In harmonic analysis, the local smoothing conjecture is a conjecture about the behavior of solutions to the wave equation. The conjecture was first proposed by Christopher Sogge in 1991. It was proven in the dimension 2 case by Guth, Wang, and Zhang in 2019.
The local smooth conjecture is the strongest in a sequence of conjectures in harmonic analysis. It implies the Bochner-Riesz conjecture, which in turn implies the restriction conjecture, which implies the Kakeya conjecture.