How far does gravity stretch out into the universe?

Pete has a points. For a homogenouos sphere it can be determined that g=GM(r)/r2. M(r) being the mass within of the sphere with radius r. The total mass outside that radius is cancelling each other. Since M(r)=4/3 * rho * pi *r^3 it follows that g=4/3 * G * rho * pi() * r. Or the gravity inside a homogenouos sphere is directly proportional to the distance to the centre.

Indeed Earth hasn't exactly a uniform density:

http://pubs.usgs.gov/gip/interior/

Now with powerfull calculation tools like Excel it is fairly easy to calculate the gravity inside the Earth. Just try it using the numbers in the bottom table:

http://pubs.usgs.gov/gip/interior/table.gif

Now where would gravity be the strongest and how strong? You'd be surprised.

 

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Classically, the field strength would only apprach zero, but never quite get there.

Bringing Quantum Mechanics in, though, the force is actually propagated by the exchange of particles called gravitons. As the distance from the mass increased, the illusion of continuity would break down, I guess, because you would only receive a graviton once in awhile. Not sure how this would work out.

 

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We measure gravity in terms of acceleration between two objects d/t/t. If there is such thing as a planck length and a planck second, and the slowest something can accelerate is 1pl/ps/ps - what happens when the force between two objects is less than necessary to cause minimal acceleration?

 

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