When searching for KK stuff in forums, I see that when g(5) is applied to L(5 R), this effectively splits the equation of motion into a (4) gravitational part, (4) electromagnetic part and the Plank mass associated with a miniscule x^5. I have no problem accepting that GR can do this and calling it the ‘KK miracle’. But when g(5) is applied to the simple L(5 u) or L(5 d) we simply get the classical eqn of motion, Klein Gordon and electron mass m. This is associated with a large x^5 approx= proper time tau (i.e. NOT 1/the Plank mass). Is there a name for this second miracle? Please help me to find out more about it. Thanks. ‘Appendices’ This idea is not new, back in 1978 Franchi and in 1984 Kubo developed 5d QFT using s = x^5. id_s <=> mass of electron etc. Definitions i,j run 0-3 a,b run 0-3,5 u = d_tau x L(5 R) involves curvature & GR L(5 u) = u^a g(5)_ab u^b m /2 L(5 d) = d_a f* g(5)^ab d_b f /2 Where u^a g(5)_ab u^b = u^i g(4)_ij u^j + u^a g(5)_a5 g(5)_5b u^b and g(5) has -++++ signature, g(5)_55 = 1 and g(5)_j5 = g(5)_5j = A_j q/m (as it turns out by the 2nd KK miracle) Useful bits from calculations: A = A(4) ensures g(5)^ab g(5)_bc = KronDelta^a_c So u^a A_a q/m = 1 => u^5 = (1 - A_a u^a q/m) approx= 1 So x^5 approx= tau >>>>>>>>>>>> the x^5 associated with Plank mass.