Sabine Hossenfelder's Bimetric Theory of Gravity

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Recorded: 2019/08/15 Released: 2019/11/23

Randy introduces Jim to Sabine Hossenfelder's bimetric theory of gravity. This theory postulates two types of matter that don't interact directly with each other. They both do, however, interact with space-time gravitationally and so indirectly interact with each other.
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Notes:

1. The papers we read for this program:

• Hossenfelder, S., "Anti-Gravitation." Phys Lett B, 6 (2005). [arXiv]
• Hossenfelder, S., "A Bi-Metric Theory with Exchange Symmetry." Phys Rev D 78 044015 (2008). [arXiv]
• Hohmann, M. and M. Wohlfarth, "No-go theorem for bimetric gravity with positive and negative mass." Phys Rev D 80 104011 (2009). [arXiv]
• Hossenfelder, S., "Comment on 'No-go theorem for bimetric gravity with positive and negative mass.'" Phys Rev D 78 044015 (2009). [arXiv]

2. Related Episodes of Physics Frontiers:

• Physics Frontiers 6: General Relativity for the Experimentalist.

3. Links Related to Sabine Hossenfelder:

• Sabine Hossenfelder's Backreaction blog.
• Sabine Hossenfelder's YouTube.
• The Perimeter Institute.

4. Some books we mentioned:

• Smolin, L., The Trouble with Physics [Amazon].

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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Wigner's Friend

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Recorded: 7/18/2019 Released: 9/21/2019

Randy tells Jim about an experiment that purports to have enacted a test of the Wigner's Friend argument -- one that Jim never really cared for. The experiment uses a double Aspect experiment to test whether non-quantum conclusions can be made from multiple experiments on entangled photons. This one is important: according to Wigner, your soul is at stake.
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Notes:

1. The papers we read for this program:

• Wigner, E., "Remarks on the Mind Body Problem." The Scientist Speculates, L.J. Good, ed. (1962). (Lecture). [Free]
• Frauchiger, D., R. Renner, "Quantum Theory Cannot Consistently Describe the Use of Itself." Nat. Commun. 9 3711 (2018). [arXiv]
• Proietti, M., A. Pickston, F. Graffitti, P. Barrow, D. Kundys, C. Branciard, M. Ringbauer, and A. Fedrizzi, "Experimental Rejection of Observer-Independence in the Quantum World.." (2019). [arXiv]
Note: I can't find it published yet, so if you have seen it in print, please let me know.

2. Other articles we discussed:

• Dyson, F., "Innovation in Physics." Scientific American 199(3), 74 (1955).
• Pusey, M., "An Inconsistent Friend." Nature Physics 14 977 (2018).
• Uncredited, "A Quantum Experiment Suggests There's No Such Thing as Objective Reality." MIT Technology Review (2019).
• Brukner, Č. "A No-Go Theorem for Observer-Independent Facts." Entropy 20 (2018). [arXiv]

3. Related Episodes of Physics Frontiers:

• Physics Frontiers 44: Spooky Action at a Distance.
• Physics Frontiers 33: Retrocausality
• Physics Frontiers 30: The Consistent Histories Interpretation of Quantum Mechanics
• Physics Frontiers 18: The 2T Physics of Itzhak Bars
• Physics Frontiers 2: The de Broglie-Bohm Interpretation of Quantum Mechnics

3. Other Podcasts:

• WEP1: The Quantum Bookie

4. Some books we mentioned:

• Aharonov and Rohrlich, Quantum Paradoxes. (Review) An interesting depiction of quantum mechanics that introduces quantum phenomena by way of pseudo-paradoxes: things we think shouldn't happen, but do in quantum theory. This book was used for our first attempt at a podcast.
• Bell, Speakable and Unspeakable in Quantum Mechanics. (Review) A selection of articles by John Bell, including those where he introduces his famous theorem that provided the impetus for the Aspect experiment.
• Rae, Quantum Physics: Illusion or Reality?. I remember finding this to be an interesting popular book on quantum mechanics, and it's a Canto imprint -- one of my favorite book series.
• Bars and Terning, Extra Dimensions in Space and Time (Review) Descriptions of the way high-energy theorists look at space and time, mainly in terms of string theory and symmetries, as I recall.
• Mermin, Boojums All the Way Through. David Mermin's automemoirgraphy -- which is why I said his renaming Quantum Bayesianism as QBism was evidence of his mercurial personality.

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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Loop Quantum Gravity

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Recorded: 6/13/2019 Released: 8/16/2019

Randy and Jim explore loop quantum gravity. Loop quantum gravity is a theory of space-time that emphasizes the random, pre-metric connections between points of a reasonably small size (the surface areas are on the order of the square of the Planck length) and the uncertainties therein.
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Notes:

1. The papers we read for this program:

• Ashtekar, A., "Introduction to Loop Quantum Gravity." (Lecture). [arXiv]
• Rovelli, C., "Space and Time in Loop Quantum Gravity." Philosophy Beyond Spacetime and Beyond Spacetime: Foundations of Quantum Gravity (2018). [arXiv]

2. Related Episodes of Physics Frontiers:

• Physics Frontiers 30: The Consistent Histories Interpretation of Quantum Mechanics
• Physics Frontiers 35: The String Theory Landscape
• Physics Frontiers 42: Entropic Gravity

4. Carlo Rovelli has a very readable, and so far not too technical, introductory book on Loop Quantum Gravity, cleverly entitled Covariant Loop Quantum Gravity: an elementary introduction to quantum gravity and spinfoam theory. I think this is a pdf, if you want him to continue to live his monkish lifestyle.

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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Spooky Action at a Distance

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Recorded: 5/2/2019 Released: 7/15/2019

Randy and Jim discuss the lower bound on the speed of communication within a wave function, and the limits associated with it.
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Notes:

1. The papers we read for this program:

• Salart, D., A. Bass, C. Branciard, N. Gisin, and H. Zbinden, "Testing Spooky Action at a Distance." Nature 454, 861 (2008). [arXiv]
• Bancal, J-D., S. Pironio, A. Acin, H-L. Liang, V. Scarani, and N. Gisin, "Quantum Non-Locality Based on Finite-Speed Causal Influences Leads to Superluminal Signalling." Nat. Phys. 8, 867 (2012). [arXiv]
• Yin, J., Y. Cao, Y-C. Yong, J-G. Ren, H. Liang, S-K Liao, F Zhou, C. Liu, Y-P Wu, G-S. Pan, Li Li, N-L. Liu, Q. Zhang, C-Z. Peng, and J-W Pan, "Lower Bound on the Speed of Nonlocal Correlations without Locality and Measurement Choice Loopholes." Phys. Rev. Lett 110, 260407 (2013). [arXiv]
• Kofler, J., Ursin, R., Brukner, C, and Zeilinger, A., "Comment on: Testing the speed of ‘spooky action at a distance’." (2008). [arXiv]
• Wang, S. and X. Wang, "Comment on “Lower Bound on the Speed of Nonlocal Correlations without Locality and Measurement Choice Loopholes”" (2014). [arXiv]

2. Related Episodes of Physics Frontiers:

• Physics Frontiers 2: The de Broglie-Bohm Interpretation of Quantum Mechanics
• Physics Frontiers 5: Pilot Wave Hydrodynamics
• Physics Frontiers 30: The Consistent Histories Interpretation of Quantum Mechanics
• Physics Frontiers 33: Retrocausality
• Physics Frontiers 42: Entropic Gravity

3. Related Episodes of PhysicsFM: Quantum Paradoxes:

• Quantum Paradoxes Intermission: Quantum Metaphysics

4. Related Episodes of the Weekly Electronic Paper:

• WEP1: The Quantum Bookie

4. The experiments in this podcast were based on Bell's Theorem, and if you're unfamiliar with it, you should check out The Speakable and Unspeakable in Quantum Mechanics, a collection of Bell's essays, which I review here. I also have discussions of The Wave Function and Quantum Sense and Nonsense, the first a philosophical and the second an advanced non-technical account of the same phenomena.

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 Positive Energy Theorem

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Recorded: 12/9/2017 Released: 6/6/2019

Randy introduces a theory that purports to allow negative mass to Jim. It has been thought for quite a long time that negative mass was incompatible with general relativity, because it is possible to show that negative mass solutions are impossible. However Paranjape and his students noticed the proofs of this all relied on a flat background (zero cosmological constant). When trying to extend the theorems to a space with a negative cosmological constant, they found instead that negative mass is not prohibited.
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Notes:

1. The papers we read for this program:

• Belletête, J. and M.B. Paranjape, "On Negative Mass." (2014). [arXiv]
• Mbarek, S. and M.B. Paranjape, "Negative Mass Bubbles in de Sitter Space-Time." Phys. Rev. D 90, 101502(R) (2014). [arXiv]

2. Additional related paper for the positive energy theorem.:

• Komar, A., "Positive-Definite Energy Density and Global Consequences for General Relativity" Phys. Rev. 119, 1873 (1963).

3. Related Episodes of Physics Frontiers:

• Physics Frontiers 25: Gravitational Field Propulsion
• Physics Frontiers 31: The Parameterized Post-Newtonian Framework

4. Details about just how well general relativity works can be found in Wills' Theory and Experiment in Gravitational Physics, whose work we reference in the podcast.

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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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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