We recount the successful long career of classical physics, from Newton to Einstein, which was based on the philosophy of scientific realism. Special emphasis is given to the changing status and number of ontological entitities and arguments for their necessity at any time. Newton, initially, began with (i) point particles, (ii) aether, (iii) absolute space and (iv) absolute time. The electromagnetic theory of Maxwell and Faraday introduced `fields' as a new ontological entity not reducible to earlier ones. Their work also unified electricity, magnetism and optics. Repeated failure to observe the motion of earth through aether led Einstein to modify the Newtonian absolute space and time concepts to a fused Minkowski space-time and the removal of aether from basic ontological entities in his special theory of relativity. Later Einstein in his attempts to give a local theory of gravitation was led to further modify flat Minkowski space-time to the curved Riemannian space time. This reduced gravitational phenomenon to that of geometry of the space time. Space-time, matter and fields all became dynamical. We also abstract some general features of description of nature in classical physics and enquire whether these could be features of any scientific description?
Realism has been the dominant ontology among the practicing scientist until at least the discovery of quantum mechanics in mid nineteen twentities. Indeed the origin of science among the ancient greeks itself depended on it. As Erwin Schrödinger, in his delightful Shearman lectures given at University College at London in 1948 and later printed as "Nature and Greeks", emphasized that Greeks based their study of Nature on the following presuppositions:
(i) “the hypothesis that the display of Nature can be understood”, and (ii) “the hypothesis of a real world around us”.
The first of these leads one away from arbitrary mythological way of thinking, and the second of these to the “objectivation of the world”. These are essentially the creed of scientific-realism.
The foundations of the classical physics, with which modern development of physics begins, at the end of the medieval world, were laid down by the great Isaac Newton (1642-1727).
Newtonian mechanical view of the physics takes the matter in the world to consist of a number of “absolutely hard indestructible particles”, each endowed with a mass, moving on the stage of unchanging three-dimensional space with time under the action of mutual forces. He also discovered the “inverse square of the distance” law for the gravitational force between two bodies. The law was of an “action at a distance form”. This law of gravitation, together with Newtons three laws of dynamics, gave a remarkably accurate description of planetary motion. He thus laid the foundations of his system of the world in his magnum opus “Principia” (1687).
Newton also postulated an elastic medium “aether” to pervade the entire space and all the bodies contained theirin. It’s density was taken to be greatest in the interplatenatry space and variable in the various bodies. It was also, on the analogy of water vapour in the air, taken to contain various ‘aetherial spirits’, suitable to produce the phenomenon of electricity, magnetism and even gravitation.
Unlike Hooke and others who took light to be waves the medium ‘aether’, Newton rejected the conception of light as waves. His two main arguments for the rejection were (i) the propagation of light rays in straight lines, and (ii) the phenomenon of polarisation of light which he had observed. Another reason as to why Newton did not favour wave nature for light was his theory of colours arising out of his experiments on light refraction through glass prisms. They proved to him that different colours are already present in white light before it is incident and these are not produced due to it’s refraction. Hooke had regarded colours to be produced due to the effect of medium of wave propagation. This not being the case Newton rejected the Hooke’s wave hypothesis for light as well. The light for Newton thus had a corpuscular nature. The light and aether however affected each other.
When we observe the collision of two bodies on earth, we see a slowing down of the motion due either to inelasticity of the bodies or friction. Nowadays we attribute this to a conversion of mechanical energy to other forms of energy. But, in Newton’s time, such a principle of conservation of energy had not yet been formulated. So for Newton, another reason for the ‘aether’ was it’s need to avoid the slowing down of the observed planetary motions over long durations of time.
Thus Newtonian mechanics, with which classical physics begins, and which is one of it’s magnificient achievements, subscribes to realism. It’s ontology has (i) massive particles, (ii) space, (iii) time and (iv) aether as the basic real entities.
The observation of the burning power of convex glasses at their focus, however, suggested to Christiaan Huygens strongly that light must be basically a wave motion. The burning implies that light is associated with some kind of motion. In this experiment light beams moving in different direction do not obstruct each other in any way but are rather reinforcing in their effect which is possible with wave motion in a medium but unlikely for projectiles moving in different dimensions. He therefore came out strongly in favour of wave theory of light. He also made great advances in the mathematical theory of wave propagation. He reported all these researches to the French Academy in 1678. Light was now regarded as waves in the universal medium aether.
Further strong support for wave theory of light came in 1801 when Thomas Young explained “Neweton’s rings” on the wave theory, and later using the same ideas the colours of thin films. He clearly formulated the general laws of interference of light waves and his “double slit” interference experiment is one of the celebrated experiments in history of physics. As interference phenomenon is not possible to understand on the corpuscular theory of light, it provides strong evidence for the wave theory. The mathematical treatment of diffraction of light, using wave theory was achieved by Auguste Jean Frencl in h
This content is AI-processed based on open access ArXiv data.
