When you open a map app and watch the little blue dot guide you, it feels simple. But behind the scenes, satellites orbiting Earth are doing complicated physics to keep your location accurate.

Without adjustments from Einstein’s theory of relativity, your GPS could be wrong by kilometers each day. For Lykkers, this is one of the funniest facts in science: your phone works properly because time itself flows differently in space!

Understanding Time Dilation

To see why GPS needs Einstein, let’s first explore what time dilation really means.

Time Doesn’t Flow Equally

According to Einstein’s relativity, time isn’t absolute—it can stretch or shrink depending on speed and gravity. A clock moving quickly or sitting far from Earth’s pull will tick differently compared to one on the ground.

The Role of Speed

Satellites orbit Earth at high speeds—about 14,000 kilometers per hour. Because of this motion, their onboard clocks tick more slowly than those on Earth. This is called special relativity’s effect, and it causes satellite time to lag behind.

The Role of Gravity

Here’s the twist: satellites are also farther from Earth’s center, so gravity is weaker where they are. General relativity says that in weaker gravity, clocks tick faster. So while speed slows them down, gravity actually speeds them up.

Why GPS Depends on It?

Now that you know time doesn’t behave the same everywhere, let’s connect this to your GPS.

Satellites Need Perfect Timing

GPS works by measuring how long signals from satellites take to reach your device. Even a billionth-of-a-second error creates a big location mistake. Without correction, the system would drift by about 10 kilometers every day—hardly useful for finding your favorite café.

Relativity Keeps It Accurate

Engineers build relativity into the satellites’ design. They adjust the onboard clocks so that once in orbit, their tick matches Earth-based time. This ensures that when signals reach your phone, the calculations are precise and consistent.

Your Phone, Powered by Physics

Every time you use GPS, you’re casually using Einstein’s theories. Without those corrections, maps would fail within minutes. So the funny truth is that relativity isn’t just about distant galaxies or thought experiments—it’s baked into your daily routine.

Time dilation, once a strange idea from Einstein, has become an everyday necessity. Satellites move fast and sit in weaker gravity, causing their clocks to run at a different pace than ours on Earth. By adjusting for both effects, engineers keep GPS accurate down to the meter. For Lykkers, the lesson is delightful: the same physics that reshaped our view of the universe is also guiding your morning commute. The next time your phone says “turn right,” thank Einstein for keeping the clock in sync.