Physics & Astronomy Colloquium

Thursdays, 4:00-5:00 pm

Virtual Colloquium Meetings are held via Zoom, in-person events in PAB 1-434. Meeting information will be sent in email. You may watch past presentations by clicking the title link when available.

For more information, contact Katsushi Arisaka.

Click here for the 2022-2023 archived Physics & Astronomy Colloquium.

Click here for the 2021-2022 archived Physics & Astronomy Colloquium.

Click here for the 2020-2021 archived Physics & Astronomy Colloquium.

Click here for the 2019-2020 archived Physics & Astronomy Colloquium.

Fall 2023

Thursday, September 28, 2023

The Biggest and Darkest Questions in The Universe
Tom Melia
Kavli IPMU, Tokyo University

Abstract: At this very moment in time, the big, dark machines of physics are telling us some extraordinarily big, dark answers about the universe. The only problem is, we can not make sense of them. This implies the next great leap in our understanding of the universe is just around the corner. The stakes are particularly high: never before in science have puzzles been framed so sharply, yet gone unsolved by an entire generation of the brightest minds. What a time to be a physicist!

So, in this colloquium, I'll address the biggest and darkest questions of the universe. The big questions about what we do know, i.e. the standard model, and the big questions about what we dont know, i.e. everything dark out there in the cosmos. And I'll describe some new and novel ways in which we might be able to make sense of it all, including a radical re-examination of two of the most famous equations in physics.

Thursday, October 5, 2023

Quantum materials for eventual quantum computing
Vivien Zapf
Los Alamos National Lab

I will review two routes to quantum materials that are being studied in the context of eventual quantum computing. The first is molecule-based magnetic compounds where spins can function as qubits. These molecule-based materials have unique magnetic functionalities that differ from those of inorganic materials and are intriguing to study. This field is seeking long coherence times for spins and methods to control and architecture them into devices. In particular we investigate how symmetry principles can be used to design magnetoelectric coupling so electric voltages can control spins and vice versa.

The second topic is quantum spin liquids. In certain spin liquids, quasiparticles are predicted to have topological properties and their braiding properties could be used for topologically-protected quantum computing. Both of these topics are in the scientific discovery stage and offer rich potential for physics discovery as well as being motivated by eventual applications. This work is funded by LANL, the NSF, and DOE - in molecular materials Zapf is a thrust lead for an Energy Frontier Research Center on molecule-based materials. In quantum spin liquids, Zapf is the deputy director of the Quantum Science Center, a DOE-funded National Quantum Initiative center.

Thursday, October 12, 2023

A Career in Astronomical Instrumentation
Ian McLean

My career began with a degree in Physics and Astronomy from the University of Glasgow, Scotland in 1971. Although other paths were open to me, I was inspired by one of my astronomy instructors, David Clarke, who captured my imagination during my upper division years with his ideas about using modern (1970s!) technology to build better telescopes, new optical instruments, and improved astronomical detectors. I did not know for sure where this path would take me, but during my thesis work I soon learned that a novel instrument would yield new science. My first instrument (University of Glasgow 1971-1974), designed for a 24-inch (0.61-m) telescope, used two photomultiplier tubes for optical detection, and was capable of scanning the H-alpha and H-beta lines of relatively bright stars while measuring sequentially the linear or circular polarization and flux at each point in the scan. Compare this to MOSFIRE, the multi-object spectrograph for the 10-m Keck telescopes in Hawaii, which has a four megapixel wide-field near-infrared camera that can record simultaneously up to 46 medium-resolution spectra of very faint sources.

Delivered in 2012, MOSFIRE was led by the UCLA Infrared Lab, which I established here at UCLA in 1989 when Eric Becklin and I joined the faculty. In 2017, four and a half decades after my first degree, the American Astronomical Society honored me with the Joseph Weber Award for lifetime achievements in Astronomical Instrumentation. Many impactful technological breakthroughs occurred in the decades since 1971. Using descriptions of the instruments I have built and used over the years, I will illustrate how these events influenced the twists and turns of my career path and research experience.

Thursday, October 19, 2023

Early Galaxies and the (re)ionization of Intergalactic Hydrogen
Stuart Wyithe
Australian National University

Astrophysics seeks to both understand how the Universe works today, and to uncover how it formed and evolved throughout cosmic history. Fortunately, the finite speed of light allows us to view the Universe at large distances as it existed in the past. Recently the James Webb Space Telescope has further revolutionized our knowledge of the earliest galaxies in the Universe, pushing the epoch where galaxies are known to be forming stars out to z~15, only a few 100 million years after the big bang. The ionizing radiation from these early stars ionized and heated hydrogen throughout the Universe, a process referred to as reionization which is constrained to end at a redshift of ~5, approximately 10 billion years later. The evolution of cosmic hydrogen is tightly coupled with the formation of galaxies and is being studied by current and forthcoming radio telescopes including the Square Kilometer Array. In this talk I will present results from simulations that aim to describe this coupled evolution, including the implications of recent high redshift observations with the James Webb Space Telescope, and how early galaxy properties will be measured using the Square Kilometer Array.

Thursday, November 02, 2023

FASER and the Future of Particle Physics
Jonathan Feng
University of California, Irvine

Particle physics is at a critical juncture. All the particles of the Standard Model have been discovered, but no new ones have appeared, and there are still many outstanding questions. In recent years, it has become clear that the physics potential of the Large Hadron Collider at CERN has not been fully explored. In particular, forward collisions, which produce particles along the beamline with enormous rates, have been almost completely ignored. It turns out that these collisions are a treasure trove of physics, containing the highest-energy neutrinos ever produced by humans, possible evidence for dark matter, milli-charged particles, and new forces, and a wealth of other valuable information. This talk will describe FASER, the Forward Search Experiment, which was constructed in 18 months and has just released its first physics results, as well as the Forward Physics Facility, a proposal to fully realize the potential of forward physics in the High Luminosity LHC era.