Another important contribution of Greek philosophy to the understanding of the world, not by way of single principles but by an insight into its matter constituents, was that of the atomists, its best representative being Democritus (460–370 BC). In their view, the universe consisted of empty space and an infinite number of independent, indivisible, and eternal atoms which interacted with each other mechanically. The existence of atoms was later confirmed by scientific physics, though the present quantum mechanical atomic concept is very different from its philosophical model.
With the conquest of Greece by the Romans, Greek philosophy came to a halt and was subsequently greatly obscured by the rise and spread of Christianity. Throughout the Middle Ages, the universe was explained by a blend of religious and concordant philosophical concepts but between AD 1600 and 1650, a dramatic transformation occurred: the establishment of scientific thought.
The tool enabling that historical revolution was the scientific method of investigation, based on quantity. The agents were Kepler (1571–1630) and Galileo (1564–1642), among others. They proclaimed that measurement holds the key to the understanding of nature. With the development of analytical geometry by Descartes (1596–1650), the way was opened for Newton (1642–1726) to discover the laws of motion and universal gravitation, which laid down the foundation for classical mechanics.
Newton derived his laws of motion from the observation of the movement of the planets, and in the mathematics he assumed the reversibility of time. By “reversible” it is meant that the laws governing the process remain unchanged when the direction of time is reversed—when -t is substituted for +t in the equations. In the real world, this means it does not matter to the laws of motion whether the planets rotate from left to right or from right to left. After confirmation of Newton’s laws, it was assumed by physics that all elementary processes in nature were reversible.
But by experience we know that in our universe time is not reversible. We grow older with every breath and cannot get younger. The nonreversibility of time occurs with every process in nature. We cannot, for instance, fry an egg and then put it back raw into the shell. The reason why Newton’s laws of motion work so well is that they deal with simple two-body systems (earth-moon, sun-planet) under conditions where irreversibility effects are negligible. It is in the passage from two-body to many-body, from simple to complex systems, such as proteins and organisms, that the irreversible nature of time becomes manifested. In effect, we can say that all processes in nature are irreversible, the apparent reversible processes being just limiting cases. But so far, all attempts to introduce irreversibility into contemporary physics have been unsuccessful.
During the nineteenth century, following extensive work in electricity and magnetism carried out by several physicists and mathematicians, Maxwell (1831–1879) introduced the concept of electromagnetic waves and, by declaring that all energy resides in the field, set down the basis of field theory.
Electrical concepts differ from those of mechanics in a very significant way: they are not supported by direct representations of visual observations. The concept of electric charge is a good illustration of this point. Presumably it holds some essential clues to fundamental structure, but this fact has not been definitely established and until it does, electrical charge remains an abstract concept. The introduction of abstract concepts into fundamental theory has compromised its objectivity and the reliability of its mathematical expressions. This tendency has increased ever since.
In mid-nineteenth century, with the invention of the steam engine, it was recognized that heat always moves by itself from hotter to colder bodies. And it soon became evident that all forms of energy move in a unique direction, from a higher to a lower energy state. The inability of the mechanical physics of the time to explain these observations led to the introduction of thermodynamics theory in late nineteenth century.
Thermodynamics is the branch of physics concerned with heat and temperature and their relation to energy and work. It applies to a wide variety of topics in science and engineering and, since organisms are heat-producing systems, it also applies to us. In effect, its first law, which embodies the principle of the conservation of mass-energy, forms the basis of present biology.
But it is its second law that possesses a unique position among the laws of physics: it is the first law to impose on time a sense of direction. It states that in any closed system, there must be either conservation or increase in entropy. In other words, entropy production can only be positive, which means that entropy increase is irreversible. Entropy has been loosely correlated with the degree of randomness or disorder within a system (water molecules in steam have an entropy level higher than in liquid water). Applied to the universe as a whole, considering it as a closed system, the second law predicts that “the entropy of the universe always increases.” In fact, it was in these terms that Claudius (1822–1888), one of the founders of thermodynamic theory, formulated the second law. Since then and for over a hundred years, physical scientists have paid much attention to processes moving toward states of greater dynamical disorder, leading them to even suggest that the universe displays only one tendency: toward disorder.
In the early twenty century, a complex mathematical theory —relativity theory—was developed by Einstein (1879–1955). It was to change the course of theoretical physics. Since the concern of this book is the place of human beings in the vast system of nature, we just want to address two pertinent assumptions of relativity.
In the special theory, it was postulated that physical laws can best be expressed if it is assumed that space and time are so similar that physics can make no absolute distinction between them—the spacetime concept. Under these conditions the symmetry of space involves the symmetry of time, and therefore the reversibility of the physical laws. As in Newtonian theory, time in relativity continues to be reversible and, in addition, space becomes less real: a four-dimensional continuum does not fit the space surrounding us. We perceive spacetime as space and time, the spacetime notion being meaningless to us. The other assumption concerns the origin of gravity, the central idea of the general theory. While for Newton it is mechanical—an invisible force attracting two material bodies—for Einstein it becomes geometrical—a curvature of the very fabric of spacetime, a distortion induced by mass itself. This concept of gravity has proved very difficult to reconcile with other theories. It thus appears that relativity theory is only applicable to a narrow range of relatively simple systems, at the level of stars and galaxies. Certainly, it does not apply to complex systems, such as human beings.
Ever since Newton, the nature of light—particle, wave, or both at once—was a subject of intense interest to physicists. In 1900, Planck (1858–1947) noted that a blackbody emitted electromagnetic radiation (which includes light) in small discrete packets, later called quanta, rather than as a continuum emission—energy was quantized. His law, giving the distribution of the radiated energy, formed the basis of quantum theory. Einstein later theorized that a beam of light is not a wave propagating through space but a collection of discrete wave packets, which he called photons, whose energy content is proportional to the wave frequency. He then demonstrated that one sufficiently energetic photon can transmit its energy to a single electron in a metal, ejecting it. In 1923, De Broglie (1892–1987) showed that electrons can be diffracted in a similar way to light: that is, particles can act as waves—the wave-particle duality. Photon-electron—or more generally radiation-matter—interactions form the basis of modern quantum mechanics theory.
To comply with the requirements of wave-particle duality, in quantum mechanics an electron is represented by a complex quantity called a wave function, based on the conservation of energy and momentum. The wave function cannot be identified