square root of the Lorentzian function, with a maximum of about 8.2 billion people at t=ts. The width 2\tau of the population peak is given by the cutoff time \tau=32 years. We also find that the increase in the atmospheric CO2 level since 1700 is well fitted by arccot[(ts-t)/\tau_F] with \tau_F=40 years. This fit gives a forecast of the CO2 level in the near future for the 21st century.

Fast and Flexible Group Decision-Making

A wide range of animals live and move in groups. Many animals do better in groups than alone when, for example, foraging for food, migrating, and avoiding predators. A key to group success is social interaction. Less well understood is how a group, with no centralized control, is capable of the fast and flexible decision-making required to carry out its tasks in an environment with uncertainty, variability, and dynamic change.

I will introduce an approach to modeling group decision-making dynamics that reveals the fundamental importance of nonlinearity, feedback, and social interaction. Analysis of the model provides new insights into fast and flexible decision-making: how indecision can be broken as fast as it becomes costly, and how sensitivity to stimulus can be tuned as context and environment change. I will discuss the significance of these results for the study and design of collective intelligence in nature and technology.