Randy introduces Jim to Sabine Hossenfelder's bimetric theory of gravity. In this gravitational theory, there are two types of matter whose only interaction is through gravitation. However, each one reacts to space-time differently, resulting in different metric tensors for each. In low-curvature situations, this creates a kind of anti-gravitation.
Show Notes: http://frontiers.physicsfm.com/47
Randy tells Jim about experiments with Neutrons and Photons in materials that exhibit negative effective mass. Not only do these effects show that the inertial mass of quasiparticles in a material can become negative, they show that these negative mass quasiparticles act like they have negative gravitational mass, as well.
Show Notes: http://frontiers.physicsfm.com/39
Jim discusses why the world we observe is 4-dimensional with Randy. We discuss anthropic and fundamental reasons why we need 3 dimensions and no more than one time dimension for reasons of complexity, predictability and stability.
Show Notes: http://frontiers.physicsfm.com/38