He assumed that the speed of light is the maximum velocity any mass-energy can attain. Obviously, no experiment will ever detect what is greater than an attainable maximum. Theories deal with generic features of a subject, with explanations for groups of facts or classes of events as a whole. They serve our understanding precisely because they exist in the ideal, operate in the abstract, and lend themselves to perfectibility. For many of Nature's secrets lie beyond experience.
Experiments yield controlled experiences.
By their very character, experiments must focus on particular observations. They furnish concrete examples of a subject in the reality we know best. But experiments cannot penetrate to the ideal core of a theory, and they cannot take us to the repository of the theory's meaning. Experiments may let us examine a theory's consequences and test its predictions. They may produce the results a theory forecasts, and by so doing establish widespread belief in the theory.