What is the best 3D description of Gravitational waves?

[Robittybob1]

What does this mean? What is spiralling?

 

We already know they are 3D and move at c.

it is a 3D spiral. The wavefronts form a spiral. It is a bit like the usual form of representation but they need to be drawn in 3D.

This is a 2D representation, but there is no 3D representation of GW on the internet.

https://en.wikipedia.org/wiki/Gravitational_wave#/media/File:Wavy.gif

 

The waves in the gif seem to have some 3D effect but even that is wrong. A 2D wave should have no depth. Amplitude could be represented by shading that falls off with the 1/r ratio.

 

This has been covered in several threads already. The strength of the waves is not completely isotropic (they are slightly stronger in the orbital plane than in the orthogonal axis) but they travel at the speed of light and so will be spherical (once you are far enough away to ignore the slight asymmetry of the source; i.e. a few radii away).

You would need to explain why they are stronger in those planes? They never draw 2D waves as concentric circles so why should we think of the 3D wave as concentric? Any suggestion they are spherical is just based on an approximation. Are you saying they have a point source, for if they did they would be spherical waves?

Edited March 26, 2016 by Robittybob1

[Strange]

You would need to explain why they are stronger in those planes?

 

It is a result from hundreds of hours of simulations of GR. But feel free to replace that detailed analysis with your personal guesses.

 

Are you saying they have a point source, for if they did they would be spherical waves?

 

Once you get a small distance away, it will effectively be a point source.

[Robittybob1]

 

It is a result from hundreds of hours of simulations of GR. But feel free to replace that detailed analysis with your personal guesses.

 

 

Once you get a small distance away, it will effectively be a point source.

There would have to be some physical logic behind the concept. OK the computer simulations may give a more accurate picture.

 

Once you get a small distance away, it will effectively be a point source.

Large distance allows for approximations to be used. I am not applying forces or energy calculations to the 3D model, but we are looking at how it is formed and therefore what shape it has as the wave spreads out in a 3D fashion. There has to be two waves per orbit those two wrap into each other as 3D spirals.

 

The model is the 3D spiral I hope all of you can comprehend what a 3D spiral is like for there is no image like what I want on Google images (so I can't show you).

The predictions would follow. Firstly it explains how the same chirp wavefront can be picked up in all directions around the BBHs. The 3D linearly polarized tubes, 2D models of ripples or 2D sinusoidal waves do not do this.

Swansont asked me "How does your model, such as it is, differ from the model we already have?"

One would think it is different from what we already have. If it is the model "we already have" why isn't it described this way? instead of using tubes, ripples and sinusoidal waves?

 

Katie Mack has a similar 3D concept for she referred to that ugly 3D animation [similar to the one in "Have Gravitational Waves Been Discovered?!? | Space Time | PBS Digital Studios" YT], and she said in that tweet "the GW was stronger perpendicular to the orbital plane" which shows she is thinking in terms of a 3D model.

If her team was the source of that 3D animation, their model the waves were not moving at the speed of light. This was evident by the spacing of the waves. At the speed of light the G-waves would not interfere in the patterns as they were showing.

If the two BBH are going at even 0.5c and the orbit is r , the circumference of the orbit is 2 * pi() * r

Therefore each of the waves should be around 6.28 times further than the radius apart.

Edited March 27, 2016 by Robittybob1

[Robittybob1]

 

You may have added another random guess. There is no model and no quantitatively testable predictions. Therefore no hypothesis.

The model the 3D spiral model is a model in itself. OK I can't animate it as yet but I can think of it. I hope all of you can comprehend what a 3D spiral is like for there is no image like what I want on Google images (so I can't show you).

The predictions would follow once the model is envisioned. Firstly it explains how the same wavefront can be picked up in all directions around the BBHs. 3D tubes, 2D models of ripples or 2D sinusoidal waves will not do this.

Edited March 26, 2016 by Robittybob1

[swansont]

How does your model, such as it is, differ from the model we already have?

Firstly it explains how the same wavefront can be picked up in all directions around the BBHs. 3D tubes, 2D models of ripples or 2D sinusoidal waves will not do this.

 

They aren't meant to, so I think that's not particularly surprising. And you also may be making a common mistake in thinking that the sinusoidal representations describe 2D, when in fact they typically only represent 1D. The orthogonal axis is not a spatial dimension, but rather is the amplitude.

[Robittybob1]

How does your model, such as it is, differ from the model we already have?

One would think it is different. For if it was the same as we already have why doesn't someone just claim "that is what we already have"? That would have set me back a bit, but I'd still say "if it is the model "we already have" why isn't it described this way?", instead of using tubes, ripples and sinusoidal waves?

 

I listened to Katie Mack a bit during my holiday, maybe she has it for she referred to that ugly 3D animation, and she said in that tweet "the GW was stronger perpendicular to the orbital plane" which shows she is thinking in terms of a 3D model.

[swansont]

One would think it is different. For if it was the same as we already have why doesn't someone just claim "that is what we already have"? That would have set me back a bit, but I'd still say "if it is the model "we already have" why isn't it described this way?", instead of using tubes, ripples and sinusoidal waves?

 

I listened to Katie Mack a bit during my holiday, maybe she has it for she referred to that ugly 3D animation, and she said in that tweet "the GW was stronger perpendicular to the orbital plane" which shows she is thinking in terms of a 3D model.

 

 

Yes. The way she knows it's stronger in that direction is because we already have a 3D model. Is yours different? I doubt anyone can decipher your description well enough to know.

 

But if it is different, why is it different? What's the physics that's behind the difference? That's what would make this a true hypothesis, rather than you trying to imagine an answer.

[Robittybob1]

 

 

Yes. The way she knows it's stronger in that direction is because we already have a 3D model. Is yours different? I doubt anyone can decipher your description well enough to know.

 

But if it is different, why is it different? What's the physics that's behind the difference? That's what would make this a true hypothesis, rather than you trying to imagine an answer.

If her team was the source of that ugly 3D animation we are definitely different.

In their model the waves were not moving at the speed of light. This was evident by the spacing of the waves. The G-waves would not interfere in the patterns as they were showing.

Edited March 26, 2016 by Robittybob1

[Strange]

One would think it is different.

 

Then it will be wrong.

 

 

In their model the waves were not moving at the speed of light.

 

Of course they were.

[Robittybob1]

 

Then it will be wrong.

 

 

Of course they were.

That is not fair. Please don't be so biased against me.

 

If the waves were moving at the speed of light the spacing of the waves is so much larger than was shown in the model she used in her lecture.

If the BH is going at even 0.5c and the orbit is r , circumference is 2 * pi() * r each of the waves should be around 6.28 times further than the radius apart.

Edited March 27, 2016 by Robittybob1

[Robittybob1]

How does your model, such as it is, differ from the model we already have?

 

They aren't meant to, so I think that's not particularly surprising. And you also may be making a common mistake in thinking that the sinusoidal representations describe 2D, when in fact they typically only represent 1D. The orthogonal axis is not a spatial dimension, but rather is the amplitude.

I had written 1D and then amended it to 2D.

Does a speculation if proven become accepted science?

 

I am having a debate over the 3D structure of a gravitational wave and I feel the speculation is proven. Can I then use that result in another thread as science fact?

If there is already a 3D model of the gravitational wave does anyone know where this is described? For then the problem may be solved already and I can use the 3D description of the wave in other science threads.

[Strange]

If there is already a 3D model of the gravitational wave does anyone know where this is described?

 

https://en.wikipedia.org/wiki/Gravitational_wave#Mathematics

[swansont]

 

In their model the waves were not moving at the speed of light. This was evident by the spacing of the waves. The G-waves would not interfere in the patterns as they were showing.

 

 

How do you know they aren't moving at c? The spacing itself doesn't tell you. And what does interference have to do with anything?

[Robittybob1]

 

 

How do you know they aren't moving at c? The spacing itself doesn't tell you. And what does interference have to do with anything?

If we are talking about the same model, and I suspect we are, for I saw it being used in Katie's lecture, if you look at the dimensions of the model they are not what you'd get if the waves are moving at c. At c the waves would travel 2*pi times as far as the distance of r (the radius of the binary), if the binaries are traveling at 0.5c. At slower rates the distances are even greater.

These longer distances are not evident in their model.

In their model there appears to be overlapping GWs. Is that summation? Interference may not have been the right word, but it was something like the interference pattern of the two slit experiment where waves cross over each other.

 

I have not seen a written description, only the animation model. If you know of a paper explaining the 3D model Katie Mack was using would you share that with the forum please? It doesn't feel right to knock it harshly if I'm uncertain that we are discussing the same model.

[http://www.schoolphysics.co.uk/age14-16/Wave%20properties/text/Interference_/index.html from that page interference is the right word.]

 

The spacing itself doesn't tell you.

Would you ever get a GW interfering with another GW between the binaries?

This seems to be the place where the wave originates rather than a place of interference as was evident in their animation.

Edited March 27, 2016 by Robittybob1

[ajb]

I have not seen a written description, only the animation model.

I think I said this before, but one has to take great care with pictures and animations: they are one facet of the mathematics. A lot of effort goes into making mathematical results of gravitational wave simulations into pictures and movies. They are usually designed to show some generic features or to allow researchers to quickly spot something. Kip Thorn when he was last in Warsaw discussed some of these methods that use electromagnetic theory as an analogy to break up the gravitational field into different pieces and produce various 'field lines'.

 

Anyway, if you want the full description then you need to examine the solutions to Einstein's field equations. You can only do this explicitly for not so realistic sources. I suggest you look up the description of plane fronted waves in general relativity. The lecture notes of Carroll describe them and how to derive then quite explicitly.

Edited March 27, 2016 by ajb

[Robittybob1]

Thanks Ajb - in the end it is the 3D structure I'm interested in. Hopefully seeing why the strength is greater perpendicular to the orbital plane. That increase in strength won't alter the shape. But a 3D spiral has issues where the spirals meet perpendicular to the orbital plane. It is difficult to see how the two sides meet just using my imagination. I need someone to make a 3D computer graphic to help me see what happens.

 

https://en.wikipedia.org/wiki/Gravitational_wave#Mathematics

Bombing me again. There is no 3D description there. If you think there was which formula was it?

Some of that math could become useful. I see they work with assumption of a point source.

Edited March 27, 2016 by Robittybob1

[swansont]

If we are talking about the same model, and I suspect we are, for I saw it being used in Katie's lecture, if you look at the dimensions of the model they are not what you'd get if the waves are moving at c. At c the waves would travel 2*pi times as far as the distance of r (the radius of the binary), if the binaries are traveling at 0.5c. At slower rates the distances are even greater.

These longer distances are not evident in their model.

In their model there appears to be overlapping GWs. Is that summation? Interference may not have been the right word, but it was something like the interference pattern of the two slit experiment where waves cross over each other.

You must link to sources that you cite. Further, animations may only be conceptual, and those would not be to scale. Especially in Anstronomy/Astrophysics, where you couldn't even put a picture of our solar system up and have everything be portrayed to scale.

 

And we are not talking about the same model. My model is General Relativity. You are proposing something else, so your model can't be the same as mine.

 

I have not seen a written description, only the animation model. If you know of a paper explaining the 3D model Katie Mack was using would you share that with the forum please? It doesn't feel right to knock it harshly if I'm uncertain that we are discussing the same model.

[http://www.schoolphysics.co.uk/age14-16/Wave%20properties/text/Interference_/index.html from that page interference is the right word.]

Would you ever get a GW interfering with another GW between the binaries?

This seems to be the place where the wave originates rather than a place of interference as was evident in their animation.

It's been mentioned multiple times that the GWs emanate from the system rather than the individual BHs. Unless you can point to some reference says there is interference or provide a model to us, you need to drop it from the discussion.

 

Bombing me again. There is no 3D description there. If you think there was which formula was it?

 

 

 

The part that says linear approximation shows the wave equation. The generic function A contains the three spatial coordinates, so it works in 3D.

 

Pretty ugly, no? That's the math you are trying to reverse-engineer from simulations.

[Strange]

Bombing me again. There is no 3D description there.

 

There is.

 

I see they work with assumption of a point source.

 

That is the only way there is an analytical solution (which is why they have do massive simulations to model what happens with the black holes). And, as has been [repeatedly] pointed out, it is a reasonable approximation when you get a few diameters away.

There would have to be some physical logic behind the concept.

 

There is. It is called the theory of general relativity.

[geordief]

Hope this is on topic.

 

Does this animation (provided by Strange in his recent post) actually correspond to what that observer might see if somehow " markers" were inserted into the space surrounding the binary black hole system?

 

https://upload.wikimedia.org/wikipedia/commons/b/b8/Wavy.gif

 

I mean if the space was somehow visible by means of some kind of a huge population of visible particles like bubbles in a bubble chamber is that an accurate representation of what we would see?

 

I know that is a ridiculous hypothesis . Does it work though in principle?

[Strange]

Does this animation (provided by Strange in his recent post) actually correspond to what that observer might see if somehow " markers" were inserted into the space surrounding the binary black hole system?

 

I don't think so. It doesn't seem to represent the stretching and contraction of space (in orthogonal directions). It seems to be just a generic image of waves. (The source page is no longer there, so I don't know how this was generated or what it is supposed to represent).

[geordief]

 

I don't think so. It doesn't seem to represent the stretching and contraction of space (in orthogonal directions). It seems to be just a generic image of waves. (The source page is no longer there, so I don't know how this was generated or what it is supposed to represent).

Well ,if I was clear in what I thought might be being represented , is it possible to represent that in an accurate way ( a "bird's eye" view of the 2D plane as it bobs up and down) ?

 

(It wouldn't be a pure 2D plane more like a "physical" thin slice of the 3D region)

[Robittybob1]

 

You must link to sources that you cite. Further, animations may only be conceptual, and those would not be to scale. Especially in Anstronomy/Astrophysics, where you couldn't even put a picture of our solar system up and have everything be portrayed to scale.

 

And we are not talking about the same model. My model is General Relativity. You are proposing something else, so your model can't be the same as mine.

 

 

It's been mentioned multiple times that the GWs emanate from the system rather than the individual BHs. Unless you can point to some reference says there is interference or provide a model to us, you need to drop it from the discussion.

 

 

The part that says linear approximation shows the wave equation. The generic function A contains the three spatial coordinates, so it works in 3D.

 

Pretty ugly, no? That's the math you are trying to reverse-engineer from simulations.

 

The sources were Youtube lectures by Katie Mack. I have been told off for putting them up before, and I'm pretty shy at the moment.

I am going to try and reverse-engineer the math in Wikipedia to see if it draws a 3D spiral. It seems we only need to be 1 wavelength back from the source to get some results. We could pick some known separation of the BHs so we could workout their periods etc so we would know how far the light (and the gravitation wave) has traveled in the period.

Would you be willing to help me give each variable in those equations some value so we can work out an amplitude at all points around the source? That is all points above and below and on the orbital plane as well. (Each hemisphere should be a mirror image so we'd only need to consider the one half of the sphere.)

 

There is.

 

 

That is the only way there is an analytical solution (which is why they have do massive simulations to model what happens with the black holes). And, as has been [repeatedly] pointed out, it is a reasonable approximation when you get a few diameters away.

 

There is. It is called the theory of general relativity.

If you attempt to draw the results of GR will we get to see the source of the GW and how the GW spreads out in space from the source?

Hope this is on topic.

 

Does this animation (provided by Strange in his recent post) actually correspond to what that observer might see if somehow " markers" were inserted into the space surrounding the binary black hole system?

 

https://upload.wikimedia.org/wikipedia/commons/b/b8/Wavy.gif

 

I mean if the space was somehow visible by means of some kind of a huge population of visible particles like bubbles in a bubble chamber is that an accurate representation of what we would see?

 

I know that is a ridiculous hypothesis . Does it work though in principle?

Strange only linked to the maths section of the Wikipedia article on Gravitational waves. That confused me too once the page is opened. I like your question and it is what I have been trying to do using a mental image but it would be really great to get a 3D image on paper.

Well ,if I was clear in what I thought might be being represented , is it possible to represent that in an accurate way ( a "bird's eye" view of the 2D plane as it bobs up and down) ?

 

(It wouldn't be a pure 2D plane more like a "physical" thin slice of the 3D region)

Just having a line representing the point of maximum amplitude would be sufficient. Then we could keep all the 2D effects in the 2D plane and then we could stack the planes one on top of the other to get the 3D effect.

Edited March 27, 2016 by Robittybob1

[Strange]

It seems we only need to be 1 wavelength back from the source to get some results. We could pick some known separation of the BHs so we could workout their periods etc so we would know how far the light (and the gravitation wave) has traveled in the period.

Would you be willing to help me give each variable in those equations some value so we can work out an amplitude at all points around the source?

 

Have you got a supercomputer handy for the simulations? There is no equation that will allow you to calculate this.

 

 

Just having a line representing the point of maximum amplitude would be sufficient. Then we could keep all the 2D effects in the 2D plane and then we could stack the planes one on top of the other to get the 3D effect.

 

This image is looking "head on" to the approaching wave. Just imagine that in 3 dimensions ....

[Robittybob1]

 

Have you got a supercomputer handy for the simulations? There is no equation that will allow you to calculate this.

 

 

This image is looking "head on" to the approaching wave. Just imagine that in 3 dimensions ....

 

[That's hard on your eyes. ] That image in Wikipedia was called "Linearly polarised gravitational wave" so that to me represents the effects on a plane of test particles above or below the orbital plane, and not a point head on to an approaching wave. One point head on toward the wave would be moved in an oscillation (OK RB which way would it move as the GW passed?)

For if you reduced that image down to a point what would that mean? The center of it doesn't move so would the point be moving?

Edited March 27, 2016 by Robittybob1

[Strange]

[That's hard on your eyes. ] That image in Wikipedia was called "Linearly polarised gravitational wave" so that to me represents the effects on a plane of test particles above or below the orbital plane, and not a point head on to an approaching wave.

 

That is the view of the effect of a linear polarized wave on the x and y dimensions (where z is the direction of travel); i.e. you are looking along the z axis (direction of propagation). Linear polarization is seen looking "edge on" to the pair of black holes (http://arxiv.org/abs/1602.03840).

 

 

The center of it doesn't move so would the point be moving?

 

Movement is relative remember. So if you shift the point of view, then the point at the center in that diagram will move relative to the new central point.