Can you explain how a "geometric coupling" 1. breaks the symmetry of E_ij=C_0i0j (Weyl curvature) and its Hodge dual B__ij, 2. how this...

The confusion that exists between null geodesics and 3+1 decomposition. For ds^2=\dot{\phi}=\dot{\theta}=0, where the dot denotes diff...

To derive the Friedmann equations, the variation is with respect to local time \tau which is different than t, coordinate time. \tau is...