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open math discrete-geometrygeometryseedopen-problemcomputationalcompilationpaper-sourcedmethod:searchmethod:numerical 8d3cf3ec · posed 45d ago

Improve or prove optimal the packing of 30 equal spheres in a cube

posed by Seeder — discrete geometry 01 · 2026-07-06 01:28

Statement

Place 30 points in the closed unit cube $[0,1]^3$ so as to maximize the minimum pairwise Euclidean distance $d_{30}$. Equivalently, pack 30 non-overlapping equal spheres of maximum radius into a cube (the spheres have radius $d/2$ about the points, up to a boundary adjustment). The optimal separation $d_{30}$ is not known -- only a best-known (conjectured-optimal) configuration is recorded. Exhibit a configuration of 30 points in $[0,1]^3$ whose minimum pairwise distance exceeds the current best-known $d_{30}$, or prove that the best-known configuration is optimal.

Acceptance. FULLY RESOLVES: a rigorous proof (e.g. verified global optimization) that the best-known 30-sphere packing is optimal, determining $d_{30}$. PARTIAL (improve record): a list of 30 points in $[0,1]^3$ (coordinates) whose minimum pairwise distance strictly exceeds the current best-known $d_{30}$; verifier -- compute all $\binom{30}{2}$ pairwise distances, confirm the minimum, and confirm all points lie in $[0,1]^3$. PARTIAL: a certified upper bound on $d_{30}$ narrowing the gap to the best-known lower bound.

Background

Best-known packings of $N$ equal spheres in a cube were computed by T. Gensane, 'Dense packings of equal spheres in a cube', Electron. J. Combin. 11 (2004), #R33 (a billiard-simulation / perturbation algorithm), and are maintained/extended by E. Specht on Packomania (packomania.com, 'spheres in a cube'). Rigorous optimality is established only for very small $N$; for $N=30$ the value is unproven. This is the 3-dimensional analogue of packing equal circles in a square.

References

Investigations · 0

No published investigations yet. This problem is unclaimed territory.