Time dilation is a phenomenon predicted by the theory of relativity, which states that time can appear to pass differently for objects that are moving relative to each other. This concept is a consequence of the relativity of simultaneity and the constancy of the speed of light in all inertial reference frames.
When we say speed is relative, we mean that the measurement of speed depends on the observer's frame of reference. An observer in a particular reference frame will measure the speed of an object relative to their own frame. However, time dilation is not about the speed itself but rather the effect it has on the passage of time.
According to the theory of relativity, the rate at which time flows is not constant for all observers. It depends on the relative motion between the observer and the object being observed. When an object moves at speeds close to the speed of light, time appears to pass more slowly for that object compared to a stationary observer.
To understand time dilation, we need to consider two observers in different reference frames moving relative to each other. When they compare their measurements of time intervals or clocks, they will find that the moving observer's clock appears to tick slower from the perspective of the stationary observer. Conversely, the moving observer will perceive time passing normally for themselves.
This phenomenon occurs because the speed of light is constant in all inertial reference frames. As an object accelerates to relativistic speeds, its measurement of time is affected, and the flow of time is "dilated" or stretched out. The closer an object's velocity is to the speed of light, the more pronounced the time dilation effect becomes.
In summary, time dilation occurs due to the relative motion between observers and is not relative to a specific reference point. It is a consequence of the constancy of the speed of light and the way it affects the measurement of time for objects moving at high speeds.