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• 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.

There we go.

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B2 rubik rubik cube cube solve craze solved

# Speed Solve of a Rubik's Cube in Slow Motion - Numberphile

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林宜悉 posted on 2020/04/04
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