## Geometry & Topology

### Blocking light in compact Riemannian manifolds

#### Abstract

We study compact Riemannian manifolds $(M,g)$ for which the light from any given point $x∈M$ can be shaded away from any other point $y∈M$ by finitely many point shades in $M$. Compact flat Riemannian manifolds are known to have this finite blocking property. We conjecture that amongst compact Riemannian manifolds this finite blocking property characterizes the flat metrics. Using entropy considerations, we verify this conjecture amongst metrics with nonpositive sectional curvatures. Using the same approach, K Burns and E Gutkin have independently obtained this result. Additionally, we show that compact quotients of Euclidean buildings have the finite blocking property.

On the positive curvature side, we conjecture that compact Riemannian manifolds with the same blocking properties as compact rank one symmetric spaces are necessarily isometric to a compact rank one symmetric space. We include some results providing evidence for this conjecture.

#### Article information

Source
Geom. Topol., Volume 11, Number 2 (2007), 867-887.

Dates
Accepted: 21 March 2007
First available in Project Euclid: 20 December 2017

https://projecteuclid.org/euclid.gt/1513799863

Digital Object Identifier
doi:10.2140/gt.2007.11.867

Mathematical Reviews number (MathSciNet)
MR2326937

Zentralblatt MATH identifier
1135.53028

#### Citation

Lafont, Jean-François; Schmidt, Benjamin. Blocking light in compact Riemannian manifolds. Geom. Topol. 11 (2007), no. 2, 867--887. doi:10.2140/gt.2007.11.867. https://projecteuclid.org/euclid.gt/1513799863

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