On Thu, Nov 9, 2017 at 10:05 PM, Brent Meeker <[email protected]> wrote:
> > > On 11/9/2017 8:55 PM, [email protected] wrote: > > > > On Thursday, November 9, 2017 at 8:00:45 PM UTC-7, Brent wrote: >> >> >> >> On 11/9/2017 6:23 PM, Alan Grayson wrote: >> >> The difference between spatially flat and asymptotically flat for a huge >> universe would be virtually impossible to distinguish by measuring the sum >> of angles in a triangle. Moreover, I don't see how spatially flat can have >> nothing to do with extent, since in applying Euclidean geometry we surely >> seem to be dealing with an infinitely extended plane. TIA. >> >> >> Not necessarily. You could have periodic boundary conditions. But most >> cosmologists do assume the universe is infinite in spatial extent. Of >> course the flatness isn't measured by triangulation. It's measured by >> comparing the spatial spectrum of the CMB variations to model predictions >> with different mass densities. >> https://arxiv.org/pdf/astro-ph/0004404 >> >> Brent >> > > However flatness is measured, the criterion still seems Euclidean and > hence infinite in extent if one believes the triangle measured has combined > angles of 180 degrees. And I don't see how this is distinguishable from > asymptotically flat for a huge but finite universe. > > > It's not. > That's my point. No way of distinguishing flat from asymptotically flat for a huge universe, so the assumption of infinite spatial extent by cosmologists seems unwarranted. But as you note below, the universe could have begun with infinite spatial extent. But ours didn't AFAIK. It began as astronomically tiny and expanded via inflation. > > Moreover, it seems contradictory that a universe which has expanded for a > finite duration, could be infinite in spatial extent. TIA. > > > It can if it starts off infinite. Remember the expansion in Einstein's > equation is just a *factor*, not an absolute value. > > Brent > > -- > You received this message because you are subscribed to a topic in the > Google Groups "Everything List" group. > To unsubscribe from this topic, visit https://groups.google.com/d/to > pic/everything-list/0XZFBcBdqYU/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > [email protected]. > To post to this group, send email to [email protected]. > Visit this group at https://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > -- 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 [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
