NOTES ON PHILOSOPHY OF SCIENCE
Newton was not the first to try to explain universal gravitation; Descartes for example proposed that space was filled with unobservable particles the motion of which mediated the force of gravity on matter. The advantage of Newton's laws over such theories was that not only were the elliptic planetary orbits of Kepler accounted for but that with the aid of the mathematics discovered by Newton all motions of bodies in the solar system could be computed. To this day Newtonian celestial mechanics is adequate for problems which do not involve speeds close to that of light or immense gravitational fields. The important feature of Newton's laws, which attracted such opposition from eg Huygens and Leibniz, was that they were merely a set of mathematical rules for the computation of the motion of matter; he expressly did not attempt to give an 'explanation' of the postulated action at a distance; the justification was the successful prediction of celestial and other events.
This abstract characteristic of physical theory was repeated in the equations describing the electromagnetic field discovered by J C Maxwell around 1860. He took the experimental results of Faraday and others and produced a mathematical theory which among other things demonstrated that light (and radio waves, not then known) were electromagnetic phenomena. Many physicists in the 19C attempted to formulate mechanical models of a space-filling ether which would behave according to Maxwell's equations. All these attempts failed and we have to this day a purely mathematical picture of the electromagnetic field.
The replacement by Poincaré and Einstein of Newton's theory by relativity began with a philosophical objection : that the assumption by Newton of absolute space and time was unjustified. The requirement of the invariance of the speed of light (implicit in Maxwell's equations) gave rise by direct calculation to the equations of special relativity and their well-known and counter-intuitive consequences. His realization of the significance of the identity of inertial and gravitational mass led Einstein further to general relativity. He made use of the very complex mathematics of the curvature of surfaces and spaces to give an all-embracing geometrical description of gravitation. This theory included Newton's laws as a special case.
The advent of quantum mechanics in the 1920's gave us a theory which accounted for large numbers of otherwise incomprehensible physical phenomena. The whole of modern electronic technology (transistors, lasers, atomic clocks, ........) depends on the application of quantum mechanical principles. There have been many attempts by physicists to find an interpretation of QM which would eliminate the numerous apparent paradoxes which it contained. These attempts have been largely unsuccessful, and the majority of physicists now view the theory as purely a set of rules which if followed give extremely accurate answers.
Thus we see physics as a collection of mathematical structures which make it possible to predict with great accuracy the behaviour of a large part of the physical universe. But if we ask questions such as 'what is an electron ?' or 'what is the nature of reality?', or demand an intuitive understanding of nature, then physical theory is found wanting.
Alan Edmonds