I see that this had been asked years ago, but I want to know if something new arise from this question. Does quantum foam (virtual particles), with the sum of all these virtual particles popping into existence, may exert some gravity background? If the sum of all this virtual particles popping into existence, can exert some gravity background, are there any way to estimate this gravity exerted in a volume? If that's the case: How much of the matter missing (dark matter) can be explained by this quantum foam gravity? Do we live in a universe, where this quantum foam is homogeneous distributed? Or not all the space are of the same density, for quantum foam? I guess that at least when the space is bended by gravity, the quantum foam change in density.