3
$\begingroup$

Today, I got my hands on a Rubik's cube with text on it. It looks like this:

Rubik's cubes

Now, I would love to know whether solving the right cube will also always correctly align the text on the cube or whether it's possible to solve the cube in a way that the colors match correctly but the text is misaligned.

  • 0
    A maths professor once told us that 'there are no silly questions'. I asked him your exact question. He answered "that's not a silly question", paused, then said "no, that _is_ a silly question"2012-08-20

1 Answers 1

5

whether it's possible to solve the cube in a way that the colors match correctly but the text is misaligned

Yes. But the total amount of misalignment (if I remember correctly; it's been a while since I played with a Rubik's cube) must be a multiple of $\pi$ radians. So if only one face has the center piece misaligned, it must be upside down. On the other hand it is possible to have two center pieces simultaneously off by quarter-turns. (This is similar to the fact that without taking the cube apart, you cannot change the orientation of an edge piece (as opposed to center piece or corner piece) while fixing everything else.)

(I don't actually have a group-theoretic proof for the fact though; this is just from experience.)

Edit: Henning Makholm provides a proof in the comments

Here's the missing group-theoretic argument: Place four marker dots symmetrically on each center, and one marker at the tip of each corner cubie, for a total of 32 markers. A quarter turn permutes the 32 markers in two 4-cycles, which is even. Therefore every possible configuration of the dots is an even permutation away from the solved state. But misaligning one center by 90° while keeping everything else solved would be an odd permutation and is therefore impossible.

  • 0
    @WillieWong: Also, if you do the u-perm 3 times, you can get a quarter rotation of the right side center piece. U-perm: R U' R U R U R U' R U' R2.2014-05-09