Page added on 28 August 2019 and under construction.
Not part of talk/discussion. All pages below the Appendixes link are thus.
String Theory and Loop Quantum Gravity
1 String theory
- In physics, string theory is a theoretical framework in which the point-like particles of particle physics are replaced by one-dimensional objects called strings.
- It describes how these strings propagate through space and interact with each other.
- Thus string theory is a theory of quantum gravity. source see also here
- String theory is a set of attempts to model the four known fundamental interactions—gravitation, electromagnetism, strong nuclear force, weak nuclear force—together in one theory. ... Einstein had sought a unified field theory, a single model to explain the fundamental interactions or mechanics of the universe. source
2 Loop quantum gravity
- is string theory’s biggest competitor.
- It gets less press than string theory, in part because it has a fundamentally more limited goal: a quantum theory of gravity.
- Loop quantum gravity performs this feat by trying to quantize space itself — in other words, treat space like it comes in small chunks.
- In contrast, string theory starts with methods of particle physics and frequently hopes to not only provide a method of creating a quantum theory of gravity, but also explain all of particle physics, unifying gravity with the other forces at the same time.
- Alternately, the key insight from general relativity is that space-time is a dynamic entity, not a fixed framework.
- String theory is a background-dependent theory (built on a fixed framework), so it doesn’t currently account for the dynamic nature of space-time at the heart of relativity.
- According to the LQG researchers, a theory of quantum gravity must be background-independent, a theory that explains space and time instead of being plugged into an already-existing space-time stage.
- No background-dependent theory can ever yield general relativity as a low-energy approximation.