If one arbitrarily defines "zero force" as less than the force sufficient to accelerate one proton at one planck length per age-of-universe^2, I come up with a

If one arbitrarily defines "zero force" as less than the force sufficient to accelerate one proton at one planck length per age-of-universe^2, I come up with a distance of 10^12 meters between two protons (+/- an order of magnitude). However, (and if I didn't screw up the math) since gravity scales linearly with mass, and the size of the visible universe is about 10^27 meters, then anything with mass greater than 10^15 protons -- or about the mass of a human cell -- has a "non zero" gravitational effect on you.