The stage of the Newtonian universe, on which all physical phenomena took place, was the three-dimensional space of classical Euclidean geometry. It was an absolute space, always at rest and unchangeable. In Newton’s own words, ‘Absolute space, in its own nature, without regard to anything external, remains always similar and immovable.’6 All changes in the physical world were described in terms of a separate dimension, called time, which again was absolute, having no connection with the material world and flowing smoothly from the past through the present to the future. ‘Absolute, true, and mathematical time,’ said Newton, ‘of itself and by its own nature, flows uniformly, without regard to anything external.’7
The elements of the Newtonian world which moved in this absolute space and absolute time were material particles. In the mathematical equations they were treated as ‘mass points’ and Newton saw them as small, solid, and indestructible objects out of which all matter was made. This model was quite similar to that of the Greek atomists. Both were based on the distinction between the full and the void, between matter and space, and in both models the particles remained always identical in their mass and shape. Matter was therefore always conserved and essentially passive. The important difference between the Democritean and Newtonian atomism is that the latter includes a precise description of the force acting between the material particles. This force is very simple, depending only on the masses and the mutual distances of the particles. It is the force of gravity, and it was seen by Newton as rigidly connected with the bodies it acted upon, and as acting instantaneously over a distance. Although this was a strange hypothesis, it was not investigated further. The particles and the forces between them were seen as created by God and thus were not subject to further analysis. In his Opticks, Newton gives us a clear picture of how he imagined God’s creation of the material world:
It seems probable to me that God in the beginning formed matter in solid, massy, hard, impenetrable, movable particles, of such sizes and figures, and with such other properties, and in such proportion to space, as most conduced to the end for which he formed them; and that these primitive particles being solids, are incomparably harder than any porous bodies compounded of them; even so very hard, as never to wear or break in pieces; no ordinary power being able to divide what God himself made one in the first creation.8
All physical events are reduced, in Newtonian mechanics, to the motion of material points in space, caused by their mutual attraction, i.e. by the force of gravity. In order to put the effect of this force on a mass point into a precise mathematical form, Newton had to invent completely new concepts and mathematical techniques, those of differential calculus. This was a tremendous intellectual achievement and has been praised by Einstein as ‘perhaps the greatest advance in thought that a single individual was ever privileged to make’.
Newton’s equations of motion are the basis of classical mechanics. They were considered to be fixed laws according to which material points move, and were thus thought to account for all changes observed in the physical world. In the Newtonian view, God had created, in the beginning, the material particles, the forces between them, and the fundamental laws of motion. In this way, the whole universe was set in motion and it has continued to run ever since, like a machine, governed by immutable laws.
The mechanistic view of nature is thus closely related to a rigorous determinism. The giant cosmic machine was seen as being completely causal and determinate. All that happened had a definite cause and gave rise to a definite effect, and the future of any part of the system could—in principle—be predicted with absolute certainty if its state at any time was known in all details. This belief found its clearest expression in the famous words of the French mathematician Pierre Simon Laplace:
An intellect which at a given instant knew all the forces acting in nature, and the position of all things of which the world consists—supposing the said intellect were vast enough to subject these data to analysis—would embrace in the same formula the motions of the greatest bodies in the universe and those of the slightest atoms; nothing would be uncertain for it, and the future, like the past, would be present to its eyes.9
The philosophical basis of this rigorous determinism was the fundamental division between the I and the world introduced by Descartes. As a consequence of this division, it was believed that the world could be described objectively, i.e. without ever mentioning the human observer, and such an objective description of nature became the ideal of all science.
The eighteenth and nineteenth centuries witnessed a tremendous success of Newtonian mechanics. Newton himself applied his theory to the movement of the planets and was able to explain the basic features of the solar system. His planetary model was greatly simplified, however, neglecting, for example, the gravitational influence of the planets on each other, and thus he found that there were certain irregularities which he could not explain. He resolved this problem by assuming that God was always present in the universe to correct these irregularities.
Laplace, the great mathematician, set himself the ambitious task of refining and perfecting Newton’s calculations in a book which should ‘offer a complete solution of the great mechanical problem presented by the solar system, and bring theory to coincide so closely with observation that empirical equations would no longer find a place in astronomical tables’.10 The result was a large work in five volumes, called Mécanique Céleste in which Laplace succeeded in explaining the motions of the planets, moons and comets down to the smallest details, as well as the flow of the tides and other phenomena related to gravity. He showed that the Newtonian laws of motion assured the stability of the solar system and treated the universe as a perfectly self-regulating machine. When Laplace presented the first edition of his work to Napoleon—so the story goes—Napoleon remarked, ‘Monsieur Laplace, they tell me you have written this large book on the system of the universe, and have never even mentioned its Creator.’ To this Laplace replied bluntly, ‘I had no need for that hypothesis.’
Encouraged by the brilliant success of Newtonian mechanics in astronomy, physicists extended it to the continuous motion of fluids and to the vibrations of elastic bodies, and again it worked. Finally, even the theory of heat could be reduced to mechanics when it was realized that heat was the energy created by a complicated ‘jiggling’ motion of the molecules. When the temperature of, say, water is increased the motion of the water molecules increases until they overcome the forces holding them together and fly apart. In this way, water turns into steam. On the other hand, when the thermal motion is slowed down by cooling the water, the molecules finally lock into a new, more rigid pattern which is ice. In a similar way, many other thermal phenomena can be understood quite well from a purely mechanistic point of view.
The enormous success of the mechanistic model made physicists of the early nineteenth century believe that the universe was indeed a huge mechanical system running according to the Newtonian laws of motion. These laws were seen as the basic laws of nature and Newton’s mechanics was considered to be the ultimate theory of natural phenomena. And yet, it was less than a hundred years later that a new physical reality was discovered which made the limitations of the Newtonian model apparent and showed that none of its features had absolute validity.
This realization did not come abruptly, but was initiated by developments that had already started in the nineteenth century and prepared the way for the scientific revolutions of our time. The first of these developments was the discovery and investigation of electric and magnetic phenomena which could not be described appropriately by the mechanistic model and involved a new type of force. The important step was made by Michael Faraday and Clerk Maxwell—the first, one of the greatest experimenters in the history of science, the second, a brilliant theorist. When Faraday produced an electric current in a coil of copper by moving a magnet near it, and thus converted the mechanical work of moving the magnet into electric energy, he brought science and technology to a turning point. His fundamental experiment gave birth, on the one hand, to the vast technology of electrical engineering;