The Einstein-Cartan Torsion Field Theory

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Recorded: 6/10/2018 Released: 10/29/2018

Randy explains some recent developments in the Einstein-Cartan torsion field to Jim. This theory introduces at least one tensor field representing the intrinsic angular momentum at a space-time point, and was originally intended to remove singularities from general relativity.
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Notes:

1. The papers we read for this program:

• Minkevich, A.V., "Accelerating Universe with spacetime torsion but without dark matter and dark energy" Phys Lett B 678, 73 (2009). [arXiv]
• Poplawski, N., "Nonsingular Dirac Particles in Spacetime with Torsion" Phys Lett B 690, 73 (2010). [arXiv]
• Poplawski, N., "Spacetime torsion as a possible remedy to major problems in gravity and cosmology." J. Astron. Rev. 8, 180 (2013). 1745-1749. [arXiv]

2. My review of Will's book. This paper serves as something of an update of it. A true update is scheduled to come in December 2018.

3. Related Episodes of Physics Frontiers:

• Physics Frontiers 33: The Positive Energy Theorem
• Physics Frontiers 29: Gravitational Alternatives to Dark Energy
• Physics Frontiers 27: Gravitational Equivalence Principles
• Physics Frontiers 23: Dark Energy
• Physics Frontiers 10: Requirements for Gravitational Theories
• Physics Frontiers 9: f(R) Theories of Gravity

4. Contact Randy at randy@physicsfm.com to take him up on his offer. Actually, I don't know if those e-mail redirects really work. I set them up some time ago, but I've never seen anything come in from them.

5. Please visit and comment on our subreddit, and if you can help us keep this going by contributing to our Patreon, we'd be grateful.

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Metamaterial Stress Tensor

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Recorded: 5/26/2018 Released: 10/14/2018

Randy tells Jim about advances in the stress-momentum tensor of electrodynamics. This tensor can be integrated over the boundary of an object to describe the force on it from the magnetic field. It is closely related to the momentum carried in the electromagnetic field, and its proper formulation in materials has been the subject of debate for over a hundred years.
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Notes:

1. The papers we read for this program:

• Wang, S., J. Ng, C.T. Chan, "Electromagnetic Stress at the Boundary: Photon Pressure or Tension?" Science Advances 2, e1501485 (2016). [arXiv]
• Wang, N., S. Wang, J. Ng, "Electromagnetic Stress Tensor for Amorphous Metamaterial Medium." Phys Rev A 97, 033839 (2018). 1745-1749. [arXiv]

2. Our Patreon backers can see the Table of Stress Tensors I made for the podcast.

3. Other papers mentioned:

I found these papers useful for this program:

• Brevik, I., "Expriments in Phenomenological Electrodynamics and the Electromagnetic Energy-Momentum Tensor." Phys Rep 52 133(1979). [CiteSeerX]
• Barnett, S.M., and R. Loudon, "The Enigma of Optical Momentum in a Medium." Phil Trans R Soc A 368 927(2010)

4. Books mentioned in this podcast:

• J.D. Jackson's Classical Electromagnetism, discusses the Maxwell stress tensor twice: in a discussion about of conservation laws in macroscopic media (pp 239-40) and then in a discussion about forces in special relativity (pp 602-607). Page numbers from my copy of the 2nd edition.
• Landau & Lifshitz' Electrodynamics of Continuous Media goes into more depth on how the stress tensor is derived. Beyond being one of my favorite books in grad school, the entire series is classic.
• M. Schwartz' Principles of Electrodynamics (available from Dover, probably because of Schwartz' Nobel Prize, not because its great exposition (which it has)) uses the electromagnetic stress tensor repeatedly in different contexts and problems that gives you a good idea of what it actually means.
• U. Leonhardt and T. Philbin's Geometry and Light: The Science of Invisbility is an excellent technical book of the use of the mathematics of general relativity in optics. This includes the optical analogue of black holes and the photonic Aharonov-Bohm effect.

5. Related Shows:

• Physics Frontiers 22: Weyl and Quasiparticles

8. Randy mentions Harry Reid's Advanced Aerospace Threat Identification Program (AATIP) program, a government UFO program funded from 2007 to 2014. It was run by Luis Elizondo, who Randy mentions in the podcast. Randy says he was directed to this topic by a discussion that Joe Rogan had with Thomas DeLonge who funds AATIP's private successor, To the Stars Academy. Although they focused on things that were out in left field (Harry Reid says he met his wife on a UFO, but no one believed him), you can see from this list that they funded some good research as well (such as Ulf Leonhardt's (see above) and Maxim Tsoi's in spintronics). I didn't count, but it looked to be about a sixth solid research, a sixth reasonable research, as sixth fringy stuff, and a half to EarthTech International.

7. Please visit and comment on our subreddit, and if you can help us keep this going by contributing to our Patreon, we'd be grateful.

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