# Questions tagged [gravitational-waves]

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### How to get this metric tensor perturbation equation? (Gravitational wave）

(I need some time to come back to re-edit this post) LHS of equation 7.37 is gauge invariant The Twisted H symbol is comoving hubble parameter, the h_ij is metric perturbation, I do not know how to ...
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### Teukolsky (Bardeen-Press) equation ingoing coordinates

EDIT: I can't seem to delete this question, so I've posted the solution below (I must have made an algebra error-someone checking all this would still be appreciated!). I've left the question as is. ...
71 views

### Should LIGO have been impacted by Lorentz contraction?

What bearing would or could Lorentz-Fitzgerald length contraction have on Ligo detections? Was this accounted for?
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### Polarization of gravitational waves VS polarization of photons

This might be a stupid question, but I think i am mixing important concepts. It is well-known that gravitational waves (GWs) come in two polarizations or two states of helicity: the so called "+" and ...
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### How come this is a gravitational plane wave?

In Wikipedia's Gravitational plane wave article a metric for a gravitational plane wave is given by \begin{equation} ds^{2}=\left[a\left(u\right)\left(x^{2}-y^{2}\right)+2b\left(u\right)xy\right]du^{2}...
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### Can photon Create gravitational wave when it travel through Space-time? [duplicate]

When big Explosion occurs in space it create gravitational wave. but it is possible that when photon (a packet of energy) make displacement in space-time it also create gravitational wave after all it'...
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### Does the photon decay due to loss of energy in a gravitational shock wave that it creates? [duplicate]

If photon has energy, it has gravity. If photon has gravity and move through space at light speed, it creates gravitational shock wave (like sonic boom because gravity move at the same speed as ...
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### Can dark matter actually be gravitational radiation?

It seems to exist like only space distortion, and it seems to move just like radiation (specially when galaxy clusters collide, dark matter goes trough unaffected just like some type of radiation). ...
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### Does frequency of light change in the LIGO interferometer arms?

There are a number of questions on the internet and on this site asking about how the LIGO interferometer measurement works given that the gravitation wave stretches both the length of the ...
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### Detectability of gravitational waves emitted by a free-falling object, by different observers

Does an object falling radially in a gravitational field of a planet emit gravitational waves as seen by an observer on the surface of the planet? What about an observer falling along with the object?...
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### If gravity is a wave, what medium does it pass through? Is there a medium that it can not pass through?

I listened to a podcast discussing gravity and had this question. My apologies if it has been aptly answered somewhere else.
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### What's the shortest “safe” distance from a neutron star merger?

Take GW170817 for example, the first neutron star collision picked up by LIGO. Given how much data we got from that event, can anyone figure out what the "blast radius" is, and how far away from the ...
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### Why does everyone seem to assume that gravitational waves will always be very small? [duplicate]

The size or effective distortion field of a gravitational-wave perturbation at any given location in space-time is determined by the distance separating the source and that location. This describes a ...
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### Gravitons from linearized gravity

Linearizing gravity as follows: $$g_{\mu\nu}=\eta_{\mu\nu}+h_{\mu\nu}$$ Up to this point, everything is a 4x4 matrice. How does one eventually recover a spin-2 particle which, according to https:/...
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### Newtonian Gravitational Waves

I was thinking about the classical equations for gravity. I got stuck on two equations: $$\vec{\nabla}.\vec{g}= 0$$ and $$\vec{\nabla} \times \vec{g}= 0$$ The first equation is Gauss law of ...
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### Can gravitational waves be visualized in the elastic rubber sheet model of gravity?

To visualize the space curvature related to gravity, there is a model or analogy using an elastic sheet and a weight. A rubber sheet is spanned like a very soft trampoline, and a heavy ball on it ...
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### Why gravitational waves can only be generated by a time-varying quadrupole moment of the mass distribution?

The (rather old) source I dispose of "Sexl, Urbantke : Gravitation and Cosmology" describes the radiation of gravitational waves only rather sketchy. So why gravitational waves are only generated by ...
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### Can GWs move objects (excerpt pressure on matter) like EM waves?

Gravitational waves are real, they have been observed. Gravitational waves are disturbances in the curvature of spacetime, generated by accelerated masses, that propagate as waves outward from ...
130 views

### Can gravitational waves be used to investigate the inside of black holes?

I do understand that nothing, no particles and no information can escape a BH. Gravitational waves are real, they have been observed. Gravitational waves are disturbances in the curvature of ...
168 views

### Do gravitational waves disperse/refract (like EM waves in a prism)?

I have read this question: What is the relationship between a gravitational wave and a graviton? where kingledion says: Gravitational waves were theorized a century ago and recently ...
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### Confused about the gauge transformation of the amplitude tensor for gravitational waves

Far away from the field sources, where the energy-momentum tensor $$T_{mn}=0 \tag{m,n=0,1,2,3}$$ The linearized EFE becomes $$\Box \bar h_{mn}=0 \tag{1}$$ where $\bar h_{mn}$ is the trace-reverse ...
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### What really is GW quanta?

I have read this question: What is the difference between gravitons and gravitational waves? where annav says: So photons are the building blocks of light, and gravitons are (hopefully) the ...
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### Tianqin project vs LISA

How does Tianqin space-based gravitational wave detector compare to LISA? Will it be able to detect gravitational waves from e.g. inflation (considering possible upgrades)?
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### Gravitons (real) passing through a black hole

This is not a duplicate. I do not ask about the gravitational field of the black hole, or why it extends farther out then the event horizon. I do understand that the gravitational field is described ...
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### Superposition of gravitational waves and the dark energy

Is it theoretically possible to create a superposition of gravitational waves that form a locally static negative curvature, something like the dark energy?
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### What happens in theory if we focus gravitational waves into a point?

https://www.youtube.com/watch?v=iWKFPTgkpXo Basically inspired by this video and its comparison with wormholes. While many other questions on the site have already covered the weak strength of ...
106 views

### Could a scientist use the internet to detect gravitational waves?

According to my understanding (I'm not a physicist just a fan), LIGO measures the changes in two path's lengths to detect gravitational waves by sending a particle down each path at the constant speed ...
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### Theoretical solution to binary black hole merger based on Hawking and Ellis

Following Hawking and Ellis, Chapter 9, Fig. 60, Pg. 322, the following figure is meant to illustrate the contrast between apparent horizons and event horizons in the case of a binary black hole ...
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### LIGO test masses in free fall

I know that the LIGO test masses are considered to be in free fall. However, they are supported by pendula. I thought that free fall means the only acting force is gravity - doesn't the tension in the ...
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### Can a system be engineered to cause a standing wave resonance with gravitational waves

Can a system be engineered to cause a standing wave resonance with gravitational waves? It appears that gravity waves can be reflected. Do Mirrors for Gravitational Waves Exist? Stephen J. Minter, ...
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### How Does LIGO’s Splitter Mirror Cause Two Different Frequencies When a GW is Present?

When a gravitational wave is present in LIGO, how does the splitter mirror work to send out a different frequency than the laser frequency on the arm perpendicular to the laser direction? What are ...
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### Is the gravitational waves velocity also $c$, regardless the adopted inertial frame, and the source movement conditions? [duplicate]

The second postulate of STR was made exclusively for light (electromagnetic waves)? If gravitational waves also travel at velocity $c$, then are they obliged to fulfill this second postulate? Any ...
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### Gravitational $N$-body mergers?

Beyond binary systems and its mergers, have numerical relativity groups computed an approximation to $N$-body GW signals/waveforms or is that a hard unsolved task?
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### Why aren't gravitons spin 1?

Expressing the metric as $g_{\mu \nu} = \eta_{\mu \nu} + h_{\mu \nu}$, assuming $h_{mu \nu} \ll 1$ we can write the Einstein Hilbert action to leading order in $h_{\mu \nu}$ and quantize the ...
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### Is a body in passing gravitational wave still in free fall?

I have a simple apparatus: a box and inside it a test particle (small bullet). If the device is in inertial motion or affected only but (static) gravitational field of another massive body (in free ...
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### Could the persistent effects of gravitational waves solve the black hole information paradox?

I am not bothered that much by the fact that two observers describe the same phenomenon differently. Something similar , in principle ,  happens with simultaneity in special relativity,  and special ...
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### Could two atomic clocks really be used to detect gravitational waves from a distant source? If so, how?

Three articles report on the recent paper in Phys Rev. D: Flanagan, Éanna É. et al. 2019 Persistent gravitational wave observables: General framework (also ArXiv): Phys.org: Gravitational waves leave ...
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### Could gravitational waves be the cause of inflation? [closed]

Ok, crazy idea time. Context: https://www.livescience.com/65441-gravitational-wave-memory.html Quick lay summary: Apparently gravitational waves alter the structure of the space they pass through. ...
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### How to convert from a tensor GW perturbation to a scalar one?

Typically the gravitational wave (GW) strain is calculated (e.g. by the Quadrupole formula) as some tensor object $h^{ij} (t)$. However, I often read of the strain as some scalar time series, i.e. \$h(...
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### What does it mean to hear the gravitational waves?

In last few years, I watched a lot of YouTube videos claiming that gravitational waves can be and has been heard. They also play a short audio signal. How do experiments such as LIGO replicate the ...
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### How do LIGO and Virgo know that a gravitational wave has its origin in a neutron star or a black hole?

It is being said that gravitational-wave detectors are now able to distinguish neutron star waves from those originating from black holes. Two Questions: How do LIGO and Virgo know that a ...
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### In general relativity, is there a difference between matter-energy and spacetime?

This is the third time I try to formulate a question in a proper format so as to understand what is going on with gravitational waves at a physical level. I am told that a spacetime oscillation and/...
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### From a gravitational wave detector perspective, what is the difference between a gravitational wave and a phonon?

I already asked a question but it seemed that it was not precise enough. My problem is that I cannot see how gravitational waves have anything to do with spacetime. An EM wave or a phonon can put ...
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### Does charging and discharging a capacitor create very small gravitational waves?

If I understand it correctly, curvature in a region of spacetime is due to concentration of energy and momentum in that region. If I further understand things (I don't) a gravitational wave is a ...
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### Direct observation of Gravitational Waves via increased resolution

First, congrats to the event horizon team for the first photograph of a black hole. Not to downplay the significance of the photo, but it is a bit blurry. Still, it got me thinking. One might expect ...
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### Is it possible to use the principle of EHT to build a virtual gravitational wave detector to detect very long wavelength gravitational waves?

The press conference of the EHT is fascinating. While there are some features such as the asymmetry in the ring that is to be followed up by the team, I was actually wondering, whether it is possible ...
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### How much more precise would LIGO have to be?

The planets and a spinning black hole both drag their local frames and thus generate gravitational waves The amplitude should be proportional to the size of the celestial body, while the frequency of ...
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### Can expanding space stretch the wavelength of GWs? [duplicate]

I have read this question: Redshifting of Light and the expansion of the universe Now analogously, we could talk about GWs traveling in the empty voids of space, where the expansion of space is ...