The year 1848 brought revolutions and political unrest to many European countries, but the Old World was out of synch in a more fundamental way: cities, towns and villages all had ornate clock towers but their clocks didn’t show the same time. What time was it in Vienna when it was midnight in Berlin? Not even the Kaiser knew.
“Finding local time on the spot was a matter of watching the sky, then setting a clock by the moment when the sun passed its highest point,” writes Peter Gallison in his book Einstein’s Clocks and Poincare’s Maps. It was not until the arrival of telegraph and train time that clocks started beating in unison.
In Bern, Switzerland, the old train station was one of the first buildings in the city to have coordinated clocks. It stood across the street from the Bern patent office and the desk of Albert Einstein. Gallison writes that Einstein was wrestling with two questions in Bern: What does it mean that two distant events are simultaneous? How do I compare the reading of my watch here to a train’s arrival at another station there at 7 o’clock? The answer led him to the theory of relativity.
Synchronization has since expanded from train schedules to many other industries. One of the latest is power distribution. “When it comes to the modern grid, timing is everything,” says Rich Hunt, senior product manager at GE Digital Energy. “Without it relays would trip and power lines could go out.”
The grid is now getting digitized and connected to the Industrial Internet to better predict outages and improve maintenance. But there’s a hitch. The digital signals controlling grid get slightly delayed by the network’s hardware and, like Einstein’s trains, don’t arrive exactly at the same time.
In the past, companies used expensive and complex analog copper wire systems to deal with the problem. But GE engineers now found a clever way to turn the digital network that’s causing the delays into the solution.
Like Einstein, they are “accounting for the relativistic effects of the network,” Hunt says. “We time-stamp the signals as they leave the control room. The devices at their destination have their own clocks. They use the stamps to figure out the delays and account for it. We are essentially synchronizing their clocks over the network.”
The system can do this because the devices on the network use clocks connected to the Global Positioning System (GPS). They can be synchronized to 100 millionths of a second, or 100 nanoseconds. That’s well within the accuracy requirements.
Which brings us back to Einstein again. GPS satellites fly so high and fast that their clocks run slightly slower compared to ours and we must include relativity to make the system work. Without correcting for it, GPS would give readings that are off the mark by as much as 7 miles a day. Many drivers, hikers and other users would get quickly lost.
“Our industry may be the last adopter of the technology,” Hunts says. “But with the GPS clocks, we can make synchronous real-time remote measurements of multiple points on the grid.”
Top Image: Animation illustrating relativity of simultaneity. The three events (A, B, C) are simultaneous from the reference frame of an observer moving at v = 0. From the reference frame of an observer moving at v = 0.3c, the events appear to occur in the order C, B, A. From the reference frame of an observer moving at v = -0.5c, the events appear to occur in the order A, B, C. The white line represents a plane of simultaneity being moved from the past of the observer to the future of the observer, highlighting events residing on it. The gray area is the light cone of the observer. Credit: Acdx
Center Image: This visualization shows what Einstein envisioned. Researchers crunched Einstein’s theory of general relativity on the Columbia supercomputer at the NASA Ames Research Center to create a three-dimensional simulation of merging black holes. This was the largest astrophysical calculation ever performed on a NASA supercomputer. The simulation provides the foundation to explore the universe in an entirely new way, through the detection of gravitational waves. Credit: NASA