Topic: group theory
The importance of group theory was emphasized very recently when some physicists using group theory predicted the existence of a particle that had never been observed before, and described the properties it should have. Later experiments proved that this particle really exists and has those properties.
Nowadays, group theoretical methods—expecially those involving characters and representations, pervade all branches of quantum mechanics.
The theory of groups is a branch of mathematics in which one does something to something and then compares the results with the result of doing the same thing to something else, or something else to the same thing.
The universe is an enormous direct product of representations of symmetry groups.