科研之友
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摘要
We consider the scenario where our observable universe is devised as a dynamical four-dimensional hypersurface embedded in a five-dimensional bulk space-time, with a large extra dimension, which is the generalization of the flat FRW cosmological metric to five dimensions. This scenario generates a simple analytical model where different stages of the evolution of the universe are approximated by distinct parametrizations of the same space-time. In this model the evolution from decelerated to accelerated expansion can be interpreted as a "first-order" phase transition between two successive stages. The dominant energy condition allows different parts of the universe to evolve, from deceleration to acceleration, at different redshifts within a narrow era. This picture corresponds to the creation of bubbles of new phase, in the middle of the old one, typical of first-order phase transitions. Taking Omega(m) = 0.3 today, we find that the crossover from deceleration to acceleration occurs at z similar to 1-1.5, regardless of the equation of state in the very early universe. In the case of primordial radiation, the model predicts that the deceleration parameter "jumps" from q similar to +1.5 to q similar to -0.4 at z similar to 1.17. At the present time q = -0.55 and the equation of state of the universe is w = p/rho similar to -0.7, in agreement with observations and some theoretical predictions.
- 出版日期2006-8
