Time Travel IS Real...Just Probably Not How You Thought

Is time travel possible? Physics says yes, and you're doing it right now. Just not the way the movies promised. Things Your Brain Can't Hold, Episode 3A. GPS satellites gain 38 microseconds a day on your phone. Particles from space survive long enough to hit the ground only because their clocks run slow. Astronauts come home slightly younger than they'd otherwise be. That's real, measured, forward time travel, and Einstein called it over a century ago. Going backwards is a different story. Einstein's equations allow it on paper, but you'd have to get past four separate fences: a loop in spacetime, exotic matter nobody has ever made, a start date you can never go back before, and the paradox problem. We go through Kurt Gödel's rotating universe, Kip Thorne's wormhole time machine, the billiard-ball paradox, and Stephen Hawking's idea that physics itself keeps the past safe for historians. ▶ This series is built to be watched in order. Start with Episode 1, on the Mandela effect: ▶ Full playlist: ▶ Next, Episode 3B: Parallel universes, and why the theory people cite rules them out: CHAPTERS 0:00 Time travel is real 0:23 You have never seen the present 2:01 The "dead stars" myth 2:58 GPS: real time travel 4:35 Muons and astronauts 5:33 Going backwards: the loopholes 7:06 The start date 8:47 The billiard ball paradox 9:55 The four fences SOURCES Time dilation in GPS: N. Ashby, "Relativity in the Global Positioning System," Living Reviews in Relativity (2003) Muon lifetime and time dilation: B. Rossi & D. B. Hall, Physical Review (1941) Rotating-universe solution: K. Gödel, Reviews of Modern Physics (1949) Wormhole time machines: M. Morris, K. Thorne & U. Yurtsever, Physical Review Letters (1988) Billiard-ball paradox: F. Echeverria, G. Klinkhammer & K. Thorne, Physical Review D (1991) Chronology protection: S. Hawking, Physical Review D (1992) Further reading: Kip Thorne, Black Holes and Time Warps (1994) VISUALS NASA, NASA/SVS, ESA/Hubble & NASA, ESO, NIST. Used under their respective licences. ABOUT I'm Justin, an Emmy-winning journalist. I take the things your brain can't hold and check them against the actual sources. Corrections go in the pinned comment. #TimeTravel #Physics #Einstein