Le mer. 26 févr. 2025, 12:02, Alan Grayson <[email protected]> a écrit :
> > > On Wednesday, February 26, 2025 at 4:44:05 AM UTC-7 Quentin Anciaux wrote: > > AG, the question isn’t whether I conclude the universe is infinite—it’s > whether the cosmological models allow for an infinite universe and what > their implications are. > > We don’t know if the universe is infinite or finite. > > > *OK, but in the post I responded to, you categorically stated that the > universe is infinite, and that's on you! AG * > I did not and never have. You're so entrenched in your own prejudices that you forget to read. Quentin > > Observations are consistent with both possibilities. If it is infinite, > then it has always been infinite, and the observable region shrinking as we > go back in time is just a consequence of our causal horizon contracting, > not the entire universe shrinking. If it is finite, then its total volume > could decrease over time. > > This isn’t about opinion, it’s about following the logical consequences of > each assumption. If you’re struggling with that distinction, that’s on you. > > > > Le mer. 26 févr. 2025, 11:38, Alan Grayson <[email protected]> a écrit : > > > > On Wednesday, February 26, 2025 at 4:29:13 AM UTC-7 Quentin Anciaux wrote: > > AG, the key point is that the observable universe is just a finite portion > of an infinite whole. As we go back in time, the observable region > contracts because the horizon of what we can see shrinks, but the entire > universe remains infinite. > > Why does the unobservable part remain infinite? Because spatial infinity > doesn’t depend on what we can observe. If the universe was infinite at one > moment, it stays infinite—shrinking only applies to what is within our > causal past, not the entire space. > > The density increases everywhere, meaning in any finite region—including > our observable universe—matter gets packed into a smaller space. But an > infinite universe still has no overall “volume”, so it never “shrinks,” > only becomes denser. > > The dichotomy isn’t a contradiction, it’s a consequence of causal > horizons—our observable universe is just a window into an infinite cosmos. > > > And you know that how? How did you conclude it's infinite, other than > having an opinion? AG > > > Quentin > > Le mer. 26 févr. 2025, 11:08, Alan Grayson <[email protected]> a écrit : > > > > On Wednesday, February 26, 2025 at 3:51:50 AM UTC-7 Quentin Anciaux wrote: > > AG, your statement "density can't diverge unless volume goes to zero" > assumes a finite volume, which doesn’t apply in an infinite universe. In an > infinite universe, density can increase indefinitely everywhere without > requiring a total volume to shrink. > > > I was explicit, that the observable universe shrinks, but according to you > and Brent the unobservable part remains infinite. I can't imagine such a > dichotomy. AG > > > Brent is correct that the observable universe (the region we can see) > shrinks as we go back in time, but that doesn’t mean the entire universe > (including the unobservable part) does the same. > > > Why not? Is that just your opinion, or something demonstrable? AG > > The observable universe is just a region within an infinite space, and as > we go back in time, the light cone that defines what we can observe gets > smaller. > > If the entire universe is infinite, its total volume remains infinite at > all times > > > OK. AG > > > —but its density can still increase without bound. > > > Density of what region? AG > > There’s no contradiction. > > > The contradiction is the dichotomy between the behavior of the two > regions. AG > > > Quentin > > Le mer. 26 févr. 2025, 10:47, Alan Grayson <[email protected]> a écrit : > > > > On Wednesday, February 26, 2025 at 3:33:55 AM UTC-7 Quentin Anciaux wrote: > > > > Le mer. 26 févr. 2025, 10:24, Alan Grayson <[email protected]> a écrit : > > > > On Wednesday, February 26, 2025 at 1:22:21 AM UTC-7 Alan Grayson wrote: > > On Tuesday, February 25, 2025 at 10:07:41 PM UTC-7 Brent Meeker wrote: > > On 2/25/2025 7:59 PM, Alan Grayson wrote: > > On Tuesday, February 25, 2025 at 6:40:35 PM UTC-7 Brent Meeker wrote: > > > > On 2/25/2025 3:48 PM, Alan Grayson wrote: > > > > On Tuesday, February 25, 2025 at 12:46:46 PM UTC-7 Brent Meeker wrote: > > I think all cosmologist, like Hartle, recognize that *the observable > universe* was much smaller in the past. Which is perfectly compatible > with *the universe* be spacially flat and infinite. > > Brent > > > I fully anticipated that response. But why would the observable universe > behave radically different from the entire principle, particularly in light > of the Cosmological Principle? AG > > It's not radically different. It's different in exactly the way that > finite subsets of infinite sets behave. > > Brent > > > But if the observable universe contracts to zero volume, the entire > universe has a singularity, which is inherently contradictory. So, the > model is, to say the least, inconsistent. AG > > It's not contradictory or inconsistent, it's unphysical, i.e. it can't be > physically realized; which just means the theory of general relativity > doesn't work there. This is not a surprise since GR is not a quantum > theory and if you're concerned with a subatomic scale region you'll > probably need a quantum theory. > > Brent > > > My conjecture is that there's a fifth force, repulsive in Nature, that > prevents the mass of a high mass collapsing star to reach zero volume. AG > > > I don't imagine a quantum theory. More important, I can't grasp the idea > of the observable universe contracting to zero or near zero volume as we go > backward in time, while the unobservable universe remains infinite in > spatial extent. Can you grasp it? Can you explain it? AG > > > As I've explained already, it's not that the volume goes to zero, but > density that goes to infinity, everywhere, there is no valid notion of > volume in an infinite universe. > > Quentin > > > Density can't diverge unless volume goes to zero. FWIW, Brent thinks the > observable universe shrinks to zero or near zero as we go backward in time, > while the unobservable part remains infinite. 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