One thing is certain. We could no longer attribute an invariant length to the pole. This length would no longer be immanent in the pole, since it is impossible to discover an invariant expression of spatial length holding for all observers, hence independent of their existence. We cannot, therefore, escape the conclusion that spatial length by itself can have no more universal existence than the apparent height or visual angle of classical science. Unless we abandon all hope of discovering a something universally objective, we much search for some substitute for that absolute spatial distance in which classical science believed.[72] Minkowski found that such an absolute could be constructed; but it was made up of the relative length and duration under which every observer perceived any two instantaneous events. In exactly the same way as classical science had constructed the absolute spatial magnitude, so now Minkowski constructed the absolute space-time magnitude, i.e., the Einsteinian interval. Objectivity is at last rediscovered, though this objectivity refers neither to space magnitudes nor to durations, but to a combination of both. In other words, the analogue of the absolute objective length of the pole in classical science is now given by the absolute objective space-time interval. The analogue of the relative visual angle, or apparent height of the pole, of classical science is given by its relativistic length as measured by the observer; and this length is no more an illusion than was the visual angle. By omitting to analyse the meaning of his words, the critic has argued as though the visual angle, or apparent height, in classical science were an illusion. But the visual angle is not an illusion. The illusion arises only from faulty inferences, when, having identified visual angle with apparent height, we then proceed to confuse the apparent height with the real height of the pole, thereby crediting it with too short a length. It is this last confusion that is unjustified, for it amounts to confusing visual angle, or apparent height (which, though real for the individual, has no universal significance, hence which is relative) with real length (which is absolute in classical science). In the same way the FitzGerald contraction is not an illusion. It can be measured, and manifests itself physically in every conceivable manner. But again it is a relative for the very concept of spatial magnitude is essentially a relative, since, according to our motion, it will have one value or another. That which is absolute, that which endures unchanged, is the Einsteinian interval; and unless we wish to continue to talk about such shadows as space and time, it is in the space-time world and there alone that we shall obtain universal objectivity.