Two nonpolar molecules are attracted to each other primarily through London dispersion forces, which are a type of van der Waals force. These forces arise due to the temporary fluctuations in electron distribution within molecules, leading to the formation of instantaneous dipoles.
When nonpolar molecules are in close proximity, the temporary dipole of one molecule can induce a dipole in a neighboring molecule, causing a slight attraction between them. Although these forces are relatively weak compared to dipole-dipole interactions or hydrogen bonds, they can still be significant, especially when dealing with larger molecules that have more electrons and a larger electron cloud. This attraction is essential for the condensation of nonpolar gases into liquids and the overall behavior of nonpolar substances in various conditions.