In particle physics, a generation or family is a division of the elementary particles. Between generations, particles differ by their flavour quantum number and mass, but their interactions are identical. There are three generations according to the Standard Model of particle physics. Each generation is divided into two types of leptons and two types of quarks. The two leptons may be classified into one with electric charge −1 (electron-like) and neutral (neutrino-like); the two quarks may be classified into one with charge −​1⁄3 (down-type) and one with charge +​2⁄3 (up-type). The basic features...

The neutrino theory of light is the proposal that the photon is a composite particle formed of a neutrino–antineutrino pair. It is based on the idea that emission and absorption of a photon corresponds to the creation and annihilation of a particle–antiparticle pair. The neutrino theory of light is not currently accepted as part of mainstream physics, as according to the standard model the photon is an elementary particle, a gauge boson. == History == In the past, many particles that were once thought to be elementary such as protons, neutrons, pions, and kaons have turned out to be compo...

In theoretical physics, a no-go theorem is a theorem that states that a particular situation is not physically possible. Specifically, the term describes results in quantum mechanics like Bell's theorem and the Kochen–Specker theorem that constrain the permissible types of hidden variable theories which try to explain the apparent randomness of quantum mechanics as a deterministic model featuring hidden states. == Examples == The Weinberg–Witten theorem states that massless particles (either composite or elementary) with spin j > ​1⁄2 cannot carry a Lorentz-covariant current, while massle...

A proof of impossibility, also known as negative proof, proof of an impossibility theorem, or negative result, is a proof demonstrating that a particular problem cannot be solved as described in the claim, or that a particular set of problems cannot be solved in general. Proofs of impossibility often put decades or centuries of work attempting to find a solution to rest. To prove that something is impossible is usually much harder than the opposite task; as it is often necessary to develop a theory. Impossibility theorems are usually expressible as negative existential propositions, or universal...