Quarks: The Search for the Elementary Particle
The History of the Atom
The Greeks
The ancient Greek philosphers posed the first recorded questions as to the nature of the physical world. There was a firm belief in the ultimate simplicity of the world - that in the end, it would be found that only a few things were the basis of all the matter and phenomena that we see around us. There arose two schools of thought: the idea of the 'atom', and the idea of the 'elements'.
The most popular theory at the time was Aristotle's theory of the elements. He believed that one could divide up a piece of matter an infinite number of times, that is, one never came up with a piece of matter that could not be further divided. He suggested that everything in the world was made up of some combination of four elements: earth, fire, water, and air. The elements were acted upon by the two forces of gravity and levity. Gravity was the tendency for earth and water to sink, and levity the tendency for air and fire to rise.
The second theory was headed by a man named Democritus. He believed in the existence of an 'elementary particle', which he called the 'atom'. These atoms were indivisible, the smallest particle possible. He suggested that there were many different types of unchangeable atoms, each with its own shape and size, in constant motion. Matter, therefore, was made up of large numbers of different types of atoms.
Because Aristotle's theory was highly popular, Democritus' theory of atoms soon faded into obscurity, and was largely forgotten by the time of Christ. The atomic concept of material as we know it today really only came into being less than two hundred years ago.
Newtonian Era
In the seventeenth century, the concept of the atom was revived. Robert Boyle used the concept in his work on chemistry. Sir Isaac Newton had the theory in mind when formulating his theories in physics and optics. But it was not until the latter half of the eighteenth century that the atomic theory truly became a part of scientific thought.
French chemist Antoine Lavoisier spent many years of the eighteenth century investigating why things burn. He discovered a number of pure chemical substances which could not be separated into other chemical substances, and he realized that burning was simply the process in which oxygen combined with those elements.
Chemist John Dalton was the first to state several of the fundamental concepts of modern atomic theory, in the early 19th century. He stated that matter is made up of indivisible atoms; that all atoms of a specific element are identical; that different elements have different atoms (size, shape, etc); that atoms cannot be created or destroyed; and that a chemical compound is composed of molecules, which are made of a small, fixed number of atoms from each element in the compound.
In 1827, British Botanist Thomas Brown noticed that when a pollen grain floating in a drop of water is examined using a microscope, it can be seen bouncing around in a random motion. This irregular motion is now called Brownian motion. In one of three papers published in the Annalen der Physik in 1905, Albert Einstein proved, as far as a theoretical paper could, the existence of atoms of finite size. He showed that Brownian motion, though random, obeys a statistical law, and that the pattern of behaviour is exactly what should be expected if the pollen grain is being repeatedly bounced around by unseen particles. With all the evidence before them, modern scientists finally began to accept the atomic theory.
Quarks: The Search for the Elementary Particle
The History
of the Atom