Three Scientific Revolutions: How They Transformed Our Conceptions of Reality (15 page)

As additional support he found that when monochromatic light is projected on a screen that has a circular opening the diameter of which is larger than the wavelength of the light passing through, it produces a circular image on the screen behind it. But if the diameter of the opening is about equal to the wave length of the light then a series of alternating light and dark bands indicative of the interference of waves appear on the posterior screen. He found that the latter effect is produced also when two holes very small and close together are cut in the screen and a beam of monochromatic light strikes the screen midway between the two points. In an essay titled “On the Theory of Light and Colors,” published in 1802, he described these bands as being “constructive (in phase) and destructive (out of phase) interference.”
⁴⁶

Despite the nearly incontrovertible evidence, as an indication of how strong Newton's influence was at the time and how difficult it is for even some scientists to question or reject their theories, Henry Brougham described Young's paper as “destitute of every species of merit . . .” (p. 19). However, Young's conclusions did resonate in the thinking of a gifted French engineer, Augustine Jean Fresnel, who rejected the corpuscular explanation of diffraction declaring that it had been refuted experimentally. When, in defense of the corpuscular theory, the supporters maintained that the diffraction patterns in Young's experiment were produced by the edges of the circular holes deflecting the particles passing through, Fresnel tested the explanation by altering the shape and the mass of the holes and finding that it had no effect at all, the diffraction pattern depending only on the relative sizes of the apertures and the wave lengths of the monochromatic waves.

He then supplemented Young's experiments by attributing mathematical dimensions to the properties of the diffracted waves. As we now know, the properties of particles and waves are the converse of each other: particles having a discrete location in space with various shapes and sizes, possess mass and momentum along with the energy of motion, and interact by deflection with a loss of energy. In contrast, waves are defined by their lengths, frequencies, amplitudes, and intensities, are diffused in space as wave trains, and interact to reinforce if in phase or destruct if out of phase. As described by Peter Achinstein:

[Fresnel's] account is much more sophisticated than Young's, not only because it is quantitative, but also because in determining the resulting vibration . . . Fresnel derives mathematical expressions for the amplitude of the vibration at any point behind the diffractor, and for the light intensity at that point. From these he infers the positions and intensities of the diffraction bands—inferences that were confirmed experimenally. (p. 21)

Fresnel was awarded a prize when he sent his results in a “Memoir on the Diffraction of Light” to the Paris Academy in 1819.

As optical investigations continued further evidence was discovered to support the wave theory. The initial inability of the wave theory to explain the polarization of light emerging from Iceland spar due to the assumption that light waves were transmitted longitudinally, running lengthwise like sound percussions, was surmounted when they were discovered to be produced by transversal vibrations (up and down)
perpendicular
to their direction of movement. Because of being transversal when they are reflected through Iceland crystal the latter's internal structure separates the vibration into perpendicular directions, thus the emerging light is polarized at right angles to each other.

Fresnel was even able to rebut the main optical evidence that had convinced Newton of the superiority of the corpuscular theory: the sharp outline of shadows cast by large objects when deflected by light. Fresnel argued that one can explain the sharp outline as due to the large object's obstruction of certain waves at the edge of their propagation, but if one reduces the size of the object to the magnitude of the light wave then the light bends around the object as sound waves do. Finally another crucial test could be made based on the change of the velocity of light when passing through a lesser to a denser medium.

Newton had predicted that on the corpuscular theory the greater gravitational attraction of the denser medium would cause an acceleration of the light particles while on the wave theory the diffraction of the light would cause a retardation of the velocity. In a series of ingenious experiments now cited as
experimentum crucis
(critical experiments) begun in 1850, by French physicist Jean Léon Foucault confirmed that water or glass impedes the velocity of light in accordance with the wave theory. Then, based on these results, another French physicist named Hippolyte Louis Fizeau determined the velocity of light to be 300,000 kilometers per second, or 186,281 miles per second.

Illustrating how the correct paradigm of scientific inquiry leads to the determination of the relative truth of hypotheses, along with opening up new vistas of discovery, by the middle of the nineteenth century, Huygens's wave theory of light had superseded Newton's corpuscular theory, although radically new interpretations were yet to come, including the discovery that light was a form of electromagnetism, and the twentieth-century discovery that it can exhibit either wave or particle properties depending on the experimental conditions.

As for the discovery of electromagnetism, since ancient times electricity and magnetism were considered separate phenomena. But then in the winter of 1819–1820 Hans Christian Oersted (1777–1851), professor of natural philosophy in Copenhagen, during a course of lectures wondered if an electric current might have an effect on a magnetic needle. To test the supposition he placed an electrified wire at a right angle to the north south axis of a compass to no effect. Deciding to align the electrified wire parallel to the N-S axis he was surprised to find it produced a pronounced deflection of the needle, showing a relation between electricity and magnetism.

This was supported by Michael Faraday (1791–1867), a bookbinder's journeyman who apprenticed at age thirteen and therefore had little formal education but became an outstanding scientist, again showing the more common backgrounds of these later scientists. Attracted to science, he began attending the lectures by Sir Humphrey Davy at the Royal Institution in London becoming a member in 1823 and then a fellow of the Royal Society the following year. In 1833 he attained the position of Fullerian Professor of Chemistry at the Royal Institution. By then his reputation was such that he was offered knighthood and the presidency of the Royal Society but declined both. He is especially noted for his discovery of electromagnetic induction.

It had long been known that when iron filings were spread on a sheet of paper and a magnet placed underneath, the filings became aligned in a curved pattern around the magnet that, according to Sir Edmund Whittaker, “suggested to Faraday the idea of
lines of magnetic force
; or curves whose direction at every point coincides with the direction of the magnetic intensity at that point. . . .”
⁴⁷
He then discovered that a moving magnet brought near an electric circuit induced a current, just as Oersted had found that an electric current changed the magnetic direction of the compass needle. As Whittaker continues:

Faraday found that a current is induced in a circuit either when the strength of an adjacent current is altered, or when a magnet is brought near to the circuit, or when the circuit itself is moved about in presence of another current or a magnet. He saw from the first that in all cases the induction depends on the relative motion of the circuit and the lines of magnetic force in its vicinity. The precise nature of this dependence was the subject of long-continued further experiments. (p. 172)

Faraday's realization that a magnetic field can induce an electric current combined with Hans Christian Oersted's complementary discovery led to the conception of an independently existing electromagnetism either as a field or a current due to the interactions, replacing the previous conception that they were fluids. Reinforcing again the importance of mathematics in modern science, James Clerk Maxwell (1831–1879), based on these experimental discoveries, formulated intriguing equations describing the structure of electromagnetic fields and how they change in time due to the interactions. It was Maxwell's equations that implied that the velocity of the propagation of the waves of the electric field is identical to that of light indicating that light too is a form of electromagnetism.

This was confirmed towards the end of the nineteenth century when Heinrich Hertz (1857–1894) experimentally proved the existence of electromagnetic waves having the same velocity as that of light. Because electromagnetism involves the interaction of contiguous fields rather than forces emanated by discrete physical bodies in space as in Newtonian science, the conceptual framework of electromagnetism represents the beginning of the third scientific revolution that transformed our conception of reality. In their book
The Evolution of Physics
, Albert Einstein and Leopold Infeld declared that the “theoretical discovery of an electromagnetic wave spreading with the speed of light is one of the greatest achievements in the history of science.”
⁴⁸
Indeed, it was these developments that made possible the later introduction of radar, electric power, telegraphy, radio, television, the internet, and so forth. As Carl Sagan states in
The Demon-Haunted World
:
Science as a Candle in the Dark
, this “has done more to shape our civilization than any ten recent presidents and prime ministers” (p. 390).

Chapter V

THE ORIGINS OF CHEMISTRY AND MODERN ATOMISM

Since modern atomic theory along with celestial mechanics represent the two most significant theoretical developments in the physical sciences that changed our conception of the modern world from the ancient Aristotelian model to the modern mechanistic one, the latter requires a separate chapter. Recall that it was the ancient Greeks who first endeavored to understand the universe in a more empirical-rationalistic manner to replace the earlier mythical or theogonic interpretations. This required describing the primal elements from which everything arose, along with explaining how the diversity of nature came to be from this primal state.

Though it was Empedocles' conception of the four elements of fire, air, earth, and water as primary that was adopted by Aristotle, which prevailed throughout most of the past, modern classical science reinstated the atomic theory of Leucippus and Democritus, along with the theory of infinite particles composing the universe introduced by Anaxagoras and adopted by Epicurus and Lucretius. Thus it was natural philosophers like Mersenne, Galileo, Gassendi, Descartes, Boyle, Locke, and Newton who revived the atomic or particle theory in the seventeenth century by adopting the corpuscular-mechanistic framework, though the conception at that time was still entirely speculative and elementary.

Although as early as the third century BCE Anaxagoras had declared that basic particles were infinitely divisible, when Newton adopted the corpuscular theory as the basic physical reality these particles were still mainly defined in terms of the Democratean primary qualities of solidity, shape, indivisibility, and motion (although Epicurus claimed they were composed of an inseparable minima), along with the more recent additions of mass, momentum, inertia, and gravitational attraction. Although the pseudosciences of alchemy and astrology were still pursued, the former by such distinguished natural philosophers as Boyle and Newton, they would soon be eclipsed by advances in modern classical science whose superior methodology led to the discovery of more elementary particles such as the electron and proton and an explanation of chemical compounds and reactions according to their exact molecular components, structures, and properties, rather than by God's will.

As was true of the transformation of the former notion of the celestial world to the modern conception of a gravity driven planetary and stellar universe according to mathematically defined astronomical laws, this new atomic and particle physics also would require a radical conceptual revision. Though not the first to use the balance to weigh the exact quantities of the reagents and products of chemical reactions, Antoine Laurent Lavoisier is considered the father of modern chemistry owing to his precise weighing of the components of combustion and oxidation that enabled him to determine that oxygen was a gas facilitating combustion, thereby refuting the prevailing phlogiston theory that postulated a fire-like element within combustible bodies. English chemist John Dalton similarly is regarded as the founder of modern atomism based on his discovery that natural elements like water, gases like carbon dioxide, and chemical compounds like sulfuric acid have a molecular structure that can be analyzed into specific atoms that combine according to simple numerical ratios according to their numbers: H
₂
O, CO
₂
and H
₂
SO
₄
respectively.

As religiously and rationally significant as was the transformation of the conception of a heavenly or celestial cosmology to a natural physical universe, for most of us, except for weather predictions and hurricanes and tornados, it is somewhat remote from our daily lives. This, however, is not true of the empirical sciences such as physics, chemistry, biology, physiology, medicine, engineering, etc. It is these sciences in particular that have radically changed our lives from what they were before the advent of science.

It was the overthrow of the theory that combustion was due to the expelling of phlogiston and replaced with the burning of oxygen that is usually credited with having been the major factor in the development of chemistry. It began with German physician Johann Joachim Becher's claim that combustion involved the burning off of the “fatty earth” described in his treatise
Physicae subterraneae
in 1669. Then German chemist George Ernest Stahl, in his book
Fundamenta Chymiae
(Fundamental Chemistry) in 1723, renamed Becher's
terra pinguis “
phlogiston,” claiming that it was “the matter and principle of fire,” though not fire as such. According to the phlogiston theory certain substances, like wood, charcoal, and phosphorus contain large amounts of this “
in
flammable principle” that they give off when heated that is combustion.