Types of Clocks: Evolution of Timekeeping
From ancient shadows to quantum vibrations - the evolution of timekeeping devices
3000 BCE
Sundial
Uses shadow position to indicate time. Only works during daylight and requires Sun.
Accuracy: ~15 minutes per day
1500 BCE
Water Clock (Clepsydra)
Water drips at constant rate into/out of a container.
Accuracy: ~30 minutes per day
1000 CE
Hourglass
Sand flows through narrow neck. Good for measuring intervals.
Accuracy: ~5 minutes per hour
1583
Pendulum Clock
Galileo discovers pendulum regularity. First reliable clock.
Accuracy: ~1 second per day
1920s
Quartz Clock
Vibrating quartz crystal keeps time. Small and affordable.
Accuracy: ~0.5 seconds per day
1955
Cesium Atomic Clock
Cesium-133 atom vibrations define the second.
Accuracy: 1 second in 30 million years
2000s
Optical Clock
Uses light waves (not microwaves). Even more precise.
Accuracy: 1 second in billions of years
Related: Atomic Clocks