GPS, NTP; OMG

The Global Positioning Satellite system (GPS) is certainly one of the modern wonders of the world.

31 (as of today) incredibly sophisticated, fine-tuned scientific instruments are falling at thousands of miles per hour around the earth. We call this constant falling orbiting, and from our perspective on earth, it seems like these satellites are flying around us, but from their perspective, they’re just falling. General relativity tells us this.

The orbiting GPS satellites give us an even clearer demonstration of special relativity, and that’s what I want to zero in on here. The key to this ability is ultra-precise time measurement.

You may have heard this explanation a dozen times by now, so I’ll be brief and cheeky. Each satellite is constantly sending out a signal in all directions, which is easily detected by your GPS-enabled phone down on earth. The signal you receive contains both time and location info, which your phone then uses to tell you exactly where you are.

The special relativity kicker is that your phone has to take the speed of the satellites themselves into account, or else they won’t measure time correctly. Your phone calculates how long the signal took from that particular location in space to reach you, and it has to take into account that time moves slower for the fast-moving satellites.

Usually, we don’t notice time dilation on Earth, but with our GPS system, things are moving fast enough not only for us to measure, but indeed for us to create a modern wonder of the world.

General relativity explains that space is curved, so that’s why the satellites are falling. Like special relativity, it also has to be taken into account when considering how high up the satellites are relative to the Earth. This means the gravity is weaker, and that in turn means that time moves faster.

If you’re reliving high school math and waiting for these values to cancel one another out, don’t hold your breath. The effects from gravity are about seven times stronger, but isn’t it cool that you have to take both gravity and speed into account anyway?

For all of these reasons, GPS satellites contain the most accurate clocks human beings have ever created.

You might have noticed that I sort of glossed over the part where your phone knows what time it is. Given that we’re talking about fractions of microseconds here, we need a similar level of precision down on Earth.

The system that handles this is appropriately called Network Time Protocol, or NTP for short. It doesn’t sound very sexy, but without it, all kinds of terrible chaos would very likely ensue almost immediately.

And, while the GPS network is run by the US military (Space Force), NTP is held together by what seems like a wing and a prayer.

Like GPS, NTP works by comparing clocks against one another. A bunch of computers will typically send a message with a precise time stamp, and then compare it to several other time stamps. In this way, your phone becomes another ultra-precise device for measuring time.

This is crucial if you want to do a bank transaction, or if one bank wants to do business with another bank. If the time is off, the system flags the transaction for fraud, and it won’t work.

Similarly, anything you need two-factor authentication or HTTPS level security for? Probably not going to work. The real chaos emerges over time, though, as nobody wants to do business online any more, and websites themselves start breaking. Security becomes a pipe dream.

I mentioned that Space Force runs the GPS system, and you might think that with something as important as the NTP system, there might be a powerful governing body at its head, but this is very, very wrong.

The NTP system doesn’t really have anyone in charge of it.

Instead, it’s a bit like the internet itself, or maybe more like the wild west. It’s decentralized, and you can get away with a lot of things. A small group of so-called Stratum 1 time servers are made up of a mixture of government agencies, universities, and big tech companies. There are also some volunteers in Stratum 1, which sets the time for all other strata.

This is more of a patchwork than one cohesive unit. Ever see a patchwork quilt start to fall apart? It’s not pretty.

Most folks I talk to know by now how much we depend on the GPS system. Not terribly many know much about NTP, though, and it’s only a recent addition to my own mind’s menu. While the GPS system would continue working just fine without the Network Time Protocol system running, if GPS stopped, NTP would hit a wall very quickly.

One system has a robust and rigid governance, while the other is an ad-hoc collection of wild-west pirates. Either one going offline would really mess things up for us.

What other hidden systems are out there, where if they went down, everyone in the world would quickly notice? How many of these systems are patchwork quilts, and how many are run by one institution?