# Who decides how long a second is?

- Institution: TED
- Department: TED-Ed
- Speaker: John Kitching
- Year: 2021
- Level: For everyone
- Language: English
- Subjects: Physics, History, Teaching and learning
- Source: [TED](https://www.ted.com/talks/john_kitching_who_decides_how_long_a_second_is)
- Licence: [CC BY-NC-ND 4.0](https://creativecommons.org/licenses/by-nc-nd/4.0/) (Non-commercial use only, and no changed versions.)
- Who can watch: Teens profiles and older (sources give no ratings; placed by Invisible Network from the source's own words)

In 1967, researchers gathered to answer a long-running scientific question: just how long is a second? It might seem obvious at first. A second is the tick of a clock, the swing of a pendulum, the time it takes to count to one. But how precise are those measurements? And what is that length based on? John Kitching digs into how we scientifically define this fundamental unit of time. \[Directed by Tjoff Koong, narrated by Addison Anderson\].

## Lectures

1. [Who decides how long a second is?](https://invisiblenetwork.ai/learn/ted/john_kitching_who_decides_how_long_a_second_is/0b0e762e8155), 6 min (TED's player)