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Gravity at its maximum range question. 
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#1
Jun2513, 07:11 PM

P: 30

Hey guys. I have an unusual question.
Lets say the universe is 100,000,000,000 Light years across. (100 billion I think) Lets say there are only 2 bodies that have mass in said universe. One body is at one end of this universe and the other body is at the opposite end. Do these 2 bodies pull on each other? Does gravity have a finite range? Or does gravity have infinite range but only gets infinitely weaker with distance? Does space/time eventually flatten out? Thanks 


#2
Jun2513, 07:20 PM

C. Spirit
Sci Advisor
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P: 5,429

The Newtonian gravitational field extends out to infinity in all directions and only goes to zero at infinity. As for spacetime eventually flattening out, if you have a system consisting of isolated bodies (bodies that are always localized to some fixed region of space) then yes spacetime will eventually flatten out (such spacetimes are called asymptotically flat).



#3
Jun2513, 08:50 PM

P: 30

Ok thanks for your well informed reply. Much appreciated.
One more question. I was under the impression that the bending of space and therefor time is what caused gravity to act on objects. So how is it possible for gravity to have infinite range but space/time not to? Doesn't space have to be slightly bent for gravity to be present? And if gravity has infinite range doesn't that mean that the bending of space also has infinite range as well? And if so doesn't that mean that time is also slightly bent/stretched as well? I'm a little confused. Please enlighten me. Thanks 


#4
Jun2513, 09:09 PM

C. Spirit
Sci Advisor
Thanks
P: 5,429

Gravity at its maximum range question.
Consider for example an isolated stationary star. The spacetime curvature produced by the star asymptotically becomes flat meaning it approaches flat spacetime as you approach spatial infinity. So in this sense it is exactly like the Newtonian gravitational field which itself approaches zero as you approach spatial infinity. Sorry if that wasn't clear before; I wasn't implying that the Newtonian gravitational field is nonzero everywhere, I was implying that it asymptotically approached zero as you approach spatial infinity.



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