geometry-topology / Scalar curvature; Urysohn width and macroscopic dimension

Gromov's codimension-two Urysohn width conjecture for positive scalar curvature, with the macroscopic dimension conjecture for universal covers

Principal manuscript, Theorem 1.1: for every n≥4n\ge4 there is CnC_n such that every connected complete boundaryless Riemannian nn-manifold with Scal≥1\mathrm{Scal}\ge1 admits a continuous map to a simplicial complex of dimension at most n−2n-2 whose entire fibers have diameter at most CnC_n; no orientability, spin, compactness or bounded-geometry assumption. Corollaries: Gromov's filling-radius bound FillRad≤Cn/(2σ)\mathrm{FillRad}\le C_n/(2\sigma) for closed manifolds with Scal≥σ2\mathrm{Scal}\ge\sigma^2, dim⁡mc≤n−2\dim_{mc}\le n-2 for universal covers of closed positive-scalar-curvature manifolds in every n≥2n\ge2, and an independent proof that closed aspherical manifolds of dimension ≥4\ge4 carry no positive scalar curvature. The October 5 companions extend the width bound to the spectral condition −4Δ+Scal≥1-4\Delta+\mathrm{Scal}\ge1 (n≥4n\ge4, and n=3n=3 with a graph target and bound 500/λ500/\sqrt\lambda). Not shown: the Lipschitz form dim⁡MC\dim_{MC}, or any explicit constant.

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geometry-topologySep 23, 2026Significance 58/100Registry: unreviewed

Gromov's codimension-two Urysohn width conjecture for positive scalar curvature, with the macroscopic dimension conjecture for universal covers

Prior state unknown→proved

Principal manuscript, Theorem 1.1: for every n≥4n\ge4 there is CnC_n such that every connected complete boundaryless Riemannian nn-manifold with Scal≥1\mathrm{Scal}\ge1 admits a continuous map to a simplicial complex of dimension at most n−2n-2 whose entire fibers have diameter at most CnC_n; no orientability, spin, compactness or bounded-geometry assumption. Corollaries: Gromov's filling-radius bound…

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Principal manuscript, Theorem 1.1: for every n≥4n\ge4 there is CnC_n such that every connected complete boundaryless Riemannian nn-manifold with Scal≥1\mathrm{Scal}\ge1 admits a continuous map to a simplicial complex of dimension at most n−2n-2 whose entire fibers have diameter at most CnC_n; no orientability, spin, compactness or bounded-geometry assumption. Corollaries: Gromov's filling-radius bound FillRad≤Cn/(2σ)\mathrm{FillRad}\le C_n/(2\sigma) for closed manifolds with Scal≥σ2\mathrm{Scal}\ge\sigma^2, dim⁡mc≤n−2\dim_{mc}\le n-2 for universal covers of closed positive-scalar-curvature manifolds in every n≥2n\ge2, and an independent proof that closed aspherical manifolds of dimension ≥4\ge4 carry no positive scalar curvature. The October 5 companions extend the width bound to the spectral condition −4Δ+Scal≥1-4\Delta+\mathrm{Scal}\ge1 (n≥4n\ge4, and n=3n=3 with a graph target and bound 500/λ500/\sqrt\lambda). Not shown: the Lipschitz form dim⁡MC\dim_{MC}, or any explicit constant.

Principal manuscript, Theorem 1.1: for every n≥4n\ge4 there is CnC_n such that every connected complete boundaryless Riemannian nn-manifold with Scal≥1\mathrm{Scal}\ge1 admits a continuous map to a simplicial complex of dimension at most n−2n-2 whose entire fibers have diameter at most CnC_n; no orientability, spin, compactness or bounded-geometry assumption. Corollaries: Gromov's filling-radius bound FillRad≤Cn/(2σ)\mathrm{FillRad}\le C_n/(2\sigma) for closed manifolds with Scal≥σ2\mathrm{Scal}\ge\sigma^2, dim⁡mc≤n−2\dim_{mc}\le n-2 for universal covers of closed positive-scalar-curvature manifolds in every n≥2n\ge2, and an independent proof that closed aspherical manifolds of dimension ≥4\ge4 carry no positive scalar curvature. The October 5 companions extend the width bound to the spectral condition −4Δ+Scal≥1-4\Delta+\mathrm{Scal}\ge1 (n≥4n\ge4, and n=3n=3 with a graph target and bound 500/λ500/\sqrt\lambda). Not shown: the Lipschitz form dim⁡MC\dim_{MC}, or any explicit constant.

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