High Quality Content by WIKIPEDIA articles! In particle physics, fundamental interactions (sometimes called interactive forces or fundamental forces) are the ways that elementary particles interact with one another. An interaction is fundamental when it cannot be described in terms of other interactions. The four known fundamental interactions are electromagnetism, strong interaction ("strong nuclear force"), weak interaction ("weak nuclear force"), and gravitation. The electromagnetic and weak interactions are often considered together as an electroweak interaction. All are non-contact forces.