AG, you keep framing this as a matter of "opinion," but the issue isn’t what either of us prefers, it’s what the mathematics of cosmology allows. The FLRW metric isn’t just "one model"; it’s the framework derived from GR that describes how a universe evolves given its initial conditions. If the universe is infinite now, it was infinite at the Big Bang, there’s no logical contradiction in that.
Starting from "nothingness" isn’t something GR addresses; that’s a separate issue in quantum cosmology. You act as if rejecting a universe "starting from nothing" is just a personal stance, but the physics we have today describes a high-density early state, not a spontaneous emergence from absolute nothing. That’s not opinion, that’s what current models describe. Your "singularity with zero volume" interpretation is fine, but it’s not the only possibility. Whether the universe was initially finite or infinite remains open, but your argument that an infinite universe must have "transitioned" from nothing to infinite is flawed. If you’re now saying the substratum from which the universe emerged is infinite, then you’ve already accepted an infinite framework, it just shifts the question one level back. Quentin Le dim. 16 févr. 2025, 10:58, Alan Grayson <[email protected]> a écrit : > > On Sunday, February 16, 2025 at 2:26:37 AM UTC-7 Quentin Anciaux wrote: > > AG, the finite age of the universe doesn’t create the problem you think it > does. If the universe is infinite now, it was infinite at the Big Bang. > There was no "transition" from finite to infinite, just a change in density > and scale factor. > > > That's your opinion. AG > > This follows directly from the FLRW metric, which allows an infinite > universe to evolve from an extremely dense state. > > > That's one metric, not necessarily the whole story. Your model assumes the > universe "began" as infinite. But couldn't it have started as Nothingness? > You dismiss that possibility, which is your OPINION! AG > > > Your claim that this transformation is "not remotely intelligible" is just > an argument from personal incredulity. You haven't provided any actual > contradiction, just a statement that you find it hard to grasp. That’s not > physics, that’s just a preference. > > > I am entitled to my opinion, and you are entitled to yours. Your opinion > is to start the universe with some non-zero density and then apply the FLRW > metric. My opinion is that it started as a singularity with zero volume and > then hugely expanded. Where the matter and energy came from I have no idea. > That's the best argument for your model. AG > > > Flatness implies infinite extent only in the absence of curvature, but > small positive curvature would still be consistent with observations. > > > We agree on that! AG > > > I have no preference for either a finite or infinite universe. The > question of whether the universe is finite or infinite remains unresolved, > and neither possibility can be dismissed outright. > > > I dismiss that our bubble is infinite, not that that from which it emerged > is finite. IOW, my opinion is that the sub-stratum from which it emerged is > infinite, but of course this is just my guess. AG > > > Quentin > > Le dim. 16 févr. 2025, 10:22, Alan Grayson <[email protected]> a écrit : > > On Sunday, February 16, 2025 at 1:57:39 AM UTC-7 Quentin Anciaux wrote: > > AG wrote > Consider this: For Nothing to become Something and also be > infinite in spatial extent, that Something must have that infinity as its > initial condition, given that it now has a finite age. But transforming > from Nothing to Something and having that infinity as its initial condition > as infinite in spatial extent, is, if you think about, not remotely > intelligible. For this reason, I conclude it can't have this infinity as > its initial condition and can't be flat, which implies this infinity. AG > > Quentin replied> AG, your argument assumes a false dichotomy between > "nothing" and "something" while making unjustified claims about infinity. > If the universe is infinite now, it was infinite at the Big Bang, there’s > no "transition" from finite to infinite. Your assertion that this is "not > remotely intelligible" is just an appeal to personal incredulity, not an > actual argument. > > You need to factor in the finite age of the universe, which shows that if > it is infinite now, that must have been its initial condition, and then > continue the analysis from the creation event. Much more important, you're > certainly entitled to your opinion, but saying that I am assuming a false > dichotomy isn't true just because you believe it's true. 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