Time dilation is a phenomenon predicted by Einstein's theory of relativity, specifically in the context of special relativity. It refers to the difference in the passage of time between two observers in relative motion relative to each other.
According to special relativity, the flow of time is not an absolute concept but depends on the relative motion between observers. When two observers are moving relative to each other at constant velocities, they will perceive time passing differently.
Specifically, if one observer is moving at a significant fraction of the speed of light relative to the other observer, time will appear to pass more slowly for the moving observer as perceived by the stationary observer. This means that clocks carried by the moving observer will appear to tick slower compared to identical clocks at rest with respect to the stationary observer.
To understand this effect, consider an example: Suppose there are two observers, Alice and Bob, and they each have a synchronized clock. If Alice is in a spaceship traveling at a high velocity relative to Bob, then from Bob's perspective, Alice's clock will appear to tick slower compared to Bob's own clock.
This time dilation effect arises from the fact that the speed of light is constant for all observers, regardless of their relative motion. To maintain this constancy, the perception of time passing must adjust to accommodate the observed effects of relative motion.
It's important to note that time dilation is a symmetrical effect. Both observers will consider the other's clock to be running slower from their own perspective. This symmetry is a fundamental aspect of special relativity.
In summary, time dilation refers to the difference in the passage of time between observers in relative motion. Clocks in different inertial frames will appear to run slower for observers in frames that are moving relative to each other.