The theory of time travel is based on Einstein's theories of relativity, and includes the following concepts.
Time travel into the future
Einstein's theory of relativity suggests that an object traveling at the speed of light could travel into the future.
Time travel and motion
Einstein's special theory of relativity states that time passes more slowly for objects moving faster.
Time travel and gravity
Einstein's general theory of relativity states that time passes more slowly in areas with stronger gravity.
Time travel and experiments
Scientists have conducted experiments using atomic clocks and high-speed travel to observe small time effects. One experiment compared two clocks, one on Earth and one on an airplane, and found that the clock on the airplane was slightly behind the clock on Earth.

The Book of Time travel reality.