A Remark on Random Vectors and Irreducible Representations

It was observed in \cite{Al2} that the expectation of a squared scalar product of two random independent unit vectors that are uniformly distributed on the unit sphere in $\mathbb{R}^n$ is equal to $1/n$. It is shown below that this is a characteristic property of random unit vectors defined on invariant probability subspaces of irreducible real representations of compact Lie groups.