Exploring Quantum Gravity Theories and Gravitons

In summary, quantum gravity theories approach the idea of gravitons differently depending on the formalism used. In general, the concept of gravitons is expected to change as these theories do not rely on a background metric. In string theories, gravitons emerge as a degree of freedom of the quantized string, while in loop quantum gravity they are not considered a fundamental degree of freedom but rather emerge as a low-energy limit. The idea of gravitons is still an active topic of discussion and further research is needed to fully understand their role in quantum gravity theories.
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Are quantum gravity theories trying to progress on the assumption that there are such things as gravitons?
 
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It seems like an odd question to me. Should it not rather be an experimental question ?
 
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noblec04 said:
Are quantum gravity theories trying to progress on the assumption that there are such things as gravitons?
We had this discussion a couple of times; it depends what you mean by gravitons - and it depends which formalism of QG you are using.

One problem with gravitons is that the whole concept of particles in quantum field theory relies on a a background metric which allows you to define Fourier modes, Hilbert spaces with operators, propagators and particles. As it is expected that QG does not have such a background structure, the whole concept of particles and gravitons is expected to change.

In SUGRA you have a graviton field which is quantized and is rather close to a formalism with gauge bosons like the photon. In string theory the graviton emerges as one degree of freedom of the quantized string. In LQG the fundamental degrees of freedom are something totally different (spin networks) but it is expected that a graviton emerges as a low-energy limit of the theory, so it is not a fundamental degree of freedom.
 

1. What is quantum gravity and how is it different from classical gravity?

Quantum gravity is a theoretical framework that attempts to reconcile the principles of quantum mechanics and general relativity. Classical gravity, as described by Newton's law of universal gravitation, is based on the concept of gravitation as a force between massive objects. In contrast, quantum gravity suggests that gravity is caused by the exchange of particles called gravitons and operates on a much smaller scale.

2. What is the current status of research on quantum gravity theories and gravitons?

Quantum gravity theories and the existence of gravitons are still highly debated and are an active area of research in theoretical physics. While there are several proposed theories, such as string theory and loop quantum gravity, no definitive theory has been established yet. Scientists are continuing to explore and test these theories through experiments and mathematical models.

3. How do gravitons fit into the standard model of particle physics?

The standard model of particle physics is a widely accepted theory that describes the fundamental particles and their interactions in the universe. Gravitons, however, do not currently fit into this model as they are not yet experimentally proven. Some quantum gravity theories attempt to incorporate gravitons into the standard model, but their existence and role in the model are still being studied.

4. Can quantum gravity theories and gravitons help explain the mysteries of the universe, such as dark matter and dark energy?

While it is possible that quantum gravity theories and gravitons could shed light on the mysteries of the universe, such as dark matter and dark energy, there is currently no conclusive evidence to support these claims. Scientists are actively researching and testing these theories, but more research is needed to fully understand the nature of these phenomena.

5. How does the concept of spacetime change in quantum gravity theories?

In classical physics, spacetime is viewed as a continuous and smooth fabric. However, in quantum gravity theories, spacetime is seen as a discrete and quantized entity. This means that at a very small scale, spacetime is not continuous but rather made up of individual, discrete units. This concept is still being explored and studied in various quantum gravity theories.

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