Alpha Orionis, popularly known as Betelgeuse, is a nearby red supergiant star visible to the naked eye. In light of the star's "Great Dimming"—a sudden, extreme drop in brightness that occurred in early 2020—a recent controversy surrounding Betelgeuse concerned whether it would explode as a supernova within the next few years, centuries, or millennia. Using a series of numerical techniques including one-dimensional stellar evolution models, hydrodynamic simulations, linear oscillation calculations, Fourier analysis, and the methods of a subfield of stellar astrophysics known as asteroseismology, my collaborators and I constrained the timeline for Betelgeuse's demise and revised many of the best estimates for its fundamental properties. In doing so, we discovered not only that Betelgeuse was not likely to undergo an imminent detonation, but that a pulsation signal unexplained by our models was, in fact, the signature of an as-yet-undiscovered binary companion. Its presence was confirmed earlier this year. What we never managed to do was explain the Great Dimming.

In this talk, I will use the story of the discovery of Betelgeuse’s hidden, low-mass binary companion, Alpha Orionis B—affectionately nicknamed “Betelbuddy”—both to highlight the computational and numerical techniques employed in modern stellar astrophysics and to illustrate how the most meaningful discoveries often arise not from confirming what we set out to find, but from venturing down the rabbit holes of unexpected problems that emerge along the way.

Nuclear spins are usually not thought to participate in chemical reactions. However, in the ultracold temperature regime, we have a new opportunity to examine this general statement with quantum mechanical details. In this talk, I will present our ongoing investigations into the roles of nuclear spins, quantum coherence, and entanglement in molecule-molecule reactions and atom-molecule collisions, utilizing a one-of-a-kind ultracold KRb molecule apparatus inspired from the original set of JILA KRb experiments 17 years ago. In addition to observing quantum interference in atom-exchange reactions [Science 384, 1117 (2024)], we hope to shed light on the puzzle of reaction complexes that live 5 orders of magnitude longer than expected.

The Department of Biochemistry invites professors and scientists from other universities and institutes to present seminars at the University of Colorado Boulder throughout the academic year. These seminars provide an opportunity for faculty and students to learn about exciting current research.

Abstract: The mineralogy of our planet is a fingerprint of history—a durable archive of the physical and chemical conditions that have evolved over 4.5 billion years. Minerals record temperatures and pressures, redox states and fluid compositions, preserving evidence that spans the earliest violent collisions of solar-system formation to human activities that occurred only yesterday. Yet Earth’s mineral story reaches far deeper in time, extending back to the very origins of the elements themselves.
This talk traces mineral evolution from the formation of the most rudimentary elements in the first few hundred thousand years after the Big Bang, through the birth of the first stars and the onset of stellar nucleosynthesis, to the creation of the heaviest elements in kilonova explosions. These elements were dispersed into interstellar gas clouds, recycled through multiple generations of stars, and ultimately assembled into planets. The first minerals to form in the universe—diamond and graphite—were forged under extreme conditions and endlessly recycled, providing the elemental backbone for life. Today, roughly 6,000 mineral species are known on Earth; each one offers a distinct window into our cosmic history.

Abstract: Effective field theories (EFTs) form the basis of our most successful theories of matter, both in particle physics and in condensed matter physics. But the structure of EFTs poses a challenge to many standard philosophical accounts of theory structure and content. In particular, the inability to cast EFTs in terms of exact mathematical objects defined at all scales suggests that philosophical accounts of theory interpretation ought to be modified to deal with approximate, scale-relative ontologies. In this talk, I take some preliminary steps toward an alternative approach to theory interpretation, suitable to EFTs as well as other mathematized theories. Starting from the assumption that EFTs currently allow us to successfully learn about the world, I explicate some features the world must have for that to be true.

For the overwhelming majority of organisms, effective communication and coordination are critical in the quest to survive and reproduce. A better understanding of these processes can benefit from physics, mathematics, and computer science – via the application of concepts like energetic cost, compression (minimization of bits to represent information), and detectability (high signal-to-noise-ratio). My lab's goal is to formulate and test phenomenological theories about natural signal design principles and their emergent spatiotemporal patterns. To that end, we adopted insect swarms as a model system for identifying how organisms harness the dynamics of communication signals, perform spatiotemporal integration of these signals, and propagate those signals to neighboring organisms. In this talk, I will focus on two types of communication in insect swarms: visual communication, in which fireflies communicate over long distances using light signals, and chemical communication, in which bees serve as signal amplifiers to propagate pheromone-based information about the queen's location. Through a combination of behavioral assays and computational techniques, we develop and test model-driven hypotheses to gain a deeper understanding of these communication processes and contribute to the broader understanding of animal communication.

CU Physics Prof. James Thompson explains how superheroes' understanding of fundamental physics ensures truth and thwarts villains! Sparks, explosions and plenty of action will punctuate this free STEM show that's open to students of all ages.

For over 40 years, CU Wizards presents FREE STEM Saturday morning shows for kids and their families. Visit: www.colorado.edu/cuwizards

Almost exactly 100 years ago, in the early months of 1926, Erwin Schrödinger published a series of four papers that would transform not only the prevailing theories of physics but also mankind’s very understanding of the nature of reality.  Though his work indisputably built upon the ideas of countless others, these papers crystalized the central and most astounding claim of what has become modern quantum mechanics: that at its heart, nature can be understood not as a collection of particles interacting in space but as the endless oscillation of an unseen “wavefunction,” which silently tallies and updates the probabilities of future events. In this talk, we will discuss the historical backdrop of these four transformative papers and then unpack the mathematical and physical innovations they contain (no background knowledge of math or physics is assumed). Finally; we will trace their centennial trajectories through the ensuing years, to reveal the enduring importance of these timeless papers, whose insights—and mysteries—have both only deepened with age. 

The Department of Biochemistry invites professors and scientists from other universities and institutes to present seminars at the University of Colorado Boulder throughout the academic year. These seminars provide an opportunity for faculty and students to learn about exciting current research.

Abstract: Low energy collisions between molecules in the atmosphere lead to about 50% of the particles that act as the seeds for cloud droplets. Many of these molecules, and many of the other particles, are the result of human activity. Therefore cloud droplet concentrations have increased over the industrial period. The increase has led to a poorly quantified cooling effect on Earth that has offset perhaps a third of historical warming from greenhouse gases. The CLOUD experiment at CERN is a laboratory facility for the study of atmospheric particle formation. In my talk I will show how we are using results from this facility to represent this process better in climate models. As particle formation in the atmosphere is strongly dependent on meteorology, it is also critical to study how it happens in situ and to test our models with real observations. I will show how we are characterizing the process using aircraft measurements, in areas including the Front Range and the remote Southern Ocean.
 

Bio: Hamish Gordon is an associate professor in the Department of Chemical Engineering and the Center for Atmospheric Particle Studies at Carnegie Mellon University. His research interests are focused on the effects of air pollution and natural airborne particles on clouds and climate. He received his first degree from the University of Cambridge in 2009, and his doctorate from the University of Oxford in experimental high energy physics in 2013. After postdoctoral positions first at CERN and then at the University of Leeds, he moved to Carnegie Mellon in 2019. In 2025 he was awarded an NSF CAREER grant for a proposal titled "Role of new particle formation in pre-industrial climate" and served as a forecaster and mission scientist for the HALO-South aircraft campaign from Christchurch, New Zealand.

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Spin glasses are canonical examples of complex matter and form a basis for describing artificial neural networks.  Repeatable control over microscopic degrees of freedom might open a new window into their structure and dynamics.  I will present how we achieved this at the atomic level using a quantum-optical system comprised of ultracold gases of atoms coupled via photons resonating within multimode cavities.  The controllability provided by this new spin glass system has allowed us to directly measure spin dynamics and replica symmetry breaking, yielding the first direct observation of ultrametricity in a physical system.  We use this spin glass to realize an associative memory with a capacity exceeding that of the Hopfield model.

Continuous-variable quantum systems enable encoding complex states in fewer modes through large-scale non-Gaussian states. Motion, as a continuous degree of freedom, underlies phenomena from Cooper pair dynamics to levitated macroscopic objects. Hence, realizing high-energy, spatially extended motional states remains key for advancing quantum sensing, simulation, and foundational tests.
In the talk, I will present the following control tasks for various nonlinear mechanical systems, including trapped atoms, levitated particles, and clamped oscillators with spin-motion coupling.
(i) Nonharmonic potential modulation: Optimal control of a particle in a nonharmonic potential enables the generation of non-Gaussian states and arbitrary unitaries within a chosen two-level subspace.
(ii) Macroscopic quantum states of levitated particles: Rapid preparation of a particle’s center of mass in a macroscopic superposition is achieved by releasing it from a harmonic trap into a static double-well potential after ground-state cooling.
(iii) Phase-insensitive displacement sensing: For randomized phase-space displacements, quantum optimal control identifies number-squeezed cat states as optimal for force sensitivity under lossy dynamics.
These approaches exploit either intrinsic nonharmonicity or coherent nonlinear coupling, providing a unified framework for motion control in continuous-variable quantum systems—from levitated nanoparticles to optical and microwave resonators—paving the way toward universal quantum control of mechanical degrees of freedom.

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I will discuss the standards of time and frequency and how these standards have evolved over the centuries. I will present the current definitions of time and frequency and how these definitions are likely to evolve in the coming years.

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