"Howard Percy Robertson was a postdoctorate student at Göttingen and Munich from 1925 to 1927. While in Göttingen he completed an important paper on relativistic cosmology in which he derived a relation between the velocity of nebulae and their distances. For the radius of the observable world he calculated R = 2 \times 10^{25} m. Although he had a velocity-distance relation and referred to Slipher's s, he did not conclude that the universe was in a state of expansion."