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 wave on two masses connected by a spring

Consider two masses $m_1$ and $m_2$ that are connected by a spring. Mass 1 follows the worldline $x_1(\tau)$ while mass 2 follows $x_2(\tau)$. Note that the argument $\tau$ is the proper time in the ...
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The Force of Gravitational Waves

How could one calculate and derive the "force" or displacement and stretching of an object due to gravitational waves?
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Mass in GW in TT frame

In the book Gravitational waves vol 1 by Maggiore page 17 it is argued that the coordinate position of a test mass does not change in the TT-frame if the test particle was at rest. I understand the ...
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The “Force” of Gravitational Waves [duplicate]

Could someone show how to calculate and derive the force or "displacement" of a mass under a gravitational wave? Thanks.
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The M2 brane of M theory creates the Type IIA string and D2; the M5 brane creates the D4 and NS5. What are the other objects grouped with the D0?

Type IIA string theory is related to M theory with the 10th spatial dimension compactified on a circle.  The origin of the F1 string, D2 brane, D4 brane and NS5 branes is simple: they come from the M2 ...
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Are there any subtle differences in the gravitational waves emitted from NSNS, NSBH and BHBH of identical masses?

LIGO has detected several NSNS and NSBH merger events. However, it’s difficult to tell their identities directly unless the neutron stars are very light in an NSNS merger (such as GW170817) or the ...
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What’s the maximum amount of angular momentum a neutron star can carry?

For Kerr black holes, the spinning rates can be described by a normalized spin parameter $a=cJ/GM^2$, which takes any values between 0 and 1 regardless of the masses of the black holes. If we use the ...
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Gravitational wave physics and their nature [closed]

I have recently learned about and have derived gravitational waves from general relativity while watching a lecture. I have many questions. All the professor did was show the nature of the metric ...
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Why can't the speed of gravitational waves be greater than the speed of light if the universe can expand faster than the speed of light?

Since the expansion speed of the universe can be greater than the speed of light, why can't gravitational waves, which also uses space as the medium, travel faster than the speed of light?
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Questions re significance of 2016 and 2020 LIGO observations

Phys. Rev. Lett. 116, 061102 (2016) - "Observation of Gravitational Waves from a Binary Black Hole Merger" (https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102) reports that ...
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The velocity of gravitational waves or the velocity of the effect of gravity [duplicate]

If the sun disappears from the solar system, the earth will remain revolving for 8 minutes and will not be freed from the sun's gravity until after 8 minutes because the speed of the effect of gravity ...
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Bounds of a black hole's spin

What are the bounds of a black hole's spin? Is it -1 to +1? Also where do I find the information about spin1x, spin1y, and spin1z? What are their bounds? What are their i.e. spin1x, spin1y, and spin1z ...
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What would a theoretical non-rotational artificial gravity generator look like? [closed]

Assuming we invented a device that can create gravitational waves or bend spacetime (or through any non-motion related phenomenon) and produce artificial gravity, would it pull everything towards a ...
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Could we detect gravitational waves emitted outside particle horizon?

As we can see from a normal spacetime diagram like below, there's an overlap of the area within the event horizon and the area outside the particle horizon. Could we detect gravitational waves from ...
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1answer
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Why gravitational waves, which could be inferred as related to dark matter interactions, are not yet detected by LIGO/VIRGO instruments?

LIGO/VIRGO instruments are functioning already for quite a while and since then they captured already quite a few instances of gravitational waves which were inferred as products of interactions such ...
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Does the ringdown phase of a black hole merger ever stop?

When binary black holes merge they emit gravitational waves in three stages, the inspiral in which the two black holes shed angular momentum through gravitational waves at a rate that becomes ...
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Gravitational wave and 1st law of thermodynamics

Introduction: A prediction of the general relativity is that any moving mass produces fluctuation in the space-time fabric, commonly referred as Gravitational-Wave. This prediction was recently ...
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Asymptotic expansion of curvature tensors in asymptotically flat spacetimes

Let us consider one asymptotically flat spacetime and consider a neighborhood of ${\cal I}^+$ with Bondi coordinates $(u,r,x^A)$ in which the metric takes the form $$ds^2=-du^2-2dudr+r^2\gamma_{AB}dx^...
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Is there an exact constant value for the speed of light in a vacuum distorted by a gravitational wave?

In a vacuum, construct a cylinder of photons arranged as follows: A 'measuring apparatus' computes the speed of light as 299,792,458 m/s. However, suppose the vacuum is distorted by a gravitational ...
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Is all the trajectory of a photon, since its emission, always accompanied by a gravitational wave?

Whenever a photon is emitted, the atom/electron that emits it loses the mass equivalent to the energy $E$ of the photon. This loss of mass automatically determines a corresponding loss of gravity or ...
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What would the wavelength of the Cosmic Background Gravitational Wave radiation be?

Considering electromagnetic CMB can only see light as old as 380,000 years after the Big Bang, whilst theoretically those being gravitational should be formed from the beginning, what would their ...
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1answer
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Quadrupole formula in TT gauge

In weak gravity limit, we can derive the celebrated quadrupole formula in Lorenz gauge $\partial^{\mu} \bar{h}_{\mu \nu} = 0$: $$ \bar{h}_{ij} = \frac{2G}{r}\frac{d^2}{dt^2}I_{ij}(t_r) $$ To get $h^{...
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1answer
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How powerful must a gravitational wave be, to be audible to a human? [duplicate]

Sufficiently powerful gravitational waves can excite an eardrum and be heard. How powerful would the waves have to be for a human to actually hear them, and what would be the side-effects of that ...
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Resources on Post-Newtonian Approximations for GW Modeling

I want some resources to learn modelling gravitational waveform from binary black holes/neutron stars using a Post-Newtonian Approximation. I am familiar with Fortran and Mathematica, and have taken a ...
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How to show that the polarization tensor of the gravitational plane wave in vacuum is transverse

This is Ta-Pei Cheng's book p.254. I am trying to understand (13.28). The Lorentz gauge condition (13.18) is like below. How can I use the (13.18) condition to show (13.28)? I am trying to calculate ...
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When can information escape from a black hole through a warp bubble-like spacetime?

It is well known that nothing can escape a black hole, including gravitational radiation. Many questions have been asked here about this topic, such as: Can gravitational waves escape a black hole? ...
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Observation of Hawking radiation

Is it conceivable that Hawking radiation could be observed using e.g. gravitational waves or imprints in the CMB?
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Does gravity bend gravity?

Let's say that there is a large mass $M$ a light-year or so away from a black hole merger, which causes a very large gravitational wave to be produced. When the gravitational wave reaches $M$, does it ...
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1answer
159 views

How do gravitational waves agree with Lorentz invariance?

Following is a simple but incorrect explanation for gravitational waves. My question is what is wrong with it? I'd like to say that a gravitational wave is a periodic variation in the local ...
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Is there a Cosmic Gravitational Background Radiation (CGBR)?

The recent discovery by the LIGO made me wonder about this. We know that there exists a CMBR, Cosmic Microwave Background Radiation, a blanket of electromagnetic energy covering the universe, made by ...
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Graph Interpretation of Gravitational Waves

In the image is the data recorded by the LIGO's 2 observatories in USA. What is its interpretation? I mean what does the zig zag lines represent? Similarly, what does the blond red and blue lines (...
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Would the 2 orbiting black holes emit gravitational waves?

Would the 2 orbiting black holes emit gravitational waves even if they are moving at a constant speed in orbits? Here, can we consider the changing direction of black holes in their orbits as ...
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Could graviton exist in a single polarisation?

Penrose's twistor theory can only construct a left-handed graviton. This is seen as a problem. But... is there anything wrong with gravitons existing in only one polarisation? How would gravity differ ...
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General Relativity: Non-static stable solution of an infinite multi-body system

If you take Einsteins field equation with a homogenous (and isotropic) mass density, no pressure, no cosmological constant and a flat, non-expanding spacetime, the result is a collapsing space-time (...
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1answer
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About Oscillation in Gravitational wave [duplicate]

I am a high school student studying about gravitational waves. I hope they are similar to other waves like sound waves, etc. So I what to know exactly what oscillates in a gravitational wave. Like in ...
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1answer
72 views

Are gravitons produced in an atomic transition?

Atomic transitions produce photons. You can create beams of photons with a laser. In lasers rays of light are produced. Will rays of gravitons (or small directed gravitational waves) be produced also?
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Why do gravitational waves move at the speed of light? [duplicate]

They are not a form of electromagnetic radiation, are they? So, why do gravitational waves move at the speed of light?
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2answers
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Does a Photon take longer to reach me when travelling in the “trough” of a gravitational Wave?

I'm struggling for a while with this question and I'm not knowledgeable enough in SRT/GRT, so I'll ask here: Suppose some big cosmic event like a Black Hole Merger that generates significant ...
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Are gravitational waves produced only when a mass accelerates? [duplicate]

Why? They are not a form of EMR, are they. Or are the rapidly changing ones the only ones we can detect?
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How does LIGO detect accurate time differences if gravitational waves are also compressing and stretching the light waves-specific confusion below [duplicate]

I was watching this veritaserum which explains my question at 5:55 https://www.youtube.com/watch?v=iphcyNWFD10 saying that the speed of light is much faster so will pass through the arms multiple ...
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1answer
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When are gravitational waves (for the major part) absorbed?

This question made me think. It was asked why matter is transparent for gravitational waves. it was said (more or less) that because the waves interact with mass very weakly, mass makes them pass ...
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3answers
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Could the Michelson-Morley experiment have detected gravitational waves?

If everything went perfectly and they had no outside noise while conducting the experiment, could they have detected gravitational waves? What would it have looked like to them?
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Could LIGO detect an Alcubierre drive being used within 10 light-years of the Solar system? [closed]

Maybe this question is too speculative... But is it possible that LIGO would detect the ramp-up and ramp-down of an Alcubierre drive being used within 10 light-years of the Solar system? Also, if the ...
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1answer
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Derivation of Bondi metric

I was trying to understand the BMS formalism from the beginning. The whole formalism depends on the expression of the Bondi metric. I don't understand how this expression of the metric was derived. ...
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2answers
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Gravitational Waves + impedance

Why isn't there an Impedance with gravitational waves? http://www.scientificamerican.com/video/gravitational-waves-are-the-ringing-of-spacetime/
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1answer
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Why do interferometers only split a wave into two beams?

I was recently reading about interferometers and was wondering why it isn't common practice to split a wave into three orthogonal beams? I know very little about the topic, but I thought if you were ...
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1answer
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Projection on transverse traceless Gauge

I am reading this book about Gravitational waves. On page 10 and 11 Maggiore says that Given a plane wave solution $h_{\mu\nu}$ propagating in the direction $\hat{n}$, outside the sources, already in ...
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3answers
205 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 ...
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2answers
109 views

Frequency sensitivity of gravitational wave interferometer with its armlength and with mass of the mergers

To the best of my knowledge, LIGO is capable of observing gravitational waves (GW) from stellar mass black hole (BH) mergers but not mergers of supermassive black holes. In order to detect the latter ...
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Warp drive with gravitational waves in the nonlinear regime

gravitational waves are strictly transversal (in the linear regime at least), also their amplitudes are tiny even for cosmic scale events like supernovas or binary black holes (at least far away, ...

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