# Thread: If the universe was infinite in size wouldnt there be infinite gravity?

1. ## If the universe was infinite in size wouldnt there be infinite gravity?

If the universe was infinite in size wouldnt there be infinite gravity?

Gravity propogates at speeds in excess of the speed of light. ( how fast does gravity propogate)?

If gravity can propogate faster than the expansion of the universe.
Using the ant and the rope thing ...
and assuming that the universe is infinitely large
and assuming that a gravitational field extends forever

the gravitational pull at any point in space would be infinite???

Is that right?

2. Originally Posted by tommac
If the universe was infinite in size wouldnt there be infinite gravity?
Only if it contained infinite mass.

Gravity propogates at speeds in excess of the speed of light. ( how fast does gravity propogate)?
Gravity propagates at the speed of light and we think the amount of mass in the universe is finite, therefore the rest of your post doesn't really apply.

3. Originally Posted by speedfreek

Gravity propagates at the speed of light
Can you please show source of this? I have been reading differently.

4. Originally Posted by tommac
If the universe was infinite in size wouldnt there be infinite gravity?
If there was infinite gravity wouldn't we be back at the singularity?

5. Ummmm ... wouldnt an orbit be unstable if gravity propogated at the speed of light?

I am pretty sure that gravity propogates at speeds much faster than the speed of light if not instantaneously.

Originally Posted by speedfreek
Only if it contained infinite mass.

Gravity propagates at the speed of light and we think the amount of mass in the universe is finite, therefore the rest of your post doesn't really apply.

6. Originally Posted by cosmocrazy
If there was infinite gravity wouldn't we be back at the singularity?
Hah ...

This is more of a thought experiment that real life question.

But I think at the end it would prove that either gravity is not instantaneous or that the universe is not infinite.

7. How can a black hole have gravity then?

Originally Posted by speedfreek
Gravity propagates at the speed of light and we think the amount of mass in the universe is finite, therefore the rest of your post doesn't really apply.

8. Originally Posted by tommac
Can you please show source of this? I have been reading differently.
Where did you read about this? i raised this as my first question on this forum and most answers indicated that it propagates at the speed of light along with the other known forces. I am still unclear so would like to find out either way.

9. Originally Posted by speedfreek
... we think the amount of mass in the universe is finite, therefore the rest of your post doesn't really apply.
If the universe is truly infinite in spatial extent there should be infinite mass as long as the mass density is non-zero, right?

10. Originally Posted by Amber Robot
If the universe is truly infinite in spatial extent there should be infinite mass as long as the mass density is non-zero, right?
only if the all infinite spatial extent was filled with mass?

11. Originally Posted by tommac
Can you please show source of this? I have been reading differently.
Does Gravity Travel at the Speed of Light?

First speed of gravity measurement revealed

12. Originally Posted by Amber Robot
If the universe is truly infinite in spatial extent there should be infinite mass as long as the mass density is non-zero, right?
I guess in a way it does prove that the mass density is not infinite if it was then surely space would contract to zero?

13. Originally Posted by cosmocrazy
Where did you read about this? i raised this as my first question on this forum and most answers indicated that it propagates at the speed of light along with the other known forces. I am still unclear so would like to find out either way.

Heh ... nothing would work then ... Who told you that it was at the speed of light ... that is rediculous. That would mean a black hole could not have gravity. That would mean that nothing could be in orbit ... Think about the effects on the earth if there was a delay of gravity from the sun.

14. Originally Posted by speedfreek
OK ... in GR. ... yes speed of light ... but relative to us it is instantaneous.
That is what it is saying right?

15. No, we think gravity travels at the speed of light relative to us, just like light does. Did you read the second link?

16. Originally Posted by tommac
Heh ... nothing would work then ... Who told you that it was at the speed of light ... that is ridiculous. That would mean a black hole could not have gravity. That would mean that nothing could be in orbit ... Think about the effects on the earth if there was a delay of gravity from the sun.
I have! and i have just read the 2 links provided by Speedfreek there is strong mathematical evidence to support either way, all depending on our definition of how we describe gravity, Newtonian or by GR. I wonder whether the underlining constant of C is actually the constant of space-time expansion and that the forces we known are instantaneous but are perceive to propagate at that speed because of this?

17. Originally Posted by speedfreek
Does GR ignore aberation?

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Do me a favor and google "precession of mercury" . We will continue once you have consulted this test of GR.

19. I think even in GR it propogates faster than the speed of light if you take abberration into account.

Originally Posted by cosmocrazy
I have! and i have just read the 2 links provided by Speedfreek there is strong mathematical evidence to support either way, all depending on our definition of how we describe gravity, Newtonian or by GR. I wonder whether the underlining constant of C is actually the constant of space-time expansion and that the forces we known are instantaneous but are perceive to propagate at that speed because of this?

20. Originally Posted by alainprice
Do me a favor and google "precession of mercury" . We will continue once you have consulted this test of GR.
Yes this proves to support very strongly that GR describes the true effect of gravity.

21. And the underlying difference between Newton and GR is that Newton had gravity propagating instantly, whereas in GR it propagates at the speed of light.

22. Originally Posted by tommac
I think even in GR it propogates faster than the speed of light if you take abberration into account.
Explain this argument to me, please.

23. Originally Posted by cosmocrazy
Explain this argument to me, please.
http://www.sciencedirect.com/science...606db9eff773ea

I am not sure if I have it right so I could tell you what I think but it is probably best if you read it yourself.

24. Originally Posted by cosmocrazy
only if the all infinite spatial extent was filled with mass?
So is speedfreek implying that there is an infinitely large universe that is only partially filled with mass? If this were the case, what stops all that mass from gravitationally attracting itself? There would be an "edge" to matter and object on the edge would feel a net gravitational attraction toward the center of the mass distribution.

25. Originally Posted by tommac

I am not sure if I have it right so I could tell you what I think but it is probably best if you read it yourself.
I read the link and i,m not sure it is saying that in GR gravity propagates faster than C

"aberration in general relativity is almost exactly canceled by velocity-dependent interactions, permitting cg=c. This cancellation is dictated by conservation laws and the quadrupole nature of gravitational radiation"

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If I spill a gallon of beer on the floor and wait 10 minutes. Now I come back and walk a small distance away from where I dropped the beer. My feet are wet. Did the spill travel at the speed of beer or was it instantaneous since my socks are wet as soon as they touch the ground.

It's important to understand that once gravity has propagated to a certain place, the effect on a moving mass is instantaneous. The speed of gravity is still the speed of light.

Did you research the precession of mercury, bro?

27. Originally Posted by Amber Robot
So is speedfreek implying that there is an infinitely large universe that is only partially filled with mass? If this were the case, what stops all that mass from gravitationally attracting itself? There would be an "edge" to matter and object on the edge would feel a net gravitational attraction toward the center of the mass distribution.
There could be a net gravitational effect towards the center of the mass distribution of the finite mass spread. But maybe expansion of space could counter act this for now. Prior to the discovery of accelerating spatial "expansion" was this not the theory of the big crunch?

28. Originally Posted by alainprice
If I spill a gallon of beer on the floor and wait 10 minutes. Now I come back and walk a small distance away from where I dropped the beer. My feet are wet. Did the spill travel at the speed of beer or was it instantaneous since my socks are wet as soon as they touch the ground.

It's important to understand that once gravity has propagated to a certain place, the effect on a moving mass is instantaneous. The speed of gravity is still the speed of light.

Did you research the precession of mercury, bro?
Well put! this was the way i was thinking but could not put it into clear understanding to post.

29. Originally Posted by Amber Robot
So is speedfreek implying that there is an infinitely large universe that is only partially filled with mass? If this were the case, what stops all that mass from gravitationally attracting itself? There would be an "edge" to matter and object on the edge would feel a net gravitational attraction toward the center of the mass distribution.
The original question was

If the universe was infinite in size wouldnt there be infinite gravity?
Define infinite gravity. In my definition, you need infinite mass-density to produce infinite gravity. What is your definition of infinite gravity? Am I barking up the wrong tree here?

Second point, who said the universe is infinite? I am certainly not implying that the universe is infinite, that's for sure. I tend to go with "finite but unbounded".
Last edited by speedfreek; 2008-Apr-29 at 10:00 PM. Reason: clarification

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