Bill Bryson - A short history of nearly everything

For a century after Dalton made his proposal, it remained entirely hypothetical, and a few eminent scientists-notably the Viennese physicist Ernst Mach, for whom is named the speed of sound-doubted the existence of atoms at all. “Atoms cannot be perceived by the senses . . . they are things of thought,” he wrote. The existence of atoms was so doubtfully held in the German-speaking world in particular that it was said to have played a part in the suicide of the great theoretical physicist, and atomic enthusiast, Ludwig Boltzmann in 1906.

It was Einstein who provided the first incontrovertible evidence of atoms’ existence with his paper on Brownian motion in 1905, but this attracted little attention and in any case Einstein was soon to become consumed with his work on general relativity. So the first real hero of the atomic age, if not the first personage on the scene, was Ernest Rutherford.

Rutherford was born in 1871 in the “back blocks” of New Zealand to parents who had emigrated from Scotland to raise a little flax and a lot of children (to paraphrase Steven Weinberg). Growing up in a remote part of a remote country, he was about as far from the mainstream of science as it was possible to be, but in 1895 he won a scholarship that took him to the Cavendish Laboratory at Cambridge University, which was about to become the hottest place in the world to do physics.

Physicists are notoriously scornful of scientists from other fields. When the wife of the great Austrian physicist Wolfgang Pauli left him for a chemist, he was staggered with disbelief. “Had she taken a bullfighter I would have understood,” he remarked in wonder to a friend. “But a chemist . . .”

It was a feeling Rutherford would have understood. “All science is either physics or stamp collecting,” he once said, in a line that has been used many times since. There is a certain engaging irony therefore that when he won the Nobel Prize in 1908, it was in chemistry, not physics.

Rutherford was a lucky man-lucky to be a genius, but even luckier to live at a time when physics and chemistry were so exciting and so compatible (his own sentiments notwithstanding). Never again would they quite so comfortably overlap.

For all his success, Rutherford was not an especially brilliant man and was actually pretty terrible at mathematics. Often during lectures he would get so lost in his own equations that he would give up halfway through and tell the students to work it out for themselves. According to his longtime colleague James Chadwick, discoverer of the neutron, he wasn’t even particularly clever at experimentation. He was simply tenacious and open-minded. For brilliance he substituted shrewdness and a kind of daring. His mind, in the words of one biographer, was “always operating out towards the frontiers, as far as he could see, and that was a great deal further than most other men.” Confronted with an intractable problem, he was prepared to work at it harder and longer than most people and to be more receptive to unorthodox explanations. His greatest breakthrough came because he was prepared to spend immensely tedious hours sitting at a screen counting alpha particle scintillations, as they were known-the sort of work that would normally have been farmed out. He was one of the first to see-possibly the very first-that the power inherent in the atom could, if harnessed, make bombs powerful enough to “make this old world vanish in smoke.”

Physically he was big and booming, with a voice that made the timid shrink. Once when told that Rutherford was about to make a radio broadcast across the Atlantic, a colleague drily asked: “Why use radio?” He also had a huge amount of good-natured confidence. When someone remarked to him that he seemed always to be at the crest of a wave, he responded, “Well, after all, I made the wave, didn’t I?” C. P. Snow recalled how once in a Cambridge tailor’s he overheard Rutherford remark: “Every day I grow in girth. And in mentality.”

But both girth and fame were far ahead of him in 1895 when he fetched up at the Cavendish. [20]It was a singularly eventful period in science. In the year of his arrival in Cambridge, Wilhelm Roentgen discovered X rays at the University of Würzburg in Germany, and the next year Henri Becquerel discovered radioactivity. And the Cavendish itself was about to embark on a long period of greatness. In 1897, J. J. Thomson and colleagues would discover the electron there, in 1911 C. T. R. Wilson would produce the first particle detector there (as we shall see), and in 1932 James Chadwick would discover the neutron there. Further still in the future, James Watson and Francis Crick would discover the structure of DNA at the Cavendish in 1953.

In the beginning Rutherford worked on radio waves, and with some distinction-he managed to transmit a crisp signal more than a mile, a very reasonable achievement for the time-but gave it up when he was persuaded by a senior colleague that radio had little future. On the whole, however, Rutherford didn’t thrive at the Cavendish. After three years there, feeling he was going nowhere, he took a post at McGill University in Montreal, and there he began his long and steady rise to greatness. By the time he received his Nobel Prize (for “investigations into the disintegration of the elements, and the chemistry of radioactive substances,” according to the official citation) he had moved on to Manchester University, and it was there, in fact, that he would do his most important work in determining the structure and nature of the atom.

By the early twentieth century it was known that atoms were made of parts-Thomson’s discovery of the electron had established that-but it wasn’t known how many parts there were or how they fit together or what shape they took. Some physicists thought that atoms might be cube shaped, because cubes can be packed together so neatly without any wasted space. The more general view, however, was that an atom was more like a currant bun or a plum pudding: a dense, solid object that carried a positive charge but that was studded with negatively charged electrons, like the currants in a currant bun.

In 1910, Rutherford (assisted by his student Hans Geiger, who would later invent the radiation detector that bears his name) fired ionized helium atoms, or alpha particles, at a sheet of gold foil. [21]To Rutherford’s astonishment, some of the particles bounced back. It was as if, he said, he had fired a fifteen-inch shell at a sheet of paper and it rebounded into his lap. This was just not supposed to happen. After considerable reflection he realized there could be only one possible explanation: the particles that bounced back were striking something small and dense at the heart of the atom, while the other particles sailed through unimpeded. An atom, Rutherford realized, was mostly empty space, with a very dense nucleus at the center. This was a most gratifying discovery, but it presented one immediate problem. By all the laws of conventional physics, atoms shouldn’t therefore exist.

Let us pause for a moment and consider the structure of the atom as we know it now. Every atom is made from three kinds of elementary particles: protons, which have a positive electrical charge; electrons, which have a negative electrical charge; and neutrons, which have no charge. Protons and neutrons are packed into the nucleus, while electrons spin around outside. The number of protons is what gives an atom its chemical identity. An atom with one proton is an atom of hydrogen, one with two protons is helium, with three protons is lithium, and so on up the scale. Each time you add a proton you get a new element. (Because the number of protons in an atom is always balanced by an equal number of electrons, you will sometimes see it written that it is the number of electrons that defines an element; it comes to the same thing. The way it was explained to me is that protons give an atom its identity, electrons its personality.)