Have you ever gotten lost while driving? Probably not recently thanks to GPS navigation.
The touchscreen navigation/infotainment system in every new car or truck that some colloquially refer to as “the GPS” is technology that we take for granted today. In fact, it’s so ubiquitous, it’s hard to imagine new vehicles without them (though such vehicles did exist—people used maps and turntables). But the road to today’s navigation touchscreens is a winding one marked by a trio of evolving technologies that developed over decades. It took a while before these innovations came together to ultimately doom the humble—not to mention difficult to read and refold—road map.
The next time you don’t know how to get somewhere and have to rely on maps embedded on your car’s display, you can thank the atomic clock, the satellite constellations powering actual global positioning systems, and the humble touchscreen.
What time is it, really?
Of the three technologies that led to today’s GPS inescapability, the atomic clock might be the most unexpected. But it is crucial to GPS technology. Each GPS satellite contains multiple atomic clocks that calculate the time for each GPS signal within 100 billionths of a second. This allows banks to locate the time and place of the ATM that you used to deposit a check, allowing for timestamping precision in all financial transactions. It allows the Federal Aviation Administration to precisely track hazardous weather using its network of Doppler Weather Radars. It lets your cellular provider share its limited radio spectrum more efficiently so you can always place your call. And it ensures digital broadcasters that all songs arrive on the same station at the same time regardless of where you are.
(And, no, despite the name, atomic clocks are not radioactive. Thanks for asking.)
Like a traditional clock, atomic clocks track time using oscillation. A traditional clock counts the ticks created by the oscillations of a pendulum. A mechanical wristwatch uses the energy from a wound mainspring passed through a series of gears to a balance wheel, which oscillates back and forth. A digital clock uses the oscillations of a quartz crystal or the oscillations from the power line. Regardless of technology, they all use oscillation as a way to track time, and so too does an atomic clock.
An atomic clock employs an electric oscillator regulated by an atom’s natural oscillation movement between the positive charge on the nucleus and the surrounding electron cloud. This oscillation never varies, so unlike traditional clocks, the oscillator’s frequency can be used for extraordinarily exact timekeeping.
The idea was developed by Columbia University physics professor Isidor Rabi in 1945 using a technique he developed in the 1930s called atomic beam magnetic resonance. This could accurately measure the magnetic properties of atomic nuclei by detecting single states of rotation of atoms and molecules, and the technique in turn proved feasible as a way to precisely tell time. The first clock using atomic beam magnetic resonance was introduced in 1949 by the National Bureau of Standards (now the National Institute of Standards and Technology, or NIST) using ammonia atoms, but it wasn’t accurate enough. In 1952, cesium was found to be the most exact element, and that was used for the first time on a clock named NBS-1. Seven years later, NBS-1 went into service as NIST’s primary timekeeper.
By the time the 13th General Conference on Weights and Measures was held in 1967, an international standard was established: a second of time was defined as the 9,192,631,770 cycles of radiation that it takes for a cesium atom to vibrate.
For the first time, the world’s timekeeping was no longer based on astronomy.
A cesium atomic clock is still in use today for the US government’s official time. And this concept of the atomic clock would prove essential in the development of global positioning systems during the Sputnik era—it all has to do with synchronicity, which is essential when developing GPS.
Listing image by Mazda