I am trying to get an understanding of the physical mechanics behind osmosis. About half the sources I have found say that it is due to differences in pressure, but some say that it is due to the attraction between water molecules. Is there more evidence of one than the other or is this a widely debated topic among scientists? If it is due to pressure differences then would it still work with a solute that is heavier than water? Why?
Random walks of the solvent have the net effect that more solvent molecules go to the concentrated solution than the other way around (diffusion). This dilutes the concentrated solution, thereby increasing the number of microstates.
The process continues until the pressure difference is so high that the flow due to pressure balances transport due to diffusion.