In this problem, you will be guided through an alternative (more rigorous) derivation of the Robertson-Walker metric.
1. Explain why the most general metric for a homogeneous and isotropic universe is ds^2 = -dt^2 + a^2(t)Y_ij(x)dx'^dxi, where we have set c = 1. In particular, explain why g_oo = -1 and g_oi = 0.