The concept that time moves slower in outer space is a consequence of the theory of relativity, specifically the theory of special relativity formulated by Albert Einstein. According to this theory, the rate at which time passes depends on the relative motion between observers and the strength of the gravitational field they experience.
There are two main phenomena related to time dilation: time dilation due to relative velocity (kinetic time dilation) and time dilation due to gravity (gravitational time dilation).
Kinetic Time Dilation: When an object or observer is in motion relative to another object, time appears to pass more slowly for the moving object as observed by the stationary observer. This effect becomes noticeable at speeds approaching the speed of light. For example, astronauts traveling in a high-speed spacecraft experience a slightly slower passage of time compared to someone on Earth.
Gravitational Time Dilation: Gravity also affects the passage of time. The stronger the gravitational field, the slower time appears to pass for an observer within that field. This means that time passes more slowly near massive objects like planets, stars, or black holes. For example, an observer close to a massive object would experience time passing more slowly compared to someone in a weaker gravitational field.
In outer space, away from significant gravitational influences and at high velocities, both forms of time dilation can occur simultaneously. For instance, astronauts on the International Space Station experience a combination of kinetic time dilation due to their high orbital velocity and a weaker gravitational field compared to Earth's surface. As a result, their clocks run slightly slower relative to clocks on Earth.
It's important to note that these time dilation effects are extremely subtle and become more significant at extreme speeds or in proximity to massive objects. They have been experimentally confirmed through precise measurements and are essential considerations in fields like space travel, satellite navigation, and fundamental physics.