It is based on the fact that electrons and such dont have set positions and only physically exist in theory. Mereological nihilism is the belief that as humans we choose where and when these exist to create our own reality. I mean think about it... Physically we are all just empty space. We are built of atoms which are make up of a tiny dense nucleus surrounded by a MASSIVE amount of empty space in comparison to the size of the nucleus. This empty space contains some electrons which we can only prove exist by chemical means and not physical means. So we are built of empty space, as is everything else in a basically empty universe...