Stephen Hawking Threw a Party for Time Travelers. Nobody Came.

Is time travel possible? In 2009, Stephen Hawking threw a party. Champagne, balloons, a banner that said "Welcome, Time Travellers"… and he only sent out the invitations after the party was over. Nobody came. But what if someone had? A time machine means a problem big enough to break the universe: the grandfather paradox. Go back in time, stop your grandparents from meeting — and you're never born. So who built the machine? In this video, Pip explores the three answers physics gives us — and a real experiment where scientists asked particles of light to break their own past. The result is stranger than you'd expect. And the twist at the end is about you. ⏱ Chapters 0:00 Hawking's party 0:49 A simple plan to break the universe 1:50 Is time travel even allowed? 3:15 Answer 1: The universe won't let you 4:35 Answer 2: Many worlds 5:19 Answer 3: No time machines at all 5:52 The experiment with light 6:34 The paradox in reverse 📚 Sources & further reading • Stephen Hawking's party for time travellers (28 June 2009, Cambridge) • Kurt Gödel, rotating universe solution (1949) • Igor Novikov, self-consistency principle • Echeverria, Klinkhammer & Thorne, billiard-ball paradox (1991) • David Deutsch, quantum time loops (1991) • Stephen Hawking, chronology protection conjecture (1992) • Seth Lloyd et al., photon time-loop simulation (2011) 🎵 Music: Voxscape, Rest Now, Feedback Dreams — Mixkit 🔊 Sound effects: Mixkit, Kenney (CC0) 🎙 Narration voice generated with AI. Script, research and animation by Curious Orbit. 🔔 Subscribe for more big questions — answered by one small robot. #timetravel #science #physics