What is space?

Space the final frontier?  No, it's just a region where there is nothing of the substance of our volume.  There are five volumes of things that make up the universe, it could be full of photons, or much bigger protons, and we still call it "space."  The space above a glass half full is completed by air.  The space outside the glass is full of air too.  The glass may be twice the size it needs to be holding water, but the rest of it is still full of something.  Perhaps it's only the black body radiation of the water, but something.  And for there to be the glass with water, it must exist in a greater volume (of the room it's in) containing its water molecules of their volume. 
  Just saying "half a glass of water" implies three volumes of scale.  The room the glass is in, the glass itself and the water molecules within.
We exist in an infinite scale of sizes, and we can only "see" outside of our own volume of things by magnification of the very small and the very far away.
  It is through volume that we have discovered the concept of dimensions; length, height, width, and depth.  There are only three dimensions to a volume, but there are five volumes in the universe.  Perhaps many more, but there has to be at least five, to give us the 4th dimension; this universe.
Because, 2 points make a line; 3 lines make an area, 4 areas make a volume, so 5 volumes must make the 4th dimension. Something that has volume is a size, therefor there must be five different sizes of things in the 4th dimension.  And we can see them but we cannot yet go there.