  This is a survey on the geometry of warped products, without, or essentially
with only soft, calculation. Somewhere in the paper, the goal was to give a
synthetic account since existing approaches are rather analytic. Somewhere
else, we have interpreted statements, especially by means of a physical
terminology. This is essentially heuristic, but we think it might be helpful in
both directions, that is, in going from a synthetic geometrical language to a
relativistic one, and vice-versa.
