The Book of Nothing Read online

  The ebb and flow of Newton’s views about the ether make interesting reading. In the 1670s he was seeking to persuade Boyle that there existed a subtle ethereal spirit of air (aere) because in a vacuum a swinging pendulum continued oscillating for so little longer than it did in air. Newton argued that there must exist another fluid, playing a similar role to that of air, which slows the pendulum even if it is placed in one of Boyle’s vacua. He also claimed that some metals could fuse and become heavier even when sealed within a glass container. This, he suggested, meant that some sparse fluid must be passing through the pores in the glass container in order to increase the mass of the metal. A little later he tried to use the ether as a device to explain the reflection and refraction of light, and to persuade Boyle that the non-uniformity of an ether could explain the existence of gravity.

  By the 1680s Newton had lost his enthusiasm for the ether. In the Principia (1687), he excludes the existence of such a medium permeating masses because it would have an incalculable disturbing influence upon the motion of celestial bodies. Then, in the second book of the Principia, he considers directly ‘the opinion of some that there is a certain ethereal medium extremely rare and subtle, which freely pervades the pores of all bodies’ and seeks to find experiments which might test the idea. He returns to its effects on the swinging pendulum, now interpreting the evidence as indicating that there is no discernible difference in the damping of the pendulum’s motion in air or vacuum. Thus he concludes that if an ether exists, its effects must be so subtle as to be indiscernible and so it can safely be ignored for the purposes of explaining gravity and other observable phenomena – a complete about-turn.

  Six years later Newton was trying to convince Bentley of the impossibility of an influence like gravity acting instantaneously over great distances, whilst writing to Leibniz that a fine form of matter did indeed fill the heavens above. By the time the second edition of the Principia appeared in 1713, Newton had added to the text of the first edition that there was indeed a ‘subtle spirit which pervades and lies hid in all gross bodies’ and it was this that allowed him to understand the forces of Nature: gravity, heat, light and sound. In what way it did so was not revealed, because it ‘cannot be explained in a few words’.

  Newton’s last views on the ether appear in some of the questions posed at the end of the second edition of his Opticks (1717). Here, he claims fresh experimental evidence for the ether’s existence by comparing the behaviour of thermometers in air with those sealed in an evacuated tube.9 Again, the lack of discernible differences in their response to heat convinced Newton that a medium ‘more rare and subtle than air’ must still be present in the evacuated container in order to transmit the heat from outside. Harking back to his first speculations about the existence of an ether, he then suggests that this subtle medium must be much sparser within dense bodies like the Sun and the planets than it is in the interplanetary space between them. Thus gravity arises because bodies attempt to move from where the ether is denser to where it is sparser10 – ‘every Body endeavouring to go from the denser parts of the Medium towards the rarer’– seeking to even out the distribution.11 Finally, Newton tried to offer some mechanical explanation for the elusivity of the ether. It was made of particles that are ‘exceedingly small’ and its elasticity arose from the fact that these particles repel one another. The forces are stronger in small bodies than in large ones in proportion to their mass. The result is12

  “… a Medium exceedingly more rare and elastick than Air, and by consequence exceedingly less able to resist the motion of Projectiles, and exceedingly more able to press upon gross Bodies, by endeavouring to expand itself.”

  Newton’s speculations on the links between the elusivity and the elasticity of the ether ended with these questions. He never published a detailed theory of the quantitative properties of the ether and its role in mediating the force of gravity. The clarity of his predictions of the effects of gravity and motion stood in contrast to his continual attempts to come to a satisfactory conclusion about the true nature of the vacuum and the way in which forces traverse it. Newton was ahead of his time in almost everything he deduced about the workings of the world, but in the matters of the ether and the vacuum, the jump into the future was too far even for him.

  DARKNESS IN THE ETHER

  “I have not had a moment’s peace or happiness in respect to electromagnetic theory since November 28, 1846. All this time I have been liable to fits of ether dipsomania, kept away at intervals only by rigorous abstention from thought on the subject.”

  Lord Kelvin13

  The problem of empty space was entwined with another long-standing riddle: the darkness of the night sky. Descartes’ philosophy had rested firmly upon a belief in the impossibility of empty space. He believed in a universe of unending extent. Only matter could have spatial extent and so where there was no matter there could be no space. Everything was moved by forces arising out of direct physical contact. There was no spooky action at a distance across the vacuum. His picture of celestial vortex motions which permitted interactions to occur only by contact (see Figure 4.1) led him to refute the atomists’ picture of ‘atoms’ of matter separated by void. Matter must be continuous and free from voids or other discontinuities. If atoms were introduced into his theory then they would necessarily be in continuous contact with one another and so necessarily extended rather than isolated points of matter as the atomists had imagined.

  Descartes’ Newtonian opponents rejected his conception of matter moved by purely mechanical laws. Many assumed that the darkness of the night sky between the stars was direct evidence of the infinite and eternal extracosmic void which the ancients maintained existed beyond the edge of a material world of finite size and age. We were seeing through the finite celestial world into the dark void beyond. Thus we see that the Cartesians combined Aristotelian and Epicurean ideas: like Aristotle, they rejected both the vacuum as a physical reality and the atomic nature of matter, but like Epicurus they believed that space had no limit. The Newtonians, by contrast, merged Stoic and Epicurean philosophies: like the Stoics they rejected the idea that the stars were infinite in number and extent, but like the Epicureans they accepted the existence of the vacuum and the basic atomic structure of matter. Later, the Newtonian picture would dispense with its Stoic aspect and use only the Epicurean picture of the boundless population of stars, pictured in Figure 4.2.

  Anyone who believed that the Universe contained an infinite distribution of stars was faced with explaining the darkness of the night sky.14 If one looked out into such an infinite array of stars then it would be like looking into a never-ending forest: one’s line of sight would always end on a tree. We should see the entire sky as if it were a single bright starry surface. Evidently, this was not the case.

  The hypothesis that space was filled with a tenuous ether created new possibilities for explaining the darkness of the night sky. In the nineteenth century, the Irish astronomer John Gore suggested16 that the darkness of interstellar space might be evidence for regions of total vacuum devoid of both matter and ether:

  Figure 4.2 Isaac Newton’s view of the Universe in 1667, during his early years in Cambridge.15 This picture combines ancient Epicurean and Stoic conceptions of the cosmos.

  “It has been argued by some astronomers that the number of the stars must be limited, or on the supposition of an infinite number uniformly scattered through space, it would follow that the whole heavens should shine with a uniform light, probably equal to that of the sun.”17

  Gore and the Canadian astronomer Simon Newcomb18 both believed that the puzzle of the dark night sky would be solved if our Milky Way galaxy were shielded from the stars and nebulae beyond by a perfect vacuum region across which starlight could not travel. Thermodynamically, this sounds rather odd. What happens to the starlight when it impinges upon this impervious vacuum region? They suggested that it was reflected back so that

  “we may consider … the reflecting vacuum a
s forming the internal surface of a hollow sphere.”

  In their scenario each galaxy of stars and ordinary material is surrounded by a spherical ‘halo’ of ether, but the intergalactic region between the ether halos is a perfect vacuum which light cannot penetrate (see Figure 4.3).

  One can see that for all practical purposes, the other galaxies, with their ethereal halos, might as well not exist. They are unobservable in principle. The darkness of the night sky is really being explained by supposing that the Universe is astronomically finite and contains very few stars. All the rest are an optical illusion. Unfortunately, this does not work. If each galaxy is surrounded by a mirror of perfect vacuum then the starlight from the stars it contains will be bounced back and forth across the galaxy and end up contributing a similar amount of light to the visible sky as would be incoming from the other galaxies.

  Figure 4.3 Newcomb and Gore’s solution to the puzzle of the darkness of the night sky.19 Each galaxy of stars is surrounded by a sphere of ether. The space between the galaxies contains no ether and so cannot transmit light. The spheres of ether act as if they are reflecting mirrors and prevent observers within them receiving light from other spheres.

  NATURAL THEOLOGY OF THE ETHER

  “If God had meant us to do philosophy he would have created us.”

  Marek Kohn20

  During the eighteenth and nineteenth centuries theologians were greatly impressed by arguments for the existence of God which cast Him in the role of cosmic Designer. The existence of such a Designer, they argued, was evident from the structure of the world around us. This structure had two telling strands. First, there were the apparent contrivances of the living world. Animals seemed to inhabit environments that were tailor-made for their needs. What more perfect design could be found than the camouflage markings on the coat of an animal that merged so exactly with its surroundings? These arguments about the ways in which the outcomes of Nature’s laws are in mutual harmony had been supplemented by the more sophisticated Design Argument based upon the success of Newton’s elucidation of simple laws of Nature that Richard Bentley promulgated. This second version of the Design Argument pointed to the simplicity and mathematical power of those simple, all-encompassing, Newtonian laws as the primary evidence for a Cosmic Lawgiver who framed them.21

  In all of these natural theological discussions the Universe was viewed as a harmonious whole in which all its components were wisely and optimally integrated into a grand cosmic scheme. Humanity was a beneficiary of this scheme, but only the most naive pictures of Design would insist on making humanity’s well-being the goal or final cause of the whole creation. The ether fitted into this teleological conception of the Universe because it resolved the old objection that a void space serves no purpose and implies that the Deity was responsible for making things that were a waste of space. The ether plugged this critical gap by doing away with the purposeless emptiness. It found itself elevated in the minds of some theologians to play a role just a little lower than the angels as the main secondary cause by which God regulated the motions of the celestial bodies. For example, John Cook argues that

  “Ether is the Rudder of the Universe, or as the Rod, or whatever you will liken it to, in the Hand of the Almighty, by which he naturally rules and governs all material created Beings … Now how beautiful is this Contrivance in God.”22

  This line of argument was developed most elaborately by William Whewell in his contribution to the famous Bridgewater Treatises on Natural Theology, a series of works by distinguished nineteenth-century scholars seeking to provide support for Christian religious belief by appeal to scientific discovery. Whewell’s volume23 dealt with the contribution of astronomy and physics to the argument. Since he was a strong supporter of Huygens’ wave theory of light, the ether played a key role in his conception of the physical universe and he was greatly persuaded of its crucial role in the theological scheme of things as well. He argued that ether was providentially designed by the Almighty in order to enable us to see the Universe with our visible sense. It was one of the three fundamental substances in the Universe, beside matter and fluid.24 Without it, the Universe would be dead, inert and unknowable. Its very existence was thus evidence for the wisdom, goodness and anthropocentric good intentions of God.

  Amongst notable scientists, the most speculative views on the ether are to be found in the works of the Scottish physicist Peter Guthrie Tait, who is famous for his joint work with Lord Kelvin and his pioneering ideas in the mathematical theory of knots. In 1875, Tait co-authored a popular science book with Balfour Stewart which bore the title The Unseen universe; or, physical speculations on a future state.25 Its purpose was to demonstrate the harmony of religion and science and, in seeking to do this, it had some remarkable things to say about the ether.

  Stewart and Tait suggested that all matter was composed of particles of ether, but these ether particles were composed of an even subtler collection of ether particles, and so on, ad infinitum. This hierarchy of ethers was arranged in an ascending one-way street of energies, so that lower-order ethers could always form from a higher, but not vice versa. Stewart and Tait imagined their staircase of ethers rising, like Jacob’s ladder, to attain infinite energy and ultimately becoming eternal and co-equal with God. The creation of the world was simply the cascade of energy down the spectrum of ethers so that it became localised in matter at the lowest levels, those we see around us and in which we have our being.

  A DECISIVE EXPERIMENT

  “Now the sirens have a still more fatal weapon than their song, namely their silence … someone might possibly have escaped from their singing; but from their silence never.”

  Franz Kafka26

  In the middle of the nineteenth century, it was the accepted view of almost all scientists that space was filled with a ubiquitous ethereal fluid. There was no vacuum. All forces and interactions were mediated by the presence of ether, either by waves of ether or by vortices. The favoured scenario was one in which the ether was, on average, stationary; others suggested that it was dragged around by the daily rotation of the Earth and by its annual orbit of the Sun. To question this picture seemed rather foolish, a little like questioning whether the Earth possessed an atmosphere of air. The existence of the ether was fast becoming one of those scientific truths we hold to be self-evident. Yet, whilst its existence was not doubted, its physical characteristics were the subject of lively debate.27 Some held it to be thin and tenuous, others argued it was an elastic solid, and others still that its properties changed according to the ambient conditions. In such a confused atmosphere speculative theories abound, and all manner of contrived additional properties are easily invented to modify the favoured hypothesis in the face of new objections or awkward facts. What is needed is a decisive experiment. Just as Torricelli cut through the convoluted debates about the possibility of the physical vacuum by providing an experimental window into the question, so it would be with the ether. The impetus was to come from a side of the Atlantic where few would have expected the next great step in our understanding of motion to be taken.

  Albert Michelson was born on 19 December 1852 in the small town of Strelno near the Polish-German border.28 Technically, Strelno had been in Germany since the time of Frederick the Great but its traditions were Polish, like its citizens, and it was less than eighty miles from Copernicus’ birthplace. In the face of political upheaval and persecution, the Michelson family joined thousands of other Polish emigrants to the United States when Albert was just two years old. After working as a jeweller for a time in New York, Albert’s father Samuel joined the gold rush to California to seek his fortune. Soon afterwards, California became a State of the Union and grew rather prosperous. Samuel Michelson prospered as well and set up his own store in Calaveras County. The rest of the family eventually joined him after a formidable sea voyage to Panama followed by a dangerous overland trek across the neck of the continent (in the days before the canal) to the Pacific, where they took another boa
t to San Francisco before the final overland journey to the Gold Towns. There, in a wild-west frontier atmosphere, far from the world of learning and traditional culture, the young Michelson spent his early formative years. As a child, he was exceptionally gifted at constructing mechanical devices and showed an early aptitude for mathematics, together with a fascination for the rocks and minerals that the miners dug out of the ground. On reaching his thirteenth birthday, he was sent away to high school in San Francisco, and after graduating successfully three years later he entered a fierce competition for a place at the US Naval Academy in Annapolis, Maryland. Alas, he didn’t get the place. He tied in the examinations with a younger candidate from a poor background who was given the casting vote by the selection board despite the mountain of letters written in support of Michelson.

  Michelson didn’t give up. Such was his determination to be admitted to the Academy that he appealed directly to President Grant for a further place to be created. Learning of the President’s daily routine of walking his dog, he travelled to Washington and waited on the White House steps for him to return. Grant listened patiently to the teenager’s request but said there was really nothing he could do. All the places at the college were filled. But then he remembered a letter he had received from Michelson’s congressman arguing his case on the ground of his father’s great contribution commercially and politically to the Republican cause: to reward young Michelson would bring further support to the President in his home state. For whatever reason, the President decided to intervene and sent the young Michelson to see the Superintendent of the Naval Academy in person. Interviews followed and after just a few days Michelson heard that an extra place had been created at the Academy for new entrants that year and it had been awarded to him. He entered as a cadet midshipman and gradually distinguished himself at the college in all the science courses, less so in military matters.29 After graduating, and spending a short spell at sea, he was appointed instructor in physics and chemistry at the Academy and began to develop his expertise in optics and experimental physics. His first distinguished contribution to science was a precision measurement of the speed of light. After this work was completed, in 1880, Michelson took a period of leave from the Navy and took his family to Europe. It was a trip that was to change the direction of science.