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. 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 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 [email protected]. 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 [email protected]. To view this discussion visit https://groups.google.com/d/msgid/everything-list/bce2fa4e-3a25-4257-944c-da1be1eba1b3n%40googlegroups.com.
