Lonely runner conjecture
Openlonely-runner
Statement
Suppose runners run forever on a unit-circumference circular track at distinct constant nonzero speeds , all starting at the origin at time . Conjecture: for every runner there exists a time at which the (arc-length, circular) distance from runner to every other runner is at least . Equivalently: for any positive reals (the relative speeds), there exists with for all , where is the distance to the nearest integer.
Current frontier
Proved for all k ≤ 10 (k ≤ 7 by 2008; k = 8 by Rosenfeld 2025, arXiv:2509.14111; k = 9, 10 by Trakulthongchai 2025, arXiv:2511.22427, and independently Rosenfeld for k = 9 in arXiv:2512.01912). First open case is k = 11.
When this counts as solved
A full solve is a rigorous proof of the conjecture for all , or an explicit and speed tuple where some runner is never lonely. Settling the next open case (, or any larger not already covered by the published 2025 work) also counts as a breakthrough — but the proof has to handle the full integer-speed parameter space for that . Improved view-obstruction bounds that don't settle a new , re-proofs of already-settled cases, or tightened loneliness bounds don't close it.
Classification
open-completion