(a) Animation 4a corresponds to Fig. 2a of Friedman+2013 for the case in which the event redshifts are fixed to z_A=1 and z_B=3, while the angular separation α as seen from Earth is allowed to vary from 0 to 360 degrees. The green circles show the projection of the past lightcones on the hypersurface τ=τ_AB when the lightcones first intersect; these are also shown as black circles projected onto the τ=0 plane. The movie represents a point (z_A, z_B)=(1,3) in the z_A - z_B plane which lies in the dark gray region of Fig 3b of Friedman+2013 where all event pairs have a shared causal past for any angular separation.

(b) Animation 4b for the same case as in Animation 4a, as viewed in the τ=0 plane at the big bang.