The phenomenon you are referring to is known as time dilation and length contraction, which are consequences of Einstein's theory of special relativity. Special relativity provides a framework for understanding the behavior of objects moving at speeds approaching the speed of light.
According to special relativity, the laws of physics are the same for all observers in inertial reference frames, regardless of their relative motion. However, the theory introduces the concept that the speed of light in a vacuum, denoted as "c," is a fundamental constant and is the same for all observers, regardless of their motion.
When an observer moves at speeds much slower than the speed of light, the effects of time dilation and length contraction are negligible and not readily noticeable in everyday life. However, as an object's velocity approaches the speed of light, these effects become more pronounced.
Time dilation refers to the phenomenon where time appears to slow down for a moving object relative to a stationary observer. From the perspective of the moving object, its own time appears to pass at a normal rate. However, to an outside observer, time for the moving object appears to be dilated or slowed down. This means that processes, such as aging or the ticking of a clock, would be observed to occur more slowly for the moving object.
Length contraction, also known as Lorentz contraction, is the phenomenon where the length of an object moving at high speeds appears to shorten along its direction of motion. To an observer at rest relative to the object, the object's length appears contracted or compressed compared to its length at rest.
These effects arise due to the nature of spacetime as described by special relativity. As an object's velocity increases, its motion through spacetime becomes more "tilted" towards the time dimension. This leads to the stretching of time and the contraction of length as observed by a stationary observer.
It is important to note that these effects are only significant at speeds close to the speed of light. In everyday situations, their impact is negligible because our velocities are much smaller compared to the speed of light.
In summary, as an object's velocity approaches the speed of light, time dilation and length contraction become significant. Time appears to slow down for the moving object, and its length appears contracted from the perspective of a stationary observer. These effects arise due to the nature of spacetime described by Einstein's theory of special relativity.