On Wednesday, December 26, 2018 at 3:30:58 AM UTC, [email protected] wrote: > > > > On Wednesday, December 26, 2018 at 2:37:59 AM UTC, Brent wrote: >> >> >> >> On 12/25/2018 4:42 PM, [email protected] wrote: >> >> >> >> On Tuesday, December 25, 2018 at 11:26:14 PM UTC, Brent wrote: >>> >>> >>> >>> On 12/25/2018 8:01 AM, [email protected] 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* >> >> >> And I'm saying you can't say the observable part of the universe >> satisfies the Friedman equations and the rest of can be anything. That the >> rest of the universe is constrained by what the observable part is like is >> a consequence of Einstein's equations. Could Einstein's equations be >> wrong? Sure they could, but they've passed every test, so applying them is >> not an assumption. >> > > *I concur. Using the Cosmological Principle, one would expect the > unobservable region to obey the same or similar laws as the observable > region. What's your view of whether inflation solves the flatness problem? > TIA, AG* >
*Bruce doesn't buy it and I am not sure why. Far be it from me to disagree with the Oracle from Australia, but I figure the curvature of the visible region is well know (although I don't have a clue how it's measured), and I believe there's some nominal reasonable rate of expansion based on Friedman's equations (although I haven't a clue with it is). Therefore, based on these values and my state of belief, it must be the case that the observable region is way too flat for an expansion that spanned 13.8 billion years at the assumed rate. Therefore again, it seems reasonable that inflation could account for this discrepancy. Why is this view simplistic to the point of being wrong, as Bruce would have it? TIA, AG* > > -- 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.
