Let $\mathrm{ SO}(3,\mathbb{ R})$ be the 3D-rotation group equipped with the real-manifold topology and the normalized Haar measure $\mu$. Resolving a problem by Breuillard and Green, we show that if $A \subseteq \mathrm{ SO}(3,\mathbb{ R})$ is an open subset with sufficiently small measure, then $$ \mu(A^2) > 3.99 \mu(A).$$ We also show a more general result for the product of two sets, which can be seen as a Brunn-Minkowski-type inequality for sets with small measure in $\mathrm{ SO}(3,\mathbb{ R})$.
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