Sunday, January 28, 2024

Undecidability and Theories of Everything with Claus Kiefer

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Recorded: 2023/08/07 Released: 2024/01/28

Jim talks with Claus Kiefer about his recent essay on the relationship between the Gödel's incompleteness theoerems and the possibility of developing a theory of everything. Incompleteness was originally developed to show that every axiomatic system that is sufficiently robust admits well-formed statements that have a liar's paradox-like structure - if you assume the statement is true, you can prove it's false, and vice-versa. This statement is then said to be undecidable. Undecidability also famously comes up in the halting problem of computer science and the continuum hypothesis. Professor Kiefer speculates here that theories of everything are similarly undecidable.
------------------------------------------- Notes:

1. The article that we discussed in this program:
  • Kiefer, Claus, "Gödel's undecidability theorems and the search for a theory of everything" (2023) [arXiv]
2. Other papers referred to in this podcast:
  • Cubitt, T.,D. Perez-Garcia and H.M. Wolf, "Undecidability of the Spectral Gap." Nature 528 207 (2015) [arXiv]
  • Goedel,, K., "On Formally Undecidable Propositions of Principia Mathematica and Related Systems." Monatshefte für Mathematik und Physik 38 173 (1931) [Free]
    • The Undecidable [Amazon], M. Davis, ed. Reprints Goedel's paper and other work from the 1930's. Dover book.
3. Related Episodes of Physics Frontiers:
4. Books mentioned:
5. Please visit and comment on our subreddit, YouTube Channel, or Twitter account. These are also places to look for announcements of new episodes and the like. And if you could help us keep this going by contributing to our Patreon, we'd be grateful.
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Sunday, August 20, 2023

The Measurement Problem with Nick Ormrod and V. Vilasini

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Recorded: 2023/07/17 Released: 2023/08/20

Jim talks with Nick Ormrod and V. Vilasini about their use of categorical probability theory to study the measurement problem of quantum mechanics. They use the CPT to analyze a no-go theorem to see where there are weaknesses in the underlying structure of quantum mechanics without referring to particular mathematical formualtions of the subject, allowing them to show that the measurement problem comes from difficulties in our understanding of the evolution of quantum states or the way we interpret measurements.
------------------------------------------- Notes:

1. The article that we discussed in this program:
  • Ormrod, N., V. Vilasini, and J. Barrett, "Which Theories Have a Measurement Problem?" (2023) [arXiv]
2. Other papers referred to in this podcast:
  • N. Ormrod and J. Barrett, "A No-Go Theorem for Absolute Observed Events Without Inequalities or Modal Logic." [arXiv]
  • V. Vilasini and M. P. Woods, "A General Framework for Consistent Logical Reasoning in Wigner's Friend Scenarios: Subjective Perspectives of Agents Within a Single Quantum Circuit." [arXiv]
  • Maudlin, T., "Three Measurement Problems." Topoi 14 7 (1995).
3. Related Episodes of Physics Frontiers:
4. Please visit and comment on our subreddit, YouTube Channel, or Twitter account. These are also places to look for announcements of new episodes and the like. And if you could help us keep this going by contributing to our Patreon, we'd be grateful.
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Sunday, July 9, 2023

Stochastic Thermodynamics with David Wolpert

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Recorded: 2023/05/10 Released: 2023/07/09

Jim talks with David Wolpert about the stochastic thermodynamics of compuation. The discussion focuses on recent developments in the relationship between non-equilibrium processes and information processing, having deep implications on how we view the world and how we apply statistical physics to biological, computational, and other systems.
------------------------------------------- Notes:

1. The articles that we discussed in this program:
2. Other papers referred to in this podcast:

Sunday, June 18, 2023

Quantum Money with Jiahui Liu

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Recorded: 2023/03/28 Released: 2023/06/18

Jim talks with Jiahui Liu about quantum money. Quantum Money is a key milestone in quantum crytography -- not for the breaking of codes (e.g., Shor's algothrithm), but instead for using quantum computing to improve cryptography beyond what is possible in classical cryptography. The difficulty is, however, a fully satisfactory way to implement quantum money is not currently known. Jiahui discusses both how to show that a possible implementation doesn't work, and how she developed another scheme to implemet quantum money. She also discusses the history of quantum money and some of the things quantum crytographers can do once they have a reliable quantum money scheme.
------------------------------------------- Notes:

1. The articles that we discussed in this program:
2. Related Episodes of Physics Frontiers:
3. Please visit and comment on our subreddit, YouTube Channel, or Twitter account. These are also places to look for announcements of new episodes and the like. And if you could help us keep this going by contributing to our Patreon, we'd be grateful.
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Sunday, April 23, 2023

The Born Rule and Gravity with Antony Valentini

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Recorded: 2023/03/03 Released: 2023/04/23

Jim talks with Antony Valentini about the status of the Born Rule in quantum gravity. In particular, it doesn't work. Since the wavefunction cannot be normalized in quantum gravity, there is no way to interpret Ψ as the knowledge of the observer about the quantum system. Instead, some realist interpretation of the wavefunction is required. In this regard, Jim and Anotony also discuss the de Broglie-Bohm interpretation in light of quantum gravity.
------------------------------------------- Notes:

1. The articles that we discussed in this program:
2. Some other articles mentioned in the podcast: 3. Books mentioned in the podcast:
  • Holland, P. R., The Quantum Theory of Motion: an Account of the de Broglie-Bohm Causal Interpretation of Quantum Mechanics. Cambridge, 1993. [Amazon]
  • Anderson, E., The Problem of Time: Quantum Mechanics Versus General Relativity. Springer, 2017. [Amazon]
4. Antony's lectures mentioned in the discussion:
5. Related Episodes of Physics Frontiers:
6. Please visit and comment on our subreddit, YouTube Channel, or Twitter account. These are also places to look for announcements of new episodes and the like. And if you could help us keep this going by contributing to our Patreon, we'd be grateful.
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Sunday, February 19, 2023

The Primordial Graviton Background with Sunny Vagnozzi

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Recorded: 2022/12/01 Released: 2023/2/19

Jim talks with Sunny Vagnozzi of the University of Trento about a way to disprove inflationary theories of cosmology. All of them. If we were able to see a Primordial Graviton Background, which is the graviational equivalent to the cosmic microwave background, then we would know that there was no inflation. The event that would create the graviton background would have to occur before cosmic inflation started, and inflation would smooth it out. And the background would disappear.
------------------------------------------- Notes:

1. The article that we discussed in this program:
2. Related Episodes of Physics Frontiers:
3. Please visit and comment on our subreddit, YouTube Channel, or Twitter account. These are also places to look for announcements of new episodes and the like. And if you could help us keep this going by contributing to our Patreon, we'd be grateful.
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Sunday, December 18, 2022

Path Integrals and Entanglement with Kenneth Wharton

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Recorded: 2022/11/08 Released: 2022/12/18

Jim talks with Ken Wharton of San Jose State University about how to apply path integrals to situations to entangled particles. Being an equivalent way to compute amplitudes for different experiments, when applied to various experiments, Bell-type correlations, entanglement swapping, delayed choice experiments, and the triangle network, the mathematics gives the same correlations. But, the interpretation of a path integral - a Lorentz covariant description based on local paths - is very different than that of a traditional wave function - a non-local description of the effects of measurements. This leads to a tension in how to interpret entanglement in the first place.
------------------------------------------- Notes:

1. The article that we discussed in this program:
2. Related papers that I read or Ken referred to in the podcast: 3. Books referred to in the program:
  • Feynman, R. QED: The Strange Theory of Light and Matter. [Amazon] A great, non-technical introduction to quantum electrodynamics, and therefore path integrals. As an undergraduate I found it an inspiring text, and when I ran a book club at Xavier for the physics students, we always had a good time when it came around.
  • Griffiths, R., Consistent Quantum Theory. [Amazon]. I have to confess that, although I bought a copy of this book after Randy and I did the episode on Consistent Histories, I have yet to read it.
  • Mattuck, R., A Guide to Feynman Diagrams in the Many-Body Problem. [Amazon] This has the pinball-game description the sum-over-histories approach - before getting into the deepest, darkest forest of constructing Green's functions for probability amplitudes. Since it's a Dover book, the first couple of chapters alone are worth the price. Like I said, the transition from the pinball game to the quantum pinball game was a little too much for me as an undergraduate, but after the recording podcast I've been working through it, and it's really not so difficult -- as long as you're up on your basic non-relativistic quantum mechanics. The reason why the it was called "Feynman Diagrams for Idiots" by graduate students and, looking at the preface to the second addition, much worse by reviewers (especially Russian reviewers) is that it has lots of cartoons scattered throughout the book. These are actually jewels, and are a third reason to pick up this book, either at the physics library or the bookstore, not a reason to avoid it.
  • Aharanov, A. and D. Rohrlich, Quantum Paradoxes: Quantum Theory for the Perplexed. [Amazon] Randy and I started our first podcast with this book. Partially because of that, I've read it three times, cover-to-cover. The Perimeter Institute gave a conference on the topic in 2016, "Concepts and Paradoxes in a Quantum Universe," which you can view either all contributions or just Aharonov's. I have all the talks on mp3 to play in the car (back when PIRSA allowed you to download the mp3's directly - I'm not bitter about the change [Yes I am]).
4. Related Episodes of Physics Frontiers:
5. If you'd like to know more about Ken Wharton, I have some additional questions not about path integrals on YouTube. 5. Please visit and comment on our subreddit, YouTube Channel, or Twitter account. These are also places to look for announcements of new episodes and the like. And if you could help us keep this going by contributing to our Patreon, we'd be grateful.
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