According to our current understanding of physics, a massive particle with rest mass requires infinite energy to travel at the speed of light in a vacuum. This conclusion is based on Einstein's theory of relativity, which includes the famous equation E=mc².
In the equation E=mc², "E" represents energy, "m" represents mass, and "c" represents the speed of light in a vacuum (approximately 299,792,458 meters per second). The equation states that the energy of an object with mass is equal to its mass multiplied by the square of the speed of light.
As an object with mass approaches the speed of light, its energy increases significantly. However, as the object's speed gets closer to the speed of light, the energy required to further increase its speed also increases. As the speed approaches the speed of light, the energy required becomes infinitely large. This is why it is said that it would require an infinite amount of energy for a massive particle to reach or exceed the speed of light.
On the other hand, particles with zero rest mass, such as photons (particles of light), can travel at the speed of light without requiring additional energy. For them, E=mc² simplifies to E=0, which means they have energy but no rest mass.
It's important to note that the concept of infinite energy requirements for mass to reach the speed of light is based on our current understanding of physics. The nature of space, time, and energy may have further insights in the future, and our understanding may evolve with new discoveries and theories.