What is Gravitational wave: Definition and 89 Discussions

Gravitational waves are disturbances in the curvature of spacetime, generated by accelerated masses, that propagate as waves outward from their source at the speed of light. They were proposed by Henri Poincaré in 1905 and subsequently predicted in 1916 by Albert Einstein on the basis of his general theory of relativity. Gravitational waves transport energy as gravitational radiation, a form of radiant energy similar to electromagnetic radiation. Newton's law of universal gravitation, part of classical mechanics, does not provide for their existence, since that law is predicated on the assumption that physical interactions propagate instantaneously (at infinite speed) – showing one of the ways the methods of classical physics are unable to explain phenomena associated with relativity.
The first indirect evidence for the existence of gravitational waves came from the observed orbital decay of the Hulse–Taylor binary pulsar, which matched the decay predicted by general relativity as energy is lost to gravitational radiation. In 1993, Russell A. Hulse and Joseph Hooton Taylor Jr. received the Nobel Prize in Physics for this discovery. The first direct observation of gravitational waves was not made until 2015, when a signal generated by the merger of two black holes was received by the LIGO gravitational wave detectors in Livingston and in Hanford. The 2017 Nobel Prize in Physics was subsequently awarded to Rainer Weiss, Kip Thorne and Barry Barish for their role in the direct detection of gravitational waves.
In gravitational-wave astronomy, observations of gravitational waves are used to infer data about the sources of gravitational waves. Sources that can be studied this way include binary star systems composed of white dwarfs, neutron stars, and black holes; and events such as supernovae, and the formation of the early universe shortly after the Big Bang.

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  1. K

    B Energy loss of a photon

    I've been told that a photon doesn't lose energy as it travels through a vacuum because it doesn't experience time. However, general relativity states that any energy creates a gravitational field that travels away from the energy at the speed of light. Doesn't this imply that a photon once...
  2. jedishrfu

    B FRB & Gravitational Wave Link: Scientists Baffled

  3. Narasoma

    I Gravity Wave Speed: Deriving Constancy from Maxwell Eqs.

    We can derive the constancy of the speed of light from Maxwell equations. My questions are: 1. Why it is then need to postulate it when we can obtain it from Maxwell equations? 2. It is stated in many books that gravity wave also propagates with the same speed, c. How do we conclude that? Is...
  4. DaveC426913

    B Frequency of Gravitational Waves: Limit & Possibilities

    A question elsewhere got me thinking about the frequencies/wavelengths of gravitational waves. The most obvious source of gravitational waves we are finding is from merging black holes, so presumably the orbital period will directly determine the frequency of those waves, yes? So the...
  5. B

    I Why aren't Gravitational waves factored in to inflation formulas?

    It seems to me that gravitational waves are ignored when inflationary physics are described. I'm not very well read, and honestly do not know so much about most of the physics going on with inflation. Still, wave mechanics matter, harmonics matter, and it just seems intuitive to me that in order...
  6. .Scott

    B ARC Centre reports HF Gravitational Wave Antenna

    The full title of the publication is: Rare Events Detected with a Bulk Acoustic Wave High Frequency Gravitational Wave Antenna It is published in Physics Review Letters and reported in Phys Org. They have created a small piezo-electric device (< 2cm, though it gets bigger once you create an...
  7. Buzz Bloom

    I Find GR Equation: Collapsing Orbit & Gravitational Wave

    I recall some time ago seeing a GR equation describing the rate of orbital energy loss from the moving objects in orbit generating gravitational waves. I can no longer find this equation again. I am hoping someone can help me.
  8. enorbet

    B Gravitational Wave Background: Unlocking the Mysteries of the Universe

    I don't know if this is the ideal sub-forum for this but I'd like to know more about this very recent activity I first saw here >>>>>' It looks like this could be some actually testable, actual breakthrough advances in Physics and the evolution of our Universe. Any comments appreciated.
  9. R

    B Gravitational Waves: Prevalence Across the Universe

    Would it be correct to say, that gravitational waves of the magnitude that is currently detected by LIGO and similar detectors, are prevalent to the extent that there is no single location in the known universe, that such magnitude of gravitational waves, don't pass through at least several...
  10. M

    Gravitational wave source triangulation

    In my new novel, Handwavium, renowned genius physics Professor Samuel Clements Silver has created a prototype gravitational wave radio. For plot purposes, the protagonist needs to use the signal to triangulate his location. I know LIGO has three detectors and have seen reports of sources like...
  11. pelinkovac

    I Gravitational Wave Creation: Is a Stationary Wave Possible?

    Hello, Apart from the graviton postulate, which would permit such a mechanism, my question is: would a similar mechanism be possible with a stationary wave? (the simplest scenario I can immagine is of two opposing waves). My background is in DSP and Acoustics so I might get things wrong (a...
  12. Suppaman

    B Energy in a Gravitational Wave

    By the time the gravity wave reaches us it is very small in energy, I assume. We do not know how to make gravity waves in a laboratory but we have a place where we have a very sensitive gravity wave detector. If we had a lab set up a few blocks away we might be able to do various experiments...
  13. B

    I SXS Gravitational Wave Data: Initial Conditions Explained

    Hello! I need to do some analysis for a project with the SXS gravitational wave data: https://data.black-holes.org/waveforms/catalog.html but I am a bit confused about the initial conditions of their simulations. I read the paper they published about the data (it can be found at that website)...
  14. HibyPrime

    B Gravitational wave emission from electrons

    Ok, so I've been on a kick trying to really understand why QM and GR are incompatible. I think I get that GR can't be realistically converted into a quantum field because it creates some infinite series that you can't use the normal tricks you would for other QM fields. Hard block, ok got it...
  15. S

    A Calculating the Gravitational wave spectrum with Inflation as a source

    I am interested in knowing how to calculate the gravitational wave (GW) spectrum with inflation as a source, I have some background in inflation but I am not so familiar about calculating the GW spectrum. I am reading a paper (https://arxiv.org/abs/0804.3249) about it, however, a big part of it...
  16. S

    I Gravitational wave interactions and the equivalence principle

    According to wikipedia, the strong equivalence principle states “the gravitational motion of a small test body depends only on its initial position in space time and velocity, and not on its constitution, and the outcome of any local experiment (gravitational or not) in a freely falling...
  17. S

    B Gravitational Wave Interference Graphical Computer Simulation

    I have found on the internet an article from Gizmodo magazine, in which a LIGO team member answer some readers’ questions, regarding gravitational waves, and found a specific question and answer in that article, to be very interesting. The question relates to weather gravitational waves are...
  18. R

    I Gravitational wave interference

    I am trying to understand the following: 1. Have gravitational wave constructive and deconstructive interference phenomena already been observed or is it that only after making LIGO kind of experiments more advanced, that we might be able to observe such phenomena in the future? 2. Can't...
  19. cianfa72

    I Can Gravitational Waves Affect Light Wavelengths?

    Hi, a simple question related to the gravitational wave detection. The net effect of gravitational wave is basically the stretching of the space including all the measurements tools (meter sticks just to illustrate the concept) that could be used to detect it. I am aware of laser...
  20. astroman707

    Physics Is gravitational wave research a smart direction to go in?

    Is it a fair prediction to state that in the next several years or so, globally, there will be major investments into gravitational wave research, and many more ‘LIGOs’ being developed? Is it a good idea to venture into that area of physics?
  21. astroman707

    Courses Academic Preparation for gravitational wave careers?

    If someone wanted to pursue a career in gravitational wave physics, and work at places like LIGO, studying astrophysical objects such as black holes and neutron stars, etc. What are some key courses/skills that person should take/learn as an undergraduate, and graduate student?
  22. alan123hk

    B Gravitational Wave Communication System

    Would it be possible to transmit information through gravitational waves? It must be a giant leap for mankind if we can utilize gravitational waves for communication since the electromagnetic spectrum for communication is a scarce resource and not much space is left. I imagine that the...
  23. S

    I Gravitational Waves vs Universe Expansion Rate

    Is there any relationship between the Speed of gravitational waves and the Universe's "local" expansion rate? Speed of gravitational waves is supposed to be equal to the speed of light. Gravitational waves don't travel faster than light. But we can observe far galaxies moving away from us with...
  24. A

    B Gravitational Wave Stretching: LIGO Arm vs Light

    I'm puzzled that the stretching of space by a gravitational wave stretches the LIGO arm but not the light within it. Because we are told that the red shift of a distant galaxy is caused by light being stretched by the expansion of space (the universe).
  25. H

    B Does a gravitational wave change the speed of light?

    Suppose at the instant a gravitational wave passes through an interferometer, one of the interferometer's arm get stretched by 1%. Would the wavelength of the photon traveling in the arm also get stretched by 1%? If so, then would the frequency of the photon remain the same and hence increasing...
  26. Jim Lundquist

    I Gravitational Wave Modeling: A Thought Experiment

    I am thoroughly confused regarding the modeling and graphic depictions of gravitational wave propagation. These waves must propagate in three dimensions, not in the planar rubber sheet example that is often shown or the ripples on a pond example. Even the recently publicized example of the...
  27. A

    A Speed of Gravitational Waves confirmed by Experiment?

    It seems that with the 2016 LIGO and VIRGO confirmation of the gravitational chirp that we have also experimental confirmation that the speed is indeed the speed of light. True? https://en.wikipedia.org/wiki/First_observation_of_gravitational_waves#Direct_observation
  28. R

    B What limits the speed of a gravitational wave to c?

    The speed of light (in the vacuum) is a function of the permeability and permittivity of the vacuum. In other mediums the phase velocity will be different. It is assumed (by me) that the speed of a gravitational wave does not change depending on the medium i.e. a gravitational wave would not...
  29. T

    I New Gravitational Wave Detection question

    This latest observation of gravity waves has brought up a question with me.. Since gravity is a mass-caused distortion in space-time aren't these waves wave distortions of the space-time? I know there is no such thing as ether but for this analogy and my simple mind I'll use it to illustrate...
  30. binbagsss

    Programs What is involved in gravitational wave research?

    A professor from a UK university who is a member of LIGO kindly video called me the other day regarding potential PhD projects and said that a lot of gravitational research isn't about the dynamics and source-model nor application of general relativity but high performance computation and big...
  31. T

    Orthogonality of Gravitational Wave Polarizations

    Homework Statement Two plane gravitational waves with TT (transverse-traceless) amplitudes, ##A^{\mu\nu}## and ##B^{\mu\nu}##, are said to have orthogonal polarizations if ##(A^{\mu\nu})^*B_{\mu\nu}=0##, where ##(A^{\mu\nu})^*## is the complex conjugate of ##A^{\mu\nu}##. Show that a 45 degree...
  32. A

    I What would happen in following condition?

    If a conduction band is placed in a current loop with gravitational waves acting upon it in parallel direction. It is also assumed that all the basic conditions relating to frequency are met for parallel propagation case as per gravitational wave damping papers below. Since nuclear precession...
  33. DrClaude

    European gravitational wave detector falters

    http://science.sciencemag.org/content/355/6326/673?utm_campaign=toc_sci-mag_2017-02-16&et_rid=34818699&et_cid=1169695 Bummer :frown:
  34. grauitate

    I Can a gravitational wave (GW) propagate in a flat universe?

    As the universe expands and is per definition gravitationally decoupled on long distances and the overall metric therefore is "flat" and apparently no gravitational background exists, the question in some discussion arose: Can GWs propagate in in a gravitational empty space at all? If not, and...
  35. Meerio

    I Gravitational Wave: Energy & Amplitude Changes

    I was wondering how the energy and amplitude change over a distance
  36. J

    B Gravitational wave signal duration

    I have a question about why the duration of the gravitational wave signal detected by LIGO was 0.25 seconds or so. I think I understand correctly that as the two binary black holes rotate around each other and move closer together there is a loss of angular momentum that is converted to...
  37. Meerio

    I Need help with some calculations with gravitational waves

    I have some questions about the first discovery paper that was released about gravitational waves, especially some of the maths. How did they: 1. Calculate the masses of the black holes that merged 2. Calculate the energy radiated away in gravitational waves 3. Calculate how far away the event...
  38. S

    A Solve Gravitational Interferometer & Geodesics

    I was trying to solve this excercise: Now I was able to find the eq. of geodetics (or directly by Christoffel formulas calculation or by the Lagrangian for a point particle). And I verified that such space constant coordinate point is a geodetic. Now, for the second point I...
  39. E

    I Gravitational wave like a harmonic oscillator?

    Electromagnetic wave behaves like a harmonic oscillator. Similarly a photon behaves like a quantum harmonic oscillator. http://www.physics.usu.edu/torre/3700_Spring_2015/What_is_a_photon.pdf ##dA/dt## and ##A## behaves like ##dx/dt## and ##x## at a harmonic oscillator. I suppose that...
  40. P

    Did Einstein believe in Gravitational waves?

    In 1916 Einstein has published the first paper of gravitational wave bu linearize approximation but It contain an error of his calculation then In 1918 he published a new paper of gravitational wave that has a correction of the his last error and conclude that there are the Gravitational wave...
  41. mmusiak

    B What is the amplitude of a gravitational wave at the source?

    In the most recent postings on LIGO, it is stated that the amplitude of the signal is less than the diameter of a proton after the propagation of the wave over billions of light years. I am assuming that the wave amplitude will decay as 1/r^2, but perhaps that is an incorrect assumption. So is...
  42. G

    A Effect of Blue-Shifted GWs on Particles

    I assume that the energy transported by a gravitational wave is dependent on its frequency, just like EM waves. If that is the case, let's imagine a particle traveling at relativistic speeds relative to the lab frame. Let's imagine the interaction of this relativistic particle with a...
  43. C

    Is there a smallest possible gravitational wave?

    An accelerating mass produces gravitational waves. Is there a smallest possible gravitational wave? Is there some quantum energy level lower than which a wave will not be produced? For example, would a slowly accelerated electron produce any gravitational waves at all?
  44. I

    Can a gravitational wave kill you?

    Specifically, I am wondering if the stretching that a gravitational wave does to you as it passes through you, if the stretching was big enough (say half a meter), could it rip you apart, or does it not work that way? I know that gravitational waves that go through Earth do not get this big...
  45. G

    GW Detection Confirmation: Time, Rate, & GRB?

    I understand that the LIGO experiment was very lucky to find a very strong signal of a very energetic event (binary black hole merger). Having into account the non-negligible possibility that the signal may be spurious or some problem in the data adquisition, how much time must pass before we...
  46. T

    Gravitational waves, distance and space-time

    So the discovery of gravitational waves observed a contraction and stretching of space-time, and I've been trying to understand how the expansion of the universe means that space itself is growing. I want to understand how this actually works in relation to 'things' like a photon and an atom...
  47. T

    I Can Matter Absorb Energy from Gravitational Waves?

    So everyone knows that the energy of a photon is E = hf, I assume this is just because light also has a particle nature. But how do we calculate the energy of a gravitational wave, because from memory classical wave equations have a mass component to calculate 'kinetic' associated energy, and I...
  48. K

    B Can gravitational wave escape a black hole

    light waves created inside a black hole cannot. Can gravitational waves escape from inside of black holes? in classical GR. does the answer change in string theory?
  49. pioneerboy

    EM length of gravitational waves

    Maybe a stupid question and maybe sensless to ask, but as I don't know, I ask anyway: what is the length of the newly found gravitational waves in terms of traditional EM wavelengths?