What is Gravitational waves: Definition and 330 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. Auto-Didact

    B Can Phonon Excitations in BECs Revolutionize Gravitational Wave Detection?

    Ivette Fuentes and her group are attempting to use phonon excitations in BECs to detect gravitational waves. Their GW-detector is called MAGA, which stands for Micrometre Antenna for Gravitational-wave Astronomy. Here's a video of her explaining it: More from their blog:
  2. N

    Relativity Books about gravitational waves

    Can someone recommend me some beginner/intermediate level books about gravitational waves and some articles about their discovery. I need to write scientific paper about them for my graduation but i don't have resources where to find about them so i would really appreciate help :)
  3. 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...
  4. atyy

    Gravitational waves pioneer Ronald Drever dies

    http://www.bbc.com/news/science-environment-39212305
  5. A

    I Consequences of Rotating Objects C on Coil A Frequency

    As per the above figure coil A is situated inside a magnetic field caused by small accelerating objects B which in turn are causing the larmor frequency in coil Object C or train of objects C have quadruple movement and are rotating around the coil A giving out gravitational waves. Objects C...
  6. binbagsss

    I Why binary systems for gravitational waves?

    So a spherically symmetric object, by Birkhoff's theorem, does not emit gravitational waves. Is this why we look to binaries, so that there is some rotation of the objects with respect to each other breaking the spherical symmetry? Or mainly because the gravitational radiation is much greater...
  7. A

    I Particle accleration under gravitational waves?

    I have been through following papers for research: 1)http://cdsads.u-strasbg.fr/cgi-bin/nph-iarticle_query?1990ApJ...362..584M&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf 2)https://arxiv.org/pdf/gr-qc/9905054.pdf Conclusion of the second paper given above...
  8. wolram

    B Does the Frequency of Gravitational Radiation Alter the Cosmological Constant?

    It occurred to me that if the speed of gravity is the speed of light, then the universe must be accelerating due to Dark Energy, What my question is do we know the frequency of gravitational radiation, If we do then any compression or expansion of these waves will change the cosmological...
  9. W

    I Detecting Gravitational Waves: Is My Understanding Wrong?

    Something is wrong in my understanding of Relativity. There is an equivalence idea running around, which says that gravity and the distortion of space time by gravity waves acts the same way on all things. That would mean that all objects and light and space experience the same distortion...
  10. S

    A Gravitational waves in warm inflation

    https://arxiv.org/pdf/astro-ph/0006077v2.pdf page 5. Tensor Perturbations "Tensor perturbations do not couple strongly to the thermal background and so gravitational waves are only generated by quantum fluctuations, as in standard supercooled inflation". Why? Tensor perturbations are created...
  11. E

    I Gravitational Waves & Energy: Is There a Consensus?

    I understand that any source of gravitational waves loses energy, which is carried away by the waves. But since the waves are perturbations in spacetime rather than a physical field, they cannot carry energy the way photons do. I have read that this used to be a source of considerable...
  12. Meerio

    I By what formula is this graph predicted? Cumulative Periastron Time Shift

    I'm confused about how the predictions of this graph were formed. I have this formula: But the change in frequency per second is about : 2x 10^-12 which has a problem because when you multiply this by 10 years you don't even get a change of frequency of 1/1000 of a second and in the graph it...
  13. Meerio

    B In what direction do gravitational waves get emitted?

    https://www.ligo.caltech.edu/video/gravitational-waves How do gravitational waves get emitted here? Is it in a sphere or on a flat(?) surface?
  14. Meerio

    B Need an explanation for the chances in this graph

    In the paper Advanced LIGO they published some figures with chances. I would like to know how they know that there's a 90% chance for something to be in a specific value. https://dcc.ligo.org/public/0122/P1500218/014/PhysRevLett.116.241102.pdf paper here also have some other questions: What...
  15. 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...
  16. parshyaa

    What if the speed of gravitational waves were different from the speed of light?

    What would happened if the speed of gravitational waves were not equal to the speed of light . Please explain it with example of sun and Earth or any other but in easy way. With reference to general relativity.
  17. A

    B Gravitational waves 50X total stars and not be felt?

    Hi all, On the subject of being able to feel gravity waves as a human without machines, I couldn't find a very definitive answer to what I was looking for. First, I reference the video: at 40 tp 55 seconds. Its called: LIGO, journey of a G wave. They say in this clip that when the black...
  18. Domenico94

    A Gravitational law of induction

    By reading on the internet I ve found various websites talking about the relation between gravitation and electromagnetism, and in particular, under: - "Small" Gravitational fields -"small" changes in energy with respect to time, The linearized enstein' s field equation becomes pretty much...
  19. chaszz

    B Why are the gravitational waves we have detected so faint?

    This is a quote from an article written by a Phd student in physics in the online magazine Aeon (https://aeon.co/ideas/gravitational-waves-will-bring-the-extreme-universe-into-view): "Consider the properties of the September 14 event: the signal was generated by two objects, each roughly 35...
  20. E

    I Gravitational Waves: Propagation or Present?

    I understand gravitational waves as ripples in spacetime. As PeterDonis said in an earlier post, " The 4-d spacetime geometry does not have to "propagate" anything; it just is." On the other hand, this is block-universe speak. In this language, verbs that imply change are forbidden. We might...
  21. A

    B How do I calculate electron acceleration by gravitational waves

    If the amplitude of gravitational waves, frequency of gravitational waves and the vector potential of magnetic field in surrounding of such waves are known then what would be the easiest way to calculate resultant acceleration of electrons? My above question is based on the various researches...
  22. Piranha Butch

    B Gravitational Waves: What Happens In Between?

    Hi when i found out about the presence of gravity waves, i first thought 'what happens if they were to be reversed' and then i thought 'what happens to space time in between these waves?' thanks
  23. Ibix

    I Sticky beads and a simple wave

    A while ago, robphy posted a link to a paper by Saulson describing a "step" gravitational wave described by the metric ##ds^2=-dt^2+[1+h(t)]dx^2+[1-h(t)]dy^2##, where ##h(t)=h_0H(t-\tau)## is a step function of (constant) height ##h_0##, with the step occurring at ##t=\tau##. Presumably...
  24. Gravitational Waves: A New Era of Astronomy Begins

    Gravitational Waves: A New Era of Astronomy Begins

    Join some of the very scientists responsible for this most anticipated discovery of our age and see how gravitational waves will be used to explore the universe like never before.
  25. DuckAmuck

    I Gravitational waves affected by gravity?

    So we know that in GR electromagnetic waves have their trajectories effected by the gravity of stars and planets. But how about gravitational waves. Are their trajectories altered by gravity? If so, would this imply that gravitons are self-interacting if they exist?
  26. GeorgeDishman

    I Modeling the effects of GW and the "Earth Frame"

    First let me be clear, I am not questioning GR or the detection of gravitational waves by LIGO, I am trying to improve my own understanding of GW to the point where I can offer a graphic illustration (web video) showing what they do as they pass us to help others understand them. I started this...
  27. S

    I Gravitational Waves Vs. Aether Wind

    The Michelson-Morley Experiment (as depicted in the scishow YouTube video "The Greatest Failed Experiment Ever") which was used to test for the effects of 'Aether Wind' appears to be almost, if not completely, the same setup as the one used in a gravitational-wave observatory. Why is the success...
  28. G

    I How can gravitational waves be detected if spacetime itself warps?

    Hi, First: I'm pretty sure my question has been asked numerous times, so I'm absolutely happy with links to other threads. I've used search but it didn't come up with satisfying responses, probably mainly because I don't really know what search terms to use. So the question is: How can a...
  29. pitbull

    Bachelor's thesis about Gravitational Waves -- Too advanced?

    Hey! I am about to start my Bachelor's thesis about General Relativity. My professor mentioned that my thesis might as well be related to Gravitational Waves. Do you think that it would be appropriate to work on Gravitational Waves for a Bachelor's thesis? Isn't it too advanced? Also, any idea...
  30. M

    A Was the LIGO team over-hasty to claim black holes confirmed?

    Since the thread In LIGO’s pulse, how much comes from BH merging/ inspiraling where I questioned the late ‘ringdown’ part of the LIGO signal, scientists have pointed out that the main pre-merging signal could indicate various types of binary compact objects, including gravastars of similar mass...
  31. KarminValso1724

    B Why do gravitational waves propagate at the speed of light?

    If things such as quantum entanglement and the expansion of space can travel faster than light, then why can't gravitational waves, which are vibrations of spacetime? I thought that only matter cannot move through space faster than light. Also, has it been 100 percent proven that gravity waves...
  32. Devin

    I Production of Gravitational Waves Problem: Energy Flux

    Suppose two masses are connected via a really strong spring, where one of the masses undergo an acceleration towards a relativistic speed, by say a rocket that leaves the scene soon after. When in isolation, (the two masses), they exhibit a sinusoidal oscillation to and fro. What is the...
  33. haael

    A Do black holes lose hair in finite time?

    OK, so it's time to start a new thread. I heard many times that there exists only one black hole solution for a given mass and angular momentum, but I know already that this is not true. We all know that if we throw something into an existing black hole, its event horizon starts to ripple. So...
  34. EnumaElish

    I (How) does the LIGO experiment falsify Newtonian gravity?

    Sorry for the amateurish setup that follows. Here's my thought experiment. Consider a 2-dimensional universe on the Cartesian plane. Earth is located at point (0,0). There is a binary system {A,B} oscillating around (1,1). To simplify, assume that the oscillation is 1-dimensional and occurs on...
  35. L

    I Gravitational Waves & Black Holes: Exploring the Connection

    This is something I've been curious for some time. I've heard that there is a relation between gravitational waves and black holes. Moreover, this year the quite important paper "Observation of Gravitational Waves from a Binary Black Hole Merger" was published. Now, I'm starting to study...
  36. L

    Other Undergraduate research on gravitational waves

    Currently I'm in the last year of the Physics course and I'm interested in working on some undergraduate research project. At first I was suggested to work with statistical physics, but I believe I would prefer working with General Relativity. From the point of view of background I do have a...
  37. KarminValso1724

    B Gravitational Waves Speed: Can We Observe It?

    To me, it seems that with our current technology it would be difficult to observe the speed of gravitational waves. Can anyone correct me if I am wrong?
  38. joswitz

    I Gravitational Waves: Questions from Josh on Mass & Space-Time

    hello, I was reading a recent article about gravitational waves and I had a few questions... I actually have a lot of questions, but I digress. Let me first start with what I think I know to be right, and then move on to the questions about the subject. -Time and space are connected. This...
  39. M

    A In LIGO’s pulse, how much comes from BH merging/ inspiraling

    The inspiralling oscillations of ~20ms period (reducing to ~5ms) appear much stronger than the ringdown of ~ 3ms period (noisy, at resolution limit). Merger happens at ~440ms in the figure of Abbott et al. (Phys Res Lett link.aps.org/doi/10.1103/PhysRevLett.116.061102). This would agree with...
  40. K

    I Gravitational waves as means for communication

    Hi all, this is my first post so before my question I want to show my appreciation to this community for offering a great framework to talk physics between experts and others who chose different life career paths, such as me. I have always loved physics but the math... not that much. English is...
  41. 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...
  42. C

    B Is Gravitational Quantization Supported by the Stability of Orbital Electrons?

    Does the fact that orbital electrons are stable suggest that gravitation is quantized, analagous to the observation that the stability of orbital electrons suggested that electromagnetic energy was quantized?
  43. T

    B Gravitational Waves @ relativistic speed?

    What would happen if I were to fly toward a gravitational wave pulse at relativistic speed? Would I be destroyed by the Doppler-shifted pulse? Would the wave become visible?
  44. 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...
  45. M

    What's New in Gravitational Fields and Waves? A Welcome Back to PF!

    Hi, previously at Cardiff Uni, now at Buckingham, I'm still interested in gravitational fields, waves, Einstein, LIGO and all that.
  46. K

    I Gravitational Waves: Time, Synchronization, Speed

    Hi folks. I see there is a similar thread on grav waves and time, but I have a few specific questions. Everyone talks about grav waves "in space" -- even Brian Greene was saying this on Colbert, whereas Colbert was saying spacetime. I would like to make a video on how GWs are indeed "waves in...
  47. R

    I Do gravitational waves transmit energy in all cases?

    I was told that there are two kinds gravitational waves. One dies out as 1/r, another one dies out as 1/r^2. The former is what LIGO detected, the latter is not. While I trust the professional qualification of the person very much, as a non-physics professional, I would like to a second person...
  48. R

    Are Gravitational Waves and Waves Transmitting Curvature Changes Different?

    G-Waves is a buzzword recently :) At the beginning I thought G-waves as the propagation of the changes of the curvature caused by a mass when the status of the mass (e.g. value or location) changes...But moment ago, I was told that G-waves are different from the waves that transmitting the...
  49. S

    A Spacetime Engineering by Superposition of GWs: Feasible in Theory?

    I wanted to post the conjecture from this new paper which has recently been published within this past month - here's a direct link to the paper: http://arxiv.org/pdf/1602.01439v1.pdf Could an experimental apparatus consisting of oscillating masses be used to generate miniscule gravity waves...
  50. 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?
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