Weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four fundamental forces of nature, alongside the strong nuclear force, electromagnetism, and gravity. It is responsible for the radioactive decay of subatomic particles and initiates the process known as hydrogen fusion in stars. Weak interactions affect all known fermions; that is, particles whose spin (a property of all particles) is a half-integer.

In the Standard Model of particle physics the weak interaction is theorised as being caused by the exchange (i.e., emission or absorption) of W and Z bosons; as such, it is considered to be a non-contact force. The best known effect of this emission is beta decay, a form of radioactivity. The Z and W bosons are much heavier than protons or neutrons and it is the heaviness that accounts for the very short range of the weak interaction. It is termed weak because its typical field strength is several orders of magnitude less than that of both electromagnetism and the strong nuclear force. Most particles will decay by a weak interaction over time. It has one unique property – namely quark flavour changing – that does not occur in any other interaction. In addition, it also breaks parity-symmetry and CP-symmetry. Quark flavour changing allows for quarks to swap their 'flavour', one of six, for another.

Richard Phillips Feynman ( /ˈfaɪnmən/; May 11, 1918 – February 15, 1988) was an American physicist known for his work in the path integral formulation of quantum mechanics, the theory of quantum electrodynamics, and the physics of the superfluidity of supercooled liquid helium, as well as in particle physics (he proposed the parton model). For his contributions to the development of quantum electrodynamics, Feynman, jointly with Julian Schwinger and Sin-Itiro Tomonaga, received the Nobel Prize in Physics in 1965. He developed a widely used pictorial representation scheme for the mathematical expressions governing the behavior of subatomic particles, which later became known as Feynman diagrams. During his lifetime, Feynman became one of the best-known scientists in the world. In a 1999 poll of 130 leading physicists worldwide by the British journal Physics World he was ranked as one of the ten greatest physicists of all time.

He assisted in the development of the atomic bomb and was a member of the panel that investigated the Space Shuttle Challenger disaster. In addition to his work in theoretical physics, Feynman has been credited with pioneering the field of quantum computing, and introducing the concept of nanotechnology. He held the Richard Chace Tolman professorship in theoretical physics at the California Institute of Technology.