Twenty-six moves suffice for Rubik's cube

  • Authors:
  • Daniel Kunkle;Gene Cooperman

  • Affiliations:
  • Northeastern University, Boston, MA;Northeastern University, Boston, MA

  • Venue:
  • Proceedings of the 2007 international symposium on Symbolic and algebraic computation
  • Year:
  • 2007
  • Applications of Cayley Graphs

    AAECC-8 Proceedings of the 8th International Symposium on Applied Algebra, Algebraic Algorithms and Error-Correcting Codes

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Abstract

The number of moves required to solve any state of Rubik's cube has been a matter of long-standing conjecture for over 25 years -- since Rubik's cube appeared. This number is sometimes called "God's number". An upper bound of 29 (in the face-turn metric) was produced in the early 1990's, followed by an upper bound of 27 in 2006. An improved upper bound of 26 is produced using 8000 CPU hours. One key to this result is a new, fast multiplication in the mathematical group of Rubik's cube. Another key is efficient out-of-core (disk-based) parallel computation using terabytes of disk storage. One can use the precomputed data structures to produce such solutions for a specific Rubik's cube position in a fraction of a second. Work in progress will use the new "brute-forcing" technique to further reduce the bound.