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Questions tagged [gravitational-waves]

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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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How is the approximate gravitational wave stress energy momentum tensor not 0?

In Section 35.7 of Misner, Thorne, and Wheeler, p. 955, an "effective" stress energy momentum tensor for gravitational waves is defined: $$T^{\text{GW}}_{\mu \nu} = \frac{1}{32 \pi} \left< \bar{h}...
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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 ...
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1answer
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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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1answer
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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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1answer
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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 ...
0
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1answer
38 views

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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2answers
332 views

Gravitons with negative mass?

I have been reading several papers on massive gravity. All of them have equations that involve the square of the graviton mass, rather than graviton mass itself. See for example, equations 43 and 44 ...
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Signal parameter estimation in PyCBC

I have a gravitational wave signal (strain vs. time). And I want to find out the corresponding parameters of the compact binary. But I do not know how to create injection for this signal in PyCBC. ...
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Converting from trace reversed to standard metric perturbation

In linearised gravity, when dealing with gravitational waves it is common to consider just the spatial part of the trace-reversed metric perturbation $\bar{h}_{ij}$. I know that in general the trace-...
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1answer
209 views

Turbulence in gravitational waves

I want to understand physical meaning and possible implications of few terms often used in physics specially with regards to gravitational waves / space-time fabric Space-time fabric is disturbed by ...
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2answers
66 views

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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2answers
68 views

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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1answer
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Why do numerical relativity papers show $\ddot{h}_\times$ instead of $h_\times$ for gravitational waves amplitude?

I am very confused about why numerical relativity papers, when talking about gravitational wave extraction, usually plot the real part of the fourth Weyl scalar, $\Psi_4$, instead of its double ...
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2answers
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Where do gravitational waves draw the energy from?

Imagine binary neutron stars inspiral, they generate gravitational wave which carries energy away and causing the pair to become ever closer. Since all wave must carry energy I wonder where do ...
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1answer
143 views

Bondi news in BMS supertranslation

What does "news" mean in "Bondi news"? Is it information? What about memory in gravitational memory, is it information as well?
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5answers
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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 ...
3
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1answer
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Why do two masses orbiting around their CM emit gravitational radiation?

Two (extended, non-point-like) masses orbiting around their CM are emitting gravitational waves. However, these masses are both in free fall and follow a geodesic path through space-time. Now ...
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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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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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1answer
40 views

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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1answer
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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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1answer
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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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0answers
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For a given chirp mass, how to decide between different binary systems?

Suppose we observe a gravitational wave with chirp mass $M$. How to decide between the different possibilities of BH mergers, NS-BH, WD-NS, WD-NS mergers? Can it be done with ONLY gravitational wave ...
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2answers
637 views

The ADM energy of gravitational waves?

I have been looking for books about this question for several days. However, almost all books use Landau–Lifshitz pseudotensor to calculate the energy of gravitational waves. And they said the result ...
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1answer
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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 ...
2
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1answer
334 views

Do gravitational waves carry energy?

We now know that gravitational waves are real. Do they carry energy? I mean thy are waves and every wave carries energy. If they carry energy, how do they do it? Is there any equation to describe ...
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5answers
114 views

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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1answer
321 views

Lowest 'Order' of Radiation

I've noticed an interesting phenomenon (admittedly from only two data points). In electromagnetism, $A^\mu$ obeys Maxwell's equations: $$ \square A^{\mu} = j^\mu . $$ where I've chosen $\mu_0 = \...
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2answers
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LIGO flawed by the identical expansion of laser wavelength and arms in presence of a gravitational wave?

LIGO, Laser Interferometer Gravitational-Wave Observatory, is a large-scale physics experiment aiming to directly detect gravitational waves. The device measures the phase shift laser beams. If I ...
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5answers
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Can gravitational wave create anti-gravity, i.e. repulsive gravity?

A very layman question as in title. Like every wave having a negative side, can a gravitational wave have anti-gravity. To put it in different words, a gravitational wave passing through a complete ...
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1answer
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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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1answer
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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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1answer
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How do gravitational waves transfer momentum?

In Electromagnetism I understand it in terms of the Lorentz force: the E-component of the field causes the charge to respond infinitesimally with a $\vec{v}$ in the E-direction such that the $\vec{v}\...
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1answer
75 views

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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2answers
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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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0answers
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Radiation Pressure Noise in Gravitational Wave Detection

I am trying to work out where equation 9 comes from in Martynov et al. (2016), who discuss the radiation pressure noise in the LIGO detector. $$L(f) = \frac{2}{cM\pi^2 f^2} \left(h \nu G_{-} P_{\rm ...
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1answer
39 views

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 ...
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0answers
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When space expands where do the energy of the gravitational wave dissipate to? [duplicate]

I think it is safe to say that gravitational wave do not dissipate unless it met matter along the way imparting some of it's energy to cause some distortion or when it's frequency is stretched even ...
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1answer
40 views

How can the big bang be “observed”?

The Big Bang Observer is a proposed spacecraft to study gravitational waves. Especially the one that are thought to originate from the Big Bang. Question. How can we observe waves that has an origin ...
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2answers
56 views

Why gravitational wave stretches on $x$-axis would necessarily compress on the $y$-axis?

I read gravitational wave is a traverse wave, usually produced by inspiraling neutron stars or black holes, and laser interferometer such as LIGO is commonly used to detect them, since the setup of ...
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2answers
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Are GWs made of gravitons (are gravitons the quanta of GWs) or not?

I have read this question: What is the difference between gravitons and gravitational waves? I have read this on wikipedia: However, if gravitons are the quanta of gravitational waves, then ...
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2answers
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Are gravitational waves longitudinal or transverse?

Waves are generally classified as either transverse or longitudinal depending on the they way the propagated quantity is oriented with respect to the direction of propagation. Then what is a ...
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0answers
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Polarization states of a massive graviton

How could I reconcile the fact that there are 6 polarization states for a gravitational wave (3 transverse and 3 with longitudinal components) with the fact that the spin-2 graviton should allow a ...
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2answers
78 views

Non-test-particle dynamics from inside a black hole horizon

It seems to me that most arguments in favor of impossibility of communication from beyond black hole horizon region are based on "test-particle" scenario, where the falling object is (very) light with ...
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0answers
31 views

Multi-Frequency gravitational wave sources

A star can emit light with different frequency at a time. Is it possible for a gravitational wave source to emit gravitational waves of more than one frequency at a time?
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Visual simulation of gravitational lensing

Is there a way to generate an accurate visual computer simulation of gravitational lensing?
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If I were to shake a black hole, does it grow bigger?

Imagine I were to shake a black hole rigorously, does it grow bigger? I think it will simply radiate all the kinetic energy gained from the shaking as gravitational wave right? In the normal case, if ...