|Quantum Field Theory|
|... no spooky action at a distance (Einstein)|
|Relativistic Quantum Mechanics|| Klein-Gordon Equation|
|The Dawn of QFT|| Spinors|
Feynman Slash Notation
Conformal Field Theory
Countdown to the Standard Model
|From a framework to a model|| Yang-Mills Theory|
|Semi-Classical Gravity and the Dark Age|| Hawking Radiation|
Problems with the Standard Model
|Beyond the Standard Model|| Beyond the Standard Model|
Theory of Everything
|Related||De Donder-Weyl Theory|
Quantum Gravity refers to a theory of Gravity that is compatible with Quantum Mechanics. It often refers to the theory of gravity being General Relativity. Usually, it is possible to quantise a fundamental force easily using the canonical method, which makes one realise that the force is mediated by particles, etc. However, this is not possible in the context of Gravity, because the Perturbation Series diverges, and the result is non-renormalisable.
Why one can't quantise gravity ordinarilyEdit this section
In the standard way of "second" quantisation, one quantises the forces in a similar way to matter, assigning their quanta with fields (not wavefunctions though), and so on. However, when one does this for gravity, this results in a non-renormalisable divergent Perturbation Series.
Intuitively, one can think of it in this way:
- If there is a system of particles with a non-vanishing Stress-Energy-Momentum Tensor, interacting gravitationally, thus through gravitons, then these gravitons themselves have a non-zero Stress-Energy-Momentum Tensor, and therefore interact gravitationally themselves. Therefore, there are more gravitons, ad infinitum. This results in a divergent series mathematically. However, this happens with Quantum Chromodynamics, too, so we do not lose faith so easily. Unfortunately, while in the case of Quantum Chromodynamics, the result is Renormalisable, it is not so in the case of gravity.
Attempt to quantiseEdit this section
Below is an out line of the attempt to quantise gravity ordinarily :
Where is the Graviton Field.
Now, write down the Einstein-Hilbert Action:
Examples of Theories of Quantum Gravity (ToQGs)Edit this section
ReferencesEdit this section