According to the theory of relativity, the speed of light in a vacuum, denoted by 'c', is considered a fundamental constant of nature. In the theory, the speed of light is postulated to be the maximum attainable speed for any object with mass. This assertion is based on experimental evidence and is a cornerstone of the theory.
The concept of tachyons, hypothetical particles that travel faster than light, arises from speculative extensions of relativity. Tachyons, if they exist, would have an imaginary rest mass and would always travel faster than the speed of light. However, it is important to note that tachyons are currently purely hypothetical and have not been observed or confirmed in experiments.
The theory of relativity, as it stands, does not allow for the existence of particles that travel faster than light because it would lead to apparent violations of causality. If information or signals could be transmitted faster than light, it could potentially result in effects preceding their causes, leading to paradoxes and inconsistencies.
The speed of light being a universal constant is a fundamental tenet of the theory, and it is supported by a vast body of experimental evidence. This constant is deeply intertwined with the structure of spacetime, as described by the theory of relativity, and plays a crucial role in understanding and explaining various phenomena in physics.
However, it is worth mentioning that theoretical physics is an ongoing field of research, and scientists continue to explore and test new ideas and theories. While the current understanding of relativity suggests the impossibility of faster-than-light travel, future discoveries could potentially lead to the revision or expansion of our knowledge on this topic.