Events

Abstract: In 1976 I predicted that an accelerated detector in the vacuum would respond as though it were immersed in a thermal bath with temperature proportional to the acceleration. The proportionality factor is very small, so that to see a temperatures of 1K would require and acceleration of about 10^22cm/(second squared). An analogous effect can take place in a fluid where the velocity of sound takes over from the light velocity. In a BEC which remains fluid at temperatures of 10^(-12)K and with a velocity of sound of mm/s, an analog of this effect holds the possibility of seeing this effect in an experiment using a novel energy laser interferometer. I will be reviewing the successes of using such analog systems to measure Hawking radiation, and our proposal of also measuring the acceleration effect in an analogue system.


This colloquium will have a remote option via zoom:
 

About the Talk: The detection of gravitational waves from events such as the collision of black holes is based on one of the most exquisitely sensitive experiments in the world.  Although the energy released in the original collision is as large as that from anything humans have ever observed, the resulting ripples in space-time are so small by the time they reach the earth that they generate displacements less than a billionth of a billionth of a meter.  This is why gravitational waves resisted detection for a century until their observation in 2015, a feat recognized by the 2017 Nobel Prize in Physics.  At present, the key source of noise  limiting the sensitivity in these experiments is due to quantum mechanics. Given that the detector mirrors weigh 40 kg, it is astounding that the quantum theory originally developed for atoms matters in this case for macroscopic objects.  This year’s Van Vleck lecture will explore this phenomenon.  Things can go strangely in the quantum world, and Professor Unruh will show how it is possible to reduce the effects of this noise by actually injecting more quantum noise into the detector.

About the speaker:

William Unruh received his Ph.D. in 1971 under John Wheeler (the person who popularized the name "Black Hole" for the phenomenon). In trying to understand the quantum mechanics of black holes, Unruh discovered the Unruh effect  and the Unruh vacuum around black holes. His work has concentrated on the overlap between quantum mechanics and gravity, leading to work on the nature and measurement of time, the study of (non-)non-locality. in quantum mechanics, the quantum origin of matter in early cosmology, the impact of quantum mechanics on the detectors of gravitational waves, and other effects in the same general area. He holds a number of honors including Fellowships in the Royal Societies of Canada and of London, and is a Foreign Honorary Member of the American Academy of Arts and Sciences. At present he is Professor of Physics and Astronomy at the University of British Columbia; Distinguished Research Chair at the Perimeter Institute; and Research Professor at Texas A&M University.

The lecture is free and open to the public, but registration is requested

Abstract: Harnessing the behavior of complex systems is at the heart of quantum technologies. Precisely engineered ultracold gases are emerging as a powerful tool for this task. In this talk I will explain how ultracold strontium atoms trapped by light can be used to create optical lattice clocks – the most precise timekeepers ever imagined. I am going to explain why these clocks are not only fascinating, but of crucial importance since they can help us to answer cutting-edge questions about complex many-body phenomena and magnetism, to unravel big mysteries of our universe and to build the next generation of quantum technologies.  

Abstract:  The CPT theorem is a well-known and well-established fundamental result in relativistic quantum field theory (QFT), stating that any such theory will be invariant under a sequence of transformations consisting of time reversal (T), spatial inversion (P), and charge conjugation (C). In my talk I will show how this combined transformation arose in the work of Julian Schwinger, Gerhart Lüders, Wolfgang Pauli and John Bell, in particular in the search for an adequate relativistic and field-theoretic generalization of the notion of time reversal in the early 1950s. I will thus aim to explain the surprising fact that the CPT theorem was first proved a couple of years before taking center stage with the discovery of parity violation in 1957. (Based on joint work with Andrés Martínez de Velasco.)

At the request of the Climate and Diversity Committee, a survey on mental health and wellness was administered this winter to graduate students in the School of Physics and Astronomy.  The survey was administered by Boynton Health Services in partnership with the Council of Graduate Students' (COGS) and Professional Student Government (PSG) Mental Health & Wellness Committee.  More than a dozen other departments have participated in this survey project since it was first developed in 2013 in cooperation with the Chemistry Department.  This is the second time we have participated in this survey; the last time was in 2018.

The goal is to assess the state of mental health and wellness among graduate and professional students, including risk and protective factors.  Following completion of the survey, each participating School holds a meeting of graduate students,faculty, and staff in which Dr. Lust (Epidemiology and Community Health) shares the results of the survey.  This year we will follow the roughly 30-minute presentation with breakout sessions facilitated by members of the Climate and Diversity Committee where we will explore the implications of the findings and how they might be addressed by follow-up actions.  All this will happen in person in the various conference rooms with refreshments served. An online option is also available.

My lab studies how the movement and shape of living cells is controlled by the dynamic biomolecular assemblies within the cell interior. In this talk, I will describe my lab’s recent efforts to understand the design principles of the active, soft materials that control the shape and motion of adherent cells. In particular, we are interested in the design principles by which protein-based materials generate, relax, sense, and adapt to mechanical force. Here I will describe our current experimental efforts using optogenetic approaches to elucidate design principles of living matter.

Neutron star binary mergers are powerful and distinctive sources of gravitational waves but also leave behind broadband electromagnetic radiation in the form of gamma-ray bursts, afterglows, and kilonovae. Multimessenger observations of them can be remarkably illuminating in topics from fundamental physics to cosmology to nucleosynthesis. To date, LIGO and Virgo have detected several neutron star mergers, one with an exceptionally bright and well-studied electromagnetic counterpart. Electromagnetic follow-up of gravitational-wave sources is highly rewarding but also highly challenging because telescopes may have only hours to scan over the LIGO/Virgo/KAGRA localization before the blast reddens and fades beyond detectability. I will discuss several interconnected topics related to observing neutron star mergers from the ground and space: ground-based kilonova searches with the Zwicky Transient Facility, a proposed NASA mission for rapid ultraviolet observations of mergers, next-generation algorithms and software to optimally coordinate follow-up with networks of telescopes, and what to expect from the upcoming observing run of LIGO, Virgo, and KAGRA.

Here's the link to sign up to meet with him.

As a child, I was fascinated by television programs about Flash Gordon. His partner in conquering the universe was Dr. Alexis Zarkov, a physicist, who had invented, among other things, a death ray gun. In my senior year of high school, I had a fabulous physics teacher, Lewis E. Love, and I knew after one week that I wanted to be a physicist, not a medical doctor, which is the career my parents wanted me to pursue.

In the late 1970s I had the inspiration to acquire an excimer laser for the Laser Physics and Chemistry group at IBM. Using this laser, my colleagues and I discovered excimer laser surgery, capable of removing human and animal tissue with great precision, while leaving the underlying and adjacent tissue free of collateral damage. This discovery laid the foundation for the laser refractive surgical procedures of PRK and LASIK, which have been used to improve the visual acuity of >50 million people, including my son Keith, General Mark Milley, and Michelle Obama.

Today, I am working on validating my concept that the argon fluoride excimer laser can serve as a “smart scalpel,” capable of debriding necrotic lesions of the skin without damaging the underlying and adjacent viable tissue, leading to faster healing, reduced pain, reduced probability of infection, and minimal scarring.

I will describe these innovations and the path to their discovery.

To quote Louis Pasteur, “Chance favors the prepared mind!”

Comets: The Rosetta Stone of the Solar System

Join the Minnesota Institute for Astrophysics for our upcoming Public Lecture Series. Professor Robert Gehrz will be describing the origin of comets and their relationship to the formation and evolution of the solar system.

Find out more about the MIfA Public Lecture Series

Abstract:  Why do we stop growing, live for 100 years and sleep 8 hours a day? Why do all companies and people die whereas cities keep growing and the pace of life continues to accelerate. And how are these related to innovation, wealth creation social networks, urbanization and the long-term sustainability of the planet? These are among the questions that will be addressed in this lecture. Although life is probably the most complex and diverse phenomenon in the Universe, many of its fundamental characteristics scale with size in a surprisingly simple, universal fashion: metabolic rate, for example, scales systematically from cells to whales, while time-scales from lifespans to growth-rates, and sizes from genome lengths to tree heights, do likewise. Remarkably, cities, companies and universities exhibit similar systematic scaling: wages, profits, patents, crime, disease, and roads all scale approximately universally. The origin of these laws will be explained and a conceptual framework based on generic principles of the underlying networks that sustain life from circulatory systems to social networks will be presented. Their dynamics, which transcend history, geography and culture, have dramatic implications for growth and long-term global sustainability and collapse.