Entropic Gravity

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Recorded: 4/4/2019 Released: 5/3/2019

Randy and Jim discuss Eric Verlinde's theory of emergent gravity that relies on statistical methods to produce both gravitational attraction and inertial effects.
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Notes:

1. The papers we read for this program:

• Verlinde ,E., " On the Origin of Gravity and the Laws of Newton." J. High Energ. Phys. 2011, 2011:029 (2011). [arXiv]
• Tortora, C., "Testing Verlinde's emergent gravity in early-type galaxies." Mon. Notices Royal Astron. Soc. 2324, 214004 (2018). [arXiv]

2. Additional related paper I half-read and we discussed:

• Verlinde, E., "Emergent Gravity and the Dark Universe" SciPost Physics. 2, 10.21468 (2016). [arXiv]

3. Related Episodes of Physics Frontiers:

• Physics Frontiers 10: Requirements for Alternative Gravity Theories
• Physics Frontiers 31: The Parameterized Post-Newtonian Framework

4. 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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The Chameleon Field

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Recorded: 11/3/2019 Released: 2/24/2019

Randy and Jim discuss the chameleon field - scalar field that mimics the effects of dark energy.
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Notes:

1. The papers we read for this program:

• Khoury, J. and A. Weltmann, " Chameleon Fields: Awaiting Surprises for Tests of Gravity in Space." Phys. Rev. Lett. 90, 171104 (2004). [arXiv]
• Khoury, J., "Chameleon Field Theories." Class. Quantum Grav. 30, 214004 (2013). [arXiv]
• Khoury, J., "Detecting Dark Energy in Orbit – the Cosmological Chameleon" Phys. Rev. D 70, 123518 (2004). [arXiv]

2. Related Episodes of Physics Frontiers:

• Coming Soon

3. 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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The Octonions

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Recorded: 10/20/2018 Released: 12/23/2018

Randy tells Jim about the octonions, a cousin to the complex numbers in eight dimensions that Cohl Furey has made some headlines with by categorizing elementary particles with them. By looking at, basically, stable sets in the octonions, she has found representations that act like the elementary particles, and found ways to characterize some of their parameters, e.g., the charge, with them.
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Notes:

1. The papers we read for this program:

• Furey, C., "Unified Theory of Ideals" Phys Rev D 86, 025024 (2012). [Free]
• Furey, C, "Three Generations, Two Unbroken Gauge Symmetries, and One Eight-Dimensional Algebra" Phys Lett B 785, 84 (2018). [Free] [Supplement]

2. Related Papers:

• Furey, C., "Standard Model Physics from an Algebra" PhD. Thesis.
• Baez, J., "The Octonions." Bull. Amer. Math. Soc. 39 145 (2002).
• The Quanta magazine article that got Randy interested.

3. Related Episodes of Physics Frontiers:

• Physics Frontiers 35: The String Theory Landscape
• Physics Frontiers 30: The Consistent Histories Interpretation of Quantum Mechanics

4. Books mentioned in this podcast:

• Crowe, Michael, A History of Vector Analysis. A little bit dry, but a third of the book is about Hamilton and the quaternions.
• Whitehead, A.N., Process and Reality. If you think you're smart, try this.
• Fano and Fano, Physics of Atoms and Molecules. Lots of perturbations. That's what I remember.

5. John Baez' webpage for all things octonion.

6. Cohl Furey's video series on the octonions and the standard model.

6. 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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Negative Effective Mass

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Recorded: 9/29/2018 Released: 12/9/2018

Randy introduces Jim to gravitational effects on quasiparticles in materials. The inertial quality of the mass of a quasiparticle gets modified by the lattice, giving rise to an effective mass in the material. But how does the effective mass behave when confronted with a gravitational field?
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Notes:

1. The papers we read for this program:

• Raum, K., M. Weber, R. Gahler, and A. Zeilinger, "Gravity and inertia in neutron crystal optics and VCN interferometry" J Phys Soc Jpn 65, 227 (1996). [Free]
• Wimmer, M., A. Regensburger, C. Bersch, M.-A. Miri, S. Batz, G. Onishchukov, D.N. Christodoulides, and U. Peschel, "Optical Diametric Drive Acceleration through Action-Reaction Symmetry Breaking" Nature Physics 9, 780 (2013). [Free] [Supplement]

2. Related Papers:

• Coletta, R., A.W. Overhauser, and S.A. Werner, "..." Phys Rev Lett 34 1472 (1975).
• Raum, K., M.Koellner, A. Zeilinger, M. Arif, and R. Gahler, "Effective Mass Enhanced Deflection of Neutrons in Noninertial Frames" Phys Rev Lett 74, 2859 (1995). [Free]
• Bondi, H. "Negative Mass in General Relativity," Rev Mod Phys 29 423 (1957)
• Foreward, R.L., "Negative Matter Propulsion", J Prop Power 6 28 (1990) .
• I'm saving this for later.

2. Related Episodes of Physics Frontiers:

We referenced a lot of old episodes in this one:

• Physics Frontiers 31: The Parameterized Post-Newtonian Framework
• Physics Frontiers 29: Gravitational Alternatives to Dark Energy
• Physics Frontiers 25: Gravitational Field Propulsion
• Physics Frontiers 23: Dark Energy
• Physics Frontiers 22: Weyl and Quasiparticles
• Physics Frontiers 13: Exotic Photon Trajectories in Quantum Mechanics
• Physics Frontiers 6: General Relativity for the Experimentalist

Don't bother looking for our discussion of Manu Paranjape's essays on the "possibility of generating an negative effective mass in space-time" in the episode entitled "The Positive Energy Theorem." We're working on getting those up, but there's a content issue that we may not be able to resolve.

3. Books mentioned in this podcast:

• I mentioned that some of this is textbook stuff, when Jim Napolitano finished J.J. Sakurai's Modern Quantum Mechanics, he included he discusses Colletta, Overhauser and Werner's gravity induced phase changes that can be measured through interferometry. Somewhere Napolitano writes that he includes these interesting tidbits because he is an experimentalist and thinks it's helpful for understanding. I just know they're fun. Be advised that, although it's not as heavy going as Cohen-Tannoudji (which, thanks only to the trauma induced by graduate school, I somehow spelled right), is a graduate level quantum mechanics textbook. Just a very well written one.

4. You can watch Martin Tejmar's talk at the 2016 breakthrough propulsion workshop put on by the Space Studies Institute

5. Martin Tejmar's group at TU-Dresden, and his publications page.

6. 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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The Dimensionality of Space Time

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Recorded: 9/8/2018 Released: 11/25/2018

Jim and Randy discuss why space-time is four dimensional. Much of what they discuss is anthropic in nature: what sort of universe can we exist in? But they also discuss the stability of orbits, the predictability of nature, and so on, all of which constrain the universe to have three (3) macroscopic dimensions of space and one of time (or one of space and three of time, but that's not us).
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Notes:

1. The papers we read for this program:

• Tegmark, M., "On the Dimensionality of Spacetime" Class Qunatum Grav 14, L69 (2009). [arXiv]
• Freeman, I.M., "Why Is Space Three-Dimensional? based on W. Buechel, "Warum hat der Raum drei Dimensionen?"" Am J Phys 37, 1222 (1969).

2. Other papers mentioned in this program:

• Dorling, J., "The Dimensionality of Time" Am J Phys 38, 539 (1970).
• Randy mentioned that Ken Wharton was working on a review of retrocausal models, which doesn't seem to have come out yet, but he has a more recent paper, "A New Class of Retrocausal Models" [arXiv that came out in Entropy.

3. Related Episodes of Physics Frontiers:

• Physics Frontiers 35: The String Theory Landscape
• Physics Frontiers 33: Retrocausality
• Physics Frontiers 17: The 2T Physics of Itzhak Bars

4. Books mentioned in the podcast:

• Tegmark talked about results discussed in Gravitation by Misner, Thorne and Wheeler. This is a standard text in the field, which I'm sad to say I never picked up. Although I did order a copy last week, and its on its way to my office right now.
• After recording the podcast, I decided I needed to look a little deeper at partial differential equations. I failed because I started reading Partial Differential Equations for Scientists and Engineers by Farlow. The presentation is very practical, not theoretical, so it doesn't address the problems in this podcast directly. However, the methods used in the text seem to directly contradict the general discussion in Tegmark (since every problem is both an initial value problem and a boundary value problem, simultaneously). I haven't worked my way through it, so maybe I'll change my mind, but not at present. I have fallen in love with the presentation. I think that if you'd like to learn to solve PDEs and have a sufficient background, this is the book for you (because this book makes me feel smart).

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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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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