Questions tagged [gravitational-waves]

For questions about the propagation of waves carried by space-time, for instance as described by general relativity. Not to be confused with gravity waves, such as ocean surface waves.

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Gravitational Waves and Quantum Gravity [duplicate]

Since we can now directly observe gravitational wave signals, can any type of future experiment be set up that might manifest the quantum nature of gravity? For example, perhaps a version of LIGO ...
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Can gravitational waves be refracted or reflected?

Graviatational waves are influenced by gravitational lensing. But are there other ways to influence gravitational waves? Could we build reflectors or refracting systems to concentrate gravitational ...
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Linearized theory and gravitational waves

I've been reading the chapter about gravitational radiation of Schutz's book. In one of the sections, he begins with the linearized Einstein's equations and tries to find an intuitive solution: $$(-\...
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Smooth vs analytic spacetimes

Recently in more technical settings (I was learning algebraic QFT), I encountered the term "real analytic" manifolds (Lorentzian manifolds, to be precise). This is in contrast to smooth ...
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Can point masses following geodesics and orbiting one another emit gravitational radiation?

I am a bit confused about this situation: according to general relativity, when two masses orbit one another, they emit graviational waves, which carry away certain energy. For example, check out ...
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How can a pulsar slow down?

I saw in some astronomy textbooks that pulsars gradually slow down due to the loss of energy by its radiation. I wonder why this is possible? Although the radiation is now not thermal but in the form ...
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How to convert from polarization modes ($h_{+}$, $h_{×}$) to obtain spin-weighted spherical harmonic $h_{lm}$ as a function of $h_{+}$, $h_{×}$?

This question arises from a discussion in the thread How to convert from plus and cross polarization modes ($h_{+}$, $h_{×}$) to spin-weighted spherical harmonic $h_{lm}$? I was looking for a ...
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How to convert from plus and cross polarization modes ($h_{+}$, $h_{×}$) to spin-weighted spherical harmonic $h_{lm}$?

I was wondering if there is a method to express the $h_{+}$ & $h_{×}$ polarization modes to spin-weighted spherical harmonic $h_{lm}$. I ask this in the context of gravitational waves. We see that ...
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Is it possible to distinguish the intensity and the frequency of the graviton?

The wave equation of the graviton was assumed to be similar to that of the EM waves, which a "frequency" parameter could be identified by comparison. However, in EM, there was intensity as ...
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Angular momentum of gravitational wave

I am thinking about what is spin and angular momentum of gravitational beams. I came up with the answer that spin is intrinsic to a wave and is related to its source. But I can not start thinking of ...
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What are the differential equations that model a self-propagating gravitational wave in space-time?

Light is a self-propagating wave, but it's very complicated. Imagine, if you will, a wave in space-time that by assumption was self-propagating like light, except that it was a gravitational wave. ...
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Gravitational wave radiation power from dimensional analysis

Let us try to find a formula for the power emitted through gravitational waves (GW) from a binary system in quasi circular orbit. The relevant quantities are the Newton's constant $G_N$, speed of ...
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Single gravitational plane wave or their interference can carry spin angular momentum?

I would be grateful if anybody could tell me if I had one gravitational wave in the form of a plane wave, it still would carry spin angular momentum? We know that gravitational waves are mostly the ...
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Why Weyl scalar $\psi_{4}$ has a spin weight -2?

In the Newmann-Penrose formalism , Weyl scalar $\psi_{4}$ is given by $\psi_{4} = C_{a b c d} n^{a} \bar m^{b} n^{c} \bar m^{d}$, where $C_{a b c d}$ are weyl tensor components and $n^{a}$, $\bar m^{...
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Distance to source of GW 150914

Looking at the original paper on this gravitational wave, PRL 116, 06112 (2016), it is difficult to determine how they estimated the distance to the source. Can anyone provide some explanation? They ...
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Excluding the case of a neutron star-black hole merger with gravitational wave GW 150914

The paper from LIGO's original gravitational wave detection (PRL 116, 061102 (2016)) defines the chirp mass as $$M=\frac{(m_1 m_2)^{3/5}}{(m_1+m_2)^{1/5}}=\frac{c^3}{G}\left[\frac{5}{96}\pi^{-8/3}f^{-...
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Gravitational wave propagating in $x$-$y$ plane with angle $\theta$ with $x$-axis

I am going to ask a question related to a paper called "Spin angular momentum of gravitational wave interference" which its link is: https://doi.org/10.1088/1367-2630/abf23f. My question is ...
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Gravitational Waves - Are all detectors finding the same gravitational waves?

I read that there have been approximately 90 recorded cases of gravitational waves. Have the 4 different gravitational wave detectors agreed on specific individual recordings or have all 90 cases been ...
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Virtual Graviton Polarisations

Is it true that in canonically quantised gravity "non-traceless" and "non-transverse" gravitons are allowed to exist as virtual particles, whereas any graviton that corresponds to ...
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Gravitational waves manifestation of 'physical' spacetime?

When a stone is thrown in water, water waves are created. The stone imparts its kinetic energy to water. Likewise a sound speaker imparts its kinetic energy to air molecules. When an electron falls ...
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Could gravitational waves be cosmologicaly 'redshifted'? [duplicate]

Is it posible that gravitational waves detected here on Earth could be cosmologicaly 'redshifted'? So, at emission they had higher frequency then after reaching Earth?
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Considering General Relativity, how long would it take for a ball to stop oscillating dropped through the center of the Earth?

In Newtonian view, if a relatively small mass was dropped through a frictionless tunnel without drag intersecting the center of a non-rotating, spherically symmetric,uniform density Earth, then the ...
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27 votes
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Where does the kinetic energy of the orbiting black holes go after the merger?

The first gravitational wave ever observed, GW150914, was calculated to be caused by a merger of two black holes of 36 and 29 solar masses. The resulting black hole had a mass of 62 solar masses, and ...
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LIGO et al: Is it possible to estimate the frequency of GW+EM detections?

In the past few years LIGO and VIRGO have detected a multitude of gravitational events. As far as I know however only GW170817 had a verifiable EM counterpart. Shouldn't it be possible, based on ...
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Propagation of gravitational waves

The mechanical waves requires medium to travel . The electromagnetic waves can travel without matter medium with the help of fields . But how do other types of waves , that don't come in either ...
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If gravity can catch up a light photon (speed=$c$) and change its wavelength is it faster than light?

Why can gravity catch up a light photon (speed=$c$) and change its wavelength? How can that be logic although nature shows somehow it is... Maybe gravity has different speed than gravitational waves ...
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What are Brinkmann coordinates?

I am studying gravitational waves and I find it hard to understand Brinkmann coordinates. All I can say is that they are such, that the GW metric takes a certain form in $(u,v,x,y)$: $$\mathrm{d}s^2 = ...
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How do Gravitons work? as compared to photons

Photons are to Electrons as Gravitons are to ... what? What is it that 'emits' a graviton? And what 'absorbs' it? I've been looking for a good layman's description of how gravitons interact with ... ...
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Gravitational waves of objects with the same angular momentum

So I read that gravitational waves are produced when the quadrupole moment of a system is not symmetric. What does it actually mean for the quadrupole moment to be asymmetric? If there are two black ...
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Does a core collapse supernova emit detectable gravitational waves?

I've read that LIGO will be the first thing to detect a "nearby" core collapse supernova, because the neutrino pulse travels slower than light, and the light is trapped inside the star for ...
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How do gravitons escape each other's gravity to spread out and form a field?

The hypothetical graviton I'm familiar with is a spin-2 particle. That implies it has angular momentum, which further implies it has energy. If energy attracts energy, what prevents gravitons from ...
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2 votes
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Faster-than-light gravitational waves and faster-than-light expansion in the inflation

I have no introduction to the inflationary epoch. I know, however, that during this time space-time expanded with a speed faster than the speed of light. If gravitational waves are perturbations of ...
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How likely is it that a typical pair of black holes will eventually merge?

Gravitational wave observatories have found many pairs of black holes merging. I understand that before they were working there were estimates of the rate at which they ought to be found. To me it ...
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How can we extrapolate gravitational waves in the early universe from CMBR?

I know it has to do with polarization of CMBR, but not sure how gravitational wave polarized early light.
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Is it possible to produce circularly polarized gravitational wave and how to determine if it is CW or CCW?

I saw the GIFs showing both "plus" and "cross" linearly polarized gravitational wave using ring of dots, how about circularly polarized gravitational wave, if so how are they ...
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Is it possible to block a gravitational wave?

As John Micheal Godier states in this video: SETI and Alien Quantum Communications. Alien civilizations might use different methods of communication beyond radio for several reasons. J.M.G uses ...
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Rotating binaries viewing geometry

I am reading this article and looking at eq. (4). I am not sure how the expressions in terms of the viewing angle $\iota$ and the phase $\Phi$ are achieved. It looks to me like it has nothing to do ...
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Why isn't the two-body problem in General Relativity completely solvable?

I do know that approximate solutions to the two-body problem come in the form of the equations of motion in the Schwarzschild metric plus post-Newtonian power radiated. However, I am more interested ...
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Do gravitational waves always travel at the speed of light? [duplicate]

So, electromagnetic waves travel below $c$ if they're not traveling through the vacuum. Do we know (or have a theory of) whether gravitational waves always travel at exactly $c$ or is there something ...
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Can a gravitational wave excite an atom and make it produce a photon?

A gravitational wave contains energy. That means it creates its own gravity field. But after the wave has passed, spacetime will be again as it was before. How is the energy of the wave given to the ...
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Why gravitational wave stretches in one direction and at the same time it is squashed in another direction at right angle?

Does it means the amount of the stretching must be equal to the squashing due to some conservation laws or because the math in GR dictates? Ligo mirrors are obviously placed deliberately so as they ...
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Frequency dependence of noise at advLIGO

Here's a picture showing how different sources of noise affect the sensitivity of LIGO I'm trying to understand the frequency dependence of each curve. I'll specifically focus on seismic noise, ...
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Detection of gravitons in gravitatonal wave detectors: what is the expected value of the squeezing parameter for astrophysical sources?

The recent progress regarding the detectability of gravitons is quite interesting, and has been theoretically controversial. A series of papers involving F. Wilczek (the full-glory paper is titled ...
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3 votes
1 answer
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Mathematically, what is a graviton?

There are numerous questions on this site asking what a graviton is, but almost all the answers are superficial. I am hoping for a more formal answer. All I know in the here and now, is that it has ...
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Discrepancy between the two different equations of the momentum operator

i am doing a thesis on the quantization of a real scalar field in a gravitational wave background. I am doing this in lightcone coordinates, so $u$ is $z-t$. I start with an action and define a ...
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Is decrease in gravitational entropy made up for by gravitational waves?

If we look at objects in the universe, they form orderly structures like spheres, planetary systems, galactic spirals, etc. Is this decrease in entropy balanced by a decrease due to gravitational ...
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Is there any possible scenario where a human could directly sense gravitational waves (preferably without being destroyed)? [duplicate]

Merging black holes radiate enormous amounts of energy - several solar masses worth! Unlike most astrophysical happenings, this happens on very human timescales. Most of the energy is released in the ...
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Dissipation caused by Gravitational Wave Emission

Two massive bodies orbiting each other can lose energy through gravitational wave emission until colliding. Can a single massive body, moving with constant velocity with respect to an observer, lose ...
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Contraction in SR vs GR

I've always had a bit of fuzziness concerning relativistic contraction which I will try to put into words. Iiuc in SR, moving objects contract in the direction of their travel, as measured by rulers ...
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8 votes
3 answers
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Gravitational waves on rigid bodies

I have a question on gravitational wave (GW) detection. I would assume that gravitational waves do not impact rigid bodies. I mean, GWs should be extremely weak with respect to electromagnetic forces ...
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