The Penguin History of the World

Once again, the historical context is complex and deep. Already before 1914 it was increasingly clear that boundaries between the individual sciences, some of them intelligible and usefully distinct fields of study since the 1600s, were tending to blur and then to disappear. The full implications of this have only begun to appear very lately, however. For all the achievements of the great chemists and biologists of the eighteenth and nineteenth centuries, it was the physicists who did most to change the scientific map of the twentieth century. James Clerk Maxwell, the first professor of experimental physics at Cambridge, published in the 1870s the work in electromagnetism which first broke effectively into fields and problems left untouched by Newtonian physics. Maxwell’s theoretical work and its experimental investigation profoundly affected the accepted view that the universe obeyed natural, regular and discoverable laws of a somewhat mechanical kind and that it consisted essentially of indestructible matter in various combinations and arrangements. Into this picture had now to be fitted the newly discovered electromagnetic fields, whose technological possibilities quickly fascinated laymen and scientists alike.

The crucial work that followed and that founded modern physical theory was done between 1895 and 1914, by Röntgen, who discovered X-rays, Becquerel, who discovered radioactivity, Thomson, who identified the electron, the Curies, who isolated radium, and Rutherford, who investigated the structure of the atom. They made it possible to see the physical world in a new way. Instead of lumps of matter, the universe began to look more like an aggregate of atoms, which were tiny solar systems of particles held together by electrical forces in different arrangements. These particles seemed to behave in a way that blurred the distinction between matter and electromagnetic fields. Moreover, such arrangements of particles were not fixed, for in nature one arrangement might give way to another and thus elements could change into other elements. Rutherford’s work, in particular, was decisive, for he established that atoms could be ‘split’ because of their structure as a system of particles. This meant that matter, even at this fundamental level, could be manipulated. Two such particles were soon identified: the proton and the electron; others were not isolated until after 1932, when Chadwick discovered the neutron. The scientific world now had an experimentally validated picture of the atom’s structure as a system of particles. But as late as 1935 Rutherford said that nuclear physics would have no practical implications – and no one rushed to contradict him.

What this radically important experimental work did not at once do was supply a new theoretical framework to replace the Newtonian system. This only came with a long revolution in theory, beginning in the last years of the nineteenth century and culminating in the 1920s. It was focused on two different sets of problems, which gave rise to the work designated by the terms ‘relativity’ and ‘quantum theory’. The pioneers were Max Planck and the man who was undoubtedly the greatest scientist of the twentieth century, Albert Einstein. By 1905 they had provided experimental and mathematical demonstration that the Newtonian laws of motion were an inadequate framework for explanation of a fact no longer to be contested: that energy transactions in the material world took place not in an even flow but in discrete jumps – quanta, as they came to be termed. Planck showed that radiant heat (from, for example, the sun) was not, as Newtonian physics required, emitted continuously; he argued that this was true of all energy transactions. Einstein argued that light was propagated not continuously but in particles. Though much important work was to be done in the next twenty or so years, Planck’s contribution had the most profound effect and it was again unsettling. Newton’s views had been found wanting, but there was nothing to put in their place.