Cosmologists were, let us be honest, pretty stunned in 1998 when observations revealed that the universe is accelerating. There was an obvious plausible explanation, the cosmological constant proposed by Einstein, which is equivalent to a constant vacuum energy pervading space. But the cosmological constant was known to be enormously smaller than its "natural" value, and it seems fine-tuned for it to be so small but not yet zero. Once burned, twice shy, and since then we have been looking for evidence that the dark energy might not be strictly constant, even though that's even more fine-tuned. We talk to cosmologist Marc Kamionkowski about recent evidence that dark energy might be changing with time, and what this might have to do with the Hubble tension and other cosmic anomalies.

Blog post with transcript: https://www.preposterousuniverse.com/podcast/2025/03/31/310-marc-kamionkowski-on-dark-energy-and-cosmic-anomalies/

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Marc Kamionkowski received his Ph.D. in physics from the University of Chicago. He is currently the William R. Kenan Jr. Professor in the Department of Physics and Astronomy at Johns Hopkins University. Among his prizes are the Gruber Cosmology Prize, the Dannie Heineman Prize for Astrophysics, membership in the National Academy of Science, and a Guggenheim Fellowship.

• Johns Hopkins web page
• Google Scholar publications
• Wikipedia
• Kamionkowski and Riess, "The Hubble Tension and Early Dark Energy"
• Dark Energy Spectroscopic Instrument paper and followup
• Dark Energy Survey paper

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Consciousness is easier to possess than to define. One thing we can do is to look into the brain and see what lights up when conscious awareness is taking place. A complete understanding of this would be known as the "neural correlates of consciousness." Once we have that, we could hopefully make progress on developing a theoretical picture of what consciousness is and why it happens. Today's guest, Christof Koch, is a leader in the search for neural correlates and an advocate of a particular approach to consciousness, Integrated Information Theory.

Blog post with transcript: https://www.preposterousuniverse.com/podcast/2025/03/24/309-christof-koch-on-consciousness-and-integrated-information/

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Christof Koch was awarded a Ph.D. from the Max Planck Institute for Biological Cybernetics. He is currently a Meritorious Investigator at the Allen Institute for Brain Science, where he was formerly president and chief scientist, and Chief Scientist at the Tiny Blue Dot Foundation. He is the author of several books, most recently Then I Am Myself the World - What Consciousness Is and How to Expand It.

• Web site
• Allen Center web page
• Google Scholar publications
• Amazon author page
• Wikipedia

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We often study cognition in other species, in part to learn about modes of thinking that are different from our own. Today's guest, psychologist/philosopher Alison Gopnik, argues that we needn't look that far: human children aren't simply undeveloped adults, they have a way of thinking that is importantly distinct from that of grownups. Children are explorers with ever-expanding neural connections; adults are exploiters who (they think) know how the world works. These studies have important implications for the training and use of artificial intelligence.

Blog post with transcript: https://www.preposterousuniverse.com/podcast/2025/03/17/308-alison-gopnik-on-children-ai-and-modes-of-thinking/

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Alison Gopnik received her D.Phil in experimental psychology from Oxford University. She is currently a professor of psychology and affiliate professor of philosophy at the University of California, Berkeley. Among her awards are the Association for Psychological Science Lifetime Achievement Award, the Rumelhart Prize for Theoretical Foundations of Cognitive Science, and a Guggenheim Fellowship. She is a past President of the Association for Psychological Science. She is the author of The Scientist in the Crib, The Philosophical Baby, and The Gardener and the Carpenter, among other works.

• Web site
• Lab web site
• Berkeley web page
• Google Scholar publications
• Amazon author page
• Wikipedia

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