Time dilation is not merely an observation of the effects on light; it is a real phenomenon predicted by the theory of relativity. Time dilation refers to the phenomenon where time runs at different rates for observers in different frames of reference relative to each other. It has been experimentally verified and is a fundamental aspect of our understanding of space and time.
According to the theory of relativity, time dilation occurs due to the relative motion between two observers or the presence of gravitational fields. When objects move relative to each other at high speeds or when they are in the vicinity of massive objects, time appears to pass slower for the moving or gravitationally influenced object as observed by a stationary observer.
One of the famous examples of time dilation is the twin paradox, where one twin travels at high speeds in space while the other remains on Earth. When the traveling twin returns, they would have experienced less time compared to their twin on Earth, leading to a noticeable difference in their ages.
Additionally, time dilation has been observed and measured in experiments such as the Hafele-Keating experiment, which involved atomic clocks being flown on airplanes. The clocks on the airplanes were found to run slower compared to synchronized clocks on the ground.
Therefore, time dilation is not solely an observation of the effects on light, but rather a consequence of the fundamental nature of spacetime as described by the theory of relativity. It has been supported by experimental evidence and is an integral part of our understanding of the universe.