Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session S05: Physics and ComputationInvited Live
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Sponsoring Units: FHP DCOMP Chair: Samuel Fletcher, University of Minnesota |
Monday, April 19, 2021 1:30PM - 1:57PM Live |
S05.00001: Computer simulations and large-scale structure formation Invited Speaker: Melissa Jacquart ~Scientific models and computer simulations are indispensable to scientific practice. Through~their use, physicists are able to learn about how the world works, and to discover~new information. However, there is a challenge in understanding how physicists can~generate knowledge from their use, stemming from the fact that simulations are necessarily incomplete representations and partial descriptions of their~target systems. In order to construct a simulation, one must make idealizations,~approximations, and abstractions.~In this talk, I focus on the role of idealization and representation in large-scale structure formation simulations. This case provides the opportunity to study the precise ways that idealization~and representational trade-offs enter into the construction of simulations, and how they~may determine values for simulation parameters. I argue that the use of simulation code~that is flexible enough to de-idealize representations plays a specific role in reasoning about~results in the context of astrophysics. This is particularly salient when the simulations aim to~connect a vast array of independent astronomical observations/phenomena to~cosmologists' more global arguments. [Preview Abstract] |
Monday, April 19, 2021 1:57PM - 2:24PM Live |
S05.00002: \textbf{Simulation Model Skill in Cosmology} Invited Speaker: Eric Winsberg What role can/could simulation play in supporting, puzzle-solving, modifying, disconfirming, or falsifying $\Lambda $CDM and its competitors? I review some of the problems cosmologists have solved or hope to solve using computer simulation, and examine some of problems and successes that have emerged. I draw some conclusions regarding the kind of simulation model skill we should expect to find in Cosmology. [Preview Abstract] |
Monday, April 19, 2021 2:24PM - 2:51PM Live |
S05.00003: Cosmology in Silico Invited Speaker: Marie Gueguen Simulations play an~ineliminable role~in~contemporary~cosmology. Given the enormous range of processes~involved-from stars forming to clusters of galaxies and cosmic filaments- and their non-linear nature, only numerical simulations can tell us what the standard cosmological model implies for structure formation. Simulations are thus~indispensable to extract predictions from models, but also to supplement sparse or non-existing observations, and to help designing the observational surveys. This ubiquity of simulations~in~cosmology~raises an important concern.~Indeed, a few astrophysicists have~insisted that simulations suffer from numerical artefacts that none of the traditional methods to assess their reliability have successfully detected. These artefacts significantly impact our ability to track the logical consequences of the physical model implemented. As a result, when simulations fail to reproduce observations, there is no tool available to determine whether this discrepancy stems from numerical artefacts or constitutes a genuine failed prediction, and thus a motivation to revise our models. Yet, not only this concern has been neglected, but the race to an ever-increased resolution and more realistic simulations have made the problem even more complex.~In~this talk, I present a new method for evaluating the reliability of cosmological simulations, based on the reasoning of these astrophysicists who have contested traditional procedures for verifying simulations. [Preview Abstract] |
Monday, April 19, 2021 2:51PM - 3:18PM Live |
S05.00004: On the status of Landauer's principle Invited Speaker: Katie Robertson Maxwell's demon is a creature who cunningly violates the second law of thermodynamics. In what sense is such a demon possible? Whilst thermodynamics legislates against such a creature, the demon looks eminently possible according to the underlying classical or quantum dynamics: Poincare's recurrence theorem and Loschmidt's reversibility objection reveal that entropy can decrease in certain situations. The orthodoxy is that Maxwell's demon is vanquished by Landauer's principle, according to which there is an entropy cost to reset the demon's memory - a vital step in the cyclic process that supposedly leads to a violation of the second law. But the status of Landauer's principle is controversial: some take it as obviously true, others (such as John Norton) have criticised the proofs of this principle. In this talk, I clarify the status of Landauer's principle. First I discuss which assumptions are required to establish Landauer's principle, and argue that establishing to which theory (thermodynamics, statistical mechanics or quantum mechanics) these principles belong reveals the status of Landauer's principle. I then consider one of Norton's counterexamples to Landauer's principle, and discuss how it depends on certain views about the physical implementation of computation. [Preview Abstract] |
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