On the Width of the Regular $n$-Simplex

Abstract

Consider the regular $n$-simplex $\Delta_n$ - it is formed by the convex-hull of $n+1$ points in Euclidean space, with each pair of points being in distance exactly one from each other. We prove an exact bound on the width of $\Delta_n$ which is $\approx \sqrt{2/n}$. Specifically, $ \mathrm{width}(\Delta_n) = \sqrt{\frac{2}{n + 1}}$ if $n$ is odd, and $ \mathrm{width}(\Delta_n) = \sqrt{\frac{2(n+1)}{n(n+2)}} $ if $n$ is even. While this bound is well known [GK92, Ale77], we provide a self-contained elementary proof that might (or might not) be of interest.