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.
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. 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—but its density can still increase without bound. There’s no contradiction. Quentin Le mer. 26 févr. 2025, 10:47, Alan Grayson <agrayson2...@gmail.com> 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 <agrays...@gmail.com> 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. 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 everything-li...@googlegroups.com. > > To view this discussion visit > https://groups.google.com/d/msgid/everything-list/24e6c716-8439-4d9d-96da-58d3529c30bfn%40googlegroups.com > <https://groups.google.com/d/msgid/everything-list/24e6c716-8439-4d9d-96da-58d3529c30bfn%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > -- > 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 everything-list+unsubscr...@googlegroups.com. > To view this discussion visit > https://groups.google.com/d/msgid/everything-list/75204ad8-707f-4c12-a5b0-fb86d41df833n%40googlegroups.com > <https://groups.google.com/d/msgid/everything-list/75204ad8-707f-4c12-a5b0-fb86d41df833n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- 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 everything-list+unsubscr...@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/everything-list/CAMW2kAptgXRbjePJ5mn7izePAZifOWd9i_Oxdt2wuuS%2Bj1CV-g%40mail.gmail.com.
