8
$\begingroup$

What is the difference between gravitons and gravitational waves? So as I understand, gravitational waves are predicted by and part of the theory of general relativity, whereas gravitons are predicted by the standard model.

We have indirect evidence for gravitational waves? So it seems that they probably exist--but what about gravitons? How are gravitons related to gravitational waves? Are gravitons and gravitational waves just two different ways of talking about the same thing?

$\endgroup$
  • 3
    $\begingroup$ Although we do not yet have a theory of gravitons, this seems to be the same question as What is the relation between electromagnetic wave and photon? $\endgroup$ – ACuriousMind Oct 28 '15 at 20:24
  • 1
    $\begingroup$ Gravitons aren't "predicted" by the standard model any more than photons or electrons are. The standard model is merely a quantum field theory fit to observed data. Since gravitons have not been observed, yet, and it's not even clear that anything resembling a graviton even exists, the folks who curate the standard model had not had any reason to fit them into the existing framework. We have indirect evidence for gravitational waves and we are trying to detect them directly at the moment, but I am not aware that anybody has made any workable suggestion on how one could detect gravitons. $\endgroup$ – CuriousOne Oct 28 '15 at 20:44
9
$\begingroup$

In physics, gravitational waves are ripples in the curvature of space-time which propagate as waves, travelling outward from the source. Predicted in 19161 by Albert Einstein to exist on the basis of his theory of general relativity,3 gravitational waves theoretically transport energy as gravitational radiation. Sources of detectable gravitational waves could possibly include binary star systems composed of white dwarfs, neutron stars, or black holes. The existence of gravitational waves is a possible consequence of the Lorentz invariance of general relativity since it brings the concept of a limiting speed of propagation of the physical interactions with it.

Gravitational* waves have not been directly observed, experiments are designed trying to detect them. Since they are predicted from the General Relativity theory there is trust that they exist and the difficulty comes from the very weak gravitational interaction. General Relativity is a classical theory.

As pointed out in the comments to the question, electrodynamics as formulated with Maxwell's equations is also a classical theory, and describes electromagnetic waves, light being one part of the spectrum.

The underlying framework of nature though is quantum mechanical. The quantization of electrodynamics QED is a successful theory which has the photons as the carrier of the electromagnetic interactions and the building stones of the classical electromagnetic wave. It can be shown that the classical wave emerges from innumerable photons with energy $=h\nu,$ $\nu$ the frequency of the classical wave.

Gravitons are to gravitational waves the theoretical analogue of photons for electromagnetic waves. They are the proposed carriers of the gravitational interactions at the quantum level, and are expected to appear naturally in a future theory of quantized gravity. At the moment quantization of gravity can be accommodated in string theories, which are at the frontier of research for particle physics. The standard model involves only the three other forces , not the gravitational. A future standard model should have both the present standard model and quantization of gravity, a Theory Of Everything (TOE).

So photons are the building blocks of light, and gravitons are (hopefully) the building blocks of gravitational waves.


*LIGO has just (Feb 11,2016) announced the observation of gravitational waves https://dcc.ligo.org/public/0122/P150914/014/LIGO-P150914%3ADetection_of_GW150914.pdf

$\endgroup$
  • 1
    $\begingroup$ Hi! You need to update the recent detection of gravitational waves, IMO. $\endgroup$ – user36790 Feb 12 '16 at 2:15
-2
$\begingroup$

In theoretical physics, a hypothesis states that the "graviton" particle is an elementary particle that mediates the force of gravitation in the framework of quantum field theory and is the source of the gravitational wave. Theory also suggests that this particle, if it exists, is expected to be massless, because the gravitational force appears to have an unlimited effective range though-out our known space-time universe. Current theory also states that the graviton particle must therefore be defined as a spin-2 boson, also known as a tensor boson, which differs from a spin-0 scalar boson or a spin-1 vector boson. This graviton/gravitational wave relationship has been theorized based on our knowledge that three other known forces of nature are also mediated by elementary particles: electromagnetism by the photon, the strong interaction by the gluons, and the weak interaction by the W and Z bosons. Additionally, the same formula which relates electromagnetic wavelength to photon energy has been proposed for determination of the relationship between the gravitational wavelength and the graviton particle. This formula suppositionaly provides a relation between wavelength and energy and is calculated with the Planck-Einstein relation: E=h/ν This states that the energy of a photon (or graviton), E, is proportional to its frequency, ν, and the constant of proportionality, h, known as the Planck Constant. Several equivalent forms of the relation exist. Additionally, the frequency, ν is related to the speed of light and wavelength as follows: ν = c/λ However, in order to substantiate this conclusion, and the resulting calculated wavelength and or frequency of a graviton or gravitational wave from this relationship, we must first make a leap of faith that the speed of light c (of a photon) 186282 miles/s is actually the governing velocity for a graviton? Additionally, we must also assume that the Quantum of Action or Planck Constant: 6.626x10-34 J.s (4.1357x10-15eV.s) is valid for describing the relationship between a graviton and a gravitational wave, like it is similarly used to describe the relationship between a Photon and an electromagnetic wave.
I would propose here that neither is the correct case and that theoretical conclusions to date are wrong not only about the velocity of a graviton particle and gravitational waves, but also regarding the (Planck) Constant that is being used to relate the graviton to the gravitational wave! If one looks simply at the phenomenon of spooky action at a distance, this near instantaneous interaction between completely unrelated particles indicates the presence of some unknown wave or particle interaction that is taking place at speeds that are several orders of magnitude higher than the speed of light, c!
And I would further propose at this time that graviton and gravitational waves are related by some unknown Constant which is differing from the Planck’s Constant.
Taking into account the above suggestions, yields a graviton to gravitational wave interrelating equation as follows:
Eg = Hg/ νg where Hg = New Constant (relationship) And: νg = d/ λg where d = Speed of a graviton through a
near hard vacuum. P. Kinsman Aerospace Scientist AIAA

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.