The assertion that the speed of light is the fastest possible speed in the universe is based on our current understanding of physics and is supported by a substantial body of experimental evidence. Here are a few key points:
Einstein's Theory of Special Relativity: In 1905, Albert Einstein introduced the theory of special relativity, which revolutionized our understanding of space, time, and the behavior of objects moving at high speeds. One of the fundamental principles of this theory is that the speed of light in a vacuum is constant and is the same for all observers, regardless of their relative motion. This constancy of the speed of light has been confirmed by numerous experiments.
Experimental Confirmation: Over the past century, a wide range of experiments and observations have consistently supported the constancy of the speed of light. These experiments include measurements of the speed of light using various techniques and the observation of relativistic effects, such as time dilation and length contraction, in high-speed particle accelerators and cosmic ray experiments.
Lack of Evidence for Faster-Than-Light Travel: Despite extensive scientific investigation, no experimental evidence has been found to suggest the existence of particles, objects, or signals that can travel faster than light. Any such discoveries would require a significant revision of our current understanding of physics.
While our understanding of the universe is continually evolving, and new theories may emerge in the future, it is worth noting that any alternative theory proposing faster-than-light travel would need to explain and be consistent with a vast range of experimental observations and fundamental principles of physics. To date, no alternative theories have gained widespread scientific acceptance that challenge the constancy of the speed of light in a vacuum as a fundamental limit.