CHAPTER 5

ELEMENTARY PARTICLES AND THE FORCES OF NATURE

Aristotle believed that all the matter in the universe was made up of four basic elements—earth,

air, fire, and water. These elements were acted on by two forces:

gravity, the tendency for earth and water to sink,

and levity, the tendency for air and fire to rise.

This division of the contents of the universe into matter and forces is still used today.

Aristotle believed that matter was continuous,

that is, one could divide a piece of matter into smaller and smaller bits without any limit:

one never came up against a grain of matter that could not be divided further.