The presence of defects in material continua is known to produce internal
permanent strained states. Extending the theory of defects to four dimensions
and allowing for the appropriate signature, it is possible to apply these
concepts to space-time. In this case a defect would induce a non-trivial metric
tensor, which can be interpreted as a gravitational field. The image of a
defect in space-time can be applied to the description of the Big Bang. A
review of the four-dimensional generalisation of defects and an application to
the expansion of the universe will be presented.Comment: 17 pages, 4 figures. Prepared for the Proceedings of Geometry,
Integrability and Quantization X, held in Varna, 6-10 June 2008. Will be
published by the Journal of Geometry and Symmetry in Physics. Fixed a LATEX
problem with figure
