Exploring the Possibility of Graviton Existence in Loop Quantum Gravity

In summary, Loop Quantum Gravity does not support the existence of graviton as a fundamental particle, but it can be approximated in a limit where spacetime behaves like a fixed background filled with gravitons. These gravitons arise from the linearized gravity approximation of GR, but higher order terms correct for the interaction between gravitons and approach the physics of full GR. This allows for the explanation of time dilation and length contraction, as observed in classical linearized gravity.
  • #1
jby
Does Loop Quantum Gravity support the existence of graviton?
I can't imagine how is it possible that graviton can exist if it is to agree with GR, since GR says that gravity is merely a curvature of spacetime and is isn't a force.

GR => SR => time dilation & length contraction =>> how does graviton be able to explain time dilation and stuff like that? Am I missing something here?
 
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  • #2
Originally posted by jby
Does Loop Quantum Gravity support the existence of graviton?

Loop quantum gravity will not have the graviton as a fundamental particle, but like any theory of quantum gravity, it (if it is viable) should have a limit in which spacetime behaves approximately like a fixed background filled with gravitons. That's what the early weave state constructions, and lately the Fock space representation and "shadow state" research is aimed toward.


I can't imagine how is it possible that graviton can exist if it is to agree with GR, since GR says that gravity is merely a curvature of spacetime and is isn't a force.

The leading terms of a perturbation expansion of GR gives rise to linearized gravity, which upon quantization leads to the graviton. The higher order terms will correct the graviton-graviton interaction to become successively closer to the physics of full GR. Of course, non-renormalizability means that you can play this game only so far, but renormalization group considerations require that the linearized gravity picture approximation to full GR become, upon quantization, a graviton approximation to full QG.


GR => SR => time dilation & length contraction =>> how does graviton be able to explain time dilation and stuff like that?

Do you understand how you can have time dilation and length contraction in classical linearized gravity?
 
  • #3
Do you understand how you can have time dilation and length contraction in classical linearized gravity?

No, I don't. Can you explain?
 
  • #4
In linearized gravity, you interpret the gravitational field as just a tensor field on flat spacetime. Nevertheless, you can recover position-dependent (i.e., gravitational) time dilation; in the linearized approximation, we calculate it as ordinary velocity-dependent SR time dilation, but because the motions of bodies in this flat spacetime are influenced by the gravitational field, so are their relative velocities, and you end up observing the same dilation you would get in a curved spacetime.

The details of this are worked out in section 3.6 of Ohanian and Ruffini, and sections 5.2 of the Feynman Lectures on Gravitation.
 

1. What is loop quantum gravity?

Loop quantum gravity is a theoretical framework that aims to reconcile general relativity and quantum mechanics by describing the fabric of spacetime as a network of tiny loops or threads. It proposes that space and time are not continuous, but rather discrete and quantized.

2. What is a graviton?

A graviton is a hypothetical particle that is believed to be the carrier of the gravitational force. In other words, it is the particle responsible for mediating the interactions between massive objects in the universe.

3. Why is it important to explore the possibility of graviton existence in loop quantum gravity?

If gravitons are found to exist in loop quantum gravity, it would provide a more complete understanding of the nature of gravity and the structure of spacetime. It could also help resolve some of the long-standing issues in physics, such as the incompatibility between general relativity and quantum mechanics.

4. How do scientists investigate the possibility of graviton existence in loop quantum gravity?

Scientists use mathematical equations and simulations to study the behavior of particles and spacetime in loop quantum gravity. They also conduct experiments using particle accelerators to test the predictions of the theory.

5. What are some potential implications of discovering gravitons in loop quantum gravity?

If gravitons are found to exist in loop quantum gravity, it could have a significant impact on our understanding of the universe and the laws of physics. It could potentially lead to the development of a unified theory of everything, which would explain all fundamental forces in nature. It could also pave the way for new technologies and advancements in space exploration.

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