According to Einstein's theory of special relativity, as an object with mass approaches the speed of light, its energy requirements to accelerate further increase significantly, and its mass effectively becomes infinite. This means that it would require an infinite amount of energy to accelerate a massive object to the speed of light. Since we don't have access to infinite energy, it is impossible to accelerate an object with mass to the speed of light.
Additionally, as an object with mass gets closer to the speed of light, time dilation occurs. This means that time appears to slow down for the object in motion relative to an observer at rest. As the object approaches the speed of light, time dilation becomes more significant, and the object's time effectively "slows down" compared to an observer at rest.
For an object with mass, such as a spacecraft or a person, it would be theoretically impossible to reach or exceed the speed of light in a vacuum due to these effects. The closer an object with mass gets to the speed of light, the more energy is required, and the slower time passes for the object.
On the other hand, light itself travels at the speed of light in a vacuum. Light is made up of massless particles called photons, and as massless particles, they do not experience the same energy and time dilation effects as massive objects do. Therefore, light can travel at the speed of light, and nothing with mass can surpass or catch up to it. This is one of the fundamental principles of special relativity, and it forms the basis for why we cannot go faster than the speed of light in our universe.