A Sharp Lower Bound for the Entropy of Closed Hypersurfaces up to Dimension Six

In [5], Colding-Ilmanen-Minicozzi-White showed that within the class of closed smooth self-shrinkers in ${\mathbb{R}}^{n+1}$, the entropy is uniquely minimized at the round sphere. They conjectured that, for $2\le n\le 6$, the round sphere minimizes the entropy among all closed smooth hypersurfaces. Using an appropriate weak mean curvature flow, we prove their conjecture. For these dimensions, our approach also gives a new proof of the main result of [5] and extends its conclusions to compact singular self-shrinkers.