Cremonian space-time(s) as an emergent phenomenon

It is shown that the notion of fundamental elements can be extended to any, i.e. not necessarily homaloidal, web of rational surfaces in a three-dimensional projective space. A Cremonian space-time can then be viewed as an emergent phenomenon when the condition of "homaloidity" of the corresponding web is satisfied. The point is illustrated by a couple of particular types of "almost-homaloidal" webs of quadratic surfaces. In the first case, the quadrics have a line and two distinct points in common and the corresponding pseudo-Cremonian manifold is endowed with just two spatial dimensions. In the second case, the quadrics share six distinct points, no three of them collinear, that lie in quadruples in three different planes, and the corresponding pseudo-Cremonian configuration features three time dimensions. In both the cases, the limiting process of the emergence of generic Cremonian space-times is explicitly demonstrated. (C) 2004 Elsevier Ltd. All rights reserved.