by Peter Watson
Although he might be too impenetrable for most people’s taste, Schoenberg was not obtuse. He knew that some people objected to his atonality for its own sake. His response was Pierrot lunaire, appearing in 1912. It features a familiar icon of the theater—a dumb puppet who also happens to be a feeling being, a sad and cynical clown allowed by tradition to raise awkward truths so long as they are wrapped in riddles. Out of this format, Schoenberg managed to produce what many people consider his seminal work, what has been called the musical equivalent of Picasso’s Les demoiselles d’Avignon or Einstein’s E=mc2. Pierrot’s main focus is a theme we are already familiar with, the decadence and degeneration of modern man. Schoenberg introduced in the piece several innovations in form, notably Sprechgesang, literally song-speech in which the voice rises and falls but cannot be said to be either singing or speaking. Listeners have found that the music breaks down “into atoms and molecules, behaving…not unlike the molecules that bombard pollen in Brownian movement.” Schoenberg saw himself more as an Expressionist, and he shared many of the aims of Kandinsky though some of his early atonal pieces have the sunny fog and silence of Caspar David Friedrich’s landscapes.47
The first performance took place in mid-October in Berlin, in the Choralionsaal on the Bellevuestrasse (destroyed by Allied bombs in 1945). Following the premieres of the Second String Quartet, the critics gathered, ready to kill off the clown. But the performance was heard in silence and, when it was over, Schoenberg was given an ovation. It was short, so many in the audience shouted for the piece to be repeated, and they liked it even better the second time. So too did some of the critics, one going so far as to describe the evening “not as the end of music; but as the beginning of a new stage in listening.” Like it or not, Schoenberg had found a way forward after Wagner.
25.
The Discovery of Radio, Relativity, and the Quantum
Two upheavals took place in physics at the turn of the twentieth century. These were, first, the unexpected discoveries of x-rays, the electron, and radioactivity; and then, what some people regard as “the real revolution,” the discovery of the quantum and the theory of relativity. As well as being possibly the greatest intellectual adventure of the twentieth century, this was also one of the most international—advances being made by New Zealanders, Danes, Italians, French, British, and Americans, besides Germans, many of whom, to begin with at least, behaved with a commendable sense of international camaraderie. So if this chapter concentrates on the German contribution, this is not in any way to belittle the contributions of others, which were vital.
Nevertheless, Amos Elon says that in the natural sciences there was at this time “talk of a new German ‘Age of Genius,’ second only to the era of Goethe, Schiller, Hegel and Kant,” and Helge Kragh, in his study of twentieth-century physics, gives two tables which show how the Germans were at least ahead of others in their physics institutions.1
PHYSICS INSTITUTES AND FACULTY
Britain
NO. OF INSTITUTES: 25
FACULTY, 1900: 87
FACULTY, 1910: 106
France
NO. OF INSTITUTES: 19
FACULTY, 1900: 54
FACULTY, 1910: 58
Germany
NO. OF INSTITUTES: 30
FACULTY, 1900: 103
FACULTY, 1910: 139
United States
NO. OF INSTITUTES: 21
FACULTY, 1900: 100
FACULTY, 1910: 169
PHYSICS JOURNALS IN 1900
Britain
CORE JOURNAL: Philosophical Magazine
PAPERS, 1900: 420
%: 19
France
CORE JOURNAL: Journal de Physique
PAPERS, 1900: 360
%: 18
Germany
CORE JOURNAL: Annalen der Physik
PAPERS, 1900: 580
%: 29
United States
CORE JOURNAL: Physical Review
PAPERS, 1900: 240
%: 12
Many new physics laboratories were built between 1890 and World War I, twenty-two in Germany, nineteen in the British Empire, thirteen in the United States, twelve in France.2 The Dictionary of Scientific Biography lists 197 physicists who were twenty years old in 1900: 52 were German (and 6 Austrian), Britain came next with 35, France with 34, and the United States with 27.
It is not altogether clear why such attention was being paid to physics. When Max Planck started at the University of Munich in 1875, he was warned by his professor that his chosen field “was more or less finished and that nothing new could expect to be discovered.”3
WAVES THROUGH THE AIR
But there was undoubtedly change in the air. Most physicists still clung to a mechanical view of the universe, even James Clark Maxwell, whose field theory found many supporters. This was accompanied by the rise to prominence of the idea of a universal ether as a “quasi-hypothetical,” continuous, and all-pervading medium through which forces were propagated at a finite speed.4 This helped people consider the possibility that the foundation of these forces was electromagnetic rather than mechanical. In this environment, new ideas began to proliferate—rudimentary notions of antimatter, for example, of extra dimensions, most important a new field of “energetics,” put forward by the German physicist Georg Helm and his chemist colleague Ludwig Ostwald. In this view, energy, not matter, was the essence “of a reality that could be understood only as processes of actions.” Energetics turned out to be important in that, although turn-of-the-century physics revolved around the two “upheavals” mentioned earlier, the first German name to shine was in a different but related field, where the “ether,” electromagnetism, and, by implication, energy, were also important elements.
Heinrich Rudolf Hertz was born in Hamburg in 1857, the son of a Jewish lawyer who had converted to Christianity. Heinrich was a clever linguist, learning Arabic and Sanskrit but he also had a liking for the natural sciences and a facility for building experimental equipment, particularly in physics. He went to the university in Munich and afterward in Berlin where he studied under Gustav Kirchoff and Hermann von Helmholtz and also attended Treitschke’s lectures.5 His PhD dissertation in 1880 was so well received that he became Helmholtz’s assistant, after which he was appointed a lecturer in theoretical physics at Kiel. Though distinguished enough as a university, Kiel was not very big and, unlike other institutions, had hardly any laboratory space—this was why theoretical physics flourished there, a relatively new discipline, as we have seen, in which Germany led the way. At Kiel, Hertz produced his first important contribution when he derived Maxwell’s equations but in a way that was different from Maxwell’s own and did not involve the assumption of an ether.6 On the strength of this, Hertz was appointed the following year at the age of twenty-eight to the chair of physics at Karlsruhe, a much bigger, better-equipped university. There his first significant discovery was of the photoelectric effect, whereby ultraviolet radiation releases electrons from the surface of a metal (Einstein’s explanation of the photoelectric effect, not his work on relativity, won him the Nobel Prize—see below). Hertz was becoming the theoretical physicist par excellence.
With his gift for manufacturing laboratory equipment, in 1888 he produced his most innovative device yet. The central element here was a metal rod in the shape of a hoop with a minute (3mm) gap at midpoint (not unlike a large key-ring).7 When a sufficiently strong current was passed through the hoop, sparks were generated across the gap (he darkened the room to facilitate observation).8 At the same time violent oscillations were set up in the rod forming the hoop. Hertz’s crucial observation was that these oscillations sent out waves through the nearby air, a phenomenon he was able to prove because a similar circuit some way off could detect them. In later experiments Hertz showed that these waves could be reflected and refracted—like light waves—and that they traveled at the speed of light but had much longer wavelengths than light. Later still, he observed that a concave refle
ctor could focus the waves and that they passed unchanged through non-conducting substances. These were originally called Hertzian waves, and their initial importance lay in the fact that they confirmed Maxwell’s prediction that electromagnetic waves could exist in more than one form—light. Later they were called radio.
Asked by a student what use might be made of his discovery, Hertz famously replied, “It’s of no use whatsoever. This is just an experiment that proves Maestro Maxwell was right—we just have these mysterious electromagnetic waves that we cannot see with the naked eye.” Asked, “So what’s next?” he answered, “Nothing, I guess.” A young Italian, on holiday in the Alps, read Hertz’s article about his discovery and immediately wondered whether the waves set off by Hertz’s spark oscillator might be used for signaling. Guglielmo Marconi rushed back home to see whether his idea might work.9 Had Hertz lived (he died from bone disease at thirty-seven) he would have been as surprised as anyone at the direction physics was about to take. Rollo Appleyard says he was in all respects “a Newtonian.” 10
A NEW KIND OF RAY
In Chapter 17, we saw that gases had claimed physicists’ attention earlier in the century, at first for the light they threw on the conservation of energy, then for the statistical behavior of their atoms and molecules. As part of this, and especially with the growth of interest in electromagnetism and the possibility that the “void” between atoms was filled, as Maxwell said, with an electromagnetic field, a new specialism grew up that entailed the discharge of electricity in gases. As this interest developed, a new piece of apparatus was conceived, eventually known as the cathode ray tube. This was a glass tube with metal plates sealed into either end, and the gas sucked out, leaving a vacuum. If the metal plates were then connected to a battery and a current generated, the empty space, the vacuum inside the glass tube, glowed or fluoresced. This glow was generated from the negative plate, the cathode, and was absorbed into the positive plate, the anode.* The Berlin physicist Eugen Goldstein in 1876 was the first to label the new equipment “cathode ray” tubes.
William Crookes in Britain hypothesized in 1879 that cathode rays were a “fourth state of matter” (i.e., neither solid, liquid, nor gas), but that wasn’t convincing and most physicists still asked what exactly cathode rays were. The situation remained both confusing and promising, and several physicists started to take a look. One was the professor of physics at the University of Würzburg, Wilhelm Conrad Röntgen.
Born in the Lower Rhine province, Röntgen grew up in the Netherlands before studying in Zurich under Clausius. At Würzburg, he started investigating cathode rays—in particular their penetrating power—toward the end of 1895. It was by then common to use a barium platino-cyanide screen to detect any fluorescence caused by cathode rays.11 This screen was not really part of the experiment, more a fail-safe device should there be any anomalies. In Röntgen’s case, the screen was some way from the cathode ray tube which was in fact covered with black cardboard and operated only in a darkened room. On November 8, 1895, now a famous date in the history of science, Röntgen noticed—to his surprise—that the screen, though a good distance from the tube, also fluoresced. This could not possibly have been caused by the cathode rays. But did that mean the apparatus was giving off other rays, invisible to the naked eye? He confirmed his results, noting also that the paper screen covered with barium platino-cyanide fluoresced “whether the treated side or the other be turned towards the discharging tube.” 12
When his discovery was published, it caused a great stir, well beyond the confines of professional scientists, and he was soon commanded to demonstrate his discovery to the Kaiser. But what exactly were the new rays?13 In his follow-up studies, Röntgen found they had some of the properties of light, in that they followed straight lines, affected photographic plates, and were not interfered with by magnetic fields. At the same time, they were different from light and from Hertz’s electromagnetic waves in not being either reflected or refracted. For as much as a decade, physicists worked fruitfully with x-rays, as they came to be called (x for unknown, though they are called Röntgenstrahlen in Germany), without understanding exactly what they were.14
Eventually, in the early twentieth century, it was shown that x-rays were a form of electromagnetic wave with an extremely short wavelength, but some confusion remained until the wave-particle duality was clarified with the advent of quantum mechanics (see Chapter 32). In 1912 Max von Laue, a physicist who worked with Planck and Einstein, realized that, with their very small wavelength, x-rays could only be studied (i.e., reflected or refracted) by substances that had a very small grid structure, and that such spacings were to be found in the “inter-atomic distances between the ions of a crystal.”15 The experiment to test this prediction was carried out by the Munich physicist Walter Friedrich and his student Paul Knipping in the spring of 1912, with this collaboration constituting the first-ever “x-ray diffraction.” This provided proof that x-rays are indeed electromagnetic waves and that their wavelength is very short indeed, somewhere near 10–13 meters. This set off a whole new area of research, the use of x-ray diffraction in crystallography, and came to play an important role in chemistry, geology, metallurgy, and, not least, biology. It was a key technique in the determination by James D. Watson and Francis Crick, in 1953, of the double-helix structure of the DNA molecule.
THE DISCOVERY OF THE QUANTUM
In 1900 Max Planck was forty-two.16 He had been born into a very religious, rather academic family, and was an excellent musician (he had a harmonium specially built for him).17 But science was Planck’s calling and by the turn of the century he was near the top of his profession, a member of the Prussian Academy and a full professor at the University of Berlin, where he was known as a prolific generator of ideas that didn’t always work out.18
In 1897, J. J. Thomson, who had followed Maxwell as director of the Cavendish Laboratory in Cambridge, England, had pumped different gases into the cathode ray tubes and at times surrounded them with magnets. By systematically manipulating conditions, he demonstrated that cathode rays were in fact infinitesimally minute particles erupting from the cathode and drawn to the anode. He discovered that the particles were lighter than hydrogen atoms, the smallest known unit of matter, and exactly the same whatever the gas through which the discharge passed. Thomson had clearly identified something fundamental, what is today known as the electron.19
Many other particles of matter were discovered in the years ahead, but it was the very notion of particularity itself that interested Max Planck, and in 1897, the year Thomson discovered electrons, Planck began work on the project that was to make his name. It had been known since antiquity that as a substance (iron, for example) is heated, it first glows dull red, then bright red, then white. This is because longer wavelengths (of light) appear at moderate temperatures, and as temperatures rise, shorter wavelengths appear. When the material becomes white-hot, all wavelengths are given off. Studies of even hotter bodies—stars, for example—show that in the next stage the longer wavelengths drop out, so that the color gradually moves to the blue part of the spectrum. Planck was fascinated by this and by its link to a second mystery, the so-called black body problem. A perfectly formed black body is one that absorbs every wavelength of electromagnetic radiation equally well. Such bodies do not exist in nature, though lampblack, for instance, comes close, absorbing 98 percent of all radiation.20 According to classical physics, a black body should only emit radiation according to its temperature, and then such radiation should be emitted at every wavelength—it should only ever glow white. But studies of the perfect black bodies available to Planck, made of porcelain and platinum and located at the Bureau of Standards in Charlottenburg, showed that when heated, they behaved more or less like a lump of iron, giving off first dull red, then bright red-orange, then white light. Why?21
Planck’s revolutionary idea first occurred to him around October 7, 1900. On that day he sent a postcard to his colleague Heinrich Rubens on which he sk
etched an equation to explain the behavior of radiation in a black body.22 The essence of Planck’s idea, mathematical only to begin with, was that electromagnetic radiation was not continuous, as Newton had claimed, but could only be emitted in packets of a definite size. It was, he said, as if a hosepipe could spurt water only in “packets” of liquid. By December 14 that year, when Planck addressed the Berlin Physics Society, he had worked out his full theory. Part of this was the calculation of the dimensions of this small packet of energy, which Planck called h and which later became known as Planck’s Constant.23 This, he calculated, had the value of 6.55 10–27 ergs each second (an erg is a small unit of energy). Planck had identified this very small packet as a basic indivisible building block of the universe, an “atom” of radiation, which he called a “quantum.” It was confirmation that nature was not a continuous process but moved in a series of extremely small jerks. Quantum physics had arrived.
Or not quite. So many of the theories Planck had come up with in the twenty years leading to the quantum had proved wrong that when he addressed the Berlin Physics Society, he was heard in polite silence, and there were no questions. It took four years for the importance of his idea to be grasped—and then by a man who would create his own revolution: Albert Einstein.24
THE “ANNUS MIRABILIS” OF SCIENCE
Germany, as we have seen, led the way in the tradition of theoretical physics—Clausius, Boltzmann, Hertz, Planck. But the most famous theoretical physicist in history was Albert Einstein, and he arrived on the intellectual stage with a bang. Of all the scientific journals in the world, the single most sought-after collector’s item by far is the Annalen der Physik, volume XVII, for 1905, for in that year Einstein published not one but three papers in the journal, causing 1905 to be dubbed the annus mirabilis of science.