Time feels constant in our everyday lives. Seconds tick steadily, minutes pass uniformly, and hours seem predictable. Yet, modern physics tells us that time is not fixed. Einstein’s theory of relativity reveals that time is flexible—it can speed up or slow down depending on motion and gravity.

Special relativity shows that when an object moves very fast, close to the speed of light, time for that object slows down compared to a stationary observer. This is not a trick of perception; it has been confirmed through experiments using precise atomic clocks on fast-moving planes or satellites. The faster you move, the slower time passes for you relative to someone at rest.

General relativity takes this a step further by linking time to gravity. Massive objects, like planets, stars, or black holes, warp the fabric of space-time around them. Clocks placed closer to these massive objects tick more slowly than clocks farther away. This effect, called gravitational time dilation, has been measured on Earth and in space, proving that time is influenced by mass.

The flexibility of time has practical implications. Global Positioning System (GPS) satellites must account for both their high speeds and the weaker gravity at their altitude. Without correcting for these effects, GPS calculations would quickly become inaccurate, leading to navigation errors.

Relativity shows that time is not universal or absolute. It is intertwined with space and responds to motion and gravity. This understanding challenges our everyday intuition and opens a window into the true nature of the universe, where time is a dynamic dimension, as flexible as the space it inhabits.