Scientists Predicted an Explosion That Already Happened

In 2015, astronomers said a star was about to appear in an empty patch of sky. On 11 December, Hubble saw it. But that star had exploded more than nine billion years ago, and its light had already reached Earth five times before: once in the late 1990s, unseen, and four times in 2014. This is the true story of Supernova Refsdal, the first explosion ever predicted in advance: how gravity gave one moment six roads to us, why Hubble is watching for a different explosion to come back right now, and whether gravity could ever show us our own past. Chapters 0:00 A star that appears on schedule 1:04 Everything you see is old 1:37 Four dots 2:30 Why light bends 3:49 The race 4:53 The showing we missed 5:43 The bet 7:03 The return 8:11 Measuring the universe 9:32 It is happening again 10:45 Black hole replays 11:46 Could we see our own past? 12:46 The sky is a mailbox 13:14 One moment, six times What's real: every telescope picture is real (Hubble, Webb, the Event Horizon Telescope, the 1919 eclipse plate) and carries its credit on screen. The lens pictures marked COMPUTED are our own, drawn with the real lens equation on a simple model, not the real cluster. The black hole is a simulation of a non-spinning one. The section on Earth's own light is a thought experiment and is marked SPECULATIVE. Status of Athena and Requiem: checked 12 October 2026, no return reported. Sources Discovery, four images: Kelly et al. 2015, arxiv.org/abs/1411.6009 The seven forecasts: Treu et al. 2016, arxiv.org/abs/1510.05750 The return, 11 Dec 2015: Kelly et al. 2016, arxiv.org/abs/1512.04654 The delay, 376 days: Kelly et al. 2023, arxiv.org/abs/2305.06377 The expansion rate: Kelly et al. 2023, arxiv.org/abs/2305.06367 Delays of the first four: Rodney et al. 2016, arxiv.org/abs/1512.05734 The kind of star: Kelly et al. 2016, arxiv.org/abs/1512.09093 Six images in all: Oguri 2015, arxiv.org/abs/1411.6443 ESA/Hubble releases: esahubble.org/news/heic1505 and esahubble.org/news/heic1525 Refsdal's 1964 paper: doi.org/10.1093/mnras/128.4.307 Fermat's principle in lensing: Blandford & Narayan 1986, doi.org/10.1086/164709 The 1919 eclipse (Eddington 1920): en.wikisource.org/wiki/Space_Time_and_Gravitation/Chapter_7 Early-universe value: Planck 2018, arxiv.org/abs/1807.06209 Nearby-stars value: Riess et al. 2022, arxiv.org/abs/2112.04510 Requiem: Rodney et al. 2021, arxiv.org/abs/2106.08935; Suyu et al. 2026, arxiv.org/abs/2509.12319 Ares and Athena: jwst-venus.github.io/news/news_20260107.html Hubble watching for Athena: science.nasa.gov/missions/hubble/nasas-hubble-seeks-lensed-supernova-marks-200000-orbits Light looping a black hole: Johnson et al. 2020, arxiv.org/abs/1907.04329 M87's black hole: EHT 2019, arxiv.org/abs/1906.11238 X-ray echoes: Wilkins et al. 2021, arxiv.org/abs/2107.13555 Light sent back by a black hole: Holz & Wheeler 2002, arxiv.org/abs/astro-ph/0209039 Credits Hubble (NASA, public domain): Refsdal and MACS J1149.6+2223: NASA, ESA, S. Rodney (JHU) and the FrontierSN team; T. Treu (UCLA), P. Kelly (UC Berkeley) and the GLASS team; J. Lotz (STScI) and the Frontier Fields team; M. Postman (STScI) and the CLASH team; Z. Levay (STScI). The 2015 return: NASA, ESA, P. Kelly (UC Berkeley). Before the supernova: NASA, ESA, W. Zheng (JHU), M. Postman (STScI), the CLASH Team. Requiem: NASA, ESA, S. Rodney (U. of South Carolina), G. Brammer (Cosmic Dawn Center); processing J. DePasquale (STScI). Hubble in orbit, the Moon, the Sun, Earth: NASA; NASA/Bill Ingalls; NASA/SDO; NASA EPIC Team. CC BY 4.0 (cropped, scaled, colour-converted): MACS J0417 (2026): NASA, ESA, STScI, M. Pascale (UCLA); processing J. DePasquale (STScI). Webb: NASA, ESA, CSA, STScI; V. Estrada-Carpenter (Saint Mary's University). M51: NASA, ESA, S. Beckwith (STScI), The Hubble Heritage Team (STScI/AURA). Einstein Cross: ESA/Hubble & NASA. SN 1987A: NASA, ESA, R. Kirshner and P. Challis (Harvard-Smithsonian CfA; Gordon and Betty Moore Foundation). 1919 eclipse: ESO/Landessternwarte Heidelberg-Königstuhl/F. W. Dyson, A. S. Eddington, & C. Davidson. Milky Way: ESO/S. Brunier. M87*: EHT Collaboration. Licence: creativecommons.org/licenses/by/4.0 Narration: AI voice. Music (original), sound design, lens renders and diagrams: original. Piano samples: Salamander Grand Piano V3 by Alexander Holm, CC BY 3.0 (creativecommons.org/licenses/by/3.0). Other instrument samples: VSCO 2 Community Edition (CC0). If one day of your life could reach you a second time, which day would you want back? #Space #Science #Hubble