During inflation,   mass and radiation ‘sprung’ up via
                              uncertainty principle
Heisenberg :       DE Dt = h / 2p
                           DE = Dm c2
                                                                    => Dm Dt  = h / 2p
 for a short time, can non-conserve mass
 
 => virtual pairs (p+ p-    e-e+)
 
 p+ + p-         g  +  g
 g  +  g        p+ + p-