Time dilation depends primarily on both proximity to a massive object and relativistic velocity.
According to Einstein's theory of relativity, there are two main factors that contribute to time dilation: gravitational time dilation and velocity time dilation.
Gravitational Time Dilation: This occurs due to the influence of gravity and the curvature of spacetime caused by massive objects. The closer an object is to a massive body, such as a planet, star, or black hole, the stronger the gravitational field. As a result, time runs slower for an observer in a stronger gravitational field compared to an observer in a weaker field. This effect is known as gravitational time dilation. The greater the proximity to a massive object, the more significant the time dilation experienced.
Velocity Time Dilation: This occurs due to relative motion between two observers. According to the theory of relativity, as an object moves closer to the speed of light, time runs slower for that object compared to a stationary observer. This effect is known as velocity time dilation or special relativity time dilation. The faster an object moves, the more pronounced the time dilation becomes.
It's important to note that the effects of gravitational time dilation and velocity time dilation are distinct and can be independently observed. However, in situations where both factors are present simultaneously, such as near a massive object with high velocity, the total time dilation experienced is a combination of the two effects.
In summary, time dilation depends on both proximity to a massive object (gravitational time dilation) and relativistic velocity (velocity time dilation), with each effect playing a significant role in different scenarios.