According to Einstein's theory of relativity, as an object approaches the speed of light, time dilation occurs. Time dilation means that time appears to pass more slowly for objects in motion relative to an observer at rest. This effect has been experimentally verified and is a fundamental aspect of our understanding of the universe.
When an object, such as a person, is moving close to the speed of light relative to another observer, time dilation occurs from the perspective of the stationary observer. However, the person moving at high speed will not subjectively perceive time slowing down for themselves. From their point of view, time continues to pass normally, and their personal experiences are unaffected.
This phenomenon can be difficult to grasp intuitively, but it arises from the nature of spacetime as described by Einstein's theory. In relativity, there is no privileged frame of reference, meaning that no observer's viewpoint is considered more "correct" than another's. Time dilation occurs because the relative motion between two frames of reference causes a difference in the perception of time between them.
To illustrate this, let's consider an example: Suppose there are two observers, one on Earth and one aboard a spacecraft traveling at a significant fraction of the speed of light. The observer on Earth sees the clock on the spacecraft ticking more slowly than their own clock due to time dilation. However, the observer aboard the spacecraft sees their own clock ticking normally while observing the clock on Earth as running slower. Each observer is correct from their perspective, and they will not personally experience time dilation.
This apparent contradiction can be resolved by considering that the observers in relative motion experience different spacetime intervals. The effects of time dilation become apparent when they reunite and compare their clocks.
In summary, a person moving at high speeds relative to an observer at rest will not subjectively perceive time slowing down for themselves. Time dilation is a relative effect observed by different observers in relative motion, and each observer will experience time passing normally from their own perspective.