On Fri, Feb 03, 2017 at 02:33:05PM -0800, Greg Nokes wrote:
> It makes sense to me —
>
> So if you assume that stuff is distributed fairly evenly, then
> gravitation would be equal in all directions.
>
> Now, if you put a big hole in the stuff to one side, there would be
> less pull towards that area.

> Thus it “pushes” you away ;-)

In the current standard model for large-scale gravitational behaviour
(Lambda-CDM), there's a cosmological constant term which corresponds
to matterless vacuum having a more directly repulsive gravitational
effect.

This is so weak that it only has any measureable effect at
ridiculously large distance scales, and certainly would have nothing
to do with "sky pushing us down" as an explanation for Earth's
gravity.  Interstellar space within a galaxy has more than enough
matter to counteract such repulsion (even without considering stars),
and the interplanetary gas density near Earth is very much greater
still.

However, almost all of the universe has virtually no matter in it, and
at the largest scales this term is very significant.


- Tim

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