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Jul 8, 2019 at 14:37 comment added Hollis Williams Does anyone have the original reference for the paper where the isoperimetric inequality was proved on the plane using curve shortening flow?
Apr 4, 2017 at 2:30 history edited Alec Payne CC BY-SA 3.0
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Apr 4, 2017 at 1:55 comment added Alec Payne @PaulBryan, thanks for the references.
Apr 4, 2017 at 1:40 comment added Paul Bryan @AlecPayne See Felix Schulze's paper arxiv.org/abs/math/0606675 for partial results in higher dimensions. Taking the convex hull in higher dimensions may worsen the isoperimetric ratio, but taking the mean-convex hull improves it. The problem is as you say, that singularities may form for mean-convex mean curvature flow and he deals with this by level set methods but with a dimensions restriction of $n\leq 7$.
Apr 4, 2017 at 1:30 history edited Alec Payne CC BY-SA 3.0
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Apr 4, 2017 at 1:25 comment added Alec Payne @IgorRivin You're absolutely correct, but it does go to show how natural curve-shortening flow is! I should also say that the convexity of an isoperimetric domain is only trivial on $\mathbb{R}^2$. It's non-trivial in higher dimensions or if you're not in Euclidean space. Perhaps this argument could suggest a higher-dimensional argument that is less trivial. Though, as far as I understand--correct me if I'm wrong here, mean curvature flow has not had much success with regards to isoperimetry.
Apr 4, 2017 at 1:21 comment added Paul Bryan @IgorRivin By distance comparison arguments it is not hard to prove the main CSF result for arbitrary embedded curves. I think that proof is MUCH easier than Gage-Hamilton.
Apr 4, 2017 at 1:20 comment added Paul Bryan Gage observed the monotonicity of the isoperimetric ratio.
Apr 4, 2017 at 1:08 comment added Igor Rivin This is a very nice argument, but, to be devil's advocate, it requires more regularity than many others, and perhaps more significantly, it is a triviality that an isoperimetric curve should be convex, so we can restrict to those, in which case the result is MUCH easier (Gage, not Grayson).
Apr 4, 2017 at 0:54 history answered Alec Payne CC BY-SA 3.0