In theoretical physics, a no-go theorem is a theorem that states that a particular situation is not physically possible. This type of theorem imposes boundaries on certain mathematical or physical possibilities via a proof by contradiction.
Instances of no-go theorems
Full descriptions of the no-go theorems named below are given in other articles linked to their names. A few of them are broad, general categories under which several theorems fall. Other names are broad and general-sounding but only refer to a single theorem.
Classical electrodynamics
- Antidynamo theorems are a general category of theorems that restrict the type of magnetic fields that can be produced by dynamo action.
- Earnshaw's theorem states that a collection of point charges cannot be maintained in a stable stationary equilibrium configuration solely by the electrostatic interaction of the charges.
Non-relativistic quantum mechanics and quantum information
- Bell's theorem
- Von Neumann's no hidden variables proof
Quantum field theory and string theory
- Weinberg–Witten theorem states that massless particles (either composite or elementary) with spin <math>\; J > \tfrac{1}{2} \;</math> cannot carry a Lorentz-covariant current, while massless particles with spin <math>\; J > 1 \;</math> cannot carry a Lorentz-covariant stress-energy. It is usually interpreted to mean that the graviton in a relativistic quantum field theory cannot be a composite particle.
- Nielsen–Ninomiya theorem limits when it is possible to formulate a chiral lattice theory for fermions.
- Haag's theorem states that the interaction picture does not exist in an interacting, relativistic, quantum field theory (QFT).
- Reeh–Schlieder theorem