When I was a kid, we got a clock that featured a radio signal so it could synchronize the time automatically. It was very finicky, most likely due to the fact that the signal was coming from Colorado and thus was bouncing off the atmosphere several times before it got to us. This usually meant that after daylight savings days, it’d need to be left in a west-facing window for several days before it correctly synced to the accurate time.
These days, there are probably very few clocks you need to manually set (we have a microwave and an oven but don’t bother setting them anymore). Your phones, smart watches, tablets, televisions, and computers all automatically seem to get the time exactly right, or within a second at least. This is accomplished through something called the Network Time Protocol.
But First, a Chemistry Lesson!
There are numerous stories throughout history about how certain units were created, such as Stones, Feet, Shots, the Twain, the Scoville, and even ones you might not think of, like the Block (as in a city block) or the Dog Year. The length of a Second has been around since the mid-1500s when mechanical clocks became complex and accurate enough to divide minutes into smaller pieces. This was first standardized in 1656 by using a pendulum clock that swung once per second. Eventually, the definition of the second was calculated to be 1/86400 of a day.
In 1967, scientists were able to measure and determine that an isotope of the chemical element Cesium (specifically Cesium-133) emitted radiation at such a consistent rate that they were able to calculate that the previously accepted definition of the second corresponded to the atom vibrating and releasing radiation 9,192,631,770 times (that’s a lot in a second!). There are now several of these clocks, which serve as the basis for the world’s timekeeping.
Sending an NTP to the World
OK, there are clocks that use radioactive elements, and very sensitive measuring devices that keep time. How does that get to us? Those time sources are known as Stratum 0, and there is a network of them throughout the world, and in space (GPS is HEAVILY dependent on accurate timekeeping of both the satellite and the GPS receiver). There exists a much larger network of computers that relay time from the Stratum 0 sources to the internet, and these are called Stratum 1 sources. If you’ve ever looked at Windows Time settings and saw you could pick between time.windows.com and time.nist.gov, you were picking between Stratum 1 sources.
End devices are Stratum 2, and they get time from Stratum 1. In the case of computers and phones, they don’t have to be perfect timekeepers because they can check in daily, or even by the minute, and get an updated signal.
This system allows every computer, phone, and many other connected devices to remain in lockstep. The sources are now so accurate that they’ll only lose an estimated one second of time in the entire future of the universe. So sadly, “My clock was off by 10 minutes” is no longer a valid excuse.