Wikipedia:Reference desk/Archives/Science/2013 September 19

= September 19 =

Borde, Guth, Vilenkin and contracting universe
I remember an interview with Guth and he says that positing a contracting universe prior to expansion would be problematic due to the probable occurrence of singularities. I don't totally understand this. If the mass was contracting, I could see why it could be probable that most of the mass would form singularities, but I don't see why it could not be probable that some small amount of the mass—however little in comparison to the total—could continue on past a state of maxiumum density into an expanding stage. I don't understand these things well at all, so any simple explanation as to why I've just got this all wrong would be great. -- Atethnekos (Discussion, Contributions) 05:36, 19 September 2013 (UTC)
 * The problem would not be that no mass would expand afterwards. The problem is with the singularities themselves. Where are they? The universe wouldn't be as smooth as we observe it to be if its initial condition (after the contraction) was that lumpy. Dauto (talk) 12:29, 19 September 2013 (UTC)
 * Ah, I see. That gives me much more to think about, thank you. -- Atethnekos (Discussion, Contributions) 18:03, 21 September 2013 (UTC)