The History of Physics from 2000BCE to 1945. Sheldon J.D. Cohen

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СКАЧАТЬ that the four basic elements of air, fire, earth, and water were each made of different atoms. Even with only four basic building blocks, the various combinations of these could result in a great variety of different forms of matter. If the proportions of the building blocks remained the same, there were twenty-four different combinations. Now consider the infinite number of combinations that would occur if you varied the amounts of each of the four basic elements.

      For the first time, a combination of actual basic substances could unite to explain the great variety of forms and events which make up our experience.

      In addition to the four basic elements of our earthly experience, there was a fifth: the aether that permeated the heavens as far as the eye could see. The aether, considered an invisible, elastic medium distributed through all space beyond the earth’s atmosphere remained a building block of physics for twenty-four centuries.

      Anaxagoras (500-428 BCE) suggested that rather then the four basic elements of earth, air, fire, and water, there were infinite seeds composing all matter and not just the basic four. The proportion of the various seeds explained the great diversity of everything around us. From this concept of infinite seeds, or building blocks, it was a simple leap to the idea that there was a smallest, ultimate basic building block of all matter---the atom. It was postulated that in solid bodies, the atoms were held together by mysterious forces, while in gases, the atoms were separate and free to move in space. Over time, the atomists began to forge ahead as the theory of the four basic substances began to wane.

      It was the Greek philosopher Leucippus (490-? BCE), who strongly supported the concept of unbreakable tiny fragments, further promoting the atomos concept.

      If traveling to Athens from a northwesterly direction, one will pass the Democritus Nuclear Research Laboratory. Naming this facility for Democritus (460-370 BCE) honors a man whose atomos philosophy comes close to modern physics theory. Although he was not the first to espouse atomism, his use of this concept allowed him to develop a much more detailed, and what would prove to be a much more insightful view of the way the world functioned physically.

      He believed that space was a vacuum, but in spite of this property of emptiness it could be thought of as existing as did the visual realities of our world. In the void of space, and in the world around us, there were an infinite number of atoms, so small that they were incapable of further division. These atoms made up the physical world. He postulated that all changes occurring in the universe were merely dependent on the density of the atoms and their movement in relation to each other. Nature itself was nothing more then a complex interaction of atoms that followed the laws of mathematics. Initially atoms moved incoherently but over time, they would randomly interact and combine in a multitude of ways responsible for the origin of the universe and the laws of mechanics and motion.

      He made many contributions to geometry and is credited with mathematical ideas that Isaac Newton would define many years later as the integral calculus.

      It is little wonder that the Greeks thought to name a nuclear research facility after him.

      Plato (429-347 BCE) and Aristotle (384-322 BCE) never accepted the atomos theory, and since they were so widely respected, their viewpoint held sway. Oposing views were not silenced, however.

      Epicurus (341-270 BCE) espoused atomos with great vigor and is supposed to have written several hundred books, but none of them survived. Epicurus attracted a following, however, and one of these was a Roman known as Lucretius (96-? BCE). He wrote a long poem, which survived through the Middle Ages, and which described Lucretius’s views on atomos.

      It would take 1500 years until Pierre Gassendi (1592-1655), a French philosopher read Lucretius and espoused his views on atomism. Since the printing press was now well established his books on the subject had a wide audience. For the first time the question could be posed to thousands. Prior to this point the subject of atomism could not be settled due to the inability to experimentally confirm or deny the theory. It served only as an interesting intellectual discussion that could not be resolved one way or the other. There needed to be some method of experimentation that could bring some rationale to the discussion.

      What we have been dealing with to this point reflects an effort to acquire knowledge through the power of reasoning alone. The name for those who were responsible for this effort of comprehension was “philosophers” (Greek for lovers of wisdom).

      Even in those days, philosophy took on two directions: first a turning within to attempt an understanding of human behavior, of morality and ethics; second a turning out to seek explanations of other than the mind---nature to be exact. Such study, the phenomenon of nature throughout the universe, was termed natural philosophy. The word science would not make its appearance until the nineteenth century.

      WHAT IS LIGHT?

      The Greeks were also responsible for the first enlightened discussion on the subject of light. Prior to their serious evaluation of this phenomenon, the world was content to accept God’s pronouncement: Let there be light: and there was light. Light was the antithesis of dark. Because of it, all life on earth was given the gift of sight.

      What was it that caused our eyes to perceive the world around us when the sun or the moon or fire allowed us to see? What did our eyes do that allowed us to visualize distant objects? Did our eyes emit something that sped rapidly to a distant or nearby object, and once having struck the object caused us to see it, or did light issue forth from any luminous object and reach our eyes, and having done so give us a visible world? Pythagoras (582-500BCE) championed this latter thought.

      These conflicting theories only served to raise many more questions. If light entered our eyes enabling us to see, or if something left our eyes giving us the same ability, what is it that entered or left? What is its size? What does it weigh? Very little, no doubt, if it has weight at all? What is its speed? Why does it pass through some objects and not others? Why does cloth block light and thick glass allow it to pass through?

      These questions would remain unanswered for centuries, and the solution would be intimately connected with the development of the atom theory that the Greeks so brilliantly propounded.

      THERE ARE ATOMS AFTER ALL

      The first to experimentally open the door to confirming the atomos theory was Robert Boyle (1627-1691). He was born in Ireland. His father was the richest man in the British Isles. Boyle, to his credit, took advantage of the opportunities that money opened up for him. He became a renaissance man, studying religion, philosophy, mathematics, languages, and the physics of such pioneers as Descartes and Galileo.

      His natural philosophic work included an improved vacuum pump that allowed him to make excellent vacuums, and in so doing he demonstrated that air was necessary to sustain life, that sound would disappear in a vacuum, and a candle would stop burning as the air was evacuated.

      His main triumph, so familiar to all students of chemistry, was the volume-pressure inverse relationship. Boyle used a J shaped glass tube closed at the shorter end and opened at the long end. When he poured mercury in the tube, air trapped in the closed short end. The more mercury he poured in the less air seemed to be trapped. He made many measurements at atmospheric pressure and also at lower and higher then atmospheric pressure. He determined that when the pressure on the air was increased by the addition of more mercury, the volume of the air decreased, and when the pressure on the air was decreased the volume of air increased.

      This was the pressure-volume inverse relationship and it lent credence to the atomistic theory: if air is made up of widely separated atoms, suggested by Democritus, this would explain the fact that air was lighter then СКАЧАТЬ