T.L. Gilbert, who thinks that scientific fact is a language-based social construct (The Scientist, Sept. 2, 1996, page 12), is actually beginning to think like a physicist. For ages, physicists have agreed with Gilbert's example that meters and seconds (and kilograms, and the imperialist feet and pounds mass) are arbitrary. Hence they use "natural" units, by taking ratios with natural constants. As an example, one measures velocities by comparing them with the greatest velocity-that of light. In this way, the measurements of the little green people in the extra-solar planet Beeblebrox II can be directly compared with our measurements, and the otherwise-fascinating sociology of the little green creatures is irrelevant here. The basic entities of physics are then ratios with natural phenomena (for example, the mass and charge of the electron) that are the same throughout the universe.
Gilbert will be delighted to hear that, for many years, the velocity ...
