Some very strange-sounding things happen in the innermost core of atomic nuclei: when two particles come close together, the force between them becomes weaker rather than stronger. Conversely, the interaction between them grows stronger as they move apart. Like a rubber band holding two balls together, this force binds the two particles together and holds them in the atomic nucleus.

Physicists call this force the “strong interaction” and it is one of the four fundamental interactions that determine the behaviour of bodies, fields, particles and systems. The other three fundamental interactions are the weak interaction, electromagnetism and gravitation.