According to our current understanding of physics, the speed of light in a vacuum, denoted by the symbol 'c', is considered to be the maximum speed at which information or causal influence can travel in the universe. This limitation is a fundamental feature of Einstein's theory of relativity, which has been extensively tested and confirmed by numerous experiments.
In quantum field theory (QFT), which combines quantum mechanics and special relativity, particles are understood as excitations or quanta of underlying quantum fields. These quantum fields pervade all of space and interact with particles. Each type of particle, such as electrons or photons, is associated with its corresponding quantum field.
It is important to note that quantum fields themselves do not possess a velocity. Rather, it is the excitations or particles that propagate and move at speeds below or equal to the speed of light. In quantum field theory, the behavior of particles and their interactions are described by mathematical equations, such as the Dirac equation for electrons or the Maxwell's equations for photons. These equations are consistent with the relativistic limit of information or causal influence propagating at or below the speed of light.
If there were particles or excitations that could travel faster than the speed of light, it would lead to significant challenges and conflicts with our current understanding of physics. It would violate causality, allowing for potential violations of cause-and-effect relationships and leading to paradoxes such as time travel or communication with the past.
While there are speculative theories and hypotheses that explore exotic concepts like tachyons (hypothetical particles that always travel faster than light), these ideas are not currently supported by empirical evidence or widely accepted within the scientific community. Until new experimental data or theoretical frameworks emerge that revise our understanding of the fundamental limitations set by relativity, the speed of light remains the upper limit for the propagation of information and causal influence in the universe.