The Thought Experiment That Haunted Physics For 150 Years

Hey guys! We’re now live on Spotify🎧 Listen here: https://open.spotify.com/show/1Nm0Qc8... In 1867, James Clerk Maxwell wrote to an old school friend about a tiny creature at a door in a wall, letting fast molecules through one way and slow ones the other. Without doing any work, it makes heat flow uphill and seems to break the most trusted law in physics. So why has no one ever built one? A slow walk through a century and a half of answers: steam engines, a one-molecule engine, beads held in light, demons made of single electrons, and the question of what knowledge really costs. Get comfortable and let this long story of heat, molecules, and one stubborn thought experiment keep you company tonight. Subscribe to Nap Theory if you enjoy the long way around the universe. CHAPTERS 0:00 Introduction 1:22 A letter between old friends 12:49 The law nobody could break 24:12 Five hundred metres a second 35:49 Two hands and ten fingers 46:58 The door that shakes 58:38 An engine made of one molecule 1:10:59 Seeing in the dark 1:22:51 What the demon has to pay 1:35:45 Catching the demon 1:47:48 Demons without hands 1:59:10 The demons inside you 2:10:24 Why the demon still haunts physics SOURCES Maxwell, "Limitation of the Second Law of Thermodynamics," Theory of Heat (1871) — https://web.lemoyne.edu/GIUNTA/demon.... Kelvin, "The Sorting Demon of Maxwell" (1879) — https://zapatopi.net/kelvin/papers/th... APS News, "June 1871: Maxwell and His Demon" — https://www.aps.org/publications/apsn... Feynman Lectures on Physics, Vol. I, Ch. 46: Ratchet and Pawl — https://feynmanlectures.caltech.edu/I... Wang et al., Violations of the Second Law for Small Systems, PRL (2002) — https://researchportalplus.anu.edu.au... Toyabe et al., Information Heat Engine, Nature Physics (2010) — https://arxiv.org/abs/1009.5287 Bérut et al., Verification of Landauer's Principle, Nature (2012) — https://www.nature.com/articles/natur... Jun, Gavrilov & Bechhoefer, High-Precision Test of Landauer's Principle, PRL (2014) — https://arxiv.org/abs/1408.5089 Koski et al., Szilard Engine with a Single Electron, PNAS (2014) — https://arxiv.org/abs/1402.5907 Aalto University, Maxwell's Demon as an Information-Powered Refrigerator (2016) — https://aalto.fi/en/news/maxwells-dem... Hong et al., Landauer's Principle in Nanomagnetic Memory Bits, Science Advances (2016) — https://pmc.ncbi.nlm.nih.gov/articles... Cottet et al., Observing a Quantum Maxwell Demon at Work, PNAS (2017) — https://arxiv.org/abs/1702.05161 Saha et al., Maximizing Power and Velocity of an Information Engine, PNAS (2021) — https://pmc.ncbi.nlm.nih.gov/articles... Kastner, Maxwell's Demon Is Foiled by the Entropy Cost of Measurement, Not Erasure (2025) — https://arxiv.org/abs/2503.18186 de Oliveira Junior, Brask & Chaves, A Friendly Guide to Exorcising Maxwell's Demon (2025) — https://arxiv.org/abs/2503.07740 https://commons.wikimedia.org/wiki/Fi... https://commons.wikimedia.org/wiki/Fi... https://commons.wikimedia.org/wiki/Fi... https://commons.wikimedia.org/wiki/Fi... — Disclaimer: Nap Theory is an education and relaxation channel. Factual material is based on peer-reviewed research and official scientific bodies; any speculation, fringe theory, or personal analysis is identified as such when it appears. This is not a news channel. Viewer discretion advised. #MaxwellsDemon #LandauersPrinciple