Ideas: A History from Fire to Freud

But physics led the way. It had been in flux for some time, due mainly to a discrepancy in the understanding of the atom. As an idea, the atom – an elemental, invisible and indivisible substance – went back to ancient Greece, as we have seen. It was built on in the seventeenth century, when Newton conceived it as rather like a minuscule billiard ball, ‘hard and impenetrable’. In the early decades of the nineteenth century, chemists such as John Dalton had been forced to accept the theory of atoms as the smallest units of elements, in order to explain chemical reactions – how, for example, two colourless liquids, when mixed together, immediately formed a white solid or precipitate. Similarly, it was these chemical properties, and the systematic way they varied, combined with their atomic weights, that suggested to the Russian Dimitri Mendeleyev, playing ‘chemical patience’ with sixty-three cards at Tver, his estate 200 miles from Moscow, the layout of the periodic table of elements. This has been called ‘the alphabet out of which the language of the universe is composed’ and suggested, among other things, that there were elements still to be discovered. Mendeleyev’s table of elements would dovetail neatly with the discoveries of the particle physicists, linking physics and chemistry in a rational way and providing the first step in the unification of the sciences that would be such a feature of the twentieth century.

Newton’s idea of the atom was further refined by Maxwell, when he took over at the Cavendish. In 1873 Maxwell introduced into Newton’s mechanical world of colliding miniature billiard balls the idea of an electro-magnetic field. This field, Maxwell argued, ‘permeated the void’ – electric and magnetic energy ‘propagated through it’ at the speed of light.⁷ Despite these advances, Maxwell still thought of atoms as solid and hard and essentially mechanical.

The problem was that atoms, if they existed, were too small to observe with the technology then available. Things only began to change with Max Planck, the German physicist. As part of the research for his PhD, Planck had studied heat conductors and the second law of thermodynamics. This law was initially identified by Rudolf Clausius, a German physicist who had been born in Poland, though Lord Kelvin had also had some input. Clausius had presented his law at first in 1850 and this law stipulates what anyone can observe, that energy dissipates as heat when work is done and, moreover, that heat cannot be reorganised into a useful form. This otherwise common-sense observation has very important consequences. One is that since the heat produced – energy – can never be collected up again, can never be useful or organised, the universe must gradually run down into complete randomness: a decayed house never puts itself back together, a broken bottle never reassembles of its own accord. Clausius’ word for this irreversible, increasing disorder was ‘entropy’, and he concluded that the universe would eventually die. In his PhD, Planck grasped the significance of this. The second law shows in effect that time is a fundamental part of the universe, or physics. This book began, in the Prologue, with the discovery of deep time, and Planck brings us full circle. Whatever else it may be, time is a basic element of the world about us, is related to matter in ways we do not yet fully understand. Time means that the universe is one-way only, and that therefore the Newtonian, mechanical, billiard ball picture must be wrong, or at best incomplete, for it allows the universe to operate equally in either direction, backwards and forwards.⁸

But if atoms were not billiard balls, what were they?