Aspen Center for Physics

2020 Colloquia

Tuesdays at 10 a.m. MDT

via Zoom

Register to Watch Here

30 minute talks followed by Q&A

You will need to register for each talk individually. Please register for one talk and then use the link above to register for an additional talk.

  • June 16, 2020
    Deep Learning and Proteins
    Speaker: Lucy Colwell, Cambridge University
    A central challenge is to be able to predict functional properties of a protein from its sequence, and thus (i) discover new proteins with specific required functionality and (ii) better understand the functional effect of genomic mutations. Experimental breakthroughs in our ability to read and write DNA allows data on the relationship between sequence and function to be rapidly acquired. This data can be used to train and validate machine learning models that predict protein function from sequence. Because in many cases phenotypic changes are controlled by more than one amino acid, the mutations that separate different phenotypes may be epistatic, requiring us to build models that take the correlation structure into account. In this talk we show that such models rival the accuracy of existing hidden Markov models at sequence annotation, even when given relatively little training data. The representation of sequence space learned by the model can be used to build families that the model did not see during training. Finally, we report experimental confirmation that machine learning models can accurately identify variants of the AAV capsid protein that assemble integral capsids and package their genome, for applications in gene therapy.
    Watch the lecture.
  • June 23, 2020
    The Formation and Growth of Supermassive Black Holes
    Speaker: Anna-Christina Eilers, MIT
    Quasars are the most luminous objects in the universe powered by accretion onto supermassive black holes (SMBHs). They can be observed at the earliest cosmic epochs, providing unique insights into the early phases of black hole, structure, and galaxy formation. Observations of these quasars demonstrate that they host SMBHs at their center, already less than ~1 Gyr after the Big Bang. It has been argued that in order to rapidly grow these SMBHs in such short amounts of cosmic time, they need to accrete matter over timescales comparable to the age of the universe, and thus the lifetime of quasars - the integrated time that galaxies shine as active quasars - is expected to be of order ~10^9 yr at a redshift of z~6, even if they accrete continuously at the theoretical maximum limit.

    I will present a new method to obtain constraints on the lifetime of high-redshift quasars with unprecedented precision, based on measurements of the sizes of ionized regions around quasars, known as proximity zones. The sizes of these proximity zones are sensitive to the lifetime of the quasars, because the intergalactic gas has a finite response time to the quasars’ radiation. Applying this method to quasar spectra at z>6, we recently discover an unexpected population of very young quasars, indicating lifetimes of only ~10,000 years, which is several orders of magnitude shorter than expected. I will discuss the consequences of such short lifetimes on the quasars' ionizing power, their black hole mass accretion rates, and highlight tensions with current theoretical models for black hole formation. Furthermore, I will present several modifications to the current SMBH formation paradigm that might explain our results, e.g. super-critical mass accretion rates, massive initial black hole seeds in excess of stellar remnants, or highly obscured quasar growth phases. In the end I will show how we aim to disentangle the various scenarios by means of future observations with the upcoming James Webb Space Telescope, in order to shed new light onto the formation and growth of the first SMBHs in the universe.
    Watch the lecture.
  • June 30, 2020
    Mixing, Climate and the Abyssal Ocean
    Speaker: Raffaele Ferrari, MIT
    Turbulent mixing plays a key role in shaping Earth's climate. This is particularly true in the abyssal ocean which stores massive amounts of heat and carbon. Oceanographers had long realized that the abyssal ocean is filled with cold and carbon-rich waters sinking to the ocean bottom near the poles. The puzzle was how these waters return back to the surface. In other words we have known for a long time how the ocean `breathes' heat and carbon in, but not how it `exhales'. Oceanographer Walter Munk proposed that these waters rise everywhere from the abyss as they are mixed with overlying warmer and lighter waters. Turbulent probes developed over the last forty years have finally provided evidence for turbulent mixing in the abyssal ocean, but in an unexpected twist have also shown that this mixing drives sinking rather than rising of waters. In this presentation we will discuss how this conundrum was resolved by realizing that abyssal waters rise toward the surface along thin boundary layers along the ocean margins.  We will then discuss the implications of this new paradigm for our understanding of Earth's climate.

  • July 7, 2020
    Galactic Phylogenetics
    Speaker: Paula Jofre, Universidad Diego Portales
    Reconstructing the history of galaxies requires understanding the complexity of several astrophysical phenomena, from star formation to supernova yields and galaxy interaction. Combining this information is not trivial, leading us often to a fragmented story of how our own Galaxy assembled.

    Stars are the main carriers of the evolutionary information. They are the main producers of metals in the Universe, inheriting the modified chemical composition down for generations. With their chemical data from spectroscopic surveys, combined with their kinematics from Gaia and their ages from stellar models, we are starting to assemble huge stellar samples that are helping us to put the fragmented stories of Milky Way evolution into one.

    In this talk I will first discuss the challenges our field is facing in assembling the chemical data from spectroscopic surveys into single consistent datasets. Then I will discuss how can we use phylogenetic trees in order to put this vast information together to study the different astrophysical phenomena shaping the evolution of our Galaxy.

  • July 14, 2020
    Higher Order Topological Phases of Matter
    Speaker: Taylor Hughes, University of Illinois Urbana Champaign
  • Topology phases of matter have become a thriving sub-field of condensed matter physics. In this colloquium I will provide an elementary introduction to topological phases of matter, and the new discovery of higher order topology. After the basic discussion I will describe interesting connections between symmetry, geometry, and topology as well as how to create topological phases in artificial dimensions.

  • July 21, 2020
    Topic: From Chaos to Hydrodynamics in Quantum Matter
    Speaker: Pavel Kovtun, University of Victoria

  • July 28, 2020
    Topic: String Theory
    Speaker: Ibrahima Bah, Johns Hopkins University

  • August 4, 2020
    Topic: Nu Intersections: Neutrino Physics at a Crossroad
    Speaker: Andre Luiz De Gouvea, Northwestern University

  • August 11, 2020
    Topic: Dark Matter from the Laboratory to the Cosmos
    Speaker: Kimberly Boddy, Johns Hopkins University

  • August 18, 2020
    Topic: Electronic Topology Across the Correlation Spectrum
    Speaker: Silke Buehler-Paschen, Vienna University of Technology

  • August 25, 2020
    Topic: New Discoveries in the Era of High-Resolution, Low-Noise CMB Experiments
    Speaker: Mathew Madhavacheril, Perimeter Institute

  • September 1, 2020
    Looking for Imprints of Microphysics on Large Scale Structure
    Speaker: Chanda Prescod-Weinstein, University of New Hampshire
  • In this talk, I will describe my efforts to understand the nature of the mysterious dark matter. I provide an overview of the general problem and then describe my current approach to it, which is to characterize the behavior of a proposed dark matter particle, the axion. I will give some insight into how I am using a range of tools – model building, computation, and high energy astrophysics – to get at the basic question of “what is the statistical mechanics of axion dark matter?”