[Profpat]

OK I just lifted this from RP's thread below;

"...Descarte was not so far from the truth when he believed he must exclude the existence of an empty space. The notion indeed appears absurd as long as physical reality is seen exclusively in ponderable bodies. It requires the idea of the field as the representative of reality, in combination with the General Principle of Relativity, to show the true kernel of Descarte's idea, 'there exists no space empty of field'." - Einstein, p.p.375 - 6, IDEAS & OPINIONS.

So maybe field