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 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://ve42.co/Upbs

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 & Ivàn 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