Any orthonormal basis in high dimension is uniformly distributed over the sphere

Let Xd be a real or complex Hilbert space of finite but large dimension d, let S(Xd ) denote the unit sphere of Xd, and let u denote the normalized uniform measure on S(Xd ). For a finite subset B of S(Xd ), we may test whether it is approximately uniformly distributed over the sphere by choosing a partition A1, . . . , Am of S(Xd ) and checking whether the fraction of points in B that lie in Ak is close to u(Ak) for each k = 1, . . . , m. We show that if B is any orthonormal basis of Xd and m is not too large, then, if we randomize the test by applying a random rotation to the sets A1, . . . , Am, B will pass the random test with probability close to 1. This statement is related to, but not entailed by, the law of large numbers. An application of this fact in quantum statistical mechanics is briefly described.