Definition
Plain language
The proven worst-case fewest moves needed to solve any scrambled Rubik's cube — twenty.
As stated in the literature
The diameter of the Rubik's cube group under the half-turn metric, proven to be 20; used as the optimality yardstick when evaluating agent-generated cube solvers.
Why it matters: It gives a proven best-case target, so you can measure how close a cube-solving method comes to the theoretical optimum.
For example, no matter how badly someone scrambles a Rubik's cube, there is always a solution in twenty moves or fewer.
Heard on the show
“72 moves, within one move of God's number, the proven worst-case optimum of 20.”Episode 166 — A Router That Beats the Frontier Models It Calls