# What is Graviton: Definition and 159 Discussions

In theories of quantum gravity, the graviton is the hypothetical quantum of gravity, an elementary particle that mediates the force of gravity. There is no complete quantum field theory of gravitons due to an outstanding mathematical problem with renormalization in general relativity. In string theory, believed to be a consistent theory of quantum gravity, the graviton is a massless state of a fundamental string.
If it exists, the graviton is expected to be massless because the gravitational force is very long range and appears to propagate at the speed of light. The graviton must be a spin-2 boson because the source of gravitation is the stress–energy tensor, a second-order tensor (compared with electromagnetism's spin-1 photon, the source of which is the four-current, a first-order tensor). Additionally, it can be shown that any massless spin-2 field would give rise to a force indistinguishable from gravitation, because a massless spin-2 field would couple to the stress–energy tensor in the same way that gravitational interactions do. This result suggests that, if a massless spin-2 particle is discovered, it must be the graviton.

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1. ### I Are gravitons necessary?

If gravity is not a force, but rather curvature of spacetime, are gravitons necessary to couple with gravitational field?
2. ### I Researchers find experimental evidence for a graviton-like particle

Researchers find first experimental evidence for a graviton like particle in a quantum material https://phys.org/news/2024-03-experimental-evidence-graviton-particle-quantum.html A team of scientists from Columbia, Nanjing University, Princeton, and the University of Munster, writing in the...
3. ### Second order diagram for the "scalar graviton"

It has been shown in the text that ##h_0 = \frac 1 {\Box} J## with the diagram and that ##h_1 = \lambda \frac 1 {\Box} (h_0 h_0) = \lambda \frac 1 {\Box} [( \frac 1 {\Box} J)( \frac 1 {\Box}J)]## with the diagram I was not sure if the next order diagram is or rather Thus, I substitute...
4. ### I Why is anyone looking for a graviton/force mediator if it's so widely accepted that that gravity is not a force, but physical curvature?

The Wikipedia article on Quantum Gravity reads: "The observation that all fundamental forces except gravity have one or more known messenger particles leads researchers to believe that at least one must exist for gravity. This hypothetical particle is known as the graviton" To which... yikes...
5. ### A Does attraction vs repulsion depend on graviton spin?

Hi Pfs, I read somewhere that if the graviton had a spin 1, then gravity would be repelling. Is there a formula showing that the attract-repel depends on the parity of the carrier's spin? thanks
6. ### I Does the graviton have to exist?

The graviton is the helicity two particle one gets when quantizing gravity in a metric formulation. There are two reasons why I have this question. 1.) If you formulate gravity in a tetrad formulation you don't seem to have a helicity two particle just the tetrad and the connection which both...
7. ### I Research on conservation of spacetime curvature

After trying to kinda get a picture of the field of play in quantum physics according to the standard model, a question came up. I tried to formulate the known bosons each as a particle transferring some property. 1. Photons transfer electric charge: the electromagnetic force gives attraction...
8. ### B So this is a bit of a duplicate.

In a phys.org article, the investigators make these statements: If gravitons can be detected at all, that implies to me that the universe is not as transparent to them as is being asserted in the article. How can you detect something without changing it - if nothing else, wouldn't that violate...
9. ### I Is the Continuum Limit of Spin Foam Dynamics Equivalent to Massless Gravitons?

The spin-foam approach to quantum gravity is part of the class of approaches, that also include loop quantum gravity and a variety of other methods, that sets out to quantize space-time rather than the gravitational force itself. But, according to a new paper, it turns out that "the continuum...
10. ### I Has anyone done a PPN formalism on Dark Matter? Or other non-GR?

This thought surprisingly came from thinking about the definition of temperature and the symmetry breaking that separated time from temperature. Which led to thoughts about symmetry breaking that separated QM from GR. Which led to to the symmetry breaking that separated dark energy from baryonic...
11. ### A Graviton propagator in Horndeski theory

Let ##\phi## be a scalar field and ##g_{\mu \nu} = \eta_{\mu \nu}+h_{\mu \nu}/M_p## where ##M_p## is the Planck mass (so we assume we deal with perturbations). Let ##\Lambda_2,\Lambda_3## be energy scales such that ##\Lambda_2 \gg \Lambda_3##. These are defined by ##\Lambda^2_2 = M_p H_0## and...
12. ### Graviton generator/emitter/antennae

In sci-fi series The Interscission Project, spacecraft use graviton generators, both for artificial gravity and for space/time travel. If these gens extend the gravity field, what would the simplest graviton antennae/emitter look like? By analogy with a membrane making sound, a flashlight...
13. ### I Could gravitons be dimensionless?

If the metric ##g_{\mu\nu}## is dimensionless and gravitons are quantum excitations of the metric does that mean that gravitons themselves are dimensionless? I say this as locally the metric is just the flat metric ##\eta_{\mu\nu}=\hbox{diag}(-1,1,1,1)## with the dimensions in the co-ordinates...
14. ### What would be the impact of the discovery of the Graviton in the world?

Summary:: <mentor moved to general discussion> I mean of the discovery of the Graviton or of any other unification theory that would explain gravity and would be compatible with quantum mechanics. And by impact I don't necessarily mean just the understanding of the world - this is implicit -...
15. ### A A question about graviton self-interaction

Would making the graviton self-interaction easily calculable solve most of the problems of quantum gravity?
16. ### A On non-perturbative renormalization and gravity

If we were to find some way to make the graviton self-interaction easily calculable, would applying non-perturbative renormalization on it seem any promising?
17. ### I What is the cross section of a graviton?

In particle physics there is usually a cross section for a particular particle . I came up with a cross section of 1.07 x 10^-42 m^2 for a graviton.
18. ### Graviton Speed & Cherenkov Radiation Effects

Hi All, Can somebody tell me what's the speed of the Graviton? As for Cherenkov Radiation, does exist a similar effect for Graviton? Thanks
19. ### B Is it possible to stop the graviton?

Is it possible to stop the graviton? If it is then anti-gravity is possible.
20. ### A Graviton Model: Can We Describe It Mathematically?

We know that the photon is the quanta associated with the electromagnetic field; and we've successfully observed gravitational waves due to LIGO. Is there any corresponding theoretical mathematical description of the graviton?
21. ### I Do particles in the universe exchange gravitons with each other?

Does each and every, say, proton, neutron and dark matter particle (DMP) exchange gravitons with each and every other proton, neutron and DMP in the universe? (Sorry if this question has been posted to the wrong forum. Advice re correct forum would be appreciated.) Art
22. ### A Is the Nexus Graviton a Thing?

Let me preface my question with the observation that I'm not an expert in either GR or QFT. But I do know enough to realize how much I don't know. I'm merely an aging Ph.D. physicist. That said, I viewed a ResearchGate preprint and was invited to comment on it. While I don't believe I'm...
23. ### I Geometry of GR v. Spin-2 Massless Graviton Interpretation

In classical general relativity, gravity is simply a curvature of space-time. But, a quantum field theory for a massless spin-2 graviton has as its classical limit, general relativity. My question is about the topology of space-time in the hypothetical quantum field theory of a massless spin-2...
24. K

### I Detecting Gravitons: Challenging the Foundations of General Relativity

If we were to able to detect gravitons then is it not that the basic assumption over which the general theory of relativity is flawed ?
25. ### A Why isn't cosmological constant a mass of the graviton?

The Lagrangian density for cosmological constant is $${\cal L} = \sqrt{g}\Lambda$$ Let us write, schematically, $$g=\eta+h$$ where ##\eta## is the flat Minkowski metric and ##h## is the spin-2 field. Expanding the square root for small ##h## we get something like {\cal L} = \Lambda + h\Lambda...
26. ### B Question about GR and Quantum gravity

First I don't have extensive knowledge about gravity beyond General Relativity, so please forgive my ignorance about this subject. I have confusion about the relation between GR and QM and I just want a general picture so that I can connect the dots. My questions: 1- Why do we need quantum...
27. ### I Graviton Scattering: Compute Amplitudes w/Einstein Gravity

Is it possible to compute scattering amplitudes of a graviton interaction taking Einstein gravity as an effective field theory at low energies? I did not study qft the proper way yet, so any clarifications on the subject would be welcome.
28. ### B Are inflatons the same as fewer gravitons?

I'm not very conversant in the subject. But it is my impression that the acceleration of the expansion of the observable universe has generated a theory that there might be a new particle (field?) call the inflaton. On the other hand, I thought I'd heard that scientists were trying to find...
29. ### I Higgs Boson vs Graviton: What's the Difference?

What's the difference between the Higgs boson and the hypothetical graviton particle? Do they both have to do with the mass of matter? I guess what I'm trying to ask is how are the Higgs particle and the graviton related.
30. ### How Does Graviton Polarization Affect Tensor Field Interactions?

Homework Statement We will treat the graviton as a symmetric ##2##-index tensor field. It couples to a current ##T_{\mu\nu}## also symmetric in its two indices, which satisfies the conservation law ##\partial_{\mu}T_{\mu\nu}=0##. (a) Assume the Lagrangian is...
31. ### A Investigations into a heuristic Lagrangian of graviton field

The following is taken from page 40 of Matthew Schwartz's "Introduction to Quantum Field Theory." The Lagrangian for the graviton is heuristically ##\mathcal{L}=-\frac{1}{2}h\Box h + \frac{1}{3}\lambda h^{3}+Jh,## where ##h## represents the gravitational potential. We are ignoring spin and...
32. ### A What would happen if only gravitons existed?

This is a somewhat weird question, but here it goes: What would happen if there were only gravitons? Would some other kind of particle appear in the Universe sooner or later? Would there be any chance for mass to appear in such a Universe (assuming that the graviton is a massless particle)...
33. ### I Understanding Spin-2 Bosons & Graviton Theory of Gravity

I'm somewhat familiar with the General Relativity description of gravity, at least conceptually. So I thought I'd ask about the graviton theory of gravity. Specifically, I've read elsewhere that a graviton must be a Spin-2 boson. Okay, given that as it may, how does a spin-2 boson differ from a...
34. ### I If there are gravitons, is space not curved?

If gravitons are proven to exist, would that mean space is not curved?
35. ### Gravitational Waves: Exploring What They Are

What are gravitational waves exactly?
36. ### Gravitons Energy: Range & Dependence on Scientists

There is theory that masses like charges are transfering force gague bosons. According to charges they transfering the boson called photon between the charges and responsible for the electromagnetic force. Photones qualities are that it doesn't have mass and behave like a particlee and also as a...
37. ### Higgs vs Graviton: Causes of Mass & Gravity

Forums relating to this have been up constantly, but just to clarify, they are not one and the same, to the best of my knowledge. Higgs causes mass, Graviton causes gravity. Higgs has an influence on the graviton, if you think about it. The Higgs boson causes mass which in turn is affected by a...
38. ### Can the Graviton be faster than light?

Hello everyone, I was thinking of the 4 forces and in particular of the gravity force. We know that black holes and their gravity force can bend light and light gets lost on black holes. How can the ipothetic particle of the graviton interact with the photon? I thought that if the interaction...
39. ### Decay through gravitional interaction

Hello, I know that the gravitational force is the weakest of all forces (it is 10^-38 times weaker than the strong force), so it isn't possible a particle to decay through gravitational interaction. As far as I know, the strength of fundamental forces can change during different ages of the...
40. ### Why is gravity but not EM 'ripples' in spacetime?

Why do we say gravity [GR] is a theory about ‘spacetime curvature’ and gravitational waves are ‘ripples’ but nobody uses such a description for electromagnetic fields? Don't EM waves 'ripple' spacetime? For example, one might imagine different types of spacetime curvature associated with each...
41. ### How Can Gravitons Escape A Black Hole?

Past the event horizon of a black hole, gravity is so immense that even light can't escape. Wouldn't this cause the the gravitons, which travel the speed of light, to be trapped, making a singularity?
42. ### Question about the Graviton theory

In QFT, the other 3 fundamental forces (electromagnetism, weak and strong nuclear forces) are interpreted as being mediated by quanta of their particular field, what we call bosons or "force carrier particles". These mediate the relevant force between particles. As I understand it, one...
43. ### What is interaction Lagrangian of matter and graviton fields

What is the interaction Lagrangian of matter and graviton fields?So(on the answer)we can say about the nonrenormalization.Why is the divergence of two gravitons diagram able to be the limit of the coincidence of the verties.So we can say about the nonrenormalization.
44. ### Why does not the graviton cause wavefunction collapse?

The modern view of the measurement problem is that any interaction of a particle (say an electron) will cause its wavefunction to 'collapse' in the process called decoherence. No need for conscious observers, interaction with any other particle will cause decoherence hence collapse of the...
45. ### Graviton vs Einstein's Curvature of Spacetime

As far as I understand it, Einstein theorized that gravity was the result of the curvature of space created by the presence of mater/energy, but that idea seems like it does not meld well with the idea that gravity is the result of a specific force carrying particle, as with the other...
46. ### Is this idea remotely possible in the distant future?

Hello, I was just brainstorming for futuristic inventions with context for a sci-fi, high fidelity game (because I'm too cool to revise for exams) - and I thought of one, but my physics and engineering knowledge is at best sketchy when it comes to gravity and nuclear fusion combinations, I was...
47. ### Is the graviton the only thing to find in LQG?

Has anyone thought if the there are particles to find in LQG, other than gravitons, when going to a "more classical limit"? Or that GR is not the only thing to find at classical limit, but, maybe, something like a GUT, for example, naturally emerging?
48. ### Graviton represented as a gluon pair

I'm not a physicist, but I'm pathologically curious about such things. I've recently heard that there is a growing school of thought among theoretical physicists that the graviton (and resultant gravitational force) is actually just an extension of the strong force conveyed by a gluon pair. This...
49. A

### The General Theory of Gravity and Light

Hello! I am an undergraduate student currently pursuing my Bachelor's before I attain my PhD in Particle Physics. I do however have an exciting concept I would like to have to my name before I disclose it to the world; therefore, I was wondering how this would happen, and if it is possible...
50. ### Graviton exchange for two freely propagating particle:solution String theory?

Consider the feynman diagramms for two freely propagating particles...Correction from one graviton exchange. Correction from two graviton exchange.The problem at hand is the divergence (of the math) at arbitary energys and each additional graviton exchange. So there are several resoultions and...