A tour you can play
What is time?
While you read this page, roughly 1 s have already slipped by.
Six stops on the way here
Clocks got sharper. Here is how we learned to share one moment — with a “try it” link at each stop.
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Ancient
Sundials & sky
Daylight was the first clock. Shadows on stone told people when to meet, plant, and pray — until the clouds rolled in.
Feel one minute pass -
Medieval → 1700s
Gears & pendulums
Town clocks and ship chronometers made hours portable. Once time could travel, longitude at sea became solvable.
Browse time formats -
20th century
Quartz everywhere
A vibrating crystal made accuracy cheap. Wristwatches and kitchen clocks suddenly agreed within seconds of a day.
Convert a timestamp -
1950s → now
The atomic second
The SI second is defined by cesium. Atomic clocks keep the quiet reference that GPS and the internet depend on.
Check UTC now -
1800s → IANA
Zones & UTC
Railroads forced shared zones. Today IANA names like Asia/Singapore encode offsets and daylight-saving rules against UTC.
Open city clocks -
1970 → computers
Unix time
Most machines count seconds from 1970-01-01T00:00:00Z. Compact, shareable — and what powers /t/ links on time.foo.
Open this second as a link
Same instant, three cities
One moment on the timeline — three civil clocks. Watch them tick together.
Singapore
--:--:--
London
--:--:--
New York
--:--:--
Why “3pm” is slippery
Without a zone, 3:00 pm is a label, not an instant. Pin the same wall time to three zones and you get three different moments.
Bare label (no zone)
15:00
Same “15:00” pinned today
Unix ↔ ISO for now
Toggle how this exact second is written. Same instant — two dialects computers speak.
Watch videos (English)
Optional deep dives. Folded so they do not interrupt the tour.
How an atomic clock works
engineerguy on YouTube (youtube-nocookie). English.
When time breaks down (relativity)
PBS Space Time on YouTube. English.
Measuring light and synchronizing clocks
Veritasium on YouTube. English.
Keep exploring on time.foo
Videos are third-party embeds via youtube-nocookie. Educational links only; time.foo is not affiliated with the channels. Live demos use your browser clock (Date / Intl) — no network call.