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Can LIGO actually detect gravitational waves?


aramis720

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And with respect to the mirror positions and arm lengths, Faraoni states the effect is "different from zero" (p. 683):

 

"In the approximation λgw >> L the time dependence disappears and del x/L = h+(t = 0)/2, Eq. (4.2), which is different from zero..."

 

But one could just as well argue that this "different from zero" result should also be considered negligible in the approximation lambda >> L. No numbers are offered in this paper with respect to the negligibility decisions.

 

As you say, there are no numerical values. So you do not appear to have any justification for assuming that "differs from zero" is the same as "approximately equal to zero". As you appear to understand the maths, I assume you could put some values in and see how "different from zero" this result is.

 

So, even without being able to follow all of the maths, I find their (and other) arguments convincing because:

 

1. If someone says "not zero" I do not immediately think that they mean "approximately zero".

 

2. We know already that light and matter are affected differently by the curvature of spacetime.

 

3. They detected something; if not gravitational waves, then what?

But this is manifestly incorrect when we recognize that GWs are defined as waves of spacetime itself. So, as I've stated numerous times since my OP, this definition of GWs seems to render any detection of such waves by a physical apparatus in principle impossible simply because any distortion of spacetime itself will distort the physical apparatus occupying that slice of spacetime by exactly the same amount as the wave itself, in every direction. So the direction of the wave doesn't matter.

 

Not in every direction. For example, there is (as I understand it) no distortion in the z (direction of travel) direction). And the distortion in x and y are not the same.

 

However, you would be right if one were trying to use a material ruler to measure the change in another material object.

 

But we know that light and massive objects do not respond to changes in the curvature of space-time in the same way (otherwise, for example, the prediction for the degree of gravitational lensing by GR would match that for Newtonian gravity). And this is what the Faraoni paper shows, in the case of the interferometer.

 

So we can measure the differential change in the effect on the arms and the light.

 

 

 

 

I'm not sure why this point isn't sinking in, but as I just mentioned to Mordred it seems that a lot of people continue to envision GWs as traveling through space rather than being waves of space itself.

 

They may well be waves of space-time, but they also travel through space. (Not that I can see the relevance of this comment either way.)

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I'm not sure why this point isn't sinking in, but as I just mentioned to Mordred it seems that a lot of people continue to envision GWs as traveling through space rather than being waves of space itself.

Space and spacetime are not the same; space is just volume.

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Business as usual, that's how science works. People have had serious doubts about Einstein's GR and SR for a century but they are still there. The doubters are as important to science as the people that make the discoveries.

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Mordred, your discussion reveals that you are thinking of the GW traveling through space (and I think this is the general conception among physicists), but as I've pointed out many times now GWs are defined as waves of space, not waves traveling through space, as described on p. 679 of the Faraoni paper.

 

A water wave is a wave of water, traveling through water.

 

This was quickly clarified by others that it does not, in fact, cast doubt on the observation, and one rebuttal is mentioned in your linked article.

 

http://www.preposterousuniverse.com/blog/2017/06/18/a-response-to-on-the-time-lags-of-the-ligo-signals-guest-post/

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A water wave is a wave of water, traveling through water.

 

This was quickly clarified by others that it does not, in fact, cast doubt on the observation, and one rebuttal is mentioned in your linked article.

 

http://www.preposterousuniverse.com/blog/2017/06/18/a-response-to-on-the-time-lags-of-the-ligo-signals-guest-post/

Yes, a wave of water travels through water but also through space more fundamentally (space is, after all, the container of all things). Any measurement device to measure the water wave is in the water but more fundamentally is in space, and it will not be distorted itself by the passage of the water wave (in terms of its fundamental dimensions). To the contrary, and my point this whole time, is that any device in space that is designed to measure waves OF space will be distorted in exactly the same way as the space it occupies, making detection in principle impossible. Is that clear?

 

In terms of the recent critiques of the GW data, see my article for the rebuttals and responses, etc., with the initial group critiquing the work standing by their critiques.

Edited by aramis720
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...To the contrary, and my point this whole time, is that any device in space that is designed to measure waves OF space will be distorted in exactly the same way as the space it occupies, making detection in principle impossible. Is that clear?

You've repeated that beyond usefulness The distortion of space at one arm is different to the distortion at the other arm; the distortion is not equal or simultaneous at all co-ordinates about the two arms. Your argument supposes that the the changes at each co-ordinate happen simultaneously to the same degree in all co-ordinates, which they don't. Relatively, there is a detectable difference when comparing the behavior of each arm against the other.

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You've repeated that beyond usefulness The distortion of space at one arm is different to the distortion at the other arm; the distortion is not equal or simultaneous at all co-ordinates about the two arms. Your argument supposes that the the changes at each co-ordinate happen simultaneously to the same degree in all co-ordinates, which they don't. Relatively, there is a detectable difference when comparing the behavior of each arm against the other.

Ok, so in plain language, at the level of concepts, how would the physical apparatus change in any measurable way when of course that apparatus is being waved in exactly the same way as the space it occupies (in every direction)?

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Ok, so in plain language, at the level of concepts, how would the physical apparatus change in any measurable way when of course that apparatus is being waved in exactly the same way as the space it occupies (in every direction)?

It isn't uniform and that's what you seem to not be grasping and why the arms are perpendicular.

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Ok, so in plain language, at the level of concepts, how would the physical apparatus change in any measurable way when of course that apparatus is being waved in exactly the same way as the space it occupies (in every direction)?

The physical apparatus, ie, the two arms at right angles to each other, have different parts of the GW affecting them, eg: as I said previously peaks and troughs.

 

 

No, casting no doubt at all, in fact the exact opposite. It actually shows how diligent, how careful, and how all contingencies have been accounted for, particularly after the BICEP2 apparent mis-diagnosis.

 

Here is a paper considering the possibility of confirming string and extra dimensions in the noise..........

http://iopscience.iop.org/article/10.1088/1475-7516/2017/06/048/meta;jsessionid=DA6583EDF04658CD0AA33069D4A3BFEB.c3.iopscience.cld.iop.org

and an article on the same matter......

https://phys.org/news/2017-06-hints-extra-dimensions-gravitational.html

 

and of course we have GOTO which will look at another aspect of GW's....

https://phys.org/news/2017-07-telescope-optical-gravitational.html

 

Once again, as I mentioned previously, if you are certain of your so far unsupported claims, in your own mind, then why not contact LIGO as I did regarding GWs and their validity?

Edited by beecee
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It isn't uniform and that's what you seem to not be grasping and why the arms are perpendicular.

That doesn't matter. Obviously if the apparatus is being stretched in exactly the same manner as space is being stretched it doesn't matter what direction the wave comes from.

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Ok, so in plain language, at the level of concepts, how would the physical apparatus change in any measurable way when of course that apparatus is being waved in exactly the same way as the space it occupies (in every direction)?

1. It isn't the same in every direction.

 

2. The apparatus is affected differently to the light.

 

Which of these don't you understand?

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That doesn't matter. Obviously if the apparatus is being stretched in exactly the same manner as space is being stretched it doesn't matter what direction the wave comes from.

We have repeatably told you the arms Are not being stretched in the same manner repeating this again and again and again is getting tedious and rather annoying.

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1. It isn't the same in every direction.

 

2. The apparatus is affected differently to the light.

 

Which of these don't you understand?

I said it doesn't matter what direction the waves are coming from -- it could be any or all directions and 1 or a hundred different waves. Based on simple logic, if the apparatus that occupies space is stretched to exactly the same degree as the space it occupies it cannot detect the waves. Think it through. It will sink in eventually.

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No everyone else understands how the detector works.

 

Everyone except you.

 

The arms spacetime nor the lasers stetch in the same time dependant manner on the x and y coordinates.

Edited by Mordred
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We have repeatably told you the arms Are not being stretched in the same manner repeating this again and again and again is getting tedious and rather annoying.

I know you have repeated your assertions and I mine but you haven't yet addressed the basic logical objection. Here's a visual metaphor: think of a balloon with two perpendicular lines drawn on it. If the balloon expands the two lines will expand in exactly the same way as the balloon so there will be no way to detect the expansion by using the lines only. You have to take a higher level viewpoint outside of the balloon to know that it has expanded. Does that make sense?

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No everyone else understands how the detector works.

 

Everyone except you.

 

The arms spacetime nor the lasers stetch in the same time dependant manner on the x and y coordinates.

Again: you haven't addressed my basic logical objection and I hope you will. I'm addressing the fundamentals here. The basic logic. That hasn't been addressed and until we can get past that step the foundation is not firm.

I have addressed it I even posted the mathematics

I'm not asking about the mathematics -- I'm asking about the basic logic. Everyone is being confused by the higher order concepts and mathematics and skipping over the basic logic of how the apparatus is supposed to work. "Look, here are the equations that show it works, but let's ignore the basic logic of the situation."

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The fundamental your ignoring is the polarity of a quadrupole wave.

 

If you continue to ignore that you will never understand how the Ligo detector works.

Edited by Mordred
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The fundamental your ignoring is the polarity of a quadrupole wave.

 

If you continue to ignore that you will never understand how the Ligo detector works.

And how does the quadrupole wave relate to my metaphor of lines drawn on a balloon?

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Draw 4 dots on your balloon.

 

Label the dots x_1 x_2 y_1 and y_2.

 

Squeeze the balloon. Does the distances between x_1- x_2 and y_1 - y_2 change the same way.

 

Of course not welcome to quadrupole wave polarity change demonstration

Edited by Mordred
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Draw 4 dots on your balloon.

 

Label the dots x_1 x_2 y_1 and y_2.

 

Squeeze the balloon. Does the distances between x_1- x_2 and y_1 - y_2 change the same way.

 

Of course not welcome to quadrupole wave polarity change demonstration

With respect to the lines drawn on the balloon of course the distances change exactly the same way. You can't use the lines themselves on the balloon to measure these changes. Does that make sense?

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Here's a visual metaphor: think of a balloon with two perpendicular lines drawn on it. If the balloon expands the two lines will expand in exactly the same way as the balloon so there will be no way to detect the expansion by using the lines only. You have to take a higher level viewpoint outside of the balloon to know that it has expanded. Does that make sense?

 

 

But if one should depress the skin of the balloon where the two lines meet, one will find that each are affected differently.

aLIGO and the other detector are not measuring expansion.

In the mean time here is a link.......

https://www.ligo.caltech.edu/page/about-aligo

I am sure if you E-Mail them, you will find someone that will explain why your so called concerns are totally invalid.

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With respect to the lines drawn on the balloon of course the distances change exactly the same way. You can't use the lines themselves on the balloon to measure these changes. Does that make sense?

Did I state anything about lines? I asked you to place 4 coordinates onto the surface of the balloon.

 

If you compress along the y axis, the total volume of air inside the balloon remains unchanged.

 

Therefore the y axis must expand to conserve the total volume of air.

 

Rudimentary elementary school physics.

 

Now apply that to a GW wave and treat the effected volume under the conservation laws. The effective mass density or energy density the affected region must be preserved.

Edited by Mordred
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