Also called "Atomic Theory of the Universe" it was created together with his mentor, Leucipo, and is considered the first atomic model.
It must be taken into account that, at that time, knowledge was not achieved through experimentation, but through logical reasoning, based on the formulation and discussion of ideas.
Democritus knew that if you cut a stone in half, each half has the same properties as the original stone. He reasoned that if you kept cutting the stone into smaller and smaller pieces, you would reach a point so small that it could no longer be divided. So basic, yet so difficult to come to this conclusion with reasoning alone.
Therefore, his theory proposed that the world was made up of very small and indivisible particles, of eternal existence, homogeneous and incomprehensible, whose only differences were in shape and size. He named these particles “atoms”, a word that comes from the Greek atémnein and means “indivisible”.
According to Democritus, the properties of matter were determined by the way in which the atoms were grouped, which is why other philosophers, such as Epicurus, added to the theory, the random movement of the atoms.
However, Aristotle and Plato, two of the best-known philosophers of ancient Greece, rejected Democritus's theories. Aristotle accepted Empedocles' theory of Agrigento (Empedocles argued that all matter was composed of four elements: fire, air, water, and earth. The ratio of these four elements affected the properties of matter). Aristotle added his own idea (incorrect) that the four basic elements could be transformed into one another.
Due to the great influence of Aristotle, Democritus's theory would have to wait almost 2,000 years before being rediscovered.
“The entire universe is made up of unlimited space in which there are innumerable atoms. Space has no limits, it has neither an above nor a below, it has neither a center nor a border. Atoms have no qualities, apart from their shape. They have no weight, no color, no taste. The heat, the cold and the color are opinions: in reality only the atoms exist, and the emptiness.
“Atoms are indivisible, they are the elementary grains of life, which cannot be further subdivided, and everything is made of them. They move freely in space, colliding with each other.”
It is the basis of what we know, although with the corrections of our technological advances.