CPT Symmetry and Gravitation

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Recorded: 3/28/2018 Released: 8/10/2018

Jim and Randy discuss what happens when CPT symmetry is applied to gravitation. CPT symmetry -- what happens to a theory when you reverse the sign of the charge, the handedness of a particle, and the direction of time evolution all at the same time -- is a basic tenet of the standard model. Massimo Villata has applied this symmetry to gravitation and has derived consequences for the way in which antimatter particles interact with gravity and various cosmological conclusions that follow from that.

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Notes:

1. The papers we read for this program:

• Villata, M., "CPT Symmetry and Antimatter Gravity in General Relativity" EPL 94, 20001 (2011). [arXiv]
• Villata, M., "Dark Energy in the Local Void" Astrophys Space Sci 339, 7 (2012). [arXiv]

2. I found these papers in the footnotes to Alberto Vecchiato's Variational Approach to Gravity Field Theories.

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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Retrocausality

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Recorded: 3/3/2018 Released: 7/25/2018

Randy talks to Jim about retrocausality in quantum physics -- how does the future affect the past? In particular, they talk about the ideas of Huw Price and Ken Wharton on using temporal boundary conditions to constrain the wave function through its initial and final boundary conditions, effectively creating quantum harmonics in the time domain. They also discuss what this means in terms of the de Broglie-Bohm hypothesis, the multiple worlds interpretation, and Yakir Aharonov's interpretation in Quantum Paradoxes.

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Notes:

1. The papers we read for this program:

• Wharton, K., "Time Symmetric Boundary Conditions and Quantum Foundations" Symmetry 2, 272 (2010). [arXiv]
• Price H, "Does Time-Symmetry Imply Retrocausality? How the Quantum World Says "Maybe"" Studies in the History and Philosophy of Modern Physics B 43, 75 (2012). [arXiv]
• Evans, P., K. Wharton, and H. Price, "New Slant on the EPR-Bell Experiment" British Journal for the Philosophy of Science 64, 297 (2013). [arXiv]
• Leifer, M. and M. Pusey, "Is a time symmetric interpretation of quantum theory possible without retrocausality?" Studies in the History and Philosophy of Modern Physics B 43, 297 (2012). [arXiv]

2. Books discussed in the program:

• Aharonov, Quantum Paradox [PhysicsFMReview]
• Bohm, Quanatum Theory
• Bell, Speakable and Unspeakable in Qunatum Mechanics [PhysicsFM Review]
• Goldstein, Classical Mechanics

3. Huw Price also wrote a book about the philosophy of time called Time's Arrow and Archimedes' Point that, according to the plane ticket I was using as a bookmark, I last read in 2003.

4. A popular book I recently read on the de Broglie-Bohm interpretation and endorsing non-locality is Jean Bricmont's Quantum Sense and Nonsense.

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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Tunneling Time

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(Retrocausality)
Recorded: 11/25/2017 Released: 7/6/2018

Jim and Randy discuss the tunneling time problem: just how long does quantum tunneling take? No definitive answer to this question exists, but people have been trying to answer it for at least eighty years -- with answers that span from instantaneous to subluminal. In this episode, we discuss several different ideas and how experiments at ETH-Zürich have helped clarify the issue.

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Notes:

1. The papers we read for this program:

• Hauge, E.H., and J.A. Stovneng, "Tunneling Times: A Critical Review" Reviews of Modern Physics 61, 917 (1989).
• Landsman, A.S., and U. Keller, "Attosecond Science and the Tunelling Time Problem" Physics Reports 547, 1 (2015). [ETH Zürich (free)]

2. The group responsible for the attoclock measurements at ETH-Zürich, including Landsman and Keller.

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 Parameterized Post-Newtonian Framework

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Recorded: 11/12/2017 Released: 6/8/2018

Randy and Jim discuss the Parameterized Post-Newtonian Framework, a generalized way to compare metric theories of gravity to experiment in a standardized way. In this episode we discuss several theories of gravity and how they hold up under the light of experimental data.

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A Guide to the Parameters

• γ (gamma) - Coupling of matter to curvature, GR = 1 , Newton = 0
• β (beta) - Linearity of superposition, GR = 1 - Superposition linear
• ξ (xi) - Preferred location effects, GR = 0 - Spatially homogeneous
• α₁ (alpha) - Preferred frame effects, GR = 0 - Lorentz invariant
• α₂ (alpha) - Preferred frame effects, GR = 0 - Lorentz invariant
• α₃ (alpha) - Preferred frame effects, GR = 0 - Lorentz invariant
• ζ₁ (zeta) - Momentum changes, GR = 0 - Momentum conserved
• ζ₂ (zeta) - Momentum changes, GR = 0 - Momentum conserved
• ζ₃ (zeta) - Momentum changes, GR = 0 - Momentum conserved
• ζ₄ (zeta) - Momentum changes, GR = 0 - Momentum conserved

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Notes:

1. The paper we read for this program (only sections 3 and 4):

• Griffiths, R., "The Confrontation between General Relativity and Experiment" Living Rev. Relativ. 17:4 (2014). [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. If you have any information about good packages for numerical relativity for Randy, please leave them in the comments.

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 Consistent Histories Interpretation of Quantum Mechanics

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Recorded: 10/29/2017 Released: 5/24/2018

Jim and Randy investigate the Consistent Histories interpretation of quantum mechanics. This highly logical interpretation was conceived of by Robert Griffiths and is based on bundling possible histories for a particle together and only using those histories that are consistent with the measurements we perform to winnow out the possible states of the particle. Although Griffiths calls this "Copenhagen done right," the interpretation is based on the idea the quantum particles have definite values for observables in the intervening space.

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Notes:

1. The papers we read for this program:

• Griffiths, R., "EPR, Bell, and Quantum Locality." Am J Phys 79, 954 (2011). [arXiv]
• Griffiths, R. " Consistent Quantum Measurements." Stud Hist Philos Sci B 52, 188 (2015). [arXiv]

2. Griffith's book Consistent Quantum Theory, which we mention in the podcast because he continually refers to it in his papers.

3. My review of Speakable and Unspeakable in Quantum Mechanics by John Bell, which includes the paper in which he formulates Bell's Theorem -- the testable version of the EPR Paradox, which is based on the first tractable formulation of the paradox by David Bohm. I also recently reviewed a book on wave function realism, which seems to be a response to a response to Bell.

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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Gravitational Alternatives to Dark Energy

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Recorded: 10/15/2017 Released: 5/15/2018

Jim and Randy discuss the ways in which different modified gravities mimic the observed dark energy in the universe, contra a cosmological constant hypothesis. They talk about various forms of modified gravity theories and the particles associated with their "fifth fields."

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Notes:

1. The papers we read for this program:

• Carroll, S., Vikram, D., Trodden, M., and Turner, M., "Is Cosmic Speed-Up Due to New Gravitational Physics." Phys Rev D 70, 043528(R) (2005). [arXiv]
• Joyce, A., Lombriser, L., and Schmidt, F. " Dark Energy Versus Modified Gravity." Annu. Rev. Nuc. Part. Sci. 66, 95 (2016). [arXiv

2. My review of Will's book, which I talk about a little too much in this podcast.

3. Related Episodes of Physics Frontiers:

• Physics Frontiers 33: The Positive Energy Theorem
• Physics Frontiers 31: Post-Newtonian Gravitation
• 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
• Physics Frontiers 1: G4V: The Gravitational 4-Vector Formulation of Gravity

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 Quantum Vacuum and the Casimir Effect

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Recorded: 9/16/2017 Released: 4/24/2018

Jim and Randy review two very convincing papers that make the claim that the Casimir effect is due to materials fluctuations and not the zero point energy

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Notes:

1. The papers we read for this program:

• Jaffe, R.L. "The Casimir Effect and the Quantum Vacuum." Phys Rev D 72, 021301(R) (2005). [arXiv]
• Nikolic, N., " Is Zero-point Energy Physical? A Toy Model for Casimir-like Effect." Ann Phys 383, 181 (2017). [arXiv

2. We discuss an earlier episode on the Casimir Effect and van der Waals forces repeatedly in this one.

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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