Why Do We Even Need A Clock This Accurate?

Summary

The video explains how increasingly precise atomic clocks are useful not only for keeping time, but also for navigation, measurement, and scientific research.

How atomic clocks work

A pendulum clock keeps time by counting swings. Atomic clocks instead count radiation associated with atoms’ predictable vibrations. The NIST-F3 cesium fountain clock uses cesium-133 atoms, whose radiation vibrates 9,192,631,770 times per second.

Everyday applications

Precise clocks help GPS calculate a location by measuring how long satellite signals take to reach a phone. Meter-level positioning requires timing precise enough that light travels only about a meter between ticks—roughly nine decimal places of a second.

Accurate timing also helps coordinate financial transactions and synchronize computers for online games.

Defining measurements

The meter was once tied to a measured distance on Earth, which can vary. It is now defined using the constant speed of light and the second. More precise clocks therefore help make measurements based on physical constants more precise.

Why stability matters

A clock must keep a consistent rate over time, not merely tick rapidly. The video contrasts the drift of pendulum and quartz clocks with the exceptional long-term stability of cesium clocks.

Newer clock designs

Optical clocks using ytterbium can measure time to about 18 decimal places. A quantum logic clock using a single aluminum atom ticks about 1.12 quadrillion times per second. At these rates, light travels less than the width of a red blood cell between ticks—or, for the aluminum clock, about the length of a bacteriophage.

Research possibilities

Gravity affects the rate at which time passes, so two synchronized clocks at slightly different heights would gradually disagree. Ultra-precise clocks could use such differences to investigate gravitational effects, including possible signals from shifting tectonic plates or underground lava, weak gravitational waves, and possible irregularities linked to dark matter. These are potential applications, not established outcomes.

Researchers and sources featured

• Christiaan Huygens — inventor of the pendulum clock discussed in the video.
• Dr. Greg Hoth — scientist responsible for operating the NIST-F3 cesium fountain clock.
• Dr. Roger Brown — researcher whose lab the video visits.
• Dr. Mason Marshall and Daniel Rodriguez Castillo — members of the quantum logic clock research team.
• National Institute of Standards and Technology (NIST), Boulder, Colorado — facility and source of the clocks and researchers featured.
• 50x50: Science Across America — the science-video series of which this video is part.