you don't have to go far for gravity to become weak. it is proportional to r^-2
[math]F_g=G\frac{m_1m_2}{r^2}[/math]
so' date=' if we increase our distance infinitely, [math']\lim_{r{\to}\infty}{F_g}=0[/math].
now, we don't even have to go that far for it to be weak. just pick some random values for m1 and m2. then let r be 10, then 100, then 1000, then 10000, etc. now, if we have the sensitivity of a measuring device, it's mass, and the mass of the object whos gravity we are trying to measure, we can approxamate how far we would have to be from it to not detect it's gravity.