On Tuesday, December 25, 2018 at 11:26:14 PM UTC, Brent wrote: > > > > On 12/25/2018 8:01 AM, [email protected] <javascript:> wrote: > > > > On Tuesday, December 25, 2018 at 1:16:53 PM UTC, John Clark wrote: >> >> On Mon, Dec 24, 2018 at 3:21 PM <[email protected]> wrote: >> >> >> You can never prove that any physical quantity is exactly zero, but >>>> we do know from observations of the cosmic microwave background radiation >>>> that if the universe is curved at all it is by less than one part in >>>> 100,000. >>>> >>> >> >> *> Agreed. However, IMO the observed universe cannot be flat with exactly >>> zero curvature (which I refer to as "mathematically flat) since that would >>> imply infinite volume * >>> >> >> If information can't travel faster than light then by definition the >> radius of the spherical volume of the universe you can observe can't be >> larger than the age of the universe in years times a light year. >> >> >>> *> **which contradicts its finite age.* >>> >> >> There is no reason spacetime couldn't extend a finite distance into the >> past but an infinite distance into the future. >> > > *The observable universe could continue to expand forever, but it always > has a finite radius. We have no information about the unobserved part, so > it could be any size, maybe even tiny. AG* > > > All of those inferences are based on the universe obeying Friedman's > equations, i.e. Einstein's equations for a homogeneous, isotropic > universe. So they are inconsistent with the unobserved part of the > universe obeying some other conditions. Whether there is a solution with > the observable patch being different from the unobservable part is an open > question. If you find one, publish it. But you can't just assume that > because there's an unobserved part that it could be anything. >
*If we don't know anything about the unobservable part of the universe, it could obey any conditions; maybe consistent with the Friedman's equations, maybe not. I was just saying we can't assume anything. AG* > > Brent > -- 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.
