Abstract: Science documentary 《Time Travel》 is outlined theoretically for realistic ideas of traveling through time. It is a good multi-media material for teaching relativity theory. Data in the film, such as to orbit the black hole and GPS, are demonstrated by using the theory of relativity. The calculation methods of time dilation under the strong and weak gravitational field are discussed. Under the weak field it can be directly used time dilation equation in special relativity and gravitational time dilation equation in general relativity. The comprehensive effect is equal to the sum of the above two results approximately.

Key words: relativity, gravitational time dilation, black hole, Schwarzschild solution, GPS