[jeffreyH (OP)]

https://www.theguardian.com/science/across-the-universe/2016/feb/11/todays-gravitational-wave-announcement-could-be-two-great-discoveries-in-one

[alancalverd]

In the words of Donald Trump, wow! Hanging on every word!

[jeffreyH (OP)]

Hang no more.

http://www.bbc.co.uk/news/science-environment-35524440

[Ethos_]

Hang no more.

http://www.bbc.co.uk/news/science-environment-35524440

A new era in astronomy has birthed.

[chiralSPO]

TheBox:

I have removed your posts and the responses to them to another topic under the subforum "that CAN'T be true". Feel free to post to that thread. You are officially invited to discontinue that line of conversation in THIS thread.

Thank you.

[chiralSPO]

I hope that they are able to confirm these findings swiftly. This will certainly be an interesting new development for cosmology and astrophysics!

[timey]

Am I correct in my understanding that the premiss of detecting these gravitational waves involves sending light beams at an angle down hollow tubes that are lined with mirrors, where the light bounces around, and that the waves of gravitational energy pass through into the hollow tubes and cause the light to detectably 'shift' very slightly?

[Ethos_]

Am I correct in my understanding that the premiss of detecting these gravitational waves involves sending light beams at an angle down hollow tubes that are lined with mirrors, where the light bounces around, and that the waves of gravitational energy pass through into the hollow tubes and cause the light to detectably 'shift' very slightly?

As I understand this experiment, two sections of pipe 4 kilometers long are laid out in the shape of an L. At the junction of the two pipes a high powered laser shoots a split beam down both pipes where they both are reflected back to the junction from where they originated. When the images of the laser are inspected, any interference patterns will suggest a slight change in the spatial arrangement between both mirrors. This positional distortion of the mirrors provides the evidence that a gravitational wave has crossed their positions.

This experiment is named: "LIGO" These letters stand for; Laser Interferometer Gravity Wave Observatory.

[timey]

Thanks Ethos... I did read the bbc news link, and I do know the name LIGO and what it stands for, but I'm reading links only from my phone screen at mo...and this proves, well a bit fiddly.

Lol!  I must say that my 'visual' on the experiment is now somewhat changed rather, and has given me some food for thought, must say!

But even so... on the basis that this experiment is subject to a gravitational wave, shouldn't some form of 'shift' occur in the light itself though?

[Ethos_]

But even so... on the basis that this experiment is subject to a gravitational wave, shouldn't some form of 'shift' occur in the light itself though?

The path that light takes is dependent upon the relative positions of the mirrors. And the effect that a gravitational wave would have on the beam itself would be miniscule. However, the slight change in the positioning of the mirrors would be more greatly effected by that gravitational wave. While it is true that gravity will bend the path of the light beam, I believe the changing position of the mirrors is how the interference patterns are detected. 

[timey]

Ah, but I was not thinking about the gravitational wave bending the light beam, I was considering the premiss of gravitational redshift being synonymous to the expansion of the universe.

Any change in the 'gravitational' field should cause a gravitational shift in the light.  Being as this shift is distance related, and perhaps 'this' is where I've been getting it all wrong, but if I'm right, it would most definitely have an effect on the interference patterns, logically speaking... (rubs chin) ... whether the mirrors had moved or not...
But it would really be very hard to believe that they had been searching for proof that distance is subject to change in a gravitational field, and to have forgotten about the gravitational shifting of light... so I daresay they have accounted for the effect in some way, or that I have made a mistake in my thinking.

[Ethos_]

Ah, but I was not thinking about the gravitational wave bending the light beam, I was considering the premiss of gravitational redshift being synonymous to the expansion of the universe.

Any change in the 'gravitational' field should cause a gravitational shift in the light.  Being as this shift is distance related, and perhaps 'this' is where I've been getting it all wrong, but if I'm right, it would most definitely have an effect on the interference patterns, logically speaking... (rubs chin) ... whether the mirrors had moved or not...
But it would really be very hard to believe that they had been searching for proof that distance is subject to change in a gravitational field, and to have forgotten about the gravitational shifting of light... so I daresay they have accounted for the effect in some way, or that I have made a mistake in my thinking.

You bring up an important observation timey, they may be looking for changes in the wavelengths of light coming from both mirrors. I may have been assuming the method of detection wrongly. I'll need to check that possibility out more closely.

[timey]

Well its all certainly food for thought, and that's always good news in my book. .

It does also occur to me that gravitational waves might well cause very slight seismic activity, so to take readings based on the movement of objects of mass 'may' be suspect in any case.

In my mind, a study on how the gravitational energy is effecting the gravitational shift of light would be the logical approach.

[chiralSPO]

My understanding is that no redshift would be observed because it is a gravitational wave. There may have been a momentary change in the apparent frequency of the light as the wave passed, but it would have been undone as soon as the wave was past. The change in the time taken for the light to move between the mirror and detector would  remain changed by the momentary shift. I may be wrong.

[Ethos_]

Well its all certainly food for thought, and that's always good news in my book. .

It does also occur to me that gravitational waves might well cause very slight seismic activity, so to take readings based on the movement of objects of mass 'may' be suspect in any case.

In my mind, a study on how the gravitational energy is effecting the gravitational shift of light would be the logical approach.

I've gone back and reread the article and there are a couple entries that cause me to suspect that my first inclination was the correct one.

Quote from the article:

"Gravity waves passing through the lab should disturb the set-up."
"Theory holds they should very subtly stretch and squeeze it's space."

Measuring the time it takes for light to pass from the source to the mirrors and back should show a disparity between them as the gravitational wave passes by. This is of course, the limited amount of information that I've been able to glean as we speak. More information will surely surface as to whether measuring the time differential between these two light pathways is how they are graphing the interference pattern or whether by another means such as possible changes in wavelengths. I would personally think measurement in any change of wavelength would be extremely difficult.

[alancalverd]

As I understand it (and the official LIGO website is crap!) they are measuring the change in length of the interferometer arms. For all the superb engineering of this project, you'd still expect them to wobble a bit, but the trick seems to be to detect precisely synchronous changes in both interferometers, which would indicate a nonterrestrial source of the disturbance.

The "seismic activity" is indeed real, but amounts to coordinated movements rather less than the diameter of a proton, so is negligible in comparison with the everyday churning of the earth's crust.

[Colin2B]

Any change in the 'gravitational' field should cause a gravitational shift in the light. 

I think you would need a very intense g field to bend light to a significant degree and these are very weak effects. When I read the summary of the set up last yr it looked as though the test masses were only set to detect variations along the length of the arms ie along the light beam not across the light beam.
No doubt more details will follow soon.

Sorry Alan, noticed you have posted while I was typing, pressing the button anyway.

[timey]

Gosh... My 'visual' on this experiment has morphed again!

So... presumably the arms must be vertically oriented, do they go into the ground?

[timey]

Ah, Colin.  I was considering a gravitational 'shift' in light, that the light would be subject to, both horizontally, and vertically, in the event of a gravitational wave.

[Ethos_]

Gosh... My 'visual' on this experiment has morphed again!

So... presumably the arms must be vertically oriented, do they go into the ground?

No timey, the pictures I've seen have the L shaped installation lying horizontal the earths surface.