According to Einstein's theory of relativity, an object with mass cannot be accelerated to or beyond the speed of light in a vacuum. As an object with mass approaches the speed of light, its relativistic mass increases, and the energy required to further accelerate it also increases, making it impossible to reach or exceed the speed of light.
However, if we consider a hypothetical scenario where an object with mass were somehow able to travel at the speed of light, the concept of length contraction, also known as Lorentz contraction, would come into play. According to Lorentz contraction, objects moving at relativistic speeds appear to be contracted along the direction of their motion as observed from a stationary reference frame.
In this scenario, if a person were traveling at the speed of light, the Lorentz contraction would indeed cause their body lengthwise as observed from a stationary reference frame. However, it is important to note that from the perspective of the person traveling at the speed of light, they would not experience any change in their own length or perceive any contraction of their body. This is because, according to relativity, an object in motion experiences no change in its own dimensions.
Nevertheless, it is crucial to reiterate that according to our current understanding of physics, objects with mass cannot reach or exceed the speed of light. The concept of Lorentz contraction is applicable to objects moving at speeds below the speed of light, and its effects become more pronounced as the speed of an object approaches the speed of light.