The statement that nothing with mass can travel at 100% the speed of light is a fundamental principle of physics and is derived from Einstein's theory of special relativity, which was first published in 1905. This principle has been tested and confirmed by numerous experiments over the years.
There are a few key reasons why an object with mass cannot reach the speed of light:
Increasing mass: As an object with mass accelerates, its relativistic mass increases, meaning it requires more and more energy to continue accelerating. As it approaches the speed of light, its mass approaches infinity, and it would require an infinite amount of energy to reach the speed of light. This makes it physically impossible for a massive object to reach or exceed the speed of light.
Time dilation: As an object's speed increases, time slows down for that object relative to an observer at rest. As the object approaches the speed of light, time dilation becomes more significant. At the speed of light, time would stop altogether for the object. This poses a paradox, as infinite time would be required for the object to reach that speed from its perspective.
Lorentz factor: The Lorentz factor is a fundamental component of the equations of special relativity that describes how time, length, and mass change as an object's speed approaches the speed of light. As the speed of the object increases, the Lorentz factor approaches infinity, which leads to the previously mentioned effects like infinite mass and time dilation.
Massless particles: While objects with mass cannot reach the speed of light, massless particles, such as photons (particles of light), always travel at the speed of light in a vacuum. Since they have no rest mass, the issues related to increasing mass and time dilation do not apply to them.
In summary, based on our current understanding of physics and the principles of special relativity, anything with mass cannot reach or exceed the speed of light in a vacuum. The speed of light, denoted by "c," is a fundamental constant and represents the ultimate speed limit in the universe.