The cosmological constant, as discussed last episode, provides a perfectly good (thus far) explanation for why we observe the universe to be accelerating. But it might not be the right explanation, and demonstrating that would be yet another foundational discovery. In this episode I discuss what is required to invent a plausible theory of dynamical dark energy, This includes considerations from particle physics, possible experimental tests, and the option that we should modify gravity rather than adding a new source of energy to the equations.

Blog post with transcript: https://www.preposterousuniverse.com/podcast/2026/06/29/359-solo-theories-of-dark-energy/

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The most surprising discovery in fundamental physics during my career as a scientist was undoubtedly the acceleration of the universe, announced in 1998. The most straightforward explanation for these observations is a positive cosmological constant, or vacuum energy. I talk about the origin of the idea with Einstein, how quantum physicists started to think about it and understand the "cosmological constant problem," as well as how its discovery also raised the "coincidence problem." This is the first of two connected solo episodes; the next will be on theories of dark energy that are not the cosmological constant.

Blog post with transcript: https://www.preposterousuniverse.com/podcast/2026/06/22/358-solo-vacuum-energy-and-the-cosmological-constant/

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Messenger RNA (mRNA) plays a literally central role in the functioning of life as we know it, shuttling information back and forth between the DNA where it is stored to the ribosome where it is used to produce proteins. RNA may even have been the first molecule to kick-start the origin of life. Today, scientists are learning how to manipulate mRNA to cure and prevent diseases, whether through vaccination or literally editing one's DNA. Jeff Coller explains how it all works and how mRNA is revolutionizing medicine as we know it.

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Jeff Coller received his Ph.D. in cell and molecular biology from the University of Wisconsin-Madison. He is currently Bloomberg Distinguished Professor of Biomedical Engineering and Director of the RNA Innovation Center at Johns Hopkins University. He is co-founder of Tevard Biosciences and the Alliance for mRNA Medicines, and leads the REPAIRx consortium. He is a fellow of the American Association for the Advancement of Science.

• Web site
• Johns Hopkins web page
• Google Scholar publications
• "This May Be the Most Important Medical Story of the Decade," New York Times, April 9, 2026

All ideas have a history, no matter how inevitable and well-entrenched they may seem to us today. The later Enlightenment was a heady time when people were exploring new conceptions of nature, humanity, and the self. Andrea Wulf is a writer of narrative histories, examining the origins of ideas through the lives of the people who explored them. In this episode we discuss three of her books: The Invention of Nature, about Alexander von Humboldt and environmentalism; Magnificent Rebels, about the Jena circle of Romantics including Goethe, Schiller, Schlegel, and others; and most recently The Traveller, about George Forster, an early naturalist, ethnographer, and champion of human equality.

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Andrea Wulf was born in India, raised in Germany, and studied design history at the Royal College of Art, London. She is the author of seven books. She is a Miller Scholar at the Santa Fe Institute and a Fellow of the Royal Society of Literature. The Invention of Nature won multiple prizes, including the Royal Society science book prize and the LA Times book prize.

• Web site
• Amazon author page
• Wikipedia

Welcome to the June 2026 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 AMA questions and transcript: https://www.preposterousuniverse.com/podcast/2026/06/01/ama-june-2026/

New paper I talk about in the beginning of the episode:

• S.M. Carroll, N. Diachenko, and S. Dulani, "Toward a Phenomenologically Acceptable Quantum Cyclic Universe."

One of the major obstacles to understanding quantum mechanics is the difficulty we have in simply accepting what the theory itself is telling us. The problem is that we know what the everyday world looks like -- stuff, arranged in space, evolving through time. So we can't resist the temptation to impose that picture on the quantum description, even if it's not actually there. In this solo episode I talk about what it means to take quantum mechanics at face value, and the difficult work involved in understanding how the everyday world of our experience fits into the picture.

Blog post with transcript: https://www.preposterousuniverse.com/podcast/2026/05/25/355-solo-looking-quantum-mechanics-in-the-eyeball/

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Here is the survey on physicists' opinions about unsettled big-picture questions:

• Afshordi, Halper, Rini, and Schirber, "Big Mysteries Survey: Physicists' Views on Cosmology, Black Holes, Quantum Mechanics, and Quantum Gravity."

And here is a short technical overview on the ideas described in this episode:

• Carroll, "Reality as a Vector in Hilbert Space."

If you want further papers, look at the papers cited in this one.

Did I have any freedom in choosing this particular podcast guest? At the level of particles, fields, and the fundamental laws of physics; no. At the level of human agents navigating the world, yes. Today's guest, Christian List, is a philosopher and political scientist who has arguably done the most to articulate the "compatibilist" perspective on free will, according to which the freedom of rational agents is entirely compatible with underlying mechanistic laws. The reconciliation depends on thinking carefully about emergence and the relationship between levels of reality.

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Blog post with transcript: https://www.preposterousuniverse.com/podcast/2026/05/18/354-christian-list-on-free-will-and-levels-of-reality/

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Christian List received his D.Phil in Politics from Oxford University. He is currently Professor of Philosophy and Decision Theory and Co-Director of the Munich Center for Mathematical Philosophy at LMU Munich. He is a Fellow of the British Academy and a member of Academia Europaea the Bavarian Academy of Sciences and Humanities. Among his honors are the Joseph Gittler Award from the American Philosophical Association. He is the author of Why Free Will Is Real and (with Philip Pettit) Group Agency.

• Web site
• LMU web page
• Google Scholar publications
• Amazon author page
• Wikipedia

Economic markets are efficient ways of deciding fair prices, at least in ideal circumstances of perfect competition, information, and choice. But there is more to life than fair prices. Two people might decide on a fair price to carry out a contract killing, but society generally frowns on the idea. Many examples of morally contestable markets feature less consensus than that one: sex work, drugs, selling organs, adopting children. In his new book Moral Economics, economist Alvin Roth investigates how we should reason through such tricky cases, and what we can learn from them.

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Blog post with transcript: https://www.preposterousuniverse.com/podcast/2026/05/11/353-alvin-roth-on-the-economics-of-morally-contested-markets/

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Alvin Roth received his Ph.D. in operations research from Stanford University. He is currently the Craig and Susan McCaw Professor of Economics at Stanford University and the Gund Professor of Economics and Business Administration Emeritus at Harvard. He was President of the American Economic Association in 2017. He and Lloyd Shapley shared the 2012 Nobel Prize in Economics for "the theory of stable allocations and the practice of market design."

• Stanford web page
• Google Scholar publications
• Amazon author page
• Wikipedia

Welcome to the May 2026 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 AMA questions and full transcript: https://www.preposterousuniverse.com/podcast/2026/05/04/ama-may-2026/

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The connectome is the wiring diagram of a brain, a big matrix that tells us what neurons talk to what other neurons. Understanding it is an important step to understanding how brains work, but a long way from the final answer. A big next step is understanding how neuronal circuits connect to and guide bodily behavior. Very recent work on mapping the fruit-fly connectome has brought us closer to that goal. I talk with neuroscientist Bing Brunton about the connectome, how we can study it to understand bodily motion in flies and other creatures, and where it's all taking us.

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Blog post with transcript: https://www.preposterousuniverse.com/podcast/2026/04/27/352-bing-brunton-on-connecting-the-connectome-to-the-body/

Bing Wen Brunton received her Ph.D. in neuroscience from Princeton University.. She is currently a Professor of Biology and the Richard & Joan Komen University Chair at the University of Washington, with affiliations at the eScience Institute for Data Science, the Paul G. Allen School of Computer Science & Engineering, and the Department of Applied Mathematics.

• Web site
• University of Washington web page
• Google Scholar publications
• YouTube channel
• Bluesky
• Artworks (Instagram)

Peter Singer has been an influential philosopher for a number of decades. He was a significant early voice in animal rights, has been a leading thinker of utilitarianism, and helped inspire the effective altruism movement. In this podcast episode, we try our best to talk about all of those things -- working from metaethical questions of consequentialism vs. other approaches, to specific flavors of utilitarianism, the practical demands that ethics places on people, the rights of animals, and the decisions we make at the end of our lives.

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Peter Singer received his B.Phil. in philosophy from the University of Oxford. He retired from Princeton University in 2023, and now lives in Melbourne, Australia. He is the author of a number of influential books, including Animal Liberation (1975). He has been named a Companion of the order of Australia, and is a winner of the Berggruen Prize. He is the founder of the charity The Life You Can Save. He and philosopher Kasia de Lazari Radek are co-hosts of the Lives Well Lived podcast (YouTube, Spotify, Apple).

• Web site
• Princeton University Center for Human Values page
• Google Scholar publications
• Amazon author page
• Wikipedia
• Bluesky