Does light take all possible paths at the same time? 🌏 Get exclusive NordVPN deal here ➵ https://NordVPN.com/veritasium It’s risk free with Nord’s 30 day money-back guarantee!✌ In 2025, we launched the Elements of Truth game on Kickstarter and were thrilled by the response. We’re now in the final stages of production, with Kickstarter rewards shipping soon. If you missed the campaign, you can now pre-order the retail edition through our new website here -https://ve42.co/LA2Desc A massive thank you to Dr. Andrew Mitchell for all his help and expertise. If you want to delve further into this topic then we highly recommend his lecture on Classical physics derived from quantum mechanics: https://www.youtube.com/watch?v=2iuLwWDYC4U&t=1s We’re incredibly grateful to Prof. David Kaiser, Prof. Steven Strogatz, Prof. Geraint F. Lewis, Elba Alonso-Monsalve, Prof. Christopher S. Baird, Prof. Anthony Bloch, and Prof. Stephen Bartlett for their invaluable contributions to this video. A special thanks to Mahesh Shenoy from FloatHeadPhysics for his help with this video. Check out his excellent intuitive video on the UV Catastrophe here (Sep 2024): https://www.youtube.com/watch?v=ALEDjjAVZSY ▀▀▀ 0:00 What path does light travel? 2:40 Black Body Radiation 6:47 How did Planck solve the ultraviolet catastrophe? 9:42 The Quantum of Action 13:25 De Broglie’s Hypothesis 15:16 The Double Slit Experiment 20:00 How Feynman Did Quantum Mechanics 25:01 Proof That Light Takes Every Path 31:16 The Theory of Everything ▀▀▀ Sign up to our Patreon to watch the Q&A for free: https://www.patreon.com/c/veritasium Try Snatoms! A molecular modelling kit I invented where the atoms snap together. https://ve42.co/SnatomsV ▀▀▀ References: Armin Hermann (Nov 1974). The Genesis of Quantum Theory (1899-1913). - https://ve42.co/genquanttheor Richard P. Feynman (1985). QED The Strange Theory of Light and Matter. - https://ve42.co/qed A fantastic book on the history of the Principle of Least Action: Rojo, A. and Bloch, A. The Principle of Least Action: History and Physics. - https://ve42.co/Bloch2018 Coopersmith, J. (2017). The lazy universe: an introduction to the principle of least action. Oxford University Press. - https://ve42.co/LazyU PBS Space Time. (Nov 2021) - https://www.youtube.com/watch?v=Q_CQDSlmboA Sabine Hossenfelder. (May 2022) - https://www.youtube.com/watch?v=A0da8TEeaeE Max Planck (1901). On the Law of Distribution of Energy in the Normal Spectrum. Annalen der Physik - https://ve42.co/lawdistenergy Paul Ehrenfest (1911). Welche Züge der Lichtquantenhypothese spielen in der Theorie der Wärmestrahlung eine wesentliche Rolle?. Wiley Online Library - https://ve42.co/quantthermrad Nils-Erik Bomark and Reidun Renstrøm (Aug 2023). The Ultraviolet myth. Proceedings of Science - https://ve42.co/uvmyth Additional References - https://ve42.co/AdditionalReferences-PoLA2 Images & Video: Nobistor Altona 1880 via NDR - https://ve42.co/streetlight Edison incandescent lights by William J. Hammer via Wikimedia Commons - https://ve42.co/edinclights The full expanded form of the Standard Model Lagrangian by Chen Ning Yang et al. via Wikipedia - https://ve42.co/stmodellang Muon Ray. (2011). https://www.youtube.com/watch?v=-QUj2ZRUa7c Muon Ray. (2011). https://www.youtube.com/watch?v=1C7abO7LtV0 Bohrs Atomic Model via EEEGUIDE.COM - https://ve42.co/bohrmodel ▀▀▀ Special thanks to our Patreon supporters: Adam Foreman, Albert Wenger, Alex Porter, Alexander Tamas, Anton Ragin, Autodidactic Studios, Balkrishna Heroor, Bertrand Serlet, Blake Byers, Bruce, Dave Kircher, David Johnston, David Tseng, Evgeny Skvortsov, Garrett Mueller, Gnare, gpoly, Greg Scopel, Juan Benet, Keith England, KeyWestr, Kyi, Lee Redden, Marinus Kuivenhoven, Matthias Wrobel, Meekay, meg noah, Michael Krugman, Orlando Bassotto, Paul Peijzel, qiaohui wei, Richard Sundvall, Sam Lutfi, Tj Steyn, TTST, Ubiquity Ventures, wolfee ▀▀▀ Directed by Casper Mebius Written by Casper Mebius and Derek Muller Edited by Trenton Oliver and Peter Nelson Animated by Fabio Albertelli, Mike Radjabov, Ivy Tello, Andrew Neet and Emma Wright Illustrations by Jakub Misiek, Tommy A. Steven and Cainejan Esperanza Filmed by Derek Muller and Casper Mebius Produced by Casper Mebius, Derek Muller, Rob Beasley Spence, Gabe Strong, Geeta Thakur, Emilia Gyles, Zoe Heron, Emily Zhang and Tori Brittain Thumbnail contributions by Ignat Berbeci, Ben Powell, Jakub Misiek, Ren Hurley, and Peter Sheppard Additional video/photos supplied by Getty Images and Storyblocks Music from Epidemic Sound