Who Decides What Time It Is?

Your phone says 9:30. Who told it—and who checks that clock? Follow the hidden system behind automatic timekeeping: network time servers, national laboratories, atomic clocks, satellites and the international coordination behind Coordinated Universal Time, or UTC. Discover why some atomic reference clocks don't run around the clock, how GPS turns time into distance, why gravity changes clock rates, and why a UTC timestamp can contain a second numbered 60. The key distinction: laboratories supply time continuously, while the definitive international comparison arrives afterwards. This is the science and engineering behind the time on your screen. Subscribe to Everyday Unseen for the hidden science and technology behind the things you do every day. CHAPTERS 00:00 Who told your phone the time? 01:18 Why time signals arrive late 02:24 Who checks the world's clocks? 04:22 How atoms define one second 06:42 Why atomic clocks use fountains 08:25 Comparing clocks across the planet 09:35 Why GPS needs precise time 11:19 Time signals without the internet 11:59 Why clocks run differently in space 13:08 Time changes across a millimetre 14:20 Earth is a different kind of clock 15:41 The second numbered 60 16:21 When a leap second broke software 16:55 Why Google smears time 17:34 The future of UTC 18:08 Who chooses your local time? RESEARCH & SOURCES NIST — UTC and continuously operating laboratory time https://www.nist.gov/pml/time-and-fre... BIPM — International timekeeping and clock comparisons https://www.bipm.org/en/time-metrology NIST — How atomic clocks work https://www.nist.gov/atomic-clocks/ho... NPL — The MSF radio time signal https://www.npl.co.uk/products-servic... NIST/JILA — Relativity measured across a millimetre-scale atomic sample https://www.nist.gov/news-events/news... Cloudflare — The end-2016 leap-second incident https://blog.cloudflare.com/how-and-w... Google — Leap smear https://developers.google.com/time/smear BIPM — The 2022 decision on the future of UTC https://www.bipm.org/en/-/resolution-... Educational explainer. Animations are simplified schematics: apparatus sizes, clock-hand movement and signal travel are not shown to scale. Synchronization accuracy depends on the device, network, reference and method. #AtomicClocks #ScienceExplained #EverydayUnseen