The “theory of everything” is one of the most cherished dreams of science. If it is ever discovered, it will describe the workings of the universe at the most fundamental level and thus encompass our entire understanding of nature.
(Source: newscientist.com – Knowing the mind of God: Seven theories of everything )

String theory
String theory is a developing branch of quantum mechanics and general relativity with the aim of merging and reconciling the two areas of physics into a quantum theory of gravity. The strings of string theory are one-dimensional oscillating lines, but they are no longer considered fundamental to the theory, which can be formulated in terms of points or surfaces too.

Loop quantum gravity
Loop quantum gravity (LQG), also known as loop gravity and quantum geometry, is a proposed quantum theory of spacetime which attempts to reconcile the theories of quantum mechanics and general relativity. Loop quantum gravity suggests that space can be viewed as an extremely fine fabric or network “weaved” of finite quantised loops of excited gravitational fields called spin networks.

Causal dynamical triangulations – CDT
Causal dynamical triangulation (abbreviated as “CDT”) invented by Renate Loll, Jan Ambjørn and Jerzy Jurkiewicz, and popularized by Fotini Markopoulou and Lee Smolin, is an approach to quantum gravity that like loop quantum gravity is background independent. This means that it does not assume any pre-existing arena (dimensional space), but rather attempts to show how the spacetime fabric itself evolves.

Quantum Einstein gravity
In quantum Einstein gravity, space-time at the smallest scales is fractal and the number of dimensions shrinks from the familiar four to two.

Quantum graphity
Tomasz Konopka, Fotini Markopoulou-Kalamara, Simone Severini and Lee Smolin of the Canadian Perimeter Institute for Theoretical Physics introduced a graph model that they called Quantum Graphity. An argument based on quantum graphity combined with the holographic principle can resolve the horizon problem and explain the observed scale invariance of cosmic background radiation fluctuations without the need for cosmic inflation.

In the quantum graphity model, points in spacetime are represented by nodes on a graph connected by links that can be on or off. This indicates whether or not the two points are directly connected as if they are next to each other in spacetime. When they are on the links have additional state variables which are used to define the random dynamics of the graph under the influence of quantum fluctuations and temperature. At high temperature the graph is in Phase I where all the points are randomly connected to each other and no concept of spacetime as we know it exists. As the temperature drops and the graph cools, it is conjectured to undergo a phase transition to a Phase II where spacetime forms. It will then look like a spacetime manifold on large scales with only near-neighbour points being connected in the graph.

Internal relativity
Every particle in the universe has a property called “spin”, which can be loosely thought of as what happens to the particle when it is rotated. Dreyer’s model imagines a system of spins existing independently of matter and arranged randomly. When the system reaches a critical temperature, the spins align, forming an ordered pattern.

E8 – Grand Unification Theory
Antony Garrett Lisi’s model is a variant and extension of a Grand Unification Theory (a “GUT,” describing electromagnetism, the weak interaction and the strong interaction) to include gravitation, a Higgs boson and fermions in an attempt to describe all fields of the Standard Model and gravity as different parts of one field over four dimensional spacetime. More specifically, Lisi combines the left-right symmetric Pati-Salam GUT with a MacDowell-Mansouri description of gravity, using the spin connection and gravitational frame combined with a Higgs boson, necessitating a cosmological constant. The model is formulated as a gauge theory, using a modified BF action, with E8 as the Lie group. Mathematically, this is an E8 principal bundle, with connection, over a four dimensional base manifold.

Sources:
- Knowing the mind of God: Seven theories of everything
- Four radical routes to a theory of everything
- An Exceptionally Simple Theory of Everything

The path is not materialistic
The extraordinary in the GUT-theories is the non materialistic approach to understand the universe. In contrast to the older models, the Grand Unified Theories describes a universe only based on geometry, mathematic and language patterns, but not on fundamental particles. Is the mainstream recognizing the fact that the factory of space-time is consciousness and language?

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Tags: Antony Garrett Lisi, Causal dynamical triangulations, CDT, E8, fermion, fractal, general relativity, geometry, Grand Unification Theory, gravitation, Higgs boson, holographic universe, Internal relativity, Loop quantum gravity, LQG, mathematic, Quantum Einstein gravity, quantum fluctuation, Quantum graphity, quantum mechanic, spacetime, String Theory, symmetry, theory of everything