Reply Tue 24 Mar, 2015 01:19 pm
Does gravity hav a frame of reference
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Type: Question • Score: 2 • Views: 3,543 • Replies: 58
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maxdancona
 
  2  
Reply Tue 24 Mar, 2015 02:18 pm
@martinies,
That question doesn't make sense. A frame of reference is defined by an observer. Gravity is not an observer.
martinies
 
  1  
Reply Wed 25 Mar, 2015 02:24 am
@maxdancona,
Well a photon has a reference frame. And gravity propagates at c photon speed.
maxdancona
 
  1  
Reply Wed 25 Mar, 2015 05:06 am
@martinies,
If you consider a photon to be an observer, I guess.

Which photon are we talking about?
0 Replies
 
dalehileman
 
  1  
Reply Thu 26 Mar, 2015 01:22 pm
@martinies,
Quote:
And gravity propagates at c photon speed
Last I heard, Marty, they weren't quite sure
maxdancona
 
  1  
Reply Thu 26 Mar, 2015 01:45 pm
@dalehileman,
They are sure. Gravity propagates at C.
martinies
 
  1  
Reply Sat 28 Mar, 2015 02:37 am
@maxdancona,
Well then gravity if it propagates must have a ref frame which like light has to be zero. I would think. Does that then mean in one sense it gravity is instantainious it gravity would it seem have nonlocality as its reference frame.
layman
 
  0  
Reply Sat 28 Mar, 2015 02:46 am
@maxdancona,
Quote:
They are sure. Gravity propagates at C.


But who is "they?" This has been debated.

Quote:
Abstract. Standard experimental techniques exist to determine the propagation speed of forces. When we apply these techniques to gravity, they all yield propagation speeds too great to measure, substantially faster than lightspeed. This is because gravity, in contrast to light, has no detectable aberration or propagation delay for its action, even for cases (such as binary pulsars) where sources of gravity accelerate significantly during the light time from source to target.


http://www.metaresearch.org/cosmology/speed_of_gravity.asp

A counter view:

Quote:
To begin with, the speed of gravity has not been measured directly in the laboratory—the gravitational interaction is too weak, and such an experiment is beyond present technological capabilities. The "speed of gravity" must therefore be deduced from astronomical observations, and the answer depends on what model of gravity one uses to describe those observations...

...one can describe the theory in a sort of newtonian language. In that case, one finds that the "force" in GR is not quite central—it does not point directly towards the source of the gravitational field—and that it depends on velocity as well as position. The net result is that the effect of propagation delay is almost exactly cancelled, and general relativity very nearly reproduces the newtonian result.


http://math.ucr.edu/home/baez/physics/Relativity/GR/grav_speed.html

I wonder what "does not point directly" means, exactly?
martinies
 
  1  
Reply Sat 28 Mar, 2015 03:31 am
@layman,
Cant see how gravity can be propagating at more than c. As you can not get beond zero as a reference frame.
0 Replies
 
Anti-Trust
 
  1  
Reply Sat 28 Mar, 2015 04:43 am
@maxdancona,
If gravity propagates at 'c' - why do Newtonian and Gauss equations explain it so accurately, both equations assume instantaneous speeds.
martinies
 
  1  
Reply Sat 28 Mar, 2015 05:29 am
@martinies,
To answer my own question here .which was how do you get beond zero as a refrence frame and the answer is you dont. Gravity is always above c. Its dosnt start out its propagation at below c there for it is beond c from its source.
maxdancona
 
  1  
Reply Sat 28 Mar, 2015 05:59 am
@layman,
The MetaResearch.com site is nonsense. Not everything on the internet pretending to be science is real.

Did you read the UCR article? It makes perfect sense. The author is explaining the problem with the Newtonian model and General Relativity. The does not point to is explaining the problem of the Newtonian model given that propagation of gravity is not instantaneous.


maxdancona
 
  1  
Reply Sat 28 Mar, 2015 06:12 am
@Anti-Trust,
Newton and Gauss equations explain things pretty accurately... they are very good approximations of General Relativity in most cases. But they aren't perfect.

This is why we use General Relativity in the times when Newton breaks down. We use GR in our GPS system. I think this is the most practical instance of this.
FBM
 
  1  
Reply Sat 28 Mar, 2015 06:58 am
@martinies,
What are you talking about "zero as a reference frame"? How is zero a reference frame? Please unpack that for me a bit.
layman
 
  0  
Reply Sat 28 Mar, 2015 09:00 am
@maxdancona,
Quote:
The MetaResearch.com site is nonsense. Not everything on the internet pretending to be science is real.


"Non-sense?" Did you read that article? If so, did you understand it? It took Steve Carlip, the guy who wrote the UCR article, 3 years to understand what Van Flandern was saying.
Quote:

Did you read the UCR article? It makes perfect sense.


Yeah, I read it. Did you? He says they do NOT know the speed of gravity by virtue of experiment. So the speed is unknown. You had said:
Quote:
They are sure. Gravity propagates at C.



He then says it must be deduced and the inferences made will depend on the model one uses.

Quote:

The does not point to is explaining the problem of the Newtonian model given that propagation of gravity is not instantaneous.


Where's the "explanation" of the "problem?"

As I understand it, there are even different "interpretations" of GR. The "geometrical" interpretation, preferred by Carlip, and the "field" interpretation, preferred by Einstein.
0 Replies
 
layman
 
  0  
Reply Sat 28 Mar, 2015 09:15 am
@maxdancona,
Quote:
Newton and Gauss equations explain things pretty accurately... they are very good approximations of General Relativity in most cases. But they aren't perfect.


And, as Van Flandern notes, special relativity, which is the SOURCE as the claim that light is the limiting speed, is "not perfect," either. It was abandoned in GR, where the speed of light is NOT the same in all frames of reference (and where a preferred frame is used).

Quote:
In short, both GR and Newtonian gravity use infinite propagation speeds with aberration equal to zero. In Newton’s laws, that fact is explicitly recognized even though aberration and delay terms do not appear because of an infinity in their denominator. In GR, much effort has been expended in disguising the continued absence of the same delay terms by including retardation effects in ways that are presently unobservable and ignoring aberration. Every physicist and physics student should be at least annoyed at having been tricked by this sleight of hand, and should demand that the neglect of aberration be clearly justified by those who propose to do so.
layman
 
  0  
Reply Sat 28 Mar, 2015 09:27 am
@maxdancona,
Quote:
They are sure. Gravity propagates at C.


Again, I would ask, who are "they." As Carlip's own article clearly states:
Quote:

To begin with, the speed of gravity has not been measured directly in the laboratory... The "speed of gravity" must therefore be deduced from astronomical observations...

...the answer depends on what model of gravity one uses to describe those observations....current observations do not yet provide a direct model-independent measurement of the speed of gravity


maxdancona
 
  1  
Reply Sat 28 Mar, 2015 09:35 am
@layman,
A question for you Layman,

Why do you choose to believe this one site on the internet over the understanding of the scientific community about General Relativity?

maxdancona
 
  1  
Reply Sat 28 Mar, 2015 09:37 am
@layman,
http://www.newscientist.com/article/dn3232-first-speed-of-gravity-measurement-revealed.html#.VRbKn3W9_3A

There is overwhelming amount of evidence that gravity travels a C, and every experiment we do adds more.

We already know that it is not infinite. Not only would this create a fundamental paradox, but it would contradict observed phenomena such as gravitational lensing.

layman
 
  0  
Reply Sat 28 Mar, 2015 09:38 am
@maxdancona,
Quote:
Why do you choose to believe this one site on the internet over the understanding of the scientific community about General Relativity?


1. Why do you assume that I "choose to believe," anything?
2. The article in question was published in a peer reviewed scientific journal, not merely, "on the internet."
0 Replies
 
 

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