THE CONCEPTS OF CLASSICAL PHYSICS
Classical physics represents the theories and laws which describe medium-sized phenomena. Historically, it is the part of physics that has been developed first since it is so close to the experience of every-day life. Starting from Newton's mechanics of particles, classical physics has extended mechanics to elastic and fluid media, and it has developed a theory of optics and of electricity and magnetism, as well as a description of the phenomena of heat. Its culmination is found in the theory of relativity through which the main concepts have been re-formulated and, thereby, classical physics has been unified. To-day we cannot help looking at classical concepts with a critical attitude acquired from relativity theory. Unless we are interested in the historical development there is no reason in keeping to an original, rather vague, formulation of the basic concepts which relativity theory has done so much to analyse. When we reconstruct the system of physics to-day, it is from a more logical viewpoint that we approach it, and from a basis given by relativity. This is another example of the self-correcting method of science: a more advanced theory in turn clarifies the concepts of the original theory upon which it is built.
The great achievement of Newton lies in the introduction of the mathematical method. And his method consists not only in giving, or attempting to give, an axiom system for mechanics. It is the consistent use of an artificial symbolism--the invention of a calculus, and the power of the differential equation--that is mainly responsible for the success of Newtonian mechanics. For this enabled us to make use of vague and obscurely formulated ideas and still to achieve a precise statement of the laws. It has freed us from the limitations of the verbal formulation for our experiences upon which Galileo and Kepler had to rely.
In becoming increasingly more abstract the language of