Antonia, I have come to think of "particles" as 3 dimension knot of space. A "vacuum" is simple a volumn of space in which the "foam" has not become knotted. The foam is constantly getting tangled, but a "particle" can be detected only when the tangle cannot spontaneously untangle. Particle are anti-particle of each other when the have the effect of mutually unknotting each other.
Knotting concentrates the engaged foam, thereby stretch the surrounding foam. Knots thus tend to coagulate: gravity.
Whether the foam is smooth or granular may matter, but I cannot yet see exactly how.