Knowing Where We Are

Knowing the time has long been essential for anyone trying to get from A to B. So essential, in fact, that in the 1700s, the British government paid clockmaker John Harrison the equivalent of millions of today’s dollars for a timekeeping invention that sailors could use to track their longitude at sea. Harrison’s best chronometer kept time to within one-fifth of a second per day — record accuracy for its time.

Later, institutes such as the Royal Observatory in Greenwich, England and the U.S. Naval Observatory in Washington, D.C. tracked the stars to provide a more precise foundation for timekeeping. When atomic clocks emerged in the 1950s, however, they quickly outdid the best observatories.

There remained the problem of distributing time globally. The U.S. military solved this problem with the Global Positioning System, or GPS: a constellation of satellites, each carrying its own clocks. By integrating time as well as location information from at least four satellites, a GPS receiver can determine its location anywhere on Earth.

Atomic clocks are essential to modern GPS. Without atomic clocks, errors would build up so fast that the system would quickly become useless. The clocks on the satellites are good but not that good, meaning they drift over time. So satellite clocks are regularly corrected by even better clocks on the ground.

At first, only the military had access to high-resolution GPS signals, while civilians received a degraded signal. In the 1980s, GPS became available to commercial pilots to make aviation safer and more efficient. In 2000, President Bill Clinton directed the military to provide high-quality signals to everyone, and the civilian GPS industry took off.

GPS provides an estimated one billion dollars of benefits to the U.S. economy every day. Hundreds of millions of people use digital ride-sharing services, which have become a $100-billion global industry. GPS-guided tractors plant millions of acres of crops each year. Surveyors, miners and oil and gas prospectors all rely on GPS. More than 100 million runners track and share their routes using GPS-based apps. Roughly half of American parents say they track their teen’s movements using apps; millions of young people share their location with friends. Behind the ever-present blue dot on our phones, atomic clocks have reshaped our lives and our culture.

A NIST-sponsored study published in 2019 found that the telecommunications industry had reaped nearly $700 billion in benefits from GPS, which is used to synchronize communications networks, enabling service providers to efficiently use available spectrums and deliver high-speed wireless services. That number is surely even higher today.

Atomic clocks have even catalyzed the creation of entirely new hobbies and subcultures. For example, on May 3, 2000, one day after the government made high-resolution GPS available to everyone, a computer consultant in Oregon hid a collection of objects in the woods and tagged the location with GPS-based coordinates — the first known act of “geocaching.” More than three million people around the world have hidden or searched for geocaches — all aided by atomic clocks.

As widespread and convenient as GPS has become, it’s not a perfect solution. GPS signals can be jammed or spoofed relatively easily, and such technology is becoming more widespread. In recent years, GPS jamming has become especially common in conflict zones such as Ukraine and the Middle East, leading to widespread outages.

With a goal of enabling navigation without GPS, physicists have started developing portable atomic clocks and testing them on ships and planes. These clocks could provide a trusted backup time source, potentially allowing users to recognize a spoofed GPS signal and maintain the correct time if the GPS signal is temporarily jammed or lost. Paired with inertial sensors or accelerometers, chip-scale clocks could eventually help drivers, sailors and pilots to navigate entirely without GPS.

An ultimate solution would involve every smartphone or smartwatch containing its own atomic clock. That would require atomic clocks much smaller, more energy efficient and cheaper than any on the market today. While scientists are developing such clocks, they likely remain years away.

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