Quantum field theory is the basis for our most successful theories of fundamental physics. And yet, there are things we don't understand about it. Some of these puzzles are relatively well-known, while others are less celebrated. David Tong joins us to talk about some of the more interesting and perplexing aspects of quantum field theory. He also discusses his new project to write a series of textbooks covering (all?) important topics in theoretical physics. To date, these include Classical Mechanics, Quantum Mechanics, Fluid Mechanics, and Electromagnetism.

Blog post with transcript: https://www.preposterousuniverse.com/podcast/2025/07/14/321-david-tong-on-open-questions-in-quantum-field-theory/

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David Tong received his Ph.D. in theoretical physics from Swansea University. He is currently a professor of Theoretical Physics in the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge. He is a winner of the Adams Prize and a Simons Investigator. In addition to his books, he has written many freely-available sets of lecture notes on topics in physics.

• Cambridge web page
• Google Scholar publications
• Amazon author page
• Wikipedia
• Royal Institution lecture on quantum field theory

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Welcome to the July 2025 Ask Me Anything episode of Mindscape! These monthly excursions are funded by Patreon supporters (who are also the ones asking the questions). We take questions asked by Patreons, whittle them down to a more manageable number -- based primarily on whether I have anything interesting to say about them, not whether the questions themselves are good -- and sometimes group them together if they are about a similar topic. Enjoy!

Blog post with questions and transcript: https://www.preposterousuniverse.com/podcast/2025/07/07/ama-july-2025/

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Our universe started out looking very simple: hot, dense, smooth, rapidly expanding. According to our best current model, it will end up looking simple once again: cold, dark, empty. It's in between -- now, roughly speaking -- that things look complex. I have been working to understand the stages by which complexity comes into existence, thrives, and eventually disappears. Without going into technical details, in this solo episode I give an overview of the general picture and the clues we are looking at to better understand the process of complexogenesis.

Blog post with transcript: https://www.preposterousuniverse.com/podcast/2025/06/30/320-solo-complexity-and-the-universe/

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The Santa Fe Institute has recently published a four-volume set of classic papers on complexity. David Krakauer provided a comprehensive introduction that has been published as a standalone book.

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