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]
<javascript:>> 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.
Brent
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