What’s the time? - Marcus Brigstocke, Leon Lobo, Louise Devoy

What It Covers

The Royal Observatory Greenwich celebrates 350 years of timekeeping innovation, exploring how time measurement evolved from pendulum clocks to atomic standards accurate within one second over 158 million years, and why modern digital infrastructure depends on microsecond-level synchronization.

Key Questions Answered

• •Atomic clock precision: Current cesium atomic clocks maintain accuracy to one second over 158 million years by counting 9.2 billion cycles of cesium electron transitions. Next-generation optical clocks will achieve stability at the eighteenth decimal place, sensitive enough to detect one centimeter elevation changes through gravitational effects.
• •Digital infrastructure dependency: Modern telecommunications, energy grids, and financial trading systems require microsecond-level time synchronization to function. Stock exchanges execute tens of thousands of trades per second, all requiring precise coordination. GPS satellites and network time protocol servers distribute this timing globally through multiple redundant pathways to prevent system failures.
• •Leap second controversy: Earth's variable rotation requires periodic one-second adjustments to keep atomic time synchronized with solar days, but these unpredictable insertions disrupt digital systems. The international metrology community debates switching to leap minutes or abandoning Earth-based corrections entirely, with some companies like Google already smearing corrections across entire days.
• •Historical navigation breakthrough: The 1884 International Meridian Conference designated Greenwich as zero degrees longitude because most shipping companies already used British charts. Before atomic clocks, the Belleville family physically carried synchronized chronometers across London from the 1830s to 1940s, selling accurate time to instrument makers who trusted human delivery over telegraph networks.