Split from Gravitational waves Discovered

[Robittybob1]

https://en.m.wikipedia.org/wiki/Speed_of_gravity

 

Here is one test.

 

http://www.nrao.edu/pr/2003/gravity/

 

http://www.nbcnews.com/id/3077353/ns/technology_and_science-science/t/first-test-gravitys-speed-upholds-einstein/

The article in the 3rd link ends in this quote

 

 

Astronomer Thomas Van Flandern, who has built up a following for his views outside the scientific mainstream, said in a September commentary that the experiment may have measured the speed of gravitational waves, but “can provide no information about the propagation speed of gravitational force, which is bounded by many experiments to be much faster than light.”

I don't know if you have ever tried to prove it yourself but I am skeptical of anyone saying gravity acts at the speed of light. I haven't got all the figures at my fingertips but with that binary pulsar 1913+16 it seemed impossible to understand how they could orbit each other if their gravitational field was established at the speed of light. I spent a lot of time on this and I am none the wiser but it defies the imagination if you say it is propagated at the speed of light.

I had presented my workings on another forum but I never got a satisfactory answer from anyone except to be told it needed to be worked out by relativity, something I wasn't able to do. But the bodies are not going anywhere near the speed of light, so why weren't Newtonian physics good enough (even for a good estimation).

I would love to be shown it properly.

With the Sun in the center of the SS it is easier to see how there maybe the correctly curved spacetime for the Earth to move onto but when there were two centers as in the binary what existed moments before was not good enough for now, so how did that signal come across the vast distance of the space between them in time to keep them gravitationally bound? I never understood it.

[Mordred]

I would recommend a separate thread for that discussion. Lets not detail this one but if you think about it measuring the gravity waves from those two BH mergers shows that gravity isn't infinite in speed.

 

They can use these results as another test of the speed limit of gravity

[Robittybob1]

I would recommend a separate thread for that discussion. Lets not detail this one but if you think about it measuring the gravity waves from those two BH mergers shows that gravity isn't infinite in speed.

 

They can use these results as another test of the speed limit of gravity

 

The fact that the design of the LIGO detector requires measuring a difference in the gravitational field ... and succeeded in doing so tells us gravity doesn't infinitely propagate. PS another source of data on speed of gravity.

Well my wishes may come true yet and someone will explain it fully on another thread. So you are saying that the strength of the gravity wave is the measurement of the strength of gravitational field. (I tend not to get too involved with gravity lately so I'm behind the times as to what the gravitational waves are actually measuring.)

I understand that the measurements were measured at different times on the Earth and that confirmed gravitational waves traveled at the speed of light.

[Mordred]

Post a thread in relativity I'll reply there with a gravity wave lesson from Introductory to Cosmology by Matt Roose he has an excellent section on gravity waves and it's correlation to the propogation of gravity.

[StringJunky]

Well my wishes may come true yet and someone will explain it fully on another thread. So you are saying that the strength of the gravity wave is the measurement of the strength of gravitational field. (I tend not to get too involved with gravity lately so I'm behind the times as to what the gravitational waves are actually measuring.)

I understand that the measurements were measured at different times on the Earth and that confirmed gravitational waves traveled at the speed of light.

Spacetime, I might be wrong, is a mapping of energy-density distribution around masses and between masses. Ripples in spacetime from a BH merger describes a particular energy-density pattern and propagation

[Mordred]

Spacetime, I might be wrong, is a mapping of energy-density distribution around masses and between masses. Ripples in spacetime from a BH merger describes a particular energy-density pattern and propagation

Nothing wrong with this description.

[StringJunky]

Nothing wrong with this description.

I learnt it from you about energy-density distribution.. It took me a long time to get my head around the fact that it's not material.

Edited February 13, 2016 by StringJunky

[Robittybob1]

I learnt it from you about energy-density distribution.. It took me a long time to get my head around the fact that it's not material.

Can you measure something that is not material? Well please tell me what you mean by not material?

[StringJunky]

In the same sense that a magnetic field is not material, for example, but is measurable, and the same for energy.

 

I should make a thread about it if it still bugs you.

Edited February 13, 2016 by StringJunky

[Robittybob1]

In the same sense that a magnetic field is not material, for example, but is measurable, and the same for energy.

 

I should make a thread about it if it still bugs you.

I have started another thread exploring what a gravitational wave is http://www.scienceforums.net/topic/93485-what-is-a-gravitational-wave/so you could explain it there is you like.

 

Those 2 BHs must have been orbiting at an extreme frequency. Did that frequency increase as they got closer or not?

Edited February 13, 2016 by Robittybob1

[Robittybob1]

All I want is proof that gravity acts at the speed of light. Until that is done without any doubt why is it wrong to question this?

Edited February 13, 2016 by Robittybob1

[ajb]

All I want is proof that gravity acts at the speed of light. Until that is done without any doubt why is it wrong to question this?

Mathematically you can solve this question. You can look at how small changes in a source of gravity propagate from that source changing the space-time. These small changes are gravitational waves and propagate at the speed of light.

 

As we know that general relativity is a good theory for a wide range of gravitational phenomena, ie. it has been tested well, we can be confident that the speed of a physically observed gravitational wave is c. However, I am not sure that there is as any experiment that really shows that the speed of gravity is c, but for sure there is no reason to think this speed is much greater or much slower than c.

[Robittybob1]

Mathematically you can solve this question. You can look at how small changes in a source of gravity propagate from that source changing the space-time. These small changes are gravitational waves and propagate at the speed of light.

 

As we know that general relativity is a good theory for a wide range of gravitational phenomena, ie. it has been tested well, we can be confident that the speed of a physically observed gravitational wave is c. However, I am not sure that there is as any experiment that really shows that the speed of gravity is c, but for sure there is no reason to think this speed is much greater or much slower than c.

I have never questioned the speed of gravitational waves, for they are energy of some sort, but what about gravity?

 

Mordred said it travels at the speed of light and I asked for proof of that. It was his link that introduced the idea that others had not accepted this as a fact.

Now I followed up on the person mentioned "Astronomer Thomas Van Flandern" but I wasn't convinced by him either, but it was from my own attempt to understand the orbits of the binary that made me wonder if it is possible to have gravity bending spacetime at the speed of light. OK it could have been just my calculations were in error but it looked too slow.

 

It has been something bugging me for some years now.

[ajb]

I have never questioned the speed of gravitational waves, for they are energy of some sort, but what about gravity?

How do you want to define the speed of gravity?

 

The obvious way is to look at what happens to small perturbations of the source and see how that propagates. This is exactly how we define the speed of electromagnetism, you look at the speed of photons.

[Robittybob1]

How do you want to define the speed of gravity?

 

The obvious way is to look at what happens to small perturbations of the source and see how that propagates. This is exactly how we define the speed of electromagnetism, you look at the speed of photons.

It was the idea like discussed in the short video #1, that orbiting objects needed the full strength of the gravitational field to maintain an orbit.

The Sun is moving through space around the galaxy, it is always moving, so does the Sun's gravitation need updating continually?Can this be done in time to keep the Earth in orbit?

I know the Earth orbits the Sun, I don't doubt that, but just question how the G field seems to update quicker than the time it takes light to come from the Sun.

 

In the video he says they used the information from the binary pulsar to show the speed of gravity was "c". I don't recall that myself. I know it showed that the rate of orbital decay matched the theory on the production of gravitational waves, but I can't remember that being used as the proof of the speed of gravity.

Edited February 13, 2016 by Robittybob1

[ajb]

I am not sure that it does update faster.

 

Old calculations suggeted that the speed of gravity is much much greater than c, and so explains why Newton's theory is good. However the assumptions used do not agree with GR.

 

You can check S. Carlip, Aberration and the Speed of Gravity, Phys.Lett.A267:81-87,2000 (There is an arXiv version). The claim is that aberration in general relativity is almost exactly canceled by velocity-dependent interactions. This renders the speed of gravity to be (just about) c.

[Robittybob1]

I am not sure that it does update faster.

 

Old calculations suggeted that the speed of gravity is much much greater than c, and so explains why Newton's theory is good. However the assumptions used do not agree with GR.

 

You can check S. Carlip, Aberration and the Speed of Gravity, Phys.Lett.A267:81-87,2000 (There is an arXiv version). The claim is that aberration in general relativity is almost exactly canceled by velocity-dependent interactions. This renders the speed of gravity to be (just about) c.

That is what was claimed and I had tried to comprehend that years ago too and didn't seem gel with it. Maybe this time I will get it.

Does it seem right to you? So would you use the same claims in your own arguments?

What is it saying in very simple terms do you know? How would you explain it to a skeptic like myself?

Maybe if I understood it the behaviour of the binary pulsar makes sense as well.

[Mordred]

Here is the arxiv.

 

http://www.google.ca/url?q=http://arxiv.org/pdf/gr-qc/9909087&sa=U&rct=j&ved=0ahUKEwirvPKOxPXKAhXLJB4KHX_5DuMQFggZMAA&usg=AFQjCNEYh5zX1ThUUOvBJ-Jm3W2fVX21qQ

Course that being done I'll look it over possibly help you decipher it into layman terms.

[ajb]

Does it seem right to you? So would you use the same claims in your own arguments?

There many papers now published in good journals and just about all of them say that the speed of gravity is c or they say that current observations do not really test this.

 

All of this is really outside my area of expertise, so I am not very familiar with all the arguments.

 

 

What is it saying in very simple terms do you know? How would you explain it to a skeptic like myself?

I will have to think about it.

 

 

Maybe if I understood it the behaviour of the binary pulsar makes sense as well.

Observations of such systems suggested that gravitational waves carried away some of the energy. I am not sure if these observations tell us that the speed of gravitational radiation is c, but as the theory matches the observations well I suppose that it does.

[Mordred]

Well binary pulsars are mentioned in the paper. Where it clearly states that orbital decay rates agree with [latex]c_g=c[/latex] with an error bar of 1%. Though the math isn't extreme it still will take time to study in better detail.

Edited February 13, 2016 by Mordred

[Robittybob1]

There many papers now published in good journals and just about all of them say that the speed of gravity is c or they say that current observations do not really test this.

 

All of this is really outside my area of expertise, so I am not very familiar with all the arguments.

 

 

 

I will have to think about it.

 

 

 

Observations of such systems suggested that gravitational waves carried away some of the energy. I am not sure if these observations tell us that the speed of gravitational radiation is c, but as the theory matches the observations well I suppose that it does.

I can only see one fault in what you are saying so far and that is if gravitational waves have energy does the bending of spacetime require energy too?

I have heard that if it did the whole Universe would have run down to nothing by now.

So gravity and gravitational waves are different things, so the speed of one does not imply the speed of the other.

 

I wanted proof that is all. They might be the same speed and maybe aberration of gravity explains it but I wasn't able to comprehend it.

Here is the arxiv.

 

http://www.google.ca/url?q=http://arxiv.org/pdf/gr-qc/9909087&sa=U&rct=j&ved=0ahUKEwirvPKOxPXKAhXLJB4KHX_5DuMQFggZMAA&usg=AFQjCNEYh5zX1ThUUOvBJ-Jm3W2fVX21qQ

Course that being done I'll look it over possibly help you decipher it into layman terms.

Thanks I'd appreciate that.

[Mordred]

Consider this argument. We have now measured a gravity wave. Ask yourself the following question.

 

If gravity was instantaneous, and you have a uniform distribution of mass.

 

Could you have a gravity wave?

 

Logically the answer would be no you couldn't. If gravity was instantaneous all mass would be affected at the same exact instant.

 

I'll let you think about that statement.

Edited February 13, 2016 by Mordred

[ajb]

I can only see one fault in what you are saying so far and that is if gravitational waves have energy does the bending of spacetime require energy too?

In the sense that energy-momentum is the source of gravity.

 

I will also point out that we do not consider gravitational waves as being 'matter' in that they do not contribute to the matter content of the field equations although they carry energy.

 

 

 

So gravity and gravitational waves are different things, so the speed of one does not imply the speed of the other.

It depends on how you define things. For sure small changes propagate as c, the speed of gravity in a more general sense must be c, but this seems not to be settled completely.

 

All attempts to measure the speed of gravity either fail, or give it as c to 5% or less.

[Robittybob1]

Well binary pulsars are mentioned in the paper. Where it clearly states that orbital decay rates agree with [latex]c_g=c[/latex] with an error bar of 1%. Though the math isn't extreme it still will take time to study in better detail.

If you get a way to explain it in words (rather simply) or by analogy please let me know. I was NOT attempting to hijack the other thread but genuinely queried how you knew gravity propagated at the speed of light.

Consider this argument. We have now measured a gravity wave. Ask yourself the following question.

 

If gravity was instantaneous, and you have a uniform distribution of mass.

 

Could you have a gravity wave?

 

Logically the answer would be no you couldn't. If gravity was instantaneous all mass would be affected at the same exact instant.

 

I'll let you think about that statement.

Well my understanding of gravity wave might be wrong but I understood it to represent the energy released that ultimately allows the two orbiting bodies to merge. It is doing something completely different to gravity. Gravity would keep the two bodies at exactly the same distance, but the Gravitational Radiation (G-Rad) takes away the orbital energy and the orbit decays.

 

How those two ideas link I can't quite comprehend.

[Mordred]

Well for starters I read a buttload of articles and textbooks. In CMB measurements the speed of interactions is particularly stressed. This includes the speed of gravity. You'll often hear this expressed as sound waves. The speed of sound being the speed of light in a vacuum. It's of fundamental importance in Cosmology applications.

 

Any papers I've ever read apply the speed of gravity=c in the medium they are examining in CMB measurements.

 

Connect the dots,, gravity affects mass density. Density affects temperature... by looking at temperature anisotropy rate of change we are

Edited February 13, 2016 by Mordred