Animation 4a corresponds to Fig. 2a
for the case in which the event redshifts are fixed to zA
=1 and zB
=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=τAB
when the lightcones first intersect; these are also shown as black circles projected onto the τ=0 plane. The movie represents a point (zA
)=(1,3) in the zA
plane which lies in the dark gray region of
where all event pairs have a shared causal past for any angular separation.