Can LIGO actually detect gravitational waves?

[tar]

Strange,

 

I wonder if what you say about the waves continuing on undisturbed after intersection is completely true. I would imagine that when the sum of the amplitudes of two overlaid sine waves(1/4 wavelength out of phase) is zero there is actually no amplitude. In the case of GW waves I would imagine that means H+ and Hx cancel each other out, annihilate each other, like two antiparticles would. Like gone. In which case the stretching influence, the strain, is relieved.

 

Here is a thing I was working on for my 12 segments of a sphere topic that I never posted because it did not work, as I did not have the curvature of the pieces right, but I post it to show that if you take a square grid of wire and pull on two corners you can get the 75 degree and 105 degree intersection in the middle of the diamond. Shown to show how space might be stressed so the orthogonal direction is decreased as the other orthogonal direction is increased. Also shown to show that the x of the colored threads is 90 degrees offset from the x of the wire grid.

 

Just to visualize 3d intersections of gravity waves which would be basically two planes intersecting at a line.

 

But to the point, after an intersection would both waves, each taken as a spherical shell, be still completely intact or would certain portions of the shell be attenuated or damped by passing through another?

 

Regards, TAR

 

Ignore the grey and pink yarn, it is just used to sew the sections together and has no analog important to the discussion.

Edited June 9, 2017 by tar

[Mordred]

 

This is an interesting scenario - not sure what happens. Gravitational waves are the product of a quadrapole moment - would that allow interference in the same way. I would guess - for starters - that for any interference you would need frequency / wavelength coincidence but also h₊ and h_x similarity

there is some interference Though as you mentioned it will involve the two wavelengths to determine the type and degree.

[Strange]

Strange,

 

I wonder if what you say about the waves continuing on undisturbed after intersection is completely true. I would imagine that when the sum of the amplitudes of two overlaid sine waves(1/4 wavelength out of phase) is zero there is actually no amplitude. In the case of GW waves I would imagine that means H+ and Hx cancel each other out, annihilate each other, like two antiparticles would. Like gone. In which case the stretching influence, the strain, is relieved.

 

 

That can happen (I think - although imatfaal makes an interesting point) where they overlap. But there must be another position where the waves reinforce each other (because conservation of energy). Past the point where they overlap, nothing is changed.

 

 

But to the point, after an intersection would both waves, each taken as a spherical shell, be still completely intact or would certain portions of the shell be attenuated or damped by passing through another?

 

They would be unchanged.

[tar]

Strange,

 

Was wondering about the conservation of energy thing, when I take a square grid and pull on the corners. The diamond shows no sign of wanting to pop back into square shape. It is perfectly satisfied to stay in the new configuration. Somehow, though all the wires and lengths between welds is exactly the same, the welds seem to be balanced in terms of being compressed one way and stretched the other. They perhaps store potential energy, but two portions of the weld are wanting to relax by expanding from being compressed, while the other two opposite portions are wanting to return to their relaxed state by compressing from being stretched.

 

Regards, TAR

[Strange]

Strange,

 

Was wondering about the conservation of energy thing, when I take a square grid and pull on the corners. The diamond shows no sign of wanting to pop back into square shape. It is perfectly satisfied to stay in the new configuration. Somehow, though all the wires and lengths between welds is exactly the same, the welds seem to be balanced in terms of being compressed one way and stretched the other. They perhaps store potential energy, but two portions of the weld are wanting to relax by expanding from being compressed, while the other two opposite portions are wanting to return to their relaxed state by compressing from being stretched.

 

Regards, TAR

 

 

We are talking about the interaction of waves; constructive and destructive interference.

http://www.phys.uconn.edu/~gibson/Notes/Section5_2/Sec5_2.htm

Edited June 9, 2017 by Strange

[tar]

well right, understood, but when a wave cancels out another, like when you hold your fingers close together and see the black lines, where does the energy go?

 

I am using the sine wave as an analogy to the stress of compression cancelling out the stress of stretching in the orthogonal direction.

[swansont]

well right, understood, but when a wave cancels out another, like when you hold your fingers close together and see the black lines, where does the energy go?

 

I am using the sine wave as an analogy to the stress of compression cancelling out the stress of stretching in the orthogonal direction.

The energy is larger in places where there is no cancellation.

[Strange]

well right, understood, but when a wave cancels out another, like when you hold your fingers close together and see the black lines, where does the energy go?

 

 

To the places where the waves reinforce, instead of cancelling.

[beecee]

I have a basic question that I've never actually seen answered in discussions of LIGO and gravitational waves: if these waves are warping space itself (actually spacetime), then all matter occuping that space will be warped to exactly the same degree that space is warped, making such warps in principle undetectable. So if an interferometer like LIGO, with two perpendicular arms, is set up to measure such waves, what is it actually measuring? Any distortion of the arms in the direction of the waves will not be detected because that arm(s) will be distorted to exactly the same degree that space itself is distorted. Help?

 

 

I'm only a lay person as far as science/Cosmology is concerned but I see it as rather easy to understand that gravitational waves, are simply a distortion of spacetime..... A wave passing through the aLIGO , will lengthen space-time ever so slightly along one arm of the detector, and compress it along the other arm...

Waves by definition have peaks and troughs and travel transversely progressively away from their source.

Also of course the two detectors in operation that detected these GW's, did so at different instances of time, albeit it in milliseconds apart.

Science is a discipline in eternal progress and while false positives from experiments do happen, scientists do learn from these false results...the BICEP2 experiment being a good example, where after further investigations and data from other experiments, the original results were falsified.

While science discussion boards such as this are great for discussions and opinions to be sounded out, the scientists at the coal face, are doing the hard yards.

Edited June 9, 2017 by beecee

[Mordred]

 

 

The interaction of black holes themselves (as I understand it) cannot generate EM radiation. Obviously if there were matter surrounding them (accretion disks, nearby stars, etc) then the picture would be very different. That is what I meant by "isolated" versus other cases.

 

If they were two black holes with no accretion disks there would be no jets (these are formed from the inflaming matter).

 

 

If you shine shine two arbitrary beams of light through each other they will not affect each other. An interferometer is a very special case. And I did say there could be interference effects where they cross. But they would emerge unchanged.

 

If you had two coherent sets of gravitational waves arriving at the same time, then perhaps you could detect interference between them. But that does not sound like a very realistic scenario. If they had passed through other, then there would be no effect.

 

 

Been thinking about this myself, I can only see the potential on destructive interference. The likelyhood of matching waves on a quadrupole is extremely unlikely. You have two polarizations

 

[latex]h_+[/latex] positive and [latex]h_x[/latex] cross polarization. The angle between the two is [latex] \frac{\pi}{4}[/latex] as opposed to the electromagnetic dipolar [latex] \frac{\pi}{2}[/latex] in the z direction and setting c=1. These two polarizations are independent and can be individually interfered with.

 

The quardupole formula being given as [latex] \bar{h}_{ij}(t,r)=\frac{2G}{c^4r}\ddot{I}_{ij}(t-r/c)[/latex]

 

The thing is the interference will generate scatterings and diffractions so the outgoing waves after crossing should have a lower amplitude than the original wave amplitudes prior to crossing.

 

Now there i something called the Stochastic GW background. which is a statistical averaging of background GW wave noise.

 

The energy density in a GW wave is given by

 

[latex]\rho_{gw}=\frac{1}{32G_n}\langle\bar{h}^2\rangle[/latex]

 

for a stochanstic background the spatial averaging of the fields. The ensembel of the fourier of an unpolarized gaussian stationary background in terms of a spectral density is [latex] S_h(f)[/latex] : [latex]\langle\tilde{h}^*(f)\langle(\acute{f})\rangle=\delta(f=\acute{f})S_h(f)[/latex]

 

giving [latex]\rho_{gw}=\frac{\pi}{2G_n}\int_0^\infty df f^2S_h(f)[/latex]

 

the common practice is to relate this to the energy density per logarithmic frequency interval [latex]d\rho_{gw}ln f[/latex] scaled by the energy density needed to close the universe.

 

[latex]\Omega_{gw}(f)=\frac{1}{\rho_{crit}}\frac{d\rho_{gw}}{d\ln f}=\frac{4\pi^2}{3H^2_0}f^3S_h(f)[/latex]

 

as far as I know we haven't determined an exact value yet but the energy density of the background must be less than order of magnitude 10^-5 otherwise the universe would expand faster than what is observed. (least that was the last value I came across. I haven't followed the papers on the stochastic background in quite some time lol.

Edited June 10, 2017 by Mordred

[tar]

Mordred,

 

Your post was beyond me as I am not versed in fourier transforms and guassian stationary backgrounds and the like, but I get the idea, that you could judge, by the characteristics of a GW, something about its history. That is, not only what caused it, but what scattered it, or attenuated it, this way or that way, or interfered with it.

 

Thinking that maybe could allow us to reconstruct a wave that long ago passed through here going south, by reading the signature that it left on the GWcoming from the South that we just read.

 

That way we would not have to wait for a wave to pass through Earth to read it, we could form a mathematical "picture" of all the expanding shells that a GW passed through and draw a model of waves we have not yet seen and that have already passed, just by carefully analyzing one.

 

Regards, TAR

and maybe reconstruct a non-stationary background that a wave must have passed through to have the characteristics that it has

sort of like getting an x-ray image of space

 

The black holes merging sent a simple very powerful wave out, and we can read the shape of space between by reading what came through.

I think I made a mistake in logic there somewhere. We could figure waves that already passed through, but I don't think there is a geometrical way for the signature of a future wave to be on an arriving wave. The mathematical picture we drew would have to imply a future wave, not read its signature... I am confused...expanding shells of one event are difficult to think about, especially on universal scales that we can not easily switch into and out of mentally. Or at least I cannot.

[tar]

on further musing I do not think we sense enough of the wavefront to get a good read on the history of the wave as a whole

 

in essence we just get a point in diameter core sample of the shell, just in that one tiny area covered by the experiment, and another thin core sample at the location of the other beam splitter setup

 

for instance, there could be a "dent" in the wavefront that was missed because the dent was in the area of the wave that passed between the experiments

 

or there could be an attribute of the wave front that was missed because the lead edge of the wave front hit the one experiment while it was at amplitude h and it was slightly less or more when it hit the other experiment

 

That is, given a stack of planes of gigantic size to represent the wave front, we have as information only something about a single line, a second long, going through the planes, normal to the wave front.

The plane of the wave front hits the other station at a different time, so wavers in the wave between the time it hits station 1 and 2 are not known about.

and the beam, before it hits the splitter, is bounced back and forth 500 times or something to leverage the change in the distance between the mirrors, and this will not give us any information about the differences in the gravity wav e that occurred over that entire distance...it would just give us the average of the amplitude of the wave portion that was in the experiment, during the time beam made the trip...but maybe since its continuously read it works out...but seems like since the wave is also going the speed of light...you blink, and you miss something... only take a reading every 500 blinks, you might not have a solid stream of data...

could you make heads or tails from every 500th letter in a book?

Edited June 11, 2017 by tar

[Strange]

So, when you are listening to the radio, do you worry that you might be missing most of the program because you are only receiving a tiny bit of the wavefront?

[tar]

no. But phone conversations can be multiplexed more heavily than data lines. And data transfer needs high frequency carrier waves. We only have one main wave with some weak precursors that we don't even know are related, until after the wave is figured. We are only looking at the last gasp of two small in diameter black holes spiraling around each other at .6C. And I have no doubt we can tell a lot about the masses and their spin and speed and how many solar masses are lost in energy to the wave, but I was reversing myself on any hope of finding the signatures of other GWs on the ones we sense. We don't see enough of the wave to see what the wave looks like just 10 miles away. If we had a LIGO every mile for all the distance between this and another one, then we could hope to read the space that the wave traveled through.

or how about a LIGO on the center of each of the 12 segments of the sphere, the sphere being Earth

 

never mind about the 12 spots

 

Great in theory because you could figure direction really well and get all sorts of info the width and depth of the earth separation would provide since every station would have a twin on the opposite side of the earth and two stations one 90 degrees to the left and one 90 degrees to the right...except most of the required positions would be in an ocean which would create a whole different wave problem

Edited June 11, 2017 by tar

[swansont]

 

The thing is the interference will generate scatterings and diffractions so the outgoing waves after crossing should have a lower amplitude than the original wave amplitudes prior to crossing.

 

 

 

The waves scatter off of each other?

no. But phone conversations can be multiplexed more heavily than data lines. And data transfer needs high frequency carrier waves. We only have one main wave with some weak precursors that we don't even know are related, until after the wave is figured. We are only looking at the last gasp of two small in diameter black holes spiraling around each other at .6C. And I have no doubt we can tell a lot about the masses and their spin and speed and how many solar masses are lost in energy to the wave, but I was reversing myself on any hope of finding the signatures of other GWs on the ones we sense. We don't see enough of the wave to see what the wave looks like just 10 miles away. If we had a LIGO every mile for all the distance between this and another one, then we could hope to read the space that the wave traveled through.

 

What would you hope to gain? Detectors close to each other will have correlated noise, so it will not cancel out and you will not gain any advantage from the multiple detectors.

 

Why do you think the wave will look any different 10 miles away from the detector? The wavelength of the GWs is of order a million km, and the amplitude will not vary over such a small angular separation (10 miles, i.e. a few light microseconds, at a distance of a billion LY).

http://www.tapir.caltech.edu/~teviet/Waves/gwave_spectrum.html

[tar]

SwansonT,

 

I am thinking that a gravity wave is not pure and smooth with only one waveform on it. Like a stochastic in the stock market there are waves noticeable, cycling within a band at any time period you wish to study. The market can open 80 up and close 75 up one day and open 40 down and close 76 up the next day and it tells you little about the low or high of the day on either day or about the direction of the market over the week or the month or the year or the decade. Back when I was allowed to trade double shorts and double longs, I amazed my broker in being able to tell, by the stochastics, when the market was oversold and was about to turn up. The upturn would be proceeded by quick and strong downturns of the very short variety.

 

If we are to "see" a gravity wave by looking at a pulsar, we are seeing either one that has already passed Earth or one that is hitting Earth about the same time as the light from the pulsar. That is geometrically speaking, any gravity wave that crossed the path that the light took from the quasar to Earth, had to first cross through Earth. So, at one a year coming through Earth, and 50,000lys between here and the pulsar, the light from the pulsar, should have on it, or embedded in it, the signature of every gw that passed through here in the last 50,000 years, including the last 3 we know about.

 

The close stations were meant to pick up the less than millisecond variations in a wave, created by their previous intersection with other gws.

 

Regards, TAR

[Strange]

I am thinking that a gravity wave is not pure and smooth with only one waveform on it.

 

 

What is the evidence for that?

[tar]

the fact that each gw HAD TO have passed through others

[Strange]

the fact that each gw HAD TO have passed through others

 

That is not evidence. It is, at best, a hypothesis. And can you quantify this claimed effect and show it is significant?

Edited June 12, 2017 by Strange

[swansont]

SwansonT,

 

I am thinking that a gravity wave is not pure and smooth with only one waveform on it.

 

 

And these purported fluctuations/ripples would be much smaller in amplitude than what has been detected, so even if they existed, you wouldn't be able to see them.

[tar]

except the ripples are caused by one gw passing through another

 

The ripple is potentially as strong as the wave.

 

That is, if two waves intersect in space, that piece of space in which both exist could have portions that are double stretched or double compressed depending on the timing and incident angle.

 

If 1 wave has crossed 1 billion other waves, why would there not be evidence of the many meetings.

 

If you can tell by the fringes that a mirror got a width of a proton closer and from this discern the mass of each black hole, their spin and how many solar masses were turned to gravitational energy 1.3 billion lyrs away, I don't know why you couldn't tell where there was, in the fringes, evidence that the wave went through space that was warped this way or that already.

 

Regards, TAR

Edited June 13, 2017 by tar

[Strange]

I don't know why you couldn't tell where there was, in the fringes, evidence that the wave went through space that was warped this way or that already.

 

 

Without a model describing what to look for, there isn't any way of testing this idea.

 

As the waveform corresponds very closely to that predicted to be produced by the source, it seems that any such effect must be very small. There are people looking for other effects in the details of the waveform, but these will probably have to wait until detectors are more sensitive to draw any conclusions.

For example: https://www.universetoday.com/135690/gravitational-waves-permanently-alter-nature-spacetime-1/

[tar]

strange,

 

Well this is a new avenue of research as is expected since we only saw the first gw in Feb. 2016, so what information is already to be found in, gleened from, the fringes already recorded is still to be determined.

 

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.181103

 

This link, off of your link talks about orphan waves. This model has the space of the detector permanently malformed a little after the detection of a wave...indicating to me that there are ripples in the signal that are looking for a model to fit. It seems it is ok to suppose that the ripples can be from the source, or from the space at the detector, or according to my idea about crossing another wave, the ripples looking for a model, could be the other gw, or the many gws the gw crossed.

 

We already have data fine enough to notice the ripples we are currently calling orphan waves. Now suppose we test my theory this way.

 

We have the data from gw150914 taken from LIGO Sept.14th 2015. Because of the geometry of space, no future GW can get to Earth, without having passed through the space gw150914 was bending, stretching and compressing, so according to the theory, the signature of gw150914 should be on gw151226 data taken on Dec. 26th 2015.

 

We know the direction each wave was traveling and how the waves were oriented h+, hx wise, as they came through Earth, so it would be possible to determine where each wave was in what orientation when they had to cross paths. (take into consideration the motion of the Sun around the center of the Galaxy to model a space of intersection of the two waves irrespective of the Sun's movements, and figure how GW151226 should have been affected by going through GW150914. Then see if the pattern of GW151226 is to be recognized on GW150914. It should be there. (according to the theory)

 

Regards, TAR

the other day I was in the bathroom and a shadow went across the blinds like a person had passed by the window on the outside

my wife was inside, so I peeked out and saw no one

then another shadow passed and it gave me a chill, again no one was there

then I noticed the high boughs of the Maple where moving in the Sun, just right to cause the shadow on the blinds to move at the speed of a passing person, about the size and shape of a passing person

[Strange]

We already have data fine enough to notice the ripples we are currently calling orphan waves. Now suppose we test my theory this way.

 

 

My understanding is that we don't yet have enough accuracy to test this idea. They claim there is evidence of this. Others are more sceptical. We will have to wait and see.

 

To test your idea, you would need to predict exactly what the effect would be.

[tar]

strange,

 

I would rather look at it the other way around. What do the signals look like? THAT is what a gravity wave looks like, after passing through 1 billion other GWs. The signature of 1 billion other gws has to be on each and therefore one should expect sort of a fractal situation.

 

regards, TAR

Edited June 13, 2017 by tar