Newton eventually rejected the notion of an aether. His atomistic view would have required a particulate aether, which he found objectionable. Also the aether would have to transmit forces without impeding the motion of, for example, the planets in their inviolate orbits.
Newton's attitude is illustrated by this paragraph of his Principia:
There is a cause without which these motive forces would not be propagated through the spaces round about; whether that cause be of some central body (such as a magnet in the center of the magnetic force), or anything else that does not yet appear. For I have design only to give a mathematical notion of these forces, without considering their physical causes and feats.
At this, the audience, if they were physicists at a modern seminar, would stand up and cheer, because Newton hits the very modern theme that the test of a theory is its agreement with experiment and observation. So what if Newton (and his present-day admirers) didn't know Why gravity? What creates gravity? That is a philosophical question until someone shows that gravity is a consequence of some deeper concept, some symmetry perhaps of higher-dimensional space-time.
Enough of philosophy. Newton advanced our quest for the a-tom enormously by establishing a rigorous scheme of predicting, of synthesis that could be applied to a vast array of physical, problems. As these principles caught on, they had, as we have seen, a profound influence on practical arts such as engineering and technology. Newtonian mechanics, and its new mathematics, is truly the base of a pyramid upon which all the layers of physical sciences and technology are built. Its revolution represented a change in the perspective of human thinking. Without this change, there would have been no industrial revolution and no continuing systematic search for new knowledge and new technology. This marks a transition from a static society waiting for something to happen to a dynamic society seeking understanding, knowing that understanding implies control. And the Newtonian imprint gave reductionism a powerful boost.
Newton's contributions to physics and mathematics and his commitment to an atomistic universe are clearly documented. What remains misty is the influence on his scientific work of his "other life," his extensive research in alchemy and his devotion to occult religious philosophy, especially Hermetic ideas that harked back to ancient Egyptian priestly magic. These activities were very largely hidden. As Lucasian professor at Cambridge (Stephen Hawking is the current incumbent) and later as a member of the London political establishment, Newton could not let his devotion to these subversive religious practices be known, for that would have brought him extreme embarrassment if not total disgrace.
We may leave the last comment on Newton's work to Einstein:
Newton, forgive me; you found the only way which, in your age, was just about possible for a man of highest thought—and creative power. The concepts, which you created, are even today still guiding our thinking in physics, although we now know that they will have to be replaced by others farther removed from the sphere of immediate experience, if we aim at a profounder understanding of relationships.
THE DALMATIAN PROPHET
A final note on this first stage, the age of mechanics, the great era of classical physics. The phrase "ahead of his time" is overused. I'm going to use it anyway. I'm not referring to Galileo or Newton. Both were definitely right on time, neither late nor early. Gravity, experimentation, measurement, mathematical proofs ... all these things were in the air. Galileo, Kepler, Brahe, and Newton were accepted—heralded!—in their own time, because they came up with ideas that the scientific community was ready to accept. Not everyone is so fortunate.
Roger Joseph Boscovich, a native of Dubrovnik who spent much of his career in Rome, was born in 1711, sixteen years before Newton's death. Boscovich was a great supporter of Newton's theories, but he had some problems with the law of gravitation. He called it a "classical limit," an adequate approximation where distances are large. He said that it was "very nearly correct but that differences from the law of inverse squares do exist even though they are very slight." He speculated that this classical law must break down altogether at the atomic scale, where the forces of attraction are replaced by an oscillation between attractive and repulsive forces. An amazing thought for a scientist in the eighteenth century.
Boscovich also struggled with the old action-at-a-distance problem. Being a geometer more than anything else, he came up with the idea of fields of force to explain how forces exert control over objects at a distance. But wait, there's more!
Boscovich had this other idea, one that was real crazy for the eighteenth century (or perhaps any century). Matter is composed of invisible, indivisible a-toms, he said. Nothing particularly new there. Leucippus, Democritus, Galileo, Newton, and others would have agreed with him. Here's the good part: Boscovich said these particles had no size; that is, they were geometrical points. Clearly, as with so many ideas in science, there were precursors to this—probably in ancient Greece, not to mention hints in Galileo's works. As you may recall from high school geometry, a point is just a place; it has no dimensions. And here's Boscovich putting forth the proposition that matter is composed of particles that have no dimensions! We found a particle just a couple of decades ago that fits such a description. It's called a quark.
We'll get back to Mr. Boscovich later.
4. STILL LOOKING FOR THE ATOM: CHEMISTS AND ELECTRICIANS
The scientist does not defy the universe. He accepts it. It is his dish to savor, his realm to explore; it is his adventure and never-ending delight. It is complaisant and elusive but never dull. It is wonderful both in the small and in the large. In short, its exploration is the highest occupation for a gentleman.
—I.I. Rabi
AN ADMISSION: the physicists haven't been the only ones searching for Democritus's atom. Chemists have certainly made their mark, especially during the long era (circa 1600–1900) that saw the development of classical physics. The difference between chemists and physicists is not really insurmountable. I started out as a chemist but switched to physics partly because it was easier. Since then I have frequently noted that some of my best friends talk to chemists.
The chemists did something that the physicists before them hadn't done. They did experiments relevant to atoms. Galileo, Newton, et al., despite their considerable experimental accomplishments, dealt with atoms on a purely theoretical basis. They weren't lazy; they just didn't have the equipment. It was up to the chemists to conduct the first experiments that made atoms reveal their presence. In this chapter we'll dwell on the rich experimental evidence that supported the existence of Democritus's a-tom. We'll see many false starts, some red herrings, and misinterpreted results, always the bane of the experimenter.
THE MAN WHO DISCOVERED NINE INCHES OF NOTHING
Before we get to the hard-core chemists, we must mention one scientist, Evangelista Torricelli (1608–1647), who bridged the gap between the mechanics and the chemists in the attempt to restore atomism as a valid scientific concept. To repeat, Democritus said, "Nothing exists except atoms and empty space; everything else is opinion." Thus, to prove the validity of atomism, you need atoms, but you also need empty space between them. Aristotle opposed the very idea of a vacuum, and even during the Renaissance the Church continued to insist that "nature abhors a vacuum."
That's where Torricelli came in. He was one of Galileo's disciples in that scientist's latter days, and in 1642 Galileo set him to work on a problem. The Florentine well diggers had observed that in suction pumps water will not rise more than 10 meters. Why should this be? The initial hypothesis, advanced by Galileo and others, was that vacuum was a "force" and that the partial vacuum produced by the pumps propelled the water upward. Galileo obviously didn't want to be personally bothered with the well diggers' problem, so he delegated it to Torricelli.
Torricelli figured out that the water was not being pulled up by the vacuum at all, but rather pushed up by normal air pressure. When the pump lowers the air pressure above the column of water, the normal air
outside the pump pushes down harder on the ground water, forcing water in the pipe upward. Torricelli checked out his theory the year after Galileo died. He reasoned that since mercury is 13.5 times denser than water; air should be able to lift mercury only 1/13.5 times as high as water—or about 30 inches. Torricelli obtained a thick glass tube about 1 meter (about 39 inches) long that was closed at the bottom, open at the top, and did a simple experiment. He filled the tube to the brim with mercury, covered the top with a stopper, then turned the tube upside down, placed it in a bowl of mercury and pulled out the stopper. Some of the mercury poured down out of the tube into the dish. But as Torricelli had predicted, 30 inches of the liquid metal remained in the tube.
This pivotal event in physics is often referred to as the invention of the first barometer, which of course it was. Torricelli noted that the height of the mercury varied from day to day, measuring fluctuations in the atmospheric pressure. For our purposes, however, there was a greater significance. Let's forget about the 30 inches of mercury filling up most of the tube. What's important to us is those 9 odd inches at the top. Those few inches at the top of the tube—the closed end—contained nothing. Really nothing. No mercury, no air, nothing. Well, hardly anything. It's a fair vacuum, but it contains some mercury vapor, the amount depending on the temperature. The vacuum is about 10−6 torn (A tort; after Evangelista, is a measure of pressure; 10−6 torr is about one billionth of the normal pressure of the atmosphere.) Modern pumps can get to 10−11 torr and better. In any case, Torricelli had attained the first artificially created high-quality vacuum. There was no backing off from this conclusion. Nature may or may not abhor a vacuum, but she has to put up with it. Now that we had proved the existence of empty space, we needed some atoms to put there.
SQUEEZING GAS
Enter Robert Boyle. This Irish-born chemist (1627–1691) was criticized by his peers for being too much a physicist and too little a chemist in his way of thinking, but clearly his accomplishments belong primarily to the realm of chemistry. He was an experimentalist whose experiments often came to naught, yet he advanced the idea of atomism in England and on the continent. He was sometimes known as the Father of Chemistry and the Uncle of the Earl of Cork.
Influenced by Torricelli's work, Boyle became fascinated with vacuums. He hired Robert Hooke, the same Hooke who loved Newton so much, to build an improved air pump for him. The air pump inspired an interest in gases, which Boyle came to realize were a key to atomism. He may have had some help here from Hooke, who pointed out that the pressure a gas exerts on the walls of its container—such as air straining against the sides of a balloon—might result from a torrent of atoms. We don't see individual indentations from the atoms inside a balloon because there are billions and billions of them, which simulate a smooth outward push.
Like Torricelli's, Boyle's experiment involved mercury. Taking a seventeen-foot, J-shaped tube, he sealed the short end; then he poured mercury into the long open end to close off the bottom curve of the J. He then continued to add mercury to the open end. The more he poured, the smaller the space available for the air trapped in the short end. Correspondingly, the air pressure in the small volume increased, as he could easily measure by the extra height of mercury in the open end of the tube. Boyle discovered that the volume of the gas varied inversely with the pressure on it. The pressure on the gas trapped in the closed end results from the extra weight of the mercury plus the atmosphere pushing down on the open end. If he doubled the pressure by adding mercury, the volume of air decreased to one half.
Triple the pressure, and the volume shrank to a third, and so on. This effect became known as Boyle's law, a staple of chemistry to this day.
More important is a stunning implication of this experiment: air, or any gas, can be compressed. One way to understand this is to think of the gas as composed of particles separated by empty space. Under pressure, the particles are pushed closer together. Does this prove that atoms exist? Unfortunately, other explanations can be imagined, and Boyle's experiment only provided evidence consistent with the idea of atomism. The evidence was strong enough, however, to help convince Isaac Newton, among others, that an atomic theory of matter was the way to go. Boyle's compression experiment at the very least challenged the Aristotelian assumption that matter was continuous. There remained the problem of liquids and solids, which could not be squeezed with the same ease as gases. This didn't mean they aren't composed of atoms, just that they have less empty space.
Boyle was a champion of experimentation, which, despite the feats of Galileo and others, was still viewed with suspicion in the seventeenth century. Boyle carried on a long debate with Benedict Spinoza, the Dutch philosopher (and lens grinder), over the question of whether experiment could provide proof. To Spinoza only logical thought was proof; experiment was simply a tool for confirming or refuting an idea. Such great scientists as Huygens and Leibniz also doubted the value of experiment. Experimenters have always had an uphill battle.
Boyle's efforts to prove the existence of atoms (he preferred the term "corpuscles") advanced the science of chemistry, which was in a bit of a mess at the time. The prevailing belief of the day was still the old idea of elements, going back to the air, earth, fire, and water of Empedocles and modified through the years to include salt, sulfur, mercury, phlegm (phlegm?), oil, spirit, acid, and alkali. By the seventeenth century these were not just the simplest substances comprising matter according to the prevailing theory, they were believed to be the essential ingredients of everything. Acid, to take one example, was expected to be present in every compound. How confused chemists must have been! With these criteria even the simplest chemical reaction must have been impossible to analyze. Boyle's corpuscles led the way to a more reductionist, and simpler, method of analyzing compounds.
THE NAME GAME
One of the problems faced by chemists in the seventeenth and eighteenth centuries was that the names given to various chemicals made no sense. Antoine-Laurent Lavoisier (1743–1794) changed all that in 1787 with his classic work, Méthode de Nomenclature Chimique. Lavoisier could be called the Isaac Newton of chemistry. (Perhaps chemists call Newton the Lavoisier of physics.)
He was an amazing character. An accomplished geologist, Lavoisier was also a pioneer in scientific agriculture, an able financier, and a social reformer who had a hand in fomenting the French Revolution. He established a new system of weights and measures that led to the metric system, in use today in civilized nations. (In the 1990s the United States, not to be left too far behind, is inching toward the metric system.)
The previous century had produced a mountain of data, but they were hopelessly disorganized. The names of substances—pomph-olyx, colcothar, butter of arsenic, flowers of zinc, orpiment, martial ethiop—were colorful, but gave no clue to an underlying order. One of Lavoisier's mentors once told him, "The art of reasoning is nothing more than a language well arranged," and Lavoisier took this to heart. The Frenchman eventually shouldered the task of rearranging and renaming all of chemistry. He changed martial ethiop to iron oxide; orpiment became arsenic sulfide. The various prefixes, like "ox" and "sulf," and suffixes, like "ide" and "ous," helped organize and catalogue the countless numbers of compounds. What's in a name? Sometimes nomenclature is destiny. Would Archibald Leach have gotten all those movie roles if he hadn't changed his name to Cary Grant?
It wasn't quite that simple for Lavoisier. Before revising the nomenclature, he had to revise chemical theory itself. Lavoisier's major contributions to chemistry had to do with the nature of gases and the nature of combustion. Eighteenth-century chemists believed that if you heated water, you transmuted it to air, which they believed was the only true gas. Lavoisier's studies led to the first realization that any given element could exist in three states: solid, liquid, and "vapor." He also determined that the act of combustion was a chemical reaction in which substances such as carbon, sulfur, and phosphorus combined with oxygen. He displaced the theory of phlogiston, an Aristoteli
an-like obstacle to a true understanding of chemical reactions. More than this, Lavoisier's style of research—based on precision, exquisite experimental technique, and critical analysis of the assembled data—set chemistry on its modern course. Although Lavoisier's direct contribution to atomism was minor, without his groundwork scientists in the following century could not have discovered the first direct proof of the existence of atoms.
THE PELICAN AND THE BALLOON
Lavoisier was fascinated with water. At the time, many scientists were still convinced that water was a basic element, one that could not be split into smaller components. Some also believed in transmutation, thinking that water could be transmuted into earth, among other things. There were experiments to back this up. If you boil a pot of water long enough, eventually a solid residue will form on the surface. That's water being transmuted into another element, these scientists would say. Even the great Robert Boyle believed in transmutation. He had done experiments showing that plants grow by soaking up water. Ergo, water is transformed into stems, leaves, flowers, and so on. You can see why so many people distrusted experiment. Such conclusions are enough to make you start agreeing with Spinoza.
Lavoisier saw that the flaw in these experiments was one of measurement. He conducted his own experiment by boiling distilled water in a special vessel called a pelican. The pelican was so designed that the water vapor produced by boiling was trapped and condensed in a spherical cap, from which it returned to the boiling pot through two handlelike tubes. In this way no water was lost. Lavoisier carefully weighed the pelican and the distilled water, then boiled the water for 101 days. The long experiment produced an appreciable amount of solid residue. Lavoisier then weighed each element: the pelican, the water and the residue. The water weighed exactly the same after 101 days of boiling, which tells us something about Lavoisier's meticulous technique. The pelican, however weighed slightly less. The weight of the residue was equal to the weight lost by the vessel. Therefore the residue in the boiling water was not transmuted water but dissolved glass, silica, from the pelican. Lavoisier had shown that experimentation without precise measurement is worthless, even misleading. Lavoisier's chemical balance was his violin; he played it to revolutionize chemistry.
The God Particle: If the Universe Is the Answer, What Is the Question? Page 14
