Gravity's speed of propagation

[ianke]

OK even I don't understand what I said their

I will try again.
1. I am assuming that the view is getting larger when we look out at the edges of our seen universe. Is this true?
or
2. Are we so far away from the perceivable limits of our known universe that the farthest objects are leaving our sight because of the expansion of spacetime?

Just like before my hiatus I start by asking you folks a semingly simple sounding question, and BOOM I need to nail my foot down so I don't go wander.

I missed this site!!!!!

[ArcCentral]

2. Are we so far away from the perceivable limits of our known universe that the farthest objects are leaving our sight because of the expansion of spacetime?

These far objects shouldn't be leaving our sight, they will just become harder to detect, less photons available for viewing and more red shifted. At least thats my understanding of the current accepted model.

[MeteorWayne]

OK even I don't understand what I said their

I will try again.
1. I am assuming that the view is getting larger when we look out at the edges of our seen universe. Is this true?
or
2. Are we so far away from the perceivable limits of our known universe that the farthest objects are leaving our sight because of the expansion of spacetime?

Just like before my hiatus I start by asking you folks a semingly simple sounding question, and BOOM I need to nail my foot down so I don't go wander.

I missed this site!!!!!

Yes both are correct. Our view is getting larger as spacetime expands, and there are parts of the Universe that we can no longer see because they are receding from us faster than the speed of light.

[ramparts]

In response to your last post, spacetime isn't expanding at c.... well, I suppose it's expanding at c somewhere (relative to us), but closer galaxies are moving away from us at a speed slower than c, and faraway galaxies (beyond our sight) are moving away at speeds faster than c.

1. I am assuming that the view is getting larger when we look out at the edges of our seen universe. Is this true?

What view? What do you mean by "getting larger"?

2. Are we so far away from the perceivable limits of our known universe that the farthest objects are leaving our sight because of the expansion of spacetime?

Pretty much

[ianke]

Thankes everyone!
So If something is beyond the visible universe, then any gravitational effect from such an objec is also subject to those same distance limitations caused by cosmic expansiopn. Correct?

Now back to the article that I posted a link to... This means that any portion of the universe causing an effect on those visible galaxies that are moving in that article, because we see the effect of gravity on them then we should be seeing that far as well. This is assuming that gravity propagetes at c. Because if the light hasn't reached us yet or the universe is expanding faster than c that part of the universe causing the effect and it's gravity cannot be observed.
Does this sound correct?

Perhaps another explaination of their observation is needed.

[ramparts]

Gravity propagates at c, but unlike light, once gravity is there, it stays. That's the difference. So whatever is causing this gravitational pull (if that's in fact what this is - this result has a few question marks) was at one point visible to us (pretty much everything was at one point), but no longer is. Still, since gravity doesn't disappear instantaneously, the gravitational field remains.

[ianke]

Hi again rampart,
So if I get this straight, even thought the claim is ceretainly in need of further study at best, It doesn't break any accepted GR or SR principles as it is hypothesized?

This sounds to me like an interesting lead to follow because, as far as I know, it is the first possible evidence of the universe actually being larger than the observed size.

I realize the size of the observed universe now is several times the size we see as we are looking at what was the edge about 13.7 Billion years ago (once you factor for spacetime expansion). As far as I know though, no extra matter has ever been proved to be out past the limitations of the known stuff.

[ramparts]

Hi again rampart,
So if I get this straight, even thought the claim is ceretainly in need of further study at best, It doesn't break any accepted GR or SR principles as it is hypothesized?

Yep - nothing wrong with that No obvious violations of well-established physics.

This sounds to me like an interesting lead to follow because, as far as I know, it is the first possible evidence of the universe actually being larger than the observed size.

I realize the size of the observed universe now is several times the size we see as we are looking at what was the edge about 13.7 Billion years ago (once you factor for spacetime expansion). As far as I know though, no extra matter has ever been proved to be out past the limitations of the known stuff.

Well, it's hard to "prove" the existence of matter outside the visible universe, but we can make a pretty good guess that there's stuff we can't see. Think about it - we see the same amount of matter in every direction on the sky, and we don't see an end to any of it. So if the universe isn't bigger than what we can observe, then it has to be exactly the size of the observable universe, and we have to be directly in the center of it. That's a huge philosophical jump, and extraordinarily unlikely.

[ianke]

Thank you ramparts and the rest for giving me some more food for thought. You guys are always a great pleasure to converse with.

I had forgotten about that improbable center of the galaxy part of the whole thought experiment.

It seems like any time you try to break down the whole into smaller bite sized pieces, the whole elephant gets pissed and steps on your foot. Elephants are odd that way.

[ramparts]

Yes. Exactly. Elephants.

[SpaceTas]

Warning signs of a pissed-off elephant: staring at you flapping ears, stomping, ---> mock charges.


Yes there is/was a big debate about the speed measurement for gravity using radio waves deflected by Jupiter's gravity. This is very close to using gravity to measure the how constancy of the sped of light. There is some very deep thinking needed which hasn't been resolved. Good luck to all those who attempt it.

The "simple" experiment would be to measure the time delay between a gravity wave signal measured at two observatories.

Signs of a pissed (drunk) elephant; the mini parked in front of the pub, and the empty kegs

[xmo1]

The general consensus is the the propagation speed of gravity is the speed of light, and I would agree here, but disagree that gravity is a curvature of space. I prefer to consider it to be wave originating from matter.

I like the instantaneous idea; gravity as a geometric condition, since no particle has been found. The mathematical model is easy, as calculating instantaneous conditions is a done deal. Space-time would be observed if an object were to be removed (or destroyed) within it. There shouldn't be any question at this point in time whether gravity propagates or is an instantaneous (geometric) condition.

General consensus? Please. Haha.

[ramparts]

General consensus? Please. Haha.

I know. It's only based on silly things like theoretical consistency and rigorous experimental evidence. Pshaw.

[R1]

Is it possible that dark energy and hyperinflation are somehow closely related?

[ramparts]

It's possible - indeed, that would be an elegant solution. However, I'm unaware of any model which successfully does this (I'm sure someone has contrived one somewhere, but there's no reason to buy it), and there's certainly no observational indications of it.

[R1]

Gravity propagates at c, but unlike light, once gravity is there, it stays. That's the difference. So whatever is causing this gravitational pull (if that's in fact what this is - this result has a few question marks) was at one point visible to us (pretty much everything was at one point), but no longer is. Still, since gravity doesn't disappear instantaneously, the gravitational field remains.

I'm not sure I understand you completely.

...whatever is causing which gravitaional pull?...

[ramparts]

I was referring to an article posted somewhere back in this thread. I believe it was one talking about an observational result claiming to see distant galaxies moving in response to a gravitational source outside our observable universe.

[R1]

Oh..ok.

[R1]

Which came first, inflation?
Or such thing as 'mass' ?

[origin]

Which came first, inflation?
Or such thing as 'mass' ?

Inflation. Quark formation came at the end of the inflationary period.