How does a positive charge's electric field lines loop back to negative charge?

Question

In this video about electric dipoles, at 6:14, the speaker mentions that all of the red lines will loop back into negative (blue) charge, but I don't see how this is possible. Specifically, he gives an example with a +5 and a -5 charge. At some distance from the positive charge, there's a vector pointing towards the upper-left side. At that point, it's true that there's another vector pointing backwards in the direction of the blue charge, but I don't see how would it loop back into the blue in the end.

(Unfortunately, I couldn't find a simulation that lets me zoom out to see the picture from very far away. I checked the author's github page but I can't zoom out there either.)

Answer 1

Since you have a dipole (which has a plane of symmetry), you could draw a symmetrical gaussian surface and start a start a field line at a point on the surface. By symmetry, one could expect an opposite field-line at the point reflected by the symmetry plane. Use a graphical or numerical method to construct the rest of each field-line (intuitively by following the local electric field at each point). By symmetry, they should meet.

(It might help to consider what the equipotential surfaces you meet look like as you extend the field-lines. The plane of symmetry is an equipotential.)