**Heim theory**, first proposed by German physicist Burkhard Heim publicly in 1957, is an attempt to develop a theory of everything in theoretical physics. The theory has received little attention in the scientific literature and is regarded as being outside mainstream science but has attracted some interest in popular and fringe media.

Heim attempted to resolve incompatibilities between quantum theory and general relativity. To meet that goal, he developed a mathematical approach based on quantizing spacetime. Others have attempted to apply Heim theory to nonconventional space propulsion and faster than light concepts, as well as the origin of dark matter.

Heim claimed that his theory yields particle masses directly from fundamental physical constants and that the resulting masses are in agreement with experiment, but this claim has not been confirmed. Heim theory is formulated mathematically in six or more dimensions and uses Heim's own version of difference equations.