On 8 January 2014 11:48, meekerdb <meeke...@verizon.net> wrote: > On 1/7/2014 2:14 PM, LizR wrote: > > On 8 January 2014 11:06, meekerdb <meeke...@verizon.net> wrote: > >> >> If the universe reached a maximum and started to contract (which now >> seems unlikely) the maximum possible entropy would still be much higher >> than the actual entropy so entropy would continue to increase until the >> contracted enough to reduce the maximum to near the actual. If it were the >> reverse of the Big Bang it would be a very sudden contraction, aka >> "deflation". Of course it might actually be symmetric. Lawrence Schulman >> has a nice book about this "Times Arrow and Quantum Measurement". He did >> some computer simulations by just considering randomized initial conditions >> and then post-selecting the ones that satisfied the final conditions. >> > > We actually don't know what would happen in a "bouncing universe", or > even if such a thing is physically possible. Certainly my mental image is > that entropy would continue to increase, at least until it was approaching > the Big Crunch, which would itself look something like a Big Bang in > reverse (but with black holes thrown in). But if the BC acts as a boundary > condition on the universe, as the BB appears to do, then that > *could*constrain matter to follow an opposite arrow of time, no matter how > anti-intuitive that seems - or there could be a gradual switch over from > one arrow to another. > > > The global switch over would have to reverse the radiation arrow-of-time. > This might be possible without creating anomalies if the expansion made the > universe so dilute that there was no difference between expanding and > contracting, i.e. nothing to "measure" the difference. So an ancient > signal from the expansion phase would converge upon an antenna in the > contracting phase, but the beings there would see it as being broadcast, > not received. >
Yes that's one of the (many) unknowns. It certainly makes the whole thing seem problematic. Of course it's possible that any entropy gradient that forms is forced to respect both extremities of a universe with recollapse, which might mean it's unlikely that life can exist there. Or it might mean that there would be leftover signals that could in principle be detected and decoded (but since they would appear as emissions, that seems unlikely...) Interesting that our universe appears to not have a global future singularity. -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.
