There does arise, however, a strange difficulty. The interpretation of the galactic line-shift discovered by Hubble as an expansion (which can hardly be doubted from a theoretical point of view), leads to an origin of this expansion which lies “only” about 109 years ago, while physical astronomy makes it appear likely that the development of individual stars and systems of stars takes considerably longer. It is in no way known how this incongruity is to be overcome. I further want to remark that the theory of expanding space, together with the empirical data of astronomy, permit no decision to be reached about the finite or infinite character of (three-dimensional) space, while the original “static” hypothesis of space yielded the closure (finiteness) of space. _K_ = co-ordinate system _x, y_ = two-dimensional co-ordinates _x, y, z_ = three-dimensional co-ordinates _x, y, z, t_ = four-dimensional co-ordinates _t_ = time _I_ = distance _v_ = velocity _F_ = force _G_ = gravitational field