Speed Solve of a Rubik’s Cube in Slow Motion – Numberphile

There we go. See, most people forgot about the Rubik’s Cube back in the eighties, so it had its’ heyday and then disappeared the
mathematicians remain obsessed with it. They wanted to find out the number of moves it would take to solve the most difficult combination. People probably are aware that there is
some maths involved in a Rubik’s Cube and the group is the number of different
combinations that there are on the Rubik’s Cube. It’s all the different
ways that you can scramble up a cube Other things do have permutations and
symmetry there’s just something nice and tactile and you can gather
and you can see everything as it happens. And this number would be called God’s
number. If you have perfect knowledge of how to do the Rubik’s Cube you would be
able to solve the most difficult position in its perfect most efficient algorithm. And they managed to work out that it was
less than 30. And over the years, they started to whittle this down closer and closer. No matter how much you scramble up a Rubik’s Cube, you can solve it in 20 or fewer twists. It’s called God’s number because you
have to be some kind of omniscient being to work out those 20 moves. It’s just so difficult to calculate what those moves are. I couldn’t look at a cube and say I
need to do these 12 moves or whatever but there are people who can so they do
Rubik’s Cube solving competitions and they have obviously speed challenges
and see who can solve it the fastest but one of the other things that they do is
a kind of efficient solve and the competition there is look at a Rubik’s
Cube and then just write down a list of moves that will solve it Which I think is probably more impressive than people who can solve it really quickly. It was called the super flip. Now the
super flip is essentially completely solved except each edge position was flipped
over. If you take one of those pieces off and turn it around, you get a whole new universe and you can’t get back to the solved Rubik’s Cube if you do that. Four point three times ten to the nineteen it’s a massive number, that is a massive number of combinations It’s 43 quintillion 252 quadrillion
3 trillion 274 billion 489 million 856 thousand It’s just a mind-numbing number of
possible arrangements So this was a big craze in the 1980s. Big craze. In the 1880s, exactly 100 years earlier, there was a similar puzzle that was also a big craze. They had their code that checked the
reduced number of cases. They ran it on the Google servers and they did. They exhaustively checked and we know now for a fact that God’s number is 20. Every Rubik’s puzzle can be solved in 20 or fewer moves. You might think, well how do we know how? How do we know that? Did we just check all 43.25 billion billion different ways
of solving it and we effectively did that. And there are 12 factorial ways to
arrange the edges.

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