The large scale distribution of matter provides one of the principal observables for testing the cosmological model. The inhomogeneity of the distribution of galaxies and dark matter, the dependence of this on the scale, and its time evolution, depend critically on the parameter values of the model. The combination of measurements of the expansion rate of the Universe with those of the rate of growth of density fluctuations, allow, in principle, the basis of the theory to be tested, and also provide a verification of the theory of General Relativity. In fact, there exists the fascinating possibility that dark energy is a manifestation of a modified gravity, that is, a deviation from the Einstein equations. This is currently one of the alternatives to dark energy most actively explored. Along with observation of the cosmic microwave background, the quantitative characterisation of the large scale structure of the Universe via redshift surveys of galaxies and clusters and weak lensing measurements are surely the methods that promise the best results in this field, thanks to the large surveys either underway or planned.

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