Why Do Clocks Disagree
One of the greatest mysteries about time is why clocks can disagree. Throughout history, clocks have been built to keep time in sync with one another. Yet we find that under certain conditions, they don’t.
Fast-moving clocks disagree with stationary clocks. Clocks high above Earth disagree with clocks on the ground. Even tiny particles called muons behave as though their internal clocks have changed.
Scientists call this time dilation. But is time changing, or are clocks changing? The most common and accurate example comes from GPS clocks that disagree with reference clocks.
Millions of phones and countless modern technologies depend on GPS. Airplanes, emergency services, cars, ships, and even power grids rely on satellites whose clocks remain synchronized.
If the clocks were allowed to drift by a few microseconds each day, GPS positions would soon be wrong by several kilometers. The system works because the clocks are systematically synchronized.
GPS engineers never adjust “time itself.” They adjust clocks so that every satellite stays synchronized with Earth. That raises an interesting question.
If engineers can correct the clocks by changing their operation, have they changed time itself? Or have they simply changed the mechanisms used to measure time?
The observations are consistent with the idea that the clock’s physical mechanism has changed. There’s a possibility that what we call time dilation may actually reflect a change in the behavior of clocks rather than in time itself.
GPS satellite clocks naturally run about 38 microseconds per day faster than identical clocks on Earth, just as Einstein’s theory predicts.
Are clocks actually measuring time itself, or are they measuring physical processes that change? How can we tell the difference?
GPS provides an opportunity to study atomic clocks, satellite timing, and the physical mechanisms that keep them synchronized.
If these methods remove time dilation to keep accurate time, then is time a physical thing that is manipulated? Moreover, does time dilation affect only clocks, not time itself?
Every clock is a machine. Whether it uses gears, a quartz crystal, or vibrating cesium atoms, it measures time by counting physical events.
However, time itself is not a machine. If every clock could be slowed or sped up, would time itself change worldwide? That question leads us to one of the most remarkable experiments in modern physics.