In 2015 astronomers successfully predicted the appearance of a supernova within a couple weeks. How did they do it? Win your Ultimate Tech Bundle by entering Fasthosts’ Techie Test here: https://fasthosts.com/veritasium (Competition now closed) This video was sponsored by Fasthosts. Special thanks to Geraint Lewis for consulting on gravitational lensing. Check out his YouTube channel: https://ve42.co/gfl and books: https://ve42.co/GFLbooks The supernova image in the thumbnail is from my documentary, Uranium: Twisting The Dragon's Tail. Check it out here: https://genepoolproductions.com/uranium-project References: DEJA VU ALL OVER AGAIN: THE REAPPEARANCE OF SUPERNOVA REFSDAL P. L. Kelly et al. https://arxiv.org/abs/1512.04654 Predicted properties of multiple images of the strongly lensed supernova SN Refsdal Masamune Oguri. Monthly Notices of the Royal Astronomical Society: Letters, Volume 449, Issue 1, 01 May 2015, Pages L86–L89, https://arxiv.org/abs/1411.6443 Multiple Images of a Highly Magnified Supernova Formed by an Early-Type Cluster Galaxy Lens Patrick L. Kelly et al. https://arxiv.org/abs/1411.6009 "Refsdal" meets Popper: comparing predictions of the re-appearance of the multiply imaged supernova behind MACSJ1149.5+2223. T. Treu et al. https://arxiv.org/abs/1510.05750 Irwin I. Shapiro (1964). "Fourth Test of General Relativity". Physical Review Letters. 13 (26): 789–791. doi:10.1103/PhysRevLett.13.789 Irwin I. Shapiro; Gordon H. Pettengill; Michael E. Ash; Melvin L. Stone; et al. (1968). "Fourth Test of General Relativity: Preliminary Results". Physical Review Letters. 20 (22): 1265–1269. doi:10.1103/PhysRevLett.20.1265 Research & Writing by Stephanie Hamilton, Ralph Crewe, Petr Lebedev, Derek Muller, and Jonny Hyman Animations & VFX by Jonny Hyman & Ivy Tello Thanks to Jaime Portsmouth for his gravitational lensing simulator and help enabling it to render simulations. Supernova simulations courtesy of Adam Burrows Numerous hubble images by Hubble Legacy Archive, NASA/ESA/STScI Numerous images by ESO / NASA