Answer the following question given this paragraph: 

A: The modern kinetic theory of matter is remarkably similar to Democritus’ ideas about the motion of atoms. According to this theory, atoms of matter are in constant random motion. This motion is greater in gases than in liquids, and it is greater in liquids than in solids. But even in solids, atoms are constantly vibrating in place.


Q: What theory says atoms of matter are in constant random motion?


A:
modern kinetic theory