# Graduate Student / Postdoc Seminar

#### Space Crossing Numbers

**Speaker:**
Alfredo Hubard, Courant

**Location:**
Warren Weaver Hall 1302

**Date:**
Friday, March 4, 2011, 1 p.m.

**Synopsis:**

If a graph with many edges is drawn in the plane then some of the edges have to intersect. On the other hand, (by dimensional considerations) any graph can be drawn in three dimensional space without two edges crossing. Back to dimension two, mathematicians have wondered about the best way to draw a graph in the plane, there are many answers to this question depending on the context, one of particular interest is the crossing number. What is the smallest number of crossings of any drawing of a given graph? There is a rich theory of crossing numbers with interesting relations to engineering of circuits and to geometric measure theory. Our motivating question was: what is the analogue of the crossing number for embeddings in three dimensions? Our answer (almost) recovers the most famous result about (two dimensional) crossing numbers.