Exploring the Challenges of Quantizing Gravity and its Integration into QFT

In summary, physicists are facing several challenges in quantizing gravity and incorporating it into Quantum Field Theory. These challenges include the lack of a background for quantizing, difficulties with splicing space-time, the presence of many gauge symmetries in the metric, non-renormalizability, and issues with path integral quantization. While there may have been progress in these areas, there are still significant obstacles to overcome.
  • #1
brianhurren
71
2
why are physisist having so much trouble quantising gravity and getting it to fit into QFT?
 
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  • #2
This is a very broad question. One which cannot be answered in a short amount of space. I will list, for brevity, a few reasons:

1) Gravity is a curvature in space-time itself. There is no background with which to do the quantizing with.
2) Cannonical quantization of gravity is difficult due to the requirement of splicing space-time into space+time parts. The splicing is arbitrary and does not allow the degrees of freedom to be isolated.
3) The dynamical variable, the metric, has very many "gauge symmetries" in it which again makes the isolation of the real degrees of freedom difficult.
4) Gravity is a non-renormalizable theory (as far as we know). Which means that the infinities which arise from quantizing it cannot be canceled out with a finite number of parameters.
5) Path integral quantization already has issues relating to the measure of integration (whether it exists, whether it's a real measure, etc.), with gravity these issues have proved so far insurmountable.

I'm not at the forefront of quantum gravity, so I can't guarantee that none of the above issues have been solved. However, they do show you where some of the difficulties lie.
 
  • #3

Sabine Hossenfelder
My research area: The Phenomenology of Quantum Gravity

Incidentally, she notes that we do have a satisfactory theory of quantum gravity at low energies.
 
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1. What is the goal of quantizing gravity and integrating it into quantum field theory (QFT)?

The goal of this research is to develop a theory that can unify the two fundamental theories of physics, general relativity (describing gravity on a large scale) and quantum mechanics (describing the behavior of particles on a small scale). This theory, known as quantum gravity, would provide a more complete understanding of the fundamental nature of the universe.

2. What are the main challenges in quantizing gravity?

One of the main challenges in quantizing gravity is that the theory of general relativity, which describes gravity, is a classical theory, while quantum mechanics is a quantum theory. Combining these two theories requires overcoming mathematical and conceptual difficulties, such as the non-renormalizability of gravity and the lack of a clear picture of spacetime at the quantum level.

3. How can QFT be integrated into a theory of quantum gravity?

One possible approach to integrating QFT into a theory of quantum gravity is through the development of a quantum field theory of gravity. This approach involves treating gravity as a quantum field and applying the principles of quantum mechanics to it. Other approaches, such as string theory and loop quantum gravity, also aim to incorporate both QFT and gravity into a single framework.

4. What are the potential implications of successfully quantizing gravity and integrating it into QFT?

If successful, this research could lead to a more complete and unified understanding of the fundamental laws of nature. It could also have practical applications, such as providing a better understanding of black holes and the early universe, and potentially leading to the development of new technologies.

5. Are there any current theories or experimental evidence that support the idea of quantizing gravity and integrating it into QFT?

There are several theories, such as string theory and loop quantum gravity, that attempt to unify gravity and QFT. However, there is currently no experimental evidence to support these theories. The search for experimental evidence and the development of new theoretical frameworks are ongoing in the field of quantum gravity.

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