On Wednesday, January 22, 2020 at 6:12:35 AM UTC-7, John Clark wrote: > > On Wed, Jan 22, 2020 at 12:48 AM Alan Grayson <[email protected] > <javascript:>> wrote: > > *> **I strongly disagree that finite rates of expansion will result in an >> open universe. I believe it will be a closed hyper-sphere, but I am open to >> being wrong. AG * > > > If empty space has a residual intrinsic energy of any value greater than > zero, which General Relativity allows for and Quantum Mechanics demands, >
*WRT QM, are you depending on the HUP to make this statement? AG* > then the expansion of the universe will accelerate. > *Why? Can't there be a balance between gravity and residual intrinsic repulsive energy of the vacuum, that would create UN-accelerated expansion? AG* > If the universe is accelerating then it is open regardless of what its > spatial shape is, regardless of how many degrees the angles of a triangle > add up to (please remember the term "spatial shape" is not equivalent > with the term "spacetime shape"). > *Maybe the issue is whether the universe has infinite or finite volume, and "closure" is irrelevant? AG * > > > And when you ask "How big is the universe?" you need to know exactly what > you're really asking. You have nothing outside of the universe to compare > it to so one answer would be "The universe is as big as the universe", > but you may find that unsatisfying. What you really want to know is if > the universe is open or closed, you want to know "If you keep going in > one direction will you head out for infinity and keep getting further and > further from your starting point for eternity, OR will you eventually hit > some sort of wall or eventually start getting closer to your starting point > ?" > *A hyper-sphere has no edge or boundary, and if it is expanding, you might never return to your starting point even though it is finite in spatial volume. Same for a torus. AG * > > Today we have very good evidence the universe is accelerating and thus > open. Independently we have moderately good evidence that Inflation > occured. And we have pretty good evidence the universe is spatially pretty > flat. We'll never be able to observationally prove it has exactly zero > spatial curvature but if all you want to know is how big the universe is, > that is to say if all you want to know is if it's open or closed, then how > many degrees the angles of a triangle add up to is not important. > > John K Clark > -- 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 view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/bdb44d5c-4d0f-4552-8edf-73afe0168597%40googlegroups.com.
