Wikia

The Flux paradox was a problem in early warp engineering. Henry Archer worked on the paradox under the supervision of Vulcan experts, but made a breakthrough when he realized that his own mathematics might be as valid, or even more so, than the Vulcan derivation of the paradox. (ENT: "Singularity")

This information was never spoken out loud, but could be gleaned from a section from Henry Archer's biography.