How did Lucretius explain Epicurean atomic theory in De rerum natura?

In his didactic poem De rerum natura (On the Nature of Things), Lucretius presents the physical theory of Epicurus by establishing that the universe consists of an infinite number of irreducible atoms moving through an infinite void.1

Lucretius explains the atomic universe through several key principles:

• Nature of Atoms: Atoms are impenetrably hard, changeless, and everlasting. They differ only in shape, size, and weight, and they serve as the fundamental limit of physical division.1
• Motion and Swerve: Atoms move downward through space. Lucretius posits that they occasionally undergo an indeterminate "swerve," which allows them to collide and form atomic systems. This swerve is essential, as it creates an infinite plurality of worlds and provides the basis for free will by interrupting the causal chain.1
• Systems and Change: All observable things are systems of moving atoms separated by intervals of void. Change occurs through the addition, subtraction, or rearrangement of these atoms.1
• Perishability: Because all systems are composed of atoms and void, they are divisible and ultimately perishable, unlike the atoms themselves.1