Could the quanta of gravity be something other than a spin-2 graviton?

In summary, according to GR, gravitational waves are a predicted effect of the theory, while QM claims that all waves are also particles. However, it is not necessary for a spin 2 graviton to exist to produce gravitational waves - even "massless" particles like atoms can produce them. This information has no implications for the way gravity arises in string theory - only the linearized form of relativity is achievable.
  • #1
ensabah6
695
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GR predicts gravitational waves, and QM says all waves are also particles.

But does the particle of gravity have to be a spin-2 graviton? could the particle of gravity be, for example, a quanta of space-time curvature?
 
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  • #2
As I understand things, if you have a spin 2 boson, it HAS to be the quanta of gravity.*

But there's no rule saying it has to go the other way-- just because you have quantum gravity, doesn't mean you have to have a spin 2 boson.

This is just what I've been told.

* I've seen it claimed a couple of times on this forum that there is actually a proof that any spin 2 boson has to be the quanta of gravity, and it was claimed that this proof was written by Feynman. I'd be very curious to see that if anyone knows where to find it!
 
  • #3
Take a look at:

http://egregium.wordpress.com/2007/05/24/is-there-more-to-gravity-than-gravitons/
 
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  • #4
no gravitons

ensabah6 said:
GR predicts gravitational waves, and QM says all waves are also particles.

But does the particle of gravity have to be a spin-2 graviton? could the particle of gravity be, for example, a quanta of space-time curvature?

I think there does not even exist a graviton. Gravitation could be an induced force, resulting from all the other forces (original idea of Sakharov). Also, it is clear (for me) that describing gravitation by means of virtual particles quickly leads to a contradiction:
Let us suppose indeed that they exist. Even if they are supposed to be (rest)massless spin 2 particles, they should contribute to the total energy of the system, just like the virtual (massless) photons of the electromagnetic field somehow contribute to the mass of the system. The nonlinear character of the Einstein equations also seems to indicate that the "gravitational field" itself gravitates (I know this is strictly not correct, I use this only to guide the intuition). So, if the gravitons themselves are subject to the gravitational field, one should have virtual gravitions exchanging between these gravitons and other gravitons or other masses - AND - you can not stop this process: you just have to keep on adding gravitons to include all the reactions. So, you get an infinite number of gravitons per unit volume resulting in an infinite energy density and the whole of space would be just a massive "block" of gravitons. A ridiculous situation. This proofs that gravitons can not exist.


Rudi Van Nieuwenhove
 
  • #5
Coin said:
As I understand things, if you have a spin 2 boson, it HAS to be the quanta of gravity.*

You have not understood "things" correctly! even atoms can be a spin 2 bosons. Have you heard about particles called the tensor mesons?

But there's no rule saying it has to go the other way-- just because you have quantum gravity, doesn't mean you have to have a spin 2 boson.

It can be shown that "massless" "spin-2" object does satisfy the LINEARIZED Einstein equations, hence the name GRAVITON.

regards

sam
 
  • #6
ensabah6 said:
GR predicts gravitational waves, and QM says all waves are also particles.

But does the particle of gravity have to be a spin-2 graviton? could the particle of gravity be, for example, a quanta of space-time curvature?

In "QFT in curved spacetime", Robert Wald states that in highly curved or fast changing gravitational field there is no particle interpretation of QFT; it's all just fields. So strictly speaking, in high curvature or fast changing gravitational fields, there are no particles at all - not even gravitons.
 
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  • #7
Sorry for refreshing this older thread. So does http://arxiv.org/abs/gr-qc/0409089 have any implications for the way gravity arises in string theory? Is it only the linearized relativity that can be obtained?
 

1. What is a spin-2 graviton?

A spin-2 graviton is a hypothetical particle that is thought to be responsible for carrying the force of gravity in quantum field theory. It is predicted by the theory of general relativity and is believed to have a spin value of 2, which means it has two units of angular momentum.

2. Why do some scientists believe that the quanta of gravity could be something other than a spin-2 graviton?

Some scientists believe that the quanta of gravity could be something other than a spin-2 graviton because the current theory of general relativity, which predicts the existence of spin-2 gravitons, is not compatible with the principles of quantum mechanics. This has led to the search for alternative theories, such as string theory, which suggest that the quanta of gravity may not necessarily be spin-2 particles.

3. What are some alternative theories that suggest the quanta of gravity could be something other than a spin-2 graviton?

Some alternative theories that suggest the quanta of gravity could be something other than a spin-2 graviton include string theory, loop quantum gravity, and graviton condensate theory. These theories propose different types of particles, such as gravitons with different spin values, or even a collective state of particles, as the carriers of gravity.

4. How could we test the idea that the quanta of gravity may be something other than a spin-2 graviton?

One way to test this idea is through experiments that can measure the properties of particles that may be potential carriers of gravity. For example, the Large Hadron Collider at CERN is currently searching for evidence of supersymmetric particles, which could potentially be spin-2 gravitons or other particles that carry the force of gravity.

5. What implications would a discovery of a non-spin-2 graviton have on our understanding of the universe?

A discovery of a non-spin-2 graviton could have significant implications on our understanding of the universe. It could potentially lead to a unification of the theories of general relativity and quantum mechanics, providing a more complete understanding of the fundamental forces in the universe. It could also shed light on the mysterious concept of dark matter and dark energy, which are currently not fully understood by physicists.

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