What is Gravitational waves: Definition and 328 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. zinn

    I Separation angle between pulsars detecting Gravitational Waves

    I’m trying to understand the Hellings and Downs curve that is being used to argue for the existence of a gravitational wave background ([NANOGrav article][1]). How can it be that the angle between two pulsars is the only variable that determines if the gravitational waves will interfere...
  2. jedishrfu

    B Quanta Magazine Video on Biggest Breakthroughs in Physics in 2023

    Covers: - Low-frequency gravitational waves - Quantum energy teleportation - JWST Discoveries
  3. Precious Adegbite

    I Can gravitational lensing detect Very small deviations in light propagation?

    So normally with gravitational lensing Technique We get to see how spacetime curvature and gravitational waves affect propagation of light. So I got a questions: (1) I know gravitational waves are caused by supernovas, collisions and other related actions, but would a quantum fluctuations that...
  4. S

    I Would there be any way to avoid gravitational wave emissions?

    In principle every object orbiting another (e.g. a planet revolving around a star) would emit gravitational waves, relaxing the orbit over time.However, this would not happen if the orbits had a time-invariant and symmetric quadrupole moment. As it is indicated in this question (), it appears...
  5. S

    A Help with IPTA Gravitational Waveforms Detected

    Hi All. I am interested in finding out if the International Pulsar Timing Array team have detected specific waveform types. The waves I am particularly interested in (if they exist) would be low frequency and would be triggered at a minimum amplitude. Example below: There may be waves detected...
  6. mfb

    I NANOGrav results on Thursday (June 29)

    Supermassive black hole in close orbits should produce powerful gravitational waves, but their frequency is too low to be measured with gravitational wave detectors we can build. Luckily nature has built something we can use. The NANOGrav collaboration is studying the arrival time of signals...
  7. phinds

    B LIGO Back Online: Upgraded Detector to Spot Fainter Gravitational Waves

    From this morning's Economist briefing: The Laser Interferometer Gravitational-Wave Observatory—the world’s most sensitive device for spotting gravitational waves—starts up again on Wednesday after a three-year hiatus for upgrades. LIGO is designed to detect subtle ripples in space and time...
  8. MrFlanders

    A GW Binary Merger: Riemann Tensor in Source & TT-Gauge

    In the book general relativity by Hobson the gravitational wave of a binary merger is computed in the frame of the binary merger as well as the TT-gauge. I considered what components of the Riemann tensor along the x-axis in both gauges. The equation for the metric in the source and TT-gauge are...
  9. M

    I Is there any way in the future to determine the Universe's size?

    I am frequently contemplating the size of the universe. Logic tells me that existence cannot is end as there really can’t be anything as anti-existence but if the universe loops back on itself; it may not be an issue. Is there a possible way in the far future to semi-accurately measure its size...
  10. S

    I Can gravitational waves gain energy in an expanding FRW spacetime?

    I was reading this paper (*Green's functions for gravitational waves in FRW spacetimes:* [https://arxiv.org/abs/gr-qc/9309025](https://arxiv.org/abs/gr-qc/9309025)) and I had a specific question about one statement in the paper that I would like to ask: At page 6, the author says that...
  11. Z

    I Gravitational Waves from Vanishing Sun: What Happens?

    For some time I was wondering, what would happen if the Sun just disappeared like someone hit the delete button in Universal Sandbox. Specifically, what kind of gravitational waves will be produced in the wake of such an event? Would the law of conservation of Mass-Energy be miraculously...
  12. SH2372 General Relativity - Lecture 11

    SH2372 General Relativity - Lecture 11

    0:00 Perihelion precession of Mercury 17:15 Bending of light 24:48 Shapiro delay 33:32 Pound-Rebka experiment 41:40 Spectral lines of stars 44:58 Gravitational waves 49:22 Other important effects
  13. SH2372 General Relativity - Lecture 8

    SH2372 General Relativity - Lecture 8

    0:00 The weak field limit 27:15 The Newtonian limit 44:00 Gravitational waves 59:27 Geodesic deviation 1:22:15 Measuring gravitational waves
  14. wcivch

    B Ride Gravitational Waves to Increase Speed?

    This is my first post so I apologize if i am in error anywhere. I recently had a thought that I have had trouble confirming. Based on the following assumptions. 1.) As you accelerate an object near the speed of light it’s mass increases exponentially. 2.) Mass warps space time. 3.) Spacetime...
  15. A

    I Gravitational vs. Electromagnetic Waves: What's the Difference?

    in a nutshell what are the differences between gravitational and electromagnetic waves?
  16. Oldman too

    I Exploring Gravitational Waves with Earth-Lunar Orbital Perturbations

    Hello, This article caught my attention recently and I have several questions on the subject that I'd like to get opinions on. Before going further, I realize a technical discussion is way past the "I" tags range. Please adjust as necessary and thank you in advance. My attention was originally...
  17. N

    I Curved space and gravitational waves

    Are gravitational waves purely temporal? An object with no spatial velocity experiences gravity due to temporal velocity?
  18. Dinarchik

    Alien spaceship wormhole gravitational waves detector

    Recently viewed video about wormholes that required negative energy to create it. Suppose hypothetical aliens have discovered this technology. Spaceship enters in first point and exit at second. To prevent spaceship destruction they might have technology to smooth gravitational waves on exit...
  19. G

    I Information content in electromagnetic or gravitational waves

    Electromagnetic or gravitational wave carries energy and momentum from place to place as,I understand.Does it imply that such waves only can carry information and if their energy gets dissipated as heat, the information contained is lost. Is this information content is to be decoded by human...
  20. U

    Help with a calculation about gravitational waves

    An exact gravitational plane wave solution to Einstein's field equation has the line metric $$\mathrm{d}s^2=-2\mathrm{d}u\mathrm{d}v+a^2(u)\mathrm{d}^2x+b^2(u)\mathrm{d}^2y.$$ I have calculated the non-vanishing Christoffel symbols and Ricci curvature components and used the vacuum Einstein...
  21. 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...
  22. A

    I How do gravitational waves differ from the expansion of the Universe?

    How do gravitational waves in spacetime stretch and compress solid matter such as the LIGO experiment. I ask this because the expansion of spacetime of the Universe doesn't seem to have any effect on the small scale ie the solar system.
  23. cianfa72

    I Detecting Gravitational Waves w/ Interferometers: Explained

    Hi, I would like to ask for some clarification about the physics involved in the gravitational waves detection using interferometers. Starting from this thread Light speed and the LIGO experiment I'm aware of the two ends of an arm of the interferometer (e.g. LIGO) can be taken as the...
  24. A

    I Merging black holes: gravitational waves and information

    A popular theory is that black holes gradually leak information because of black hole evaporation due to hawking radiation. When black holes merge, a significant portion of their mass is converted into gravitational waves. If it's true that black holes leak information due to hawking radiation...
  25. thegroundhog

    I LIGO: Detecting Differences Less Than a Proton Length - How is It Possible?

    I read that the LIGO detector in the US was able to detect a difference of less that the length of a proton, or maybe even less than this. How is this possible? The perpendicular arms won't be the same length down to the nearest proton length. Also, at such small lengths the microclimate on each...
  26. E

    A Cosmological gravitational waves

    The exercise is to derive the form of the symmetric, trace-free and transverse gravitational wave perturbation ##\hat{E}_{ij}## to the FRW metric$$ds^2 = a^2(\tau) \left[ -d\tau^2 + (\delta_{ij} + 2\hat{E}_{ij})dx^i dx^j \right]$$First step is to figure out the connection coefficients, which are...
  27. D

    B Gravitational Waves: Comparing Effects on Earth

    If we compare 2 scenarios... A) 2 solar mass black hole hyperbolic flyby of Earth at 5000km/s far enough not to cause a tidal disruption event vs B) an extremely close binary pair of 1 solar mass black holes whose barycenter hyperbolically travels past Earth at 5000km/s, also far enough not to...
  28. G

    I Alcubierre Drive & Gravitational Waves: Alien Effects?

    Suppose some aliens travel to our solar system after seeing our radio broadcasts using an Alcubierre drive. Would it not create a notable gravitational disturbance? Or does it leave spacetime undisturbed around it?
  29. veraamorim

    B Next Generation Planetary Missions Hunt for Gravitational Waves

    Spacecraft heading to Uranus and Neptune in the next decade could be used to investigate gravitational waves as they venture into the outer Solar System. That is according to a new study by a team of Swiss and Danish researchers, who say that examination of the radio signals from far-flung...
  30. lomidrevo

    I Gravitational Waves Emitted by a Binary System

    Let's assume a binary system with an inclination angle ##i## (angle between the orbital plane and line of sight). Then, according to this source - equations (128) and (129) - for the amplitudes of the tensor polarization modes ("plus": ##+## and "cross": ##\times## polarization) I could write...
  31. ComradeConrad

    I Gravitational waves as not "proximal"?

    Usually spacetime curvature is localized/proximal to what is "causing" it, right? I'm wondering whether there is a term for the situation seen with gravitational waves where there is some relatively flat space between observable gravitational effects and the mass(es) that "caused" them? I'm...
  32. K

    I Gravitational Waves: Hardest GR Topic?

    Is the subject of gravitational waves the most difficult one to grasp on the theory of Relativity? Or is it just the math that is very complicated?
  33. L

    I Quantum Measurements with Gravitational Waves

    Would using gravitational waves to measure (it's obviously a gedankenexperiment!) position and momentum of, say, an electron in a specific state, disprove HUP since the quantum of energy of grav. waves does not exist? Would it be possibile to have an arbitrarily small uncertainty in position...
  34. R

    B Gravitational Waves: Impact & Effects on Gravity

    When a gravitational wave passes through a location in space, what is the magnitude of equivalent gravity that it produces at that location? Or rather, is it correct to say that gravity can influence gravitational waves but gravitational waves can't influence gravity?
  35. R

    B Measuring Gravitational Waves w/ Elevator Accelerometer

    An elevator in outer space where there is negligible gravity, accelerates at the most precise constant acceleration that current technology enables. Inside that elevator, resides an accelerometer that is the most precise accelerometer that current technology enables, but not more precise than...
  36. R

    B Gravitational Waves: A Question on Earth's Magnitude & Frequency

    Here is a video i have watched: It made me think of the following questions: A. Gravitational waves at the scale that emanate from earth: 1. It is doubtful if they exist at all. 2. They are predicted to exist, but at an extremely small magnitude. B. In case the answer is A2: 1. These...
  37. T

    B Gravitational Waves in Positively Curved Universe?

    Hello everyone! I was listening to a podcast that featured a cosmologist and she mentioned that if the universe was positively curved (and therefore a sphere overall), light would travel around the universe and then end up where it started. I wondered, would a gravitational wave do the same?
  38. R

    B Detecting Gravitational Waves: Earth-Like Planet Possibility

    Is it theoretically possible that one day a gravitational wave detector will be developed, that is sensitive enough to detect gravitation at the order of magnitude that an Earth like planet has?
  39. 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...
  40. P

    B Consequences of the Existence of Gravitational Waves?

    I'd like to see some of the consequences of the existence of gravitational waves (both expected and unexpected), in laymen's terms so a simpleton like me can understand and relate to them. A possible consequence that I thought of (and I'm sure someone will correct me if I'm wrong) is that...
  41. sbrothy

    B Lensing Gravitational Waves Like Light?

    I was reading (or at least skimming) this paper: https://arxiv.org/abs/2005.10702 in which they seem to be discussing gravitational wave lensing. Is this an analogue of light lensing or is it another subject entirely? I mean, as I understand it, light is bend using gravity (as for...
  42. X

    I Playing music with Gravitational waves

    Seems gravity waves are longitudinal waves, similar to sound waves as it is produced by the vibrations of spacetime? So in theory, if we can produce a powerful enough gravity wave, can we hear it? G-waves are usually produced by merging binary neutron stars or black holes. These celestial...
  43. .Scott

    A Black Hole Eating Gravitational Waves - A Look at Physics

    Is it fair to say that all energy from a Gravitational Wave that enters the photon sphere of a Black Hole is destine to become part of that BH? And other parts that remain just outside of the photon sphere would experience gravitational lensing? Perhaps focusing the GW to an area of much...
  44. SamRoss

    I How can the stress tensor be non-zero where there is no matter?

    You're on Earth. You throw a ball and watch its trajectory. It's curved. That's because the Earth is curving space-time at every point along the trajectory. But the Earth itself is not present along the trajectory - there is no matter along the trajectory (let's ignore the air and any radiation...
  45. Raffaele

    B Black Holes, Gravitational Waves & Gravitons Explained

    I wonder why electromagnetic waves don't escape from a black hole while gravitational waves (obviously) do. What is the difference between the two kind of waves? And between gravitons and photons? thank you for your attention
  46. JD_PM

    A Understanding gravitational waves (GR)

    I am reading the following paper on the basic physics of a binary black hole merger: https://arxiv.org/ftp/arxiv/papers/1608/1608.01940.pdf Imagine two black holes orbiting each other until a point they merge. As you can see in Figure 1, the wave period is decreasing and thus the frequency...
  47. C

    A Do Moving Masses Slow Down Due to Gravitational Waves?

    Gravitational waves are produced by accelerating masses. Since all space is curved -- more curved near large masses stars, less curved in intergalactic space -- all moving masses are being accelerated to some degree. Do all moving masses therefore produce gravitational waves? If they do, will...
  48. S

    I What happens to gravitational waves?

    Two black holes that are orbiting and collide give off mass in the form of gravitational waves before the collision. Do these waves get absorbed by something, or is this mass lost to the universe?
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