Two long years Rubik’s cube fans have been dazed with the God’s number 22 (as made possible by Tomas Rokicki and John Welborn in August, 2008) and believed that the puzzle has been solved the fastest way that one could—and so they thought.
Every Rubik’s solver uses algorithms in order to solve the mind-spinning cube puzzle. There are algorithms that use sequences that solves the top face of the cube, some use sequences to fix the middle portion, and so on. There are a lot of algorithms that may differ in complexity and the number of moves it requires.
God Himself must have a better, easier and faster algorithm in which to solve the Cube. And this is where the term “God’s algorithm” came from, and the number of moves it would require to solve a really difficult positioning of the puzzle is called “God’s number.”
And yes, thanks to Google’s computers, the newest God’s number is now 20.
For about 35 CPU-years of inactive computer time provided by Google, researchers have eventually solved all the possible positions of the Rubik’s cube, and they proved that each one of these positions could be solved in no less than twenty moves!
But how did they exactly do it?
They divided the positions into 2,217,093,120 sets of 19,508,428,800 each then decreased the count of sets they needed to work out to 55,882,296 utilizing symmetry and set covering. However, they did not find ultimate solutions to each position but instead they found solutions of length 20 or less. Then, they recorded the program that solved one set for about 20 seconds. Ultimately, Google has used 35 CPU years in order to find the solutions to all positions in each of the 55,882,296 sets.
Still sound complicated? Here’s how they did the partitioning part. They broke the trouble down into 2,217,093,120 smaller troubles. Each of these comprised 19,508,428,800 different positions. These smaller troubles were small enough to fit in a modern PC’s memory, and the way Google has broken it down made it possible for them to solve every set faster.
It is said that if you take a mixed up Cube and position it upside down, you will not make it any more difficult—it will still also take the same number of moves to bring to original position again. Instead of trying to find a solution to both of those positions, you can actually solve just one.
Now Rubik patrons could have another God’s number to focus on to. And it’s not 22—but a whopping God’s number 20!
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