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Q & A: Gravitational attraction between a body and the rest of the universe

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Most recent answer: 11/03/2015
Q:
Consider the gravitational attraction between a body and the rest of the universe, assuming the universe is uniform over very large distances. In a solid angle, for each light year you go out, its volume and mass increase with the square of the distance, while the gravitation decreases as the inverse square of the distance. Therefore, each light-year increment adds a fixed amount to the gravitational attraction. Therefore, the total gravitational attraction between a body and the rest of the universe increases linearly with the distance included, and as the distance tends toward infinity, so too will the gravitational force on the body. How can this be?
- David Noel (age 80)
Perth, Australia
A:

Hello David

Perhaps you forgot that for each cone you considered, there is a force due to an identical cone on the opposite side  that cancels it.   The net force is zero on average.

There may be some local fluctuations however,   For example our Milky Way and the nearby Andromeda Galaxy will eventually collide in four billion years or so. 

LeeH


(published on 11/03/2015)

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