Loop Quantum Gravity

<-- Previous (Spooky Action at a Distance)

( Wigner's Friend ) Next -->

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.
-------------------------------------------

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.

<-- Previous (Spooky Action at a Distance)

( Wigner's Friend ) Next -->

Spooky Action at a Distance

<-- Previous (Positive Energy Theorem)

( Loop Quantum Gravity ) Next -->

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.
-------------------------------------------

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. 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.

<-- Previous (Positive Energy Theorem)

( Loop Quantum Gravity ) Next -->

The Positive Energy Theorem

<-- Previous (Entropic Gravity)

( Spooky Action ) Next -->

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.
-------------------------------------------

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.

<-- Previous (Entropic Gravity)

( Spooky Action ) Next -->

Entropic Gravity

<-- Previous (Octonions)

( Positive Energy Theorem ) Next -->

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.
-------------------------------------------

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.

<-- Previous (Octonions)

( Positive Energy Theorem ) Next -->

The Chameleon Field

<-- Previous (Octonions)

( ??? ) Next -->

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

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

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.

<-- Previous (Octonions)

( ??? ) Next -->

The Octonions

<-- Previous (Negative Effective Mass)

(Chameleon Field) Next -->

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.
-------------------------------------------

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.

<-- Previous (Negative Effective Mass)

(Chameleon Field) Next -->

Negative Effective Mass

<-- Previous (Space-Time Dimensions)

(Octonions) Next -->

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?
-------------------------------------------

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 psychic 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.

<-- Previous (Space-Time Dimensions)

(Octonions) Next -->