Where Does the Quantum World End and Ours Begin? | PODCAST: The Joy of Why

Jonathan Halliwell explains how quantum decoherence is key to understanding how we transition from a world with a wave-like nature of matter and energy to the classical macroscopic world that we’re used to. “The Joy of Why” is a Quanta Magazine podcast about curiosity and the pursuit of knowledge. The mathematician and author Steven Strogatz and the cosmologist and author Janna Levin take turns interviewing leading researchers about the great scientific and mathematical questions of our time. For more episodes visit Quanta Magazine: https://www.quantamagazine.org/tag/the-joy-of-why/ -------- 0:00 Why Quantum Mechanics Remains a Mystery 2:17 Applying Quantum Physics to the Universe 6:55 Schrödinger’s Cat and the Double-Slit Experiment 10:51 Is Everything Fundamentally a Wave? 12:15 How the Quantum World Becomes Classical 18:38 Does Consciousness Affect Quantum Mechanics? 22:40 Is the Moon There When No One Is Looking? 29:29 Does Measuring a System Change It? 34:00 Why Keep Testing Quantum Mechanics? 37:22 Learning to Live With Scientific Mystery --------- Quantum mechanics may be one of the most precisely tested paradigms in science, but there’s still no universally accepted interpretation of what it tells us about reality. How do we get from the wave-like behavior of quantum systems to the solid, macroscopic world of objects and the universe at large? Jonathan Halliwell, a professor of theoretical physics at Imperial College London, has spent his career probing the foundations of quantum theory. In this episode, he tells Steven Strogatz why decoherence — the process by which fragile quantum behavior becomes dispersed through interactions with the surrounding environment — is key to the transition from quantum to classical behavior, and he describes the “histories” approach that he uses to understand this. Along the way, Halliwell tackles some of the field’s deepest paradoxes. He explains why the quantum-to-classical transition doesn’t require a conscious observer, and he explores Einstein’s famous question of whether the moon is really there when no one looks. The conversation ends with Halliwell explaining how yoga and meditation help him sit with the mystery of competing perspectives in science. Quanta Magazine is an editorially independent publication supported by the Simons Foundation. We focus on developments in mathematics, theoretical physics, theoretical computer science and the basic life sciences. --------- The Joy of Why is a podcast from Quanta Magazine, an editorially independent publication supported by the Simons Foundation. Funding decisions by the Simons Foundation have no influence on the selection of topics, guests, or other editorial decisions in this podcast or in Quanta Magazine. The Joy of Why is produced by PRX Productions. The production team is Caitlin Faulds, Jade Abdul-Malik, Genevieve Sponsler, and Merritt Jacob. The executive producer of PRX Productions is Jocelyn Gonzales. Edwin Ochoa is our project manager. From Quanta Magazine, Simon Frantz and Samir Patel provided editorial guidance with support from Samuel Velasco, Simone Barr, and Michael Kanyongolo. Samir Patel is Quanta’s editor-in-chief. The episode art is by Chanelle Nibbelink and our logo is by Jaki King and Kristina Armitage. Special thanks to Garth Avery at the Cornell Broadcast Studio. --------- Quanta Magazine is an editorially independent publication supported by the Simons Foundation. We focus on developments in mathematics, theoretical physics, theoretical computer science and the basic life sciences. READ free math and science articles on the Quanta website: www.quantamagazine.org LEARN about the Simons Foundation: www.simonsfoundation.org FOLLOW our social channels: - Instagram: quantamag - Bluesky: @quantamagazine.bsky.social‬ - Facebook: quantanews - X: quantamagazine