Event Time: Wednesday, March 3, 2021 | 11:00 am - 12:00 pm
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Add to Calendar 2021-03-03T11:00:00 2021-03-03T12:00:00 Minisuperspacetime Foam Event Information: It has been suggested that Planck-scale "spacetime foam" could have significant macroscopic consequences, perhaps even offering a way to address the cosmological constant problem.  I will describe progress in constructing a locally spherically symmetric minisuperspace model with a positive cosmological constant that may shed light on these questions.  Classically, the model includes spacetimes that contain both expanding and contracting regions.  Quantum mechanically, the Wheeler-DeWitt equation is relatively tractable, and has stationary solutions, although as usual there are interpretational ambiguities. The model may also admit instantons that describe the nucleation of contracting regions in an exponentially expanding spacetime. Results so far are quite incomplete, but the approach seems promising. Event Location: Connect via Zoom
Event Time: Wednesday, March 10, 2021 | 11:00 am - 12:00 pm
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Add to Calendar 2021-03-10T11:00:00 2021-03-10T12:00:00 Gravitational coupling of microscopic source masses: challenges for future quantum Cavendish experiments Event Information: No experiment today provides evidence that gravity requires a quantum description. It has been suggested that one can at least exclude the possibility for semiclassical gravity by performing an experiment whose outcome cannot be explained by a purely classical source mass configuration. It turns out that such “quantum Cavendish” experiments are challenging, to say the least. I highlight some of the practical aspects of this challenge using the concrete example of our recent measurement of the gravitational field of a 1mm gold sphere, the smallest source mass to date in table-top gravity experiments. Event Location: Connect via Zoom