![[arxiv]](/images/buttons/arxiv.png)
Title: Higher-Dimensional Algebra and Planck-Scale Physics
Authors: John C. Baez
Categories: physics.gr-qc General Relativity and Quantum Cosmology (math.CT Category Theory; math.QA Quantum Algebra; physics.hep-th High Energy Physics - Theory)
Comments: 22 pages LaTeX, 6 encapsulated Postscript figures
Abstract: This is a nontechnical introduction to recent work on quantum gravity using
ideas from higher-dimensional algebra. We argue that reconciling general
relativity with the Standard Model requires a `background-free quantum theory
with local degrees of freedom propagating causally'. We describe the insights
provided by work on topological quantum field theories such as quantum gravity
in 3-dimensional spacetime. These are background-free quantum theories lacking
local degrees of freedom, so they only display some of the features we seek.
However, they suggest a deep link between the concepts of `space' and `state',
and similarly those of `spacetime' and `process', which we argue is to be
expected in any background-free quantum theory. We sketch how
higher-dimensional algebra provides the mathematical tools to make this link
precise. Finally, we comment on attempts to formulate a theory of quantum
gravity in 4-dimensional spacetime using `spin networks' and `spin foams'.
Owner: John Baez
Version 1: Thu, 4 Feb 1999 18:54:52 GMT