The Veldkamp Space of GQ(2,4)

It is shown that the Veldkamp space of the unique generalized quadrangle GQ(2,4) is isomorphic to PG(5,2). Since the GQ(2,4) features only two kinds of geometric hyperplanes, namely point’s perp-sets and GQ(2,2)s, the 63 points of PG(5,2) split into two families; 27 being represented by perp-sets and 36 by GQ(2,2)s. The 651 lines of PG(5,2) are found to fall into four distinct classes: in particular, 45 of them feature only perp-sets, 216 comprise two perp-sets and one GQ(2,2), 270 consist of one perp-set and two GQ(2,2)s and the remaining 120 ones are composed solely of GQ(2,2)s, according as the intersection of two distinct hyperplanes determining the (Veldkamp) line is, respectively, a line, an ovoid, a perp-set and a grid (i. e., GQ(2,1)) of a copy of GQ(2,2). A direct “by-hand” derivation of the above-listed properties is followed by their heuristic justification based on the properties of an elliptic quadric of PG(5,2) and complemented by a proof employing combinatorial properties of a 2–(28, 12, 11)-design and associated Steiner complexes. Surmised relevance of these findings for quantum (information) theory and the so-called black hole analogy is also outlined. MSC Codes: 51Exx, 81R99 PACS Numbers: 02.10.Ox, 02.40.Dr, 03.65.Ca