Questions tagged [gravitational-waves]

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Do dipolar gravitational waves exist?

There seems to be some controversy (see A, B) on this topic, so I'm posting a new question for discussion and clarification. By definition, one cannot accelerate the center of mass of a closed system (...
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1answer
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Gravitational radiation from a perturbed metric other than Minkowski

When deriving the strain (either dimensionless or its polarization components...), it is standard to assume the background metric is the (flat) Minkowski metric, i.e. $$ g_{\mu\nu} = \eta_{\mu\nu} + \...
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Gravitational wave energy transport

When a gravitational wave passes through a region of space (which may be, or may not be, empty), does it deposit energy (in any form) in that region of space? A frivolous version of this question ...
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Can two magnetars collide?

Kilonova occurs when neutron stars inspiral and smash into each other releasing gigantic gravitational waves and materials, what about when their subsets were to collide? Would the powerful magnetic ...
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1answer
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Can the gravitational wave of an electron be theoretically calculated to determine its gravitational field strength?

If an electron was vibrated back and forth via oscillating electromagnetic fields, it would presumably produce a small gravitational wave. Can the gravity wave be theoretically calculated to determine ...
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Sources of quadrupole radiation from black hole

During ringdown from BH merger, the event horizon is (obviously) very far from equilibrium. This is a statement about mass distribution in spacetime. Suppose I fly a rocket across the event horizon (...
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1answer
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The detection of gravitational waves and the assumption that gravity travels at the speed of light

I read from this wikipedia article that we have obtained some empirical evidence that gives us an upper bound on the difference between the speed of light and the speed of gravitational waves. What I ...
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1answer
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Gravitational analogue for Cosmic Microwave Background?

Penzias and Wilson famously discovered the CMB as a signal that they failed to be able to account for after removing all other known radio-sources. It's apparently close to the same strength in all ...
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2answers
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Do gravitational waves travel always in a straight line (along a geodesic) like EM waves?

There are a lot of questions and answers on this site about light traveling in straight lines in vacuum (following a geodesic). And there are a lot about both EM and gravitational waves traveling at ...
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Are there black body-like thermal emissions of gravitational waves?

According to the answer to this previous question: Yes, all of the fields in quantum electrodynamics are excited in blackbody radiation, not just the electromagnetic field. But, (as I understand) ...
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3answers
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Gravitational Wave detection [closed]

Does the detection of Gravitational Waves provide any significant headway into concretely answering as to what exactly is causing the arms of the interferometer to move or even why should they move at ...
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7answers
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Is spacetime real? [closed]

The answer by John Rennie here mentions that : ...spacetime is not a thing - it is a mathematical construction. There have been studies which have detected gravitational waves from black holes which ...
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4answers
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Why can't dark matter lose energy by gravitational waves and collapse into itself?

Because of lack of electromagnetic induction, dark matter can't lose its gravitational potential energy. That is preventing it from collapsing like an ordinary matter cloud in space. But why can't ...
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1answer
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Is it true that speed of gravity was confirmed in 2017?

I was reading a Wikipedia article on speed of gravity, https://en.wikipedia.org/wiki/Speed_of_gravity . The following quote is taken from the mentioned article. In the relativistic sense, the "...
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Gravity: Wave/Particle Duality of the Graviton

It just occurred to me that the graviton is still a hypothetical quantum of gravity yet gravitational waves are proven and measurable. Should we not expect that gravity follows the same wave/particle ...
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1answer
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Green's functions for linearised gravitational waves?

Green's functions are ubiquitous in physics, or any situation where one would like to solve some set of partial differential equations with boundary conditions. It is therefore not so surprising that ...
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1answer
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Quantum Field Theory, questions about fields and their vacuum state [closed]

Are the fields in their empty state a single indivisible and static entity? I would also like to know if the gravitational field also has a vacuum state and if the other fields are permanently linked ...
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1answer
51 views

3rd Dimension on LIGO

The LIGO interferometers are 2 dimensional, they have $4\rm\ km$ legs that are perpendicular to each other. Could a 3rd $4\rm\ km$ leg either with a straight up tower or deep into the earth, provide ...
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1answer
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Do black holes resonate?

Merging black holes undergo a phenomenon called "ring-down" after the merger. If a black hole were to be perturbed by a hypothetical gravitational wave, would it exhibit a resonance type ...
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0answers
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Gravitational wave due to photon?

Does photons create gravitational waves as they travel through space? I know that when matter particle moves, they create gravitational waves but does that same thing applies to photons as well and if ...
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1answer
219 views

Why are we searching for graviton? [duplicate]

I am computer scientist and not a physicist, but I really like physics One question popped into my mind recently about gravity. General theory of relativity describes gravity not as a force but as a ...
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0answers
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If gravitational waves travel at the speed of light, how can they escape black holes? [duplicate]

It is known that gravitational waves travel at the speed of light, and are themselves subject to lensing by gravity. My question is, how then do the waves escape the black hole they came from in the ...
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2answers
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Can I form a scalar with coordinates in general relativity?

There is no position vector in general relativity. I was wondering whether a quantity like $$k_\mu x^\mu$$ where $k_\mu$ are covariant vector components is to be treated like a scalar i.e. invariant ...
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1answer
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Should gravitational waves quantize similar to photons?

A single photon's energy is given by $E=hf$. This is also generalized to massive particles as $\lambda = \frac{h}{p}$ or $E = \sqrt{m_0^2c^4 + (hc/\lambda)^2}$ (they're equivalent for photons). Having ...
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2answers
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Why is “Gravity as a result of space-time curvature” not accepted as a fact? [duplicate]

Now that gravitational waves are confirmed. Not to mention the other numerous experimental verifications. Why do we still need an elusive graviton? Isn't there not enough evidence that the space-time ...
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1answer
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Gravitational radiation in M theory and super string theory [closed]

Hey I'm trying to build a toy model of gravitational radiation for fun from M theory. I need some general help with selecting thru the ideas I have. My first "model" is to make a M2 brane ...
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1answer
67 views

Physical interpretation of the nil ADM mass of gravitational waves

The ADM mass is defined for any asymptotic flat spacetime. Using cartesian coordinates: \begin{equation}\tag{1} E_{\text{ADM}} = -\: \frac{1}{16 \pi G} \, \lim_{r \, \rightarrow \, \infty}\oint_{\...
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Why does an oscillating mass does not produce gravitational waves (in contrast with an oscillating electric charge)? [duplicate]

I would like to gain insight about this question. I have read it is related with the conservation of momentum, but cannot really differentiate it from the oscillating charge. The monopole radiation ...
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1answer
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Lagrangian in reduced Horndeski Theory for i=2

I am trying to understand the calculations of the latest Charles Dalang's paper "Scalar and Tensor Gravitational Waves", arXiv:2009.11827. Since I just learned basic general relativity, I ...
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0answers
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How do you calculate the energy stored in a gravitational wave?

If you had an oscillating boson in a vacuum with an observer some distance away, how would you calculate the energy that the observer receives or loses as a result of experiencing a gravitational wave?...
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Looking for arXiv references on Einstein doubts about reality of gravitational waves

I'm looking for good papers on arXiv that tells the story of gravitational waves theoretical discovery and Einstein's (and others) doubts on their physical existence. Of course, I searched the papers ...
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1answer
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Increase in angular momentum through classical radiation?

My question can be asked in either Einstein GR or Maxwell electromagnetism. Suppose we have a system which is localized in space (enclosed in a sphere of finite radius). For example two point masses(...
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2answers
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Andromeda & Milky Way Merger: Gravitational Waves

When the Andromeda galaxy and Milky Way merge in the future, the super-massive black holes at their respective galactic centers will likely eventually merge. Similarly to the gravitational waves ...
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3answers
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Does the oscillating electric and magnetic field of a photon generate gravitational waves?

From my understanding, little as it may be, because photons have energy they warp spacetime. The energy is expressed as an oscillating electric and magnetic field. Would this mean that the energy is ...
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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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Do neutron star merger studies probe beyond vacuum GR?

When mergers involving neutron stars and / or black holes are simulated (e.g. when predicting gravitational wave signatures for these mergers), obviously complicated numerical relativity calculations ...
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Could antimatter have disapeared from the universe simmilarly as observed matter from collisions of black holes?

As matter inside a neutron star or black hole can vanish through collisions could be possible that antimatter did so more than matter in the very beginning of the universe through a high energetic ...
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2answers
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Do gravitational waves change the color of light?

It stands to reason if gravity changes the color of light then the color will be affected by gravitational waves. My question is, when the waves pass, will the color change be permanent or will the ...
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2answers
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So what actual physical event would allow us to observe the speed of gravity?

I have read, if the sun disappeared it would take 8 minutes before this could be detected on Earth due to speed of gravity being $c$. Of course, the sun can't disappear. Perhaps realizing this ...
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1answer
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Why does large-field inflation cause bigger gravitational waves

I'm learning about inflation and tensor perturbations during it. I've read a few times that large-field inflation is "more important" with respect to inflation as it produced bigger tensor ...
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1answer
100 views

Why does linear motion not emit gravitational waves? [duplicate]

Gravitational waves have been detected emanating from the decaying orbits of massive bodies, such as binary neutron star or black hole systems. To my understanding, two such bodies in what would ...
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1answer
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What does determine the frequency of gravitational waves caused by inflation?

It is theorized that during inflation gravitational waves are produced. See this article by Guzzetti, Bartolo, Liguori, and Matarrese (Cornell University). Or this one by Liu, Guo, Cai, and Shiu (...
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How do they calculate the distance merging massive bodies are away from earth using just the gravitational waves? [duplicate]

I guess the title sums up my question nicely. So, how do physicists/cosmologists/scientists determine the distance two or more merging bodies are away from earth given just their emitted gravitational ...
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2answers
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Equivalence Principle and Gravitational Waves

From my understanding, the equivalence principle says that it is impossible to know if you are moving or are stationary (and everything else is moving around you). Do gravitational waves violate this? ...
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1answer
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Are gravitational waves subject to gravitational lensing? [duplicate]

Can gravity be focused by large massive objects?
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1answer
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Elastic modulus of space-time? [duplicate]

Intuitively, a wave is something that propagates through an elastic medium (except possibly for ocean waves); is it possible to consider space-time as such a medium? And if so, what would its elastic ...
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1answer
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Does a gravitational wave let my coffee spill? [closed]

An observer holds a cup of coffee that is filled to the brim at the moment a gravitational wave passes by. Should the observer be worried about spilling coffee because of the gravitational wave? If so,...
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1answer
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Transverse traceless gauge in linearized GR

I'm reading about gravitational waves and I'm wondering how we know we can always go to the transverse and traceless gauge? Going to the de Donder gauge is fine, I can follow that, but then showing ...
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3answers
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Why does an accelerated charge emit electromagnetic radiation, but an accelerated (point) mass does not radiate gravitational radiation?

For example, an accelerated electron will emit EM radiation, but will not emit gravitational radiation. A common argument used is that the gravitational monopole represents the total mass-energy of a ...
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Does matter follow the curvature of space-time?

How is matter affected by the warping of space-time? Does it expand and contract, follow the curvature of space? What happens the shape/volume/density of matter when it enters a gravity well, or ...

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