the statistical mechanical definition of entropy relies on the number of possible arrangements of particles in a system. In a closed system entropy approaches an equilibrium which has been sensationally described as the 'heat death of the universe'. But since we know our universe is expanding, the number of possible arrangements is also increasing so entropy may never reach equilibrium. If the universe is expanding faster than its components redistribute, then entropy could be decreasing. With this in mind, any theory involving entropy as a component of gravity would suggest a changing gravity over time