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The basic properties of Lie groups and related concepts are collected. This includes a discussion of coadjoint orbits and their symplectic structure, which helps to understand the semi-classical origin of imortant quantum spaces discussed in later chapters.
The higher-spin gauge theory arising on 3 + 1 dimensional covariant quantum spacetime is elaborated in detail, including the full fluctuation spectrum and the no-ghost theorem.
Gravitational plane waves and their detection start the chapter off in parallel with electromagnetic plane waves and their detection. Geodesic deviation is reviewed and allows for a brief introduction to LIGO. The stress tensor source of radiation (and therefore, at least local, plane waves) and its conservation of energy and momentum are tied to the radiation solution of the linearized form of Einstein’s equation. A highlight is the role of gauge freedom in making gravitational plane waves physically relevant (by gauge fixing to reveal the underlying plus and cross polarizations). Power loss to gravitational radiation is discussed in the linearized limit by comparison with electric quadrupole radiation.
This chapter discusses the problem of de-quantization. Starting with some given quantum space defined through a matrix configuration, a general procedure is developed which allows to associate a manifold and further geometrical structure underlying the given quantum space.
Spherical symmetry for a metric is defined and used to build a two-function ansatz. The Schwarzschild spacetime emerges as the solution to Einstein’s equation with, and we see how the Newtonian potential is related to the linearized Schwarzschild metric. The lightlike and spacelike geodesics of the metric are explored using exact, approximate, and numerical approaches. Many of the usual experimental tests are covered in detail: perihelion precession, bending of light, and time dilation, for example. The structure of the singularities in the Schwarzschild spacetime is studied using Eddington–Finkelstein and Kruskal–Szekeres coordinates. At the end of the chapter, the Kerr spacetime is introduced, and students are invited to explore its geodesics.
This chapter explains the generation of fuzzy extra dimensions in the context of ordinary Yang–Mills gauge theory and Yang–Mills matrix models. This will play an important role in the context of gravity.