Randy tells Jim about photonic molecules, pairs of photons that create bound states like molecules do through a force mediated through an ultracold gas and similar ideas in optical circuits. They also discuss application of the same for quantum computing.
In this episode Jim and Randy talk about how to evaluate alternative gravity theories. What sort of things do we want them to explain, what experiments do they have to predict, and what theoretical requirements do they have to meet. This is in some ways a continuation of Episode 9 - f(R) Theories of Gravity, but the discussion is relevant to all attempts to amend gravitational theory.
In the program, Randy talks about the outline I sent him. I put that up on the Physics Frontiers Blog.
Jim and Randy discuss gravitational theories that modify general relativity by changing the action using a polynomial dependence on the Ricci scalar. Although not physically motivated, some of these theories produce effects similar to those of dark matter, dark energy, and cosmological constants.
Jim and Randy discuss how vacuum fluctuations produce the van der Waals forces and the Casimir effect. Van der Waals forces are factors in atomic bonds and the Casimir effect produces an attractive force between nanoscale objects. The claim is that vacuum fluctuations -- the production and annihilation of particle-antiparticle pairs -- are the underlying reason for both effects.
Randy discusses what the Cosmological implications of a negative gravitational mass would be with Jim. If there were a negative gravitational mass (as opposed to inertial mass), then every time that an electron-positron pair was created in the vacuum, that would create a gravitational dipole. This in turn would create effects similar to dark matter, dark energy, and a cosmological constant -- and this in turn would have an effect on the origin of the universe.
Randy shares some of his favorite papers with Jim: papers on general relativity by engineer and science fiction author Robert L. Forward on how general relativity could be used in a terrestrial environment, including proposals for devices and materials. These papers are "General Relativity for the Experimentalist" and "Guidelines to Antigravity."
Randy and Jim discuss a physical analogy to quantum mechanics consisting of a droplet of fluid bouncing off of the waves in a similarly composed fluid that were generated by the droplet's own bounces. The analogy is very close to the de Broglie-Bohm interpretation of quantum mechanics.
Randy talks to Jim about gravitoelectromagnetism. Based on the similarity between Newtonian gravity and electrostatics, there should be a second gravitational field,the gravitomagnetic field. What are the implications of the existence of such a field, and how large are those effects?