Gravitational waves Definition and 334 Threads

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. 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...
  2. 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
  3. 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...
  4. 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...
  5. 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?
  6. K

    I Gravitational Waves: Prerequisites for Study

    I am interested in studying at least the basics of gravitational waves. How much knowledge do I need to have about waves in general before procceding?
  7. .Scott

    I Gravitational Waves: Questions on Mass & Escape Velocity

    A few years go, we detected a gravity chirp from the collapse of binary black holes. The initial total mass was about 21.7 solar masses. The end result was about 20.8 solar masses. The difference was presumably contained in the gravity wave. I believe, under the right conditions, an object...
  8. P

    I Gravitational Waves & Matter: Causes, Effects & Thresholds

    From what I have read gravitational waves are caused by the acceleration of massive object causing ripples in space time. What specifically causes this, and how does general relativity predict these. Does it have to be a high density of matter, or a large amount of it. How do these waves affect...
  9. 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...
  10. C

    I Detect Negative Mass Matter: Experiments in Solar System

    How could we detect negative mass matter? The only proposal I've ever heard of is that we could detect there's a cutoff frequency in the gravitational waves we receive, due to attenuation of those lower frequency waves by negative matter. Are there more experiments that could be conducted...
  11. alan123hk

    B Gravitational waves for data communication?

    When and how can the gravitational wave be used for data communication, which the speed be much faster than the current technology by means of electromagnetic wave like 5G, 6G..etc wireless systems ?
  12. Y

    B Gravitational waves of moving or vibrating masses

    I am curious if the motion of massive object can effect it's gravitational influence due to the fact that gravitational waves travel at the speed of light. For a weak analogy, consider how a small object can make bigger ripples in the water if it is moving around more. I am curious if there...
  13. 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?
  14. Kaustubh Namjoshi

    I Gravitational waves and the multiverse

    Assuming that the multiverse hypothesis is true and a singularity at the center of a black hole can give rise to another baby universe. Can we detect such an event in the LIGO observatory?
  15. Ebanflo

    I Is any attention being given to Conformal Cyclic Cosmology?

    Conformal Cyclic Cosmology, or CCC, is a hypothesis put forward by Roger Penrose in the early 2000s. My understanding of physics is lacking so my explanation will not be that clear, but I will summarize it here. Essentially, the existence of a previous spacetime, or "aeon," is postulated. This...
  16. l0st

    I Gravitational Waves Cause Uniform Space Expansion: Exploring MNRAS Papers

    I am looking at a couple of very interesting papers, published in MNRAS, that deduce, that the accelerated expansion of the Universe we observe can be attributed to gravitational waves, produced by a very distant merger of two or more universe-mass-scale black holes. The last one is on the...
  17. T

    B Neutron Star Collisions: Creation of Heavy Elements and Their Fate

    When neutron stars collide, heavy elements, such as gold, are created. Are these elements ejected from the system to be found, say, here on earth? Or do they fall back into the newly created black hole?
  18. B

    B Gravitational waves and refraction patterns....

    I was doing a thought experiment last night. Gravitational waves, being like any other type of wave would cancel each other out and create a refraction pattern of strength. While we do not have definitive proof there is a black hole at the center of every Galaxy, we do know, through...
  19. Islam Hassan

    I Gravitational Waves vs Gravitons

    Are gravitons postulated to be excitations of gravitational waves? If so, and since gravitational waves have been unambiguously observed, then gravitons must exist, no? If not, then what is the postulated relationship between gravitational waves and gravitons? Are both deemed/postulated to...
  20. yerty4235437y

    B Could Gravitational Waves Allow for Time Travel?

    it seems to me that during a high energy event that a space time compression wave would be created which would then normalize as it spread out. A particle on a back end wave would become close enough to the front end wave that it could tunnel between the two as "distance" is compressed. We...
  21. negative

    B Black Hole Paradox: Exploring Gravity Waves

    well since gravity waves are supposed to have mass, they are supposed to be effected by gravity itself, and :/ how are we supposed to detect gravitational waves emitted from a black hole when none can get out?
  22. J

    I Max Amplitude Gravitational Waves: 2?

    I am curious as to what the maximum amplitude of gravitational waves is. I have read that the maximum amplitude as such is equal to two but I cannot seem to find again a reference that states this clearly.
  23. alantheastronomer

    A Gravitational Waves: Expansion of Spacetime?

    Gravitational waves are quadrupoles, they bend and stretch spacetime. Does the expansion of spacetime due to gravitational waves exceed flat (Minkowski) spacetime or is flat spacetime it's limit?
  24. Andrew Washington

    B LIGO Observation of Gravitational Waves: Questions Answered

    I am doing a term paper on G. Waves and I have a couple of questions about them. - How do we know that the G. Waves detected by LIGO on September 14, 2015, come from 1.5 billion light years? - How is Einstein's Theory related to them?
  25. BlackholeGirl

    I [Question] Tell me the latest catching news about black holes

    Hello, Thank you for opening this thread. I am strongly interested in the universe, especially black hole. Though I am only eighteen years old, the more I read books about a black hole, the more my interest is getting powerful. Therefore, I want to know the latest and exciting news about...
  26. arupel

    A Gravitational Waves: Verification Accuracy & Physicists' Opinions

    From what I understand the LIGO experiments were the first in the road to demonstrating the existence of gravitational waves. There was a dicussion about this on Utube where someone pointed out that the polarized light scattered from dust, being much larger, could mask the the effect of...
  27. H

    B Why does a LIGO arm stretch and not move in unison?

    LIGO is most sensitive to a GW from directly above/below. As a transverse wave hits an arm why don't the laser source and the mirror move in unison -- thereby covering up the distorted motion?
  28. P

    Exploring the Surface of a Black Hole's Event Horizon

    Does the event horizon of a black hole really represents the surface of the "star" (or mass) itself? What I mean to say is: That the event horizon is the (let's say it this way) sphere surface where the scape velocity is => than the speed of light. So it is not necessary for event horizon to be...
  29. 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...
  30. V

    I Gravitational Waves Affecting EM Fields: Evidence & Implications

    Suppose a gravitational wave propagating through space encounters a strong magnetic field (for example the wave might pass through a magnetar with a B field strength of 10^{11} Tesla). Would there be any observable perturbation in the magnetic field itself? In other words would the gravitational...
  31. L

    B Implications of gravitational waves from the Big Bang?

    My understanding is that gravitational waves have not been detected from the proposed inflationary epoch of the big bang, only from the merger of two super massive objects. Is that correct? Are GWs predicted from the big bang in models where there is no inflationary epoch? If GWs are detected...
  32. N

    B How to measure Gravitational waves

    Why are clocks not used to measure gravity waves? Spacetime wriggle and time must also vary. It is possible to measure time very accurately and with a high resolution. Så why not use clocks to detect gravity waves?
  33. R

    B Do Objects in Motion Create Gravitational Waves?

    does any object with mass that moves create a gravity wave? So if I wave my hand it is in fact creating gravity waves, just very small ones
  34. A

    B How does LIGO measure gravitational waves

    I'm aware that the LIGO system uses interferometry but I'm confused how it works in this case. Do they test both beams of light? Or do they use one beam to test the wavelength of the other and see the difference? Also it is sensitive up to 10 e-18 meters, is that for the change in wavelength or...
  35. Auto-Didact

    A Falsifications and constraints due to GW measurements

    This thread is to serve as - a collection of theories that have been falsified by and/or have had new constrained placed on them by the ongoing gravitational wave measurements. - a place to discuss the further constraining/falsifying of still existing models using GW data. I'll start by posting...
  36. jerromyjon

    B Gravitational waves and "warp drive"

    I have no idea where this belongs or if it will be deleted but would Alcubierre drive cause detectable gravitational waves? And since I'm heading out on this limb would the direction of propulsion be indiscernible? As per the Wikipedia description it follows from a solution to the same general...
  37. F

    I Can two gravitational waves orbit each other?

    Since gravitational waves have energy, they can curve space all by themselves. I wonder in what conditions, if any, two gravitational waves could orbit each other. Thanks.
  38. S

    I Is the speed of gravitational waves non- dispersive?

    Dear all, In a recent talk, I have heard that speed of gravitational waves is non-dispersive. How is it proved "observationally" in LIGO detections that all the frequencies travel with the same speed, so one can say the speed is non-dispersive?
  39. nmsurobert

    B Are Gravitational Waves accepted?

    Is this accepted throughout the science community now? Is there any doubt that LIGO actually detected gravity in the form of waves?
  40. Auto-Didact

    A Erebons: Planck mass Dark Matter particles

    Erebon theory is a novel explanation of dark matter recently invented by Roger Penrose. Erebons are scalar particles of the order of a Planck mass which can only interact gravitationally. When erebons decay, they release their energy as oscillating classical gravitational waves on the order of...
  41. K

    B Can gravitational waves interfere with each other?

    Just a thought I had...
  42. mfb

    I Virgo joins the measurement of gravitational waves

    Finally... this month, Virgo and LIGO look for gravitational waves together (they started yesterday). The Virgo detector is a bit less sensitive than the LIGO detectors at the moment, but it is still a big improvement: It is an independent experiment, on a different continent run by different...
  43. 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
  44. Auto-Didact

    A Penrose: Noise in LIGO signal implies CCC

    Roger Penrose, July 2017. Correlated "noise" in LIGO gravitational wave signals: an implication of Conformal Cyclic Cosmology
  45. Buzz Bloom

    I What is the nature of the force causing deviation from a circular orbit in GR?

    I thought I understood the following, but recently I am having doubts about my understanding. https://www.physicsforums.com/threads/is-a-2-body-elliptical-orbit-stable-in-gr.898258/ @PAllen said: I don't believe any orbital system is stable in GR due to gravitational radiation. The time scale...
  46. N

    B Gravitational Waves: Mass Interaction Questions Answered

    Hey all. Since gravitational waves travel at the speed of light, when they are "escaping" from mass, doe's their intensity lower? If so what mass would be needed to completely absorb a gravitational wave given the wave's properties? Any help appreciated.
  47. A

    I Gravitational Waves Impact Earth's Orbit: Effects & Possibilities

    What happens to the path of Earth if a strong gravitational waves hit earth. Would there be a possibility of Earth moving out/changing the path of its current orbit? Can a high frequency gravitational waves knocks the Earth out from sun's gravitational field? (I know it is very unlikely that a...
  48. Paul Colby

    I Are Evanescent Gravitational Waves Measurable

    Hi, (all discussions here are in the extreme weak field approximation about Minkowski space) For the last couple of years I've been looking into the production and reception of radio frequency gravitational waves. It's kind of a retirement project the main goal of which is to get a better...
  49. K

    I Signatures of extra dimensions in gravitational waves

    Signatures of extra dimensions in gravitational waves David Andriot, Gustavo Lucena Gómez (Submitted on 24 Apr 2017) Considering gravitational waves propagating on the most general 4+N-dimensional space-time, we investigate the effects due to the N extra dimensions on the four-dimensional waves...
  50. E

    How Does LIGO Detect Gravitational Waves Using Laser Interferometry?

    Homework Statement In-phase light from a laser with an effective power of 2x105J and a wavelength of 1064nm is sent down perpendicular 4km arms of the LIGO detector. (i) Determine the number of photons traveling in the interferometer arms. (ii) Assuming the detector is sensitive enough to...
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