What Is Loop Quantum Gravity

What is loop quantum gravity?

Loop quantum gravity is a mathematically well-defined, non-perturbative and background independent quantization of general relativity, with its conventional matter couplings. Research in loop quantum gravity today forms a vast area, ranging from mathematical foundations to physical applications.

What are the predictions of loop quantum gravity?

The most appealing aspect of loop quantum gravity is that it predicts that space is not infinitely divisible, but that it has a granular structure. The size of these elementary “quanta of space” can be computed explicitly within the the- ory, in an analogous way to the energy levels of the hydrogen atom.

What is the concept of quantum gravity?

Quantum gravity is an overall term for theories that attempt to unify gravity with the other fundamental forces of physics (which are already unified together). It generally posits a theoretical entity, a graviton, which is a virtual particle that mediates the gravitational force.

What is the problem of time in loop quantum gravity?

Motivated by the Immirzi ambiguity in loop quantum gravity and the near conformal invariance of the standard model of elementary particles, Charles Wang and co-workers have argued that the problem of time may be related to an underlying scale invariance of gravity-matter systems.

Why is it called loop quantum gravity?

The word loop appears in the name because the theory’s foundation is based on a rewriting of Einstein’s general relativity in terms of lines (instead of points as it’s usually done). It doesn’t change any of the physics but makes some calculations easier, especially when it comes to quantizing space-time.

What is the introduction to loop quantum gravity?

Loop quantum gravity is an attempt to formulate a quantum theory of general rel- ativity. The quantisation is performed in a mathematically rigorous, non-perturbative and background independent manner and standard matter couplings are considered.

Who discovered loop quantum gravity?

LEE SMOLIN, a theoretical physicist, is concerned with quantum gravity, the name we give to the theory that unifies all the physics now under construction. More specifically, he is a co-inventor of an approach called loop quantum gravity.

What is the best theory of quantum gravity?

By far the two most popular approaches are string theory and loop quantum gravity. The former is an example of an approach to quantum gravity in which the gravitational field is not quantized; rather, a distinct theory is quantized which happens to coincide with general relativity at low energies.

What math is needed for loop quantum gravity?

For loop quantum gravity, the most important background math needed is differential geometry, more specifically, the theory of connections on fiber bundles. For spin network theory, the most important math background is the theory of Lie groups, more specifically, the theory of covering groups of Lie groups.

What are the three ways to quantum gravity?

Approaches discussed include string theory, M-theory, and Smolin’s preferred approach, loop quantum gravity. Smolin suggests that these approaches may be approximations of a single, underlying theory.

Why is quantum gravity unsolved?

The biggest challenge with quantum gravity, from a scientific point of view, is that we cannot do the experiments required. For example, a particle accelerator based on present technology would have to be larger than our whole galaxy in order to directly test the effects.

What is the motivation for quantum gravity?

The most essential motivations for the development of a theory of Quantum Gravity are generally supposed to be based on two (probably interrelated) types of problems: (i) the mutual conceptual incompatibility between General Relativity on the one hand and Quantum Mechanics and Quantum Field Theory on the other hand, …

What are the arguments against loop quantum gravity?

The biggest problem with loop quantum gravity is that it has not yet shown that you can take a quantized space and take out a smooth space-time, while also a huge part is that it may not be possible to test for quantum gravity. A problem with the superstring theory is that it requires supersymmetry.

Does loop quantum gravity predict the graviton?

The current main approaches to quantum gravity, such as string theory and loop quantum gravity, predict the existence of gravitons with the same properties we see in the simple “quantized wave” approach. Even if gravitons exist, it’s likely that we’d never be able to detect them.

Is loop quantum gravity testable?

(PhysOrg.com) — As a quantum theory of gravity, loop quantum gravity could potentially solve one of the biggest problems in physics: reconciling general relativity and quantum mechanics. But like all tentative theories of quantum gravity, loop quantum gravity has never been experimentally tested.

What is the loop quantum gravity singularity?

Loop quantum gravity is believed to eliminate singularities such as the big bang and big crunch singularity. This belief is based on studies of so-called loop quantum cosmology which concerns symmetry-reduced models of quantum gravity.

What is a loop in physics?

A loop is any closed path through a circuit where no node quite once is encountered. A mesh is a closed path during a circuit with no other paths inside it.

What is the loop theory of the universe?

Loop quantum cosmology (LQC) is a finite, symmetry-reduced model of loop quantum gravity (LQG) that predicts a quantum bridge between contracting and expanding cosmological branches. The distinguishing feature of LQC is the prominent role played by the quantum geometry effects of loop quantum gravity (LQG).