The reason why time appears to move slower as we approach the speed of light, rather than distance appearing to shorten, is due to the fundamental nature of spacetime and the principles of special relativity.
According to Einstein's theory of special relativity, spacetime is a four-dimensional framework that combines three dimensions of space and one dimension of time into a unified entity. In this framework, the speed of light, denoted as 'c,' plays a fundamental role.
Special relativity states that the laws of physics are the same for all observers in uniform motion relative to each other. However, it also introduces the concept of time dilation, which means that time is not absolute but depends on the relative motion between observers.
When an object moves at speeds comparable to the speed of light, the relative motion affects the passage of time for that object compared to a stationary observer. This effect is known as time dilation. As an object accelerates towards the speed of light, its internal clock, or the rate at which time is experienced within the object, appears to slow down from the perspective of an external observer.
This phenomenon occurs because the speed of light is an absolute speed limit in the universe, and as an object approaches that limit, the relationship between space and time changes. Time dilation is a consequence of the need to maintain the constancy of the speed of light for all observers, regardless of their relative motion.
On the other hand, distances do not appear to shorten for the moving object. The concept of length contraction is related to the observation of objects in motion, but it is not directly linked to the speed of light. Length contraction describes how the length of an object moving relative to an observer appears shorter in the direction of motion. However, this effect is primarily relevant in relative motion scenarios, not specifically tied to approaching the speed of light.
In summary, as an object approaches the speed of light, time dilation occurs, leading to the perception of time moving slower for the moving object relative to an observer. This is a consequence of the nature of spacetime and the constancy of the speed of light, as described by the theory of special relativity.