According to our current understanding of physics, as an object with mass approaches the speed of light, its energy and momentum increase dramatically. However, it is impossible for an object with mass to reach or exceed the speed of light in a vacuum. This is due to Einstein's theory of relativity, specifically the theory of special relativity.
According to special relativity, the closer an object with mass gets to the speed of light, the more energy is required to accelerate it further. As the object's velocity approaches the speed of light, its mass effectively increases, and it would require an infinite amount of energy to accelerate it to the speed of light itself. This concept is described by the relativistic mass equation:
m = m0 / sqrt(1 - v^2/c^2)
where m is the relativistic mass, m0 is the object's rest mass, v is its velocity, and c is the speed of light.
As an object's velocity approaches the speed of light, its relativistic mass increases, making it more and more difficult to accelerate further. This means that an object with mass can never quite reach or exceed the speed of light. Instead, its velocity can approach the speed of light asymptotically but never quite reach it.
From the perspective of an observer, time dilation and length contraction effects would also become significant as an object approaches the speed of light. Time would appear to slow down for the moving object relative to a stationary observer, and its length in the direction of motion would appear to contract. These relativistic effects become more pronounced as the object's velocity increases.
In summary, as an object with mass approaches the speed of light, its energy and momentum increase, its mass effectively increases, and time dilation and length contraction effects become significant. However, it is impossible for an object with mass to reach or exceed the speed of light.