Suppose that everything in the Universe - the radius of the sun, the astronomical units, radius of atoms, and everything else were to expand proportionately during the same period of time. This would mean also that the ratio of the time period of the various planets around the sun, and all local clocks, would also adjust their time accordingly. Can an observer in such a universe make out that such an expansion were really happening? Wouldn't all his 'scales' and 'clocks' also be correspondingly changed to match this proportion? I suppose we can assume without loss of generality that such an expansion is very very slow.