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Comment by oh_sigh | Hacker News Reader

I know gravity has a speed limit, but does it have a upper distance limit or lower magnitude limit?

As in, are we really feeling gravitational effects of mass that is 14 light years away, even if they are insignificantly tiny and we probably can't measure it, or is there a point where a force is so miniscule that the universe truncates the force to 0?

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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.

Ah, one little slip of the pen and everything changes. It's more like 3.6 * 10^16 meters.

Didn't check the math but I enjoyed your "zero force" definition!

As far as we can tell no. Of course, what we know with certainty is bounded by a nonzero experimental resolution.

Something is happening to hold galaxies and galaxy clusters together.

No, but neither does the EM force, it all just asymptotically approaches zero. Don’t let that fool you though, in that it really approaches zero to a high degree.

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