Time dilation is a phenomenon predicted by Einstein's theory of relativity, specifically the theory of special relativity. It states that the passage of time is not constant for all observers and can vary depending on relative motion or gravitational fields.
Proper time, also known as the "time experienced by a clock at rest in a particular reference frame," is affected by time dilation. When an object or observer is in motion relative to another object or observer, their respective clocks will measure time differently.
According to special relativity, as an object's velocity increases, time dilation occurs, and time appears to slow down for the moving object relative to a stationary observer. This effect becomes more prominent as the object's velocity approaches the speed of light.
In the case of gravitational time dilation, the presence of a gravitational field also affects the passage of time. According to general relativity, a massive object, such as a planet or a star, curves the fabric of spacetime around it. This curvature causes clocks closer to the massive object to run slower compared to clocks farther away from the gravitational source.
In both cases, whether due to relative motion or gravitational fields, proper time dilation means that an observer or object experiences time differently compared to another observer or object in a different reference frame. This effect has been experimentally verified, notably in experiments involving atomic clocks on high-speed aircraft or satellites.
In summary, proper time is affected by time dilation, causing time to appear to slow down or speed up depending on relative motion or the strength of a gravitational field.