This thesis presents computer simulations of the formation of super-structures in the Universe by solving the equations of Einstein’s theory of gravity: General Relativity. This differs from the usual approach which uses Newton’s law of gravity. We find that different regions of spacetime expand at different rates, but the effect is not sufficient to explain the measured accelerating expansion of the Universe, currently attributed to dark energy. Local differences are also not sufficient to explain the recently measured discrepancy between small-scale and large-scale expansion rates of the Universe. However, they could affect our observations as our instruments become more precise.