Gravitational wave interference

[roineust]

I am trying to understand the following:
1. Have gravitational wave constructive and deconstructive interference phenomena already been observed or is it that only after making LIGO kind of experiments more advanced, that we might be able to observe such phenomena in the future?
2. Can't gravitational wave constructive and deconstructive interference phenomena be observed, by finding gravity time delation anomalies and/or by finding gravitational-lensing distortions?
3. If gravitational wave constructive and deconstructive interference phenomena is observed and measured, can't this tell us about previously unknown properties of the hypothetical graviton particle?

 

[pervect]

I doubt anything has been directly observed, detection of the waves is challenging enough.

GR is a purely classical theory, and classically the additive nature of waves give rise to constructive and destructive interference. Gravity isn't linear, so the waves do not exactly add linearly, but in the weak field it's a reasonably good approximation.

Thus, on a theoretical basis, the gravitational waves should exhibit constructive and destructive interference in the weak-field where gravity is linear.

I'm not aware of any way one could create a "slit" to perform any analogue of, say, the double-slit experiment, though. Perhaps there is some clever way I haven't thought of to "block" gravitational waves so they can only pass through a slit, but I can't imagine what it would be.

Gravitons are outside the scope of GR, you'd need a theory of quantum gravity to sensibly talk about "gravitions". In GR, gravitational waves are waves, not particles.

 

[roineust]

If we know of a location (for example a black hole) where there is a constant and stable gravitational lensing being observed and then at a relatively close distance, occurs a massive gravitational event such as 2 neutron stars merging, won't that massive second even distort the gravitational lensing properties of the first phenomena, in a way that is compatible with wave interference patterns? Can't interference patterns be detected even more directly, in gravitational lensing around 2 neutron stars, as a result of their own mutual gravity wave collisions?

 

[Ibix]

If we know of a location (for example a black hole) where there is a constant and stable gravitational lensing being observed and then at a relatively close distance, occurs a massive gravitational event such as 2 neutron stars merging into each other, won't that massive second even distort the gravitational lensing properties of the first phenomena, in a way that is compatible with wave interference patterns?

In principle, probably yes. But we don't know the location of anything that we expect to emit significant gravitational radiation - the stuff we've seen is all things we find out about because of the short pulse of gravitational waves they emit. And we don't have detectors spaced widely enough to look for diffraction patterns if there are any.

Can't interference patterns be detected even more directly, in gravitational lensing around 2 neutron stars, as a result of their own mutual gravity wave collisions?

Each neutron star is not emitting gravitational radiation - it's the combination and their interaction. So no. Radio antennae don't create interference patterns from their own emissions, unless you count their beam-shaping as such. The same applies to gravitational wave sources and, once again, we don't have detectors far enough apart to detect directional variation.

All these things would be interesting tests of GR. We just can't do them because we only have sensors on Earth.

 

[roineust]

In principle, probably yes. But we don't know the location of anything that we expect to emit significant gravitational radiation - the stuff we've seen is all things we find out about because of the short pulse of gravitational waves they emit. And we don't have detectors spaced widely enough to look for diffraction patterns if there are any.

What about the existence of gravitational lensing phenomena know about in advance, located in the direction of already detected gravitational wave events, which are in such a distance from us, that are expected to meet these gravitational wave events, in the relatively near future? Perhaps not a massive far away gravitational lensing phenomena, but a close micro one, though stable enough to enable observation of interference distortion pattern, when gravitational wave passes through it? For example, if i understood correctly, Alpha Centauri had micro lensing events observed in the near past. If a LIGO detected gravity wave is advancing currently in the Alpha Centauri direction, would that be considered an interference distortion pattern observation opportunity? For example, if such an hypothetical idea was true, then a gravity wave detected on September 2015, is about to pass through Alpha Centauri in about a year from now. Here is an article link with a nice visualization of LIGO detected gravity events location: https://phys.org/news/2017-06-gravitational-insight-black-holes.html

 

[Ibix]

Again, in principle we could see gravitational lensing but in practice we won't. The sources we can detect are extremely brief and pretty rare. Lensing would manifest itself as seeing the same signal twice, once round each side of the lens. But some of these signals have traveled billions of light years - a path difference of 0.01% means hundreds of thousands of years between repetitions. The event would have to be very nearly precisely on axis of a gravitational lens - and the odds are against it.

Our instrumentation is incredibly primitive compared to our EM sensors. In GW terms, the sky is black, with single pinprick flashes every few months. Imagine trying to do astronomy like that.

 

[roineust]

One more question of the same nature, but this time not relating to LIGO as much as i understand: Would the only current way to detect a merger of two neutron stars, be by gravitational waves and LIGO (and later LISA) or is it possible also to observe and predict neutron stars binary system merger solely by using EM waves telescopy? That is predict enough time in advance before they merge, when they are about to merge using only EM radiation observations? I am asking this, since if there are current EM astronomical ways to identify binary system candidates for merger in the near future, wouldn't it be possible to look for their merger event gravitational wave effects (such as interference), on a nearby (to them) gravitational lensing star?

 

[Ibix]

Again, in principle yes. For example Hulse and Taylor got the 1993 Nobel prize for measuring the orbital decay of a binary pulsar system and showing that it matched predictions of energy loss to gravitational radiation. But it was a ten-year observation project on a rather unusual system.

The odds are against it, in short. The decay could take millions of years (Hulse Taylor will merge in 300 million years), so the chances of spotting one in the right phase to be detectable soon are really small. I'm sure that if someone came up with a method of doing a fast sky survey to spot candidates it would get done, because it would enormously increase confidence in LIGO detections. Science is all about this kind of correlation between well understood phenomena and less well understood ones.

 

[roineust]

Furthermore, it seems that there is a certain rate at which detected gravitational waves go through earth, currently 1-2 per year and growing, with advances in instruments sensitivity? If so, isn't it possible to statistically estimate the number of strong gravitational waves, crossing a given location in the sky, without regard to detecting them directly? In certain locations, couldn't these events be theoretically estimated to be in the order of tens or even hundreds of strong gravitational wave events a year? Now, if we look for a location in the sky, which properties are, that it has both estimated hundreds of gravitational wave events a year, as well as having inside this location a black hole, which causes a stable and very sharp gravitational lensing, i understand that then, we should expect to find gravitational wave interference with the lensing properties of that black hole? If the answer to the above is as previous answers: theoretically yes; then, can anyone give me some clues, as to how would an astrophysicist approach modeling such a gravitational leaning gravitational wave interference? Just some very basic thoughts on how and about the process, in which scientists would be expected to approach modeling and detecting such a phenomenon?

 

[roineust]

Here is an article that seems to lay a theoretical framework for gravitational lensing interference by gravitational waves:
http://cds.cern.ch/record/615203/files/0305055.pdf

My questions are:
1. Is it true that this is what the article content is about?
2. What would be a good way to find out, if any observations have taken place, which try to confirm the articles' expectations of finding such interference?

Here is an article, that seems to confirm all the assumptions, relating to gravity waves being affected by gravity, but just seems not to relate to the possibility, of using gravitational lensing object observation interference phenomenon, as a possible sort of huge galactic scale interferometer-telescope, that can confirm by its observer EM telescopy constructive and deconstruction visual patterns of the object it is pointing at, the existence and properties of such interference and hence of the graviton particle.

Here it a link to the article: https://www.forbes.com/sites/starts...-themselves-affected-by-gravity/#276f1fbb2f3f

My question regarding this second link, is the same as question no.2, that follows the first link above:
What would be a good way to find out, if any actual observations have taken place, which try to confirm expectations of finding such gravity lensing interference phenomenon?

Here is a link to a presentation that seems to engage in what i was asking above, but instead of considering EM telescopy as the observer, it considers LIGO as the observer, why don't they consider EM telescopy as the observer? I presume it is because of inconsistencies between frequencies/diffraction parameter of EM telescopy and frequencies/diffraction parameter of gravity waves? But can anyone explain this to me in more simple terms? Here is the link: http://moriond.in2p3.fr/J03/transparencies/2_monday/1_morning/varvella2.pdf