Democritus could explain the changes in the world as changes in motion of the atoms, or changes in the way that they were packed together. This was a significant theory which attempted to explain the whole of physics based on a small number of ideas.

          Another fundamental idea in Democritus's theory is that nature behaves like a machine; it is nothing more than a highly complex instrument. He thought that all matter, including space and time, were composed of tiny indestructible units, called atoms. This idea seems provoked by the question of how thinly someone can go cutting up matter. While Democritus didn’t do any experiments and had only the more basic evidence for proposing the existence of atoms, his theory was kept around by the Roman poet Lucretius.

     The atoms in Democritus’s theory remain unchanged, but move around in space to combine in different ways to form all macroscopic objects. Early atomic theory stated that the characteristics of an object are determined by the shape of its atoms. So, for example, sweet things are made of smooth atoms, bitter things are made of sharp atoms.