Questions tagged [gravitational-waves]

The tag has no usage guidance.

143 questions with no upvoted or accepted answers
Filter by
Sorted by
Tagged with
13
votes
1answer
329 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 = \...
9
votes
0answers
172 views

How much energy does the Earth absorb when a gravitational wave passes through it?

I understand that gravitational waves pass quite freely through massive bodies. Quoting http://www.ligo.org/science/GW-Potential.php: Gravitational waves will change astronomy because the universe ...
9
votes
2answers
646 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 ...
7
votes
0answers
450 views

Will a black hole cause scattering of a gravitational wave?

In my GR textbook, it states that gravitational waves can undergo interference but not scattering. I am just starting the chapter on linearised gravity concepts (weak field approximation) and my ...
7
votes
0answers
102 views

How do inflationary models predict the generation of gravitational waves during the inflationary period?

Recent results from the BICEP2 experiment have produced a lot of talk about the primordial gravitational waves produced during the inflationary period. I would like to have some explanation about how ...
5
votes
0answers
1k views

Energy-Momentum Tensor of a Gravitational Wave

In radiation gauge ($\gamma=0$), the Einstein field equation in vacuum for a perturbation $\gamma_{\mu\nu}:=g_{\mu\nu}-\eta_{\mu\nu}$ is given by $$ \boxed{ \partial^\alpha\partial_\alpha \gamma_{\mu\...
5
votes
1answer
175 views

Are there more unconfirmed GR predictions?

News says that we have finally observed "gravitational waves", one of GR's predictions. I've read about some other predictions of GR like how gravity affects the flow of time, gravitational lensing ...
5
votes
1answer
256 views

What effects could/can gravitational waves have on us?

Are gravitational waves something a human beeing could notice if it were powerful enough? Or would it be more like a higher dimensional force, since it would alter us in the sameway as our ...
4
votes
1answer
93 views

Gravitational waves energy source in linearized theory

By linearizing the metric in the following way (approach in most textbooks): $g_{\mu\nu}=\eta_{\mu\nu}+h_{\mu\nu}\text{ with } |h_{\mu\nu}|\ll 1$ and choosing the transverse-traceless gauge a wave ...
4
votes
0answers
128 views

Can one distinguish between near and far field for gravitational radiation?

For electromagnetic radiation one usually distinguishes between near and far field. The wave equation for the far field are based on Maxwell equations for the vacuum and predict that the radiated ...
4
votes
0answers
289 views

Degrees of freedom in General Relativity

A way one counts degrees of freedom(i.e. independent entries of the metric tensor ) in General Relativity is this: one goes to the linearized version, vacuum solution, and he sees that there are two ...
4
votes
0answers
309 views

Can gravitational waves produce “sonic boom”?

I've heard that a fast moving object such as a jet plane traveling much faster than speed of sound can produce shockwaves which is also known as sonic boom, also Cherenkov radiation is produce by ...
3
votes
0answers
64 views

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 ...
3
votes
1answer
65 views

Is there some Rindler-like horizon on this gravitational wave spacetime?

In the book Gravitation by Misner, Thorne & Wheeler (MTW), the authors present in section 35.9 "An Exact Plane-Wave Solution". The metric is $$ds^2=L^2(e^{2\beta}dx^2+e^{-2\beta}dy^2)-dudv,\quad ...
3
votes
0answers
72 views

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 ...
3
votes
0answers
59 views

What is the upper bound for the index of refraction of space?

It seems that gravitational waves and gamma waves travail at about the same speed, arriving within seconds of each other over distances in the ranges of $10^6$LY. Naively, I would assume this caps the ...
3
votes
1answer
138 views

How much uncertainty has the relic graviton background?

In the paper [1], it is mentioned that inflation predicts that a relic graviton background is about 0.9 K (cf. cosmic neutrino background, 1.945 K, and cosmic microwave background, 2.73 K). How much ...
3
votes
0answers
76 views

Neutron star merger: large scale dynamics

Yesterday was announced the first detection of a neutron star merger via gravitational and electromagnetic waves. On the announcement one of the speakers is showing a simulation of the dynamics of ...
3
votes
0answers
188 views

Does a binary system really emit gravitational waves?

In this essay from Petkov, it is stated on page 13 that when the stars follow their orbits in the binary system, they do not emit gravitational waves since they move by inertia according to general ...
3
votes
0answers
72 views

Interaction with Gravitational Radiation

I have a question about hypothetical gravitational radiation. To put it simply, is there any sort of material or field or other force which can interact with it? I'm thinking about lenses and mirrors ...
3
votes
0answers
87 views

Characteristics of wavepackets

I've been learning about wave packets and group velocities recently and had a question. Using simple trigonometric identies, we can show that the super position of two traveling waves with frequency-...
3
votes
2answers
86 views

Does shortening the path length of an excited etalon do work? What about LIGO?

Start with a high-Q etalon excited on-resonance with a laser for a time long enough that it has built up an essentially stable standing wave. There is a constant outwards-directed force on each mirror,...
3
votes
0answers
78 views

Can gravitational waves observed far from a black hole tell us anything about the multipole moments of a dynamical horizon?

In a paper by Ashtekar et al in 2013 on the approach to the final state to a stationary black hole they study the evolution of the multipole moments of dynamical horizons, which relax away (except for ...
3
votes
0answers
171 views

Non-locality of gravitational energy

Gravitational energy is non-local which is essentially because of the equivalence principle. The equivalence principle says that you can always transform your frame so that you feel like in a ...
3
votes
0answers
116 views

Maximum Power transmitted using General Relativity waves - cf Schwinger limit

In Electromagnetism, QED says that the linearity of Maxwell's equations comes to an end when field strengths approach the Schwinger limit. Its about 10^18 V/m. What is the corresponding formula for ...
3
votes
0answers
155 views

Computing linearized gravitational wave emission from point-like masses

I'm trying to compute the gravitational wavefront created from a set of moving masses. I'm trying to apply the equation $$ h_{jk} = \frac{2}{r} \frac{d^2 Q_{jk}}{dt^2}$$ Where $h$ is the linearized ...
3
votes
0answers
189 views

What does BICEP2's results tell us about gravitation waves and quantum gravity?

The BICEP2 results, unless I am mistaken, are a measurement of CMB polarization, i.e. photon polarization. That is, taken at face value they say nothing about gravity directly. Now, we can start to ...
2
votes
0answers
58 views

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 ...
2
votes
0answers
77 views

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 ...
2
votes
1answer
56 views

Does LIGO accounts for Sagnac effect?

After reading Sagnac effect one thing immediately come to my mind is LIGO, I only read that the team building LIGO have already considered the curvation of Earth surface but what about Earth's ...
2
votes
0answers
152 views

Gauge invariance of pseudo stress-energy tensor of gravitational waves

The pseudo stress-energy tensor of gravitational waves is given by $$T_{\mu\nu}^{(\mathrm{G}\mathrm{W})} = \frac{1}{32\pi}\left\langle \partial_{\mu} \bar{h}_{\alpha\beta} \partial_{\nu}\bar{h}^{\...
2
votes
0answers
38 views

Approximating a linearized gravitational wave expression

This is in the context of gauge fixing condition for obtaining linearized gravitational waves. $g_{ab}=\eta_{ab}+h_{ab}$ and $h_{ab}$ is the small perturbation that stands for the gravitational wave. ...
2
votes
2answers
62 views

Red-shifting due to emitting gravitational waves

Light waves exert their own gravitational pull and must be emitting gravitational waves, losing energy in the process. Does this mean that light becomes red-shifted as it travels even without the ...
2
votes
0answers
158 views

Effective stress-energy tensor for a gravitational wave, compared to static semi-Newtonian case

There is a calculation that I had been thinking for a long time of working out to my own satisfaction, both because of its intrinsic importance and because it seemed like it would be fun. This was to ...
2
votes
0answers
60 views

Why gravitational waves are not part of thermal phenomena?

Electromagnetic waves are part of thermal phenomena in the form of thermal radiations. But why gravitational waves do not show up as a thermal phenomenon, for example, why gravitational waves do not (...
2
votes
0answers
40 views

Redshift z=40 and gravitational waves

Why z=40 is the critical value of the redshift (more or less) to decide find out primordial gravitational waves around it? I have read that is related to the following issue: black hole mergers ...
2
votes
1answer
361 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 ...
2
votes
0answers
165 views

Can gravitational waves be absorbed near a quasar?

As the Quasar Wikipedia article explains, a quasar is powered by gas falling into a supermassive black hole at the center of a galaxy. The Luminous infrared galaxy article says that, in extreme cases, ...
2
votes
0answers
64 views

Inflationary model that predicts both gravitational waves and isocurvature perturbations

I 'm searching for inflationary models that predict both gravitational waves and isocurvature (isothermal) perturbations. If I understood well, de Sitter inflation predicts only curvature (adiabatic)...
2
votes
0answers
134 views

Help with the solution to the linearized wave equation known as Retarded Integral

I need some little help here I'm reading about gravitational waves and particularly about gravitational waves described by the linearized non-homogeneus Einstein's equations \begin{equation} \left( -...
2
votes
0answers
142 views

General Relativity and spin/helicity two massless particle

I usually read that GR can be thought of as the unique theory of a massless spin-2 particle (I think that this is the graviton). I know that GR is the unique theory that has: diffeomorphism ...
2
votes
0answers
189 views

Is there any primordial gravitational wave(form) that could explain dark energy?

First, I asked myself the question: Is there any gravitational waveform, however fantastical, that could explain dark energy. I suppose for a ubiquitous gravitational wave to be an explanation for ...
2
votes
1answer
170 views

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}\...
2
votes
0answers
125 views

Can Bose-Einstein Condensates reflect gravitational waves?

This is a question based on the paper by Raymond Chiao in 2002 where it is stated: One of the conceptual tensions between quantum mechanics (QM) and general relativity (GR) arises from the clash ...
2
votes
1answer
105 views

shouldn't a photon traversing the vacuum always be associated with a gravitational wave?

In perusing the linearized Einstein equation, it appears that even a classical electromagnetic plane wave would always have to be associated with a tensor perturbation to the background spacetime. ...
2
votes
0answers
62 views

Do gravitational vawes deplete energy even if there's nothing they can affect?

I've read multiple times that one of consequences of gravitational waves being a thing is, that they make any orbit unstable. As long as the two or bodies orbit around each other, they create ...
2
votes
1answer
84 views

light gravitational wave interaction

What happens when light photos and gravitation waves collide? Like can the photon "surf" on the gravitational wave and change direction, wavelength, velocity?
2
votes
0answers
215 views

LIGO detection statistic, SNR formula

According to B. P. Abbott paper published in Physical Review Letters, "Observation of Gravitational Waves from a Binary Black Hole Merger" http://journals.aps.org/prl/abstract/10.1103/PhysRevLett....
2
votes
0answers
88 views

Have gravitational waves any effect on the electromagnetic waves in interferometers?

I am not into general relativity, but the explanation of how an interferometric gravitational antenna works is generally pretty basic. In the recently published paper announcing the detection of ...
2
votes
0answers
145 views

Momentum transfer from gravitational wave

There has been some discussion here of the magnitude of the tidal distortion caused by a wave of the type reported on Feb. 11 2015, with the conclusion being that a tidal (distortion) effect ...