Taoists believe that wisdom is realizing our unity with nature and living in harmony with the natural cycle of life and death (the Tao). Though individuals pass away, the Tao is eternal. The Taoist soul is like a drop of water in a stream, being part of the greater flow of the Tao even after death of the individual. Democritus expanded on the atomic theory, believing all things are made up of indivisible atoms and that the cosmos follows discernible natural laws.