Divisibility of Spheres with Measurable Pieces

For an $r$-tuple $(γ_1,\ldots,γ_r)$ of special orthogonal $d\times d$ matrices, we say that the Euclidean $(d-1)$-dimensional sphere $S^{d-1}$ is $(γ_1,\ldots,γ_r)$-divisible if there is a subset $A\subseteq S^{d-1}$ such that its translations by the rotations $γ_1,\ldots,γ_r$ partition the sphere. Motivated by some old open questions of Mycielski and Wagon, we investigate the version of this notion where the set $A$ has to be measurable with respect to the spherical measure. Our main result shows that measurable divisibility is impossible for a "generic" (in various meanings) $r$-tuple of rotations. This is in stark contrast to the recent result of Conley, Marks and Unger which implies that, for every "generic" $r$-tuple, divisibility is possible with parts that have the property of Baire.

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