Double copy theory is a theory in theoretical physics, specifically in quantum gravity, that hypothesizes a perturbative duality between gauge theory and gravity. The theory says that scattering amplitudes in non-Abelian gauge theories can be factorized such that replacement of the color factor by additional kinematic dependence factor, in a well-defined way, automatically leads to gravity scattering amplitudes. It was first written down by Zvi Bern, John Joseph Carrasco and Henrik Johansson in 2010 ^[1] and was sometimes known as the BCJ duality after its creators^[2] or as "gravity = gauge × gauge".^[3]

The theory can be used to make calculations of gravity scattering amplitudes simpler by instead calculating the Yang–Mills amplitude and following the double copy prescription.^[4] This technique has been used, for example, to calculate the shape of gravitational waves emitted by two merging black hole.^[5][6] This was proven to work at tree level and at higher orders,^[1] including at fourth post-Minkowskian order.^[7] The theory has been applied to black holes.^[8]