Upper bounds on the number of incidences between points and lines, tubes, and other geometric objects, have many applications in combinatorics and analysis. On the other hand, much less is known about lower bounds. We prove a general lower bound for the number of incidences between points and tubes in the plane under a natural spacing condition. In particular, if you take n points in the unit square and draw a line through each point, then there is a non-trivial point-line pair with distance at most n^-2/3+o(1)^. This quickly implies that any n points in the unit square define a triangle of area at most n^-7/6+o(1)^, giving a new upper bound for the Heilbronn's triangle problem.
Joint work with Alex Cohen and Cosmin Pohoata.
