Wednesday 17 August 2016

general relativity - Is the Big Bang a naked spacelike singularity?


While reading some answers on similar topics, I was wondering about the nature of the Big Bang singularity in the standard cosmological model. I know it's a spacelike singularity that have a causality horizon, but I have read several contradicting answers and comments about it being "naked" or not (I admit that I may have contributed myself to the confusion!). So my question is this :



Is the Big Bang a naked singularity in the standard cosmological model?



In a flat space ($k = 0$) dust universe, the causality or particles horizon (NOT the same as event horizon) is located at a proper distance $\mathcal{D}_{\mathcal{C}}^{\text{dust}}(t_0) = 3 \, t_0$, where $t_0$ is the age of the dust universe. The scale factor is $a(t) \propto t^{\frac{2}{3}} $. Thus, a comoving observer cannot "see" what's on the other side of this horizon, until he waits for a time $t > t_0$. There is no event horizon in this spacetime. So is the Big Bang singularity at $t = 0$ clothed or naked?




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