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WayneFrancis
2008-Oct-22, 03:24 AM
I'm trying to get my head around some things.

With the universe expanding there is an horizon which we can not see beyond.

The objects at that distance are moving away from us at a relative speed > C

Gravitons theoretically travel at C

Therefor the gravitational effects of objects passing our horizon actually hits 0 instead of just the inverse square law.

This has no real effect on us for 2 reason.


the distance is so large so the effect is so small
the overall effect is zero since the universe is homogeneous thus you are tugged in all directions, at those scales, the same thus those object pass beyond our horizon in all directions in the same amount



That all said, could the loss of these gravitons be tied to the expansion of the fabric of the universe? IE the fabric grows more and more as less and less gravitons actually pass through a given period? This might account for why expansion works at the larger scale more then it does at the smaller scale.

WayneFrancis
2008-Oct-24, 12:21 AM
Hmm, I was kind of hoping someone would have a simple falsification of this weird idea.


Does anyone know what the approximate rate that the visible universe is loosing mass by the current expansion?


This is all making my head hurt. I wonder if gravitons do exist are they effected by red shift. I'm thinking they wouldn't because they would be more of a virtual photon but then again I'm still not comfortable with the virtual particle concept in my head.

Cheap Astronomy
2008-Oct-24, 02:54 AM
Hi,

Not sure I can falsify this, but ...

"The objects at that distance are moving away from us at a relative speed > C"
Well, this cannot be established by any evidence and it's only 1 possible model of the universe.

For example: (quote from this article (http://en.wikipedia.org/wiki/Observable_universe)) It is also possible that the universe is smaller than the observable universe. In this case, what we take to be very distant galaxies may actually be duplicate images of nearby galaxies, formed by light that has circumnavigated the universe.

Nonetheless, under this model I would agree that anything beyond a horizon where light could ever reach us should also have zero gravitational effect.

You are making a case for gravitons, although the context is just as easily expressed as matter getting spread out past the 'horizon' and hence having no further gravitational role in the conditions of your local observable universe.

It's not apparent in classic relativity that removing matter (mass) from the universe results in greater expansion (given the cosmological constant is constant).

My understanding is that the bigger/more spread out the universe is the more dark energy there is - though (simplisticly) that's just because there's more vacuum from which vacuum energy can arise. Not sure there is enough solid theory in this area to build a case for the role of gravitons.

My 2c worth - thanks for interesting topic.

Neverfly
2008-Oct-24, 08:48 AM
A measured effect in a local region is measured by what's measurable in that local region.

The expansion of space is most observable between galaxies and galactic clusters where the expansion is not overwhelmed and bound by gravity.

The effect we can observe from our local position is just that- What's observable from here.
But gravity, gravitons, mass- these are not lost just because they pass beyond our field of view. Losing the ability to see something is not the same as losing the object.
If you're watching a car drive off into the distance and finally that car isn't even a visible speck anymore, the car is not gone or lost.

geonuc
2008-Oct-24, 09:02 AM
Wayne,

To which Astronomy Cast episode does your question relate?

WayneFrancis
2008-Oct-27, 05:08 AM
A measured effect in a local region is measured by what's measurable in that local region.

The expansion of space is most observable between galaxies and galactic clusters where the expansion is not overwhelmed and bound by gravity.

The effect we can observe from our local position is just that- What's observable from here.
But gravity, gravitons, mass- these are not lost just because they pass beyond our field of view. Losing the ability to see something is not the same as losing the object.
If you're watching a car drive off into the distance and finally that car isn't even a visible speck anymore, the car is not gone or lost.


Sorry if I was unclear. I didn't mean to imply that these objects are lost from the universe just lost from our observable universe. At some point, due to the expansion of the universe, every point within the universe will start to get less and less gravitons passing through it.


Thinking about it some more this happens already regardless if there is any thing observable that is nearing C due to the expansion of the universe just because of the inverse square law. The current expansion just gives the opportunity for the gravitational effect to get to actual 0 rather then a infinitely small amount.


I can not reconcile my idea with the overall history of expansion. Also as it has been pointed out the universe seems to be growing in all areas rather uniformly doesn't it? Or does the universe seem to expand more in the voids between clusters more then within? Can we even measure a difference in rate of the expansion of the universe when we compare large pockets of space between super clusters and that of space within our own galaxy?

formulaterp
2008-Oct-27, 02:41 PM
I can not reconcile my idea with the overall history of expansion. Also as it has been pointed out the universe seems to be growing in all areas rather uniformly doesn't it? Or does the universe seem to expand more in the voids between clusters more then within? Can we even measure a difference in rate of the expansion of the universe when we compare large pockets of space between super clusters and that of space within our own galaxy?

I'm not exactly sure sure what you are trying to say. Are you saying the expansion of the universe is caused by the reduction in gravitational attraction between objects within the universe? Or are you referring to the accelleration of the expansion?

Regarding your questions above:

The expansion is not uniform in ALL areas. On the small scale, such as our Solar System or the Galaxy, or the Local Group, there is no measurable expansion. It only shows up on the very largest of scales, between superclusters.