According to the theory of special relativity, as an object approaches the speed of light in the reference frame of another observer, several interesting phenomena occur.
Firstly, an object with mass cannot actually reach or exceed the speed of light in classical physics. As an object with mass accelerates, its relativistic mass increases, and the energy required to accelerate it further also increases. At the speed of light, the object's relativistic mass would become infinite, making it impossible to achieve.
However, we can still discuss what happens as an object approaches the speed of light. According to the theory of special relativity, two important effects occur: time dilation and length contraction.
Time dilation refers to the phenomenon where time appears to slow down for an object moving relative to another observer. From the perspective of the stationary observer, time appears to pass more slowly for the moving object. As the object approaches the speed of light, time dilation becomes more pronounced, and the moving object's time appears to slow down significantly.
Length contraction, on the other hand, refers to the shortening of the length of an object as it moves relative to another observer. From the perspective of the stationary observer, the length of the moving object appears to contract along its direction of motion. As the object approaches the speed of light, its length contracts more and more, eventually becoming infinitely contracted at the speed of light.
It's important to note that these effects are observed from the perspective of the stationary observer. For an object moving at relativistic speeds, it would experience these effects relative to a stationary observer but would perceive time and length as normal from its own reference frame.
However, it is worth mentioning that these effects are not directly applicable to objects with mass, as they cannot reach or exceed the speed of light. These effects become significant for objects moving at a significant fraction of the speed of light but not for objects with mass moving at the speed of light itself.