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View Full Version : Gravity and "space expanding" between objects

Deid
2008-Sep-26, 02:35 PM
I don’t get this, gravity waves supposedly moves at the speed of light, then what happens if some big object almost in the near edge of the visible universe affect us gravitationally, and the space between us start to expand faster than the speed of light, would we lost the “gravity waves” from them since the speed of expansion between us is faster than light and the gravitationally waves aren’t keeping up with that rate of expansion?

Grey
2008-Sep-26, 04:25 PM
It is possible for an object in an expanding universe to be beyond the "horizon", so that its light will never reach us. If that's the case, we will never see the light form it, and since gravitational influence also travels at the speed of light, we will also never feel it's gravitational influence.

mugaliens
2008-Sep-26, 05:01 PM
I think what he means is "what happens when such an object slips over that boundary?"

I've wondered that, too, and if true, then if gravity could be rendered in song, the background gravitational noise would be punctuated by something sounding like popcorn.

Deid
2008-Sep-26, 06:22 PM
I think what he means is "what happens when such an object slips over that boundary?"

This is what i mean, maybe it wasn't that clear.

astromark
2008-Sep-26, 08:55 PM
What happens..?

Nothing.

As abject distance increases so must its gravity force diminish and light image fade... Far enough and... nothing. Gone, gone, gone.

Grey
2008-Sep-29, 03:45 PM
Astromark is correct. If an object was once on the near side of that boundary, and then at a later time is on the far side of that boudary, then we are able to see it and be affected by it gravitationally beforehand, but not afterward. You might be wondering if it just winks out, or what happens, but that's not quite the way it would work. What would happen is that it would steadily redshift away to nothing, and from our perspective, that process would be steadily more time-dilated.

John Mendenhall
2008-Sep-29, 04:55 PM
What happens..?

Nothing.

As abject distance increases so must its gravity force diminish and light image fade... Far enough and... nothing. Gone, gone, gone.

We can observe intermediate objects that are still influenced by the invisible objects.

See:

http://www.universetoday.com/2008/09/23/scientists-detect-dark-flow-matter-from-beyond-the-visible-universe/

That's it, I'm over the edge . . .