Excuse my asking, but why did Einstein decide that as C had to be a constant, time had to be a variable? Surely the equations would be just as valid if he had decided distance was the variable in the term distance/time? It seems to me such an interpretation would abolish the twin paradox, and might also show that with distance contraction rather than time dilation, the recessional velocity of distant galaxies might not actually be as rapid as current theory suggests.