The Emperor's New Mind: Concerning Computers, Minds, and the Laws of Physics (Oxford Landmark Science)

by Roger Penrose

possible type of initial singularity other than that of the big bang would be the singularity in a white hole – which, as we recall from Chapter 7, is the time-reverse of a black hole (refer back to Fig. 7.14). But we have seen that the singularities inside black holes satisfy WEYL → ∞, so for a white hole, also, we must have WEYL → ∞. But the singularity is now an initial singularity, for which WCH requires WEYL = 0. Thus WCH rules out the occurrence of white holes in our universe! (Fortunately, this is not only desirable on thermodynamic grounds – for white holes would violently disobey the second law of thermodynamics – but it is also consistent with observations! From time to time, various astrophysicists have postulated the existence of white holes in order to attempt to explain certain phenomena, but this always raises many more issues than it solves.) Note that I am not calling the big bang itself a ‘white hole’. A white hole would possess a localized initial singularity which would not be able to satisfy WEYL = 0; but the all-embracing big bang can have WEYL = 0 and is allowed to exist by WCH provided that it is so constrained.

Why white holes haven't been observed