Gravitational time dilation occurs because objects with a lot of mass create a strong gravitational field. The gravitational field is really a curving of space and time. The stronger the gravity, the more spacetime curves, and the slower time itself proceeds.

What causes time dilation?

Time dilation goes back to Einstein's theory of special relativity, which teaches us that motion through space actually creates alterations in the flow of time. ... The clock in motion will tick more slowly than the clocks we're watching on Earth.

Why does time slow down the faster you move?

As light is spread out by the observer moving away from the source of the light time is decreased. The faster the observer moves the more light is spread out and time slows down. ... Time slows down as you travel faster because momentum bends the fabric of spacetime causing time to pass slower.