On Monday, February 17, 2025 at 12:49:27 PM UTC-7 Liz R wrote:
Apparently the simplest model of the universe is one that is infinite at all times (according to Max Tegmark) - the "concordance" model? There is no reason an infinite universe couldn't have undergone scale expansion, an (in this case, presumably uncountably) infinite thing remains infinite no matter how much you expand it. Whether the universe is a continuum is key to this, so it depends on an as-yet unknown TOE. If spacetime is quantised - in some sense - then whether it could be infinite, and whether it could expand, might still be up for grabs. Note that a quantised spacetime would presumably only contain a finite number of possible states inside any volume (e.g. our cosmological horizon) and hemce an infinite universe would eventually repeat itself across sufficiently large distances. Again quoting Max Tegmark, this would occur for our Hubble sphere at something like a distance of 10^10^37 metres (from memory - the actual figures don't really matter much for any practical purpose, just note that they make a googol look ultramicroscopic). Assuming that repeated identical quantum states are indistinguishable, an infinite quantised universe would in fact be "piecewise finite" on Vast scales - repeating arbitrarily large identical volumes would be not just indistinguishable in principle but actually identical. So on this basis, the universe would be a sort of Library of Babel in which all possible quantum states exist (including "Harry Potter" and "White Rabbit" universes) - but since the number of possible states is finite for a given volume, it would eventually run out of combinations and repeat itself. Quite what this would look like on "hyperastronomical scales" I leave to the mathematicians. *FWIW, our best current measurements fail to show any quantization of spacetime. This was discussed here by Lawrence Crowell a long time ago, and I don't recall the level of fineness of these results. AG * By the way the Cosmological Principle is an observation / assumption, not an actual principle based on any physical laws. *Not exactly. Physical observation do play a significant role in generating principles. Faraday's observations of the behavior of magnetic fields comes to mind, and the MM experiment, which Einstein was aware of, which showed the velocity of light is independent of an observer's motion. In the case of the CC, we have ambiguous results. The CMBR suggests the universe was very close to homogeneous and isoptropic when its age was about 380,000 years old, but measurements much later in time show it's actually lumpy, with ultra long filaments containing galaxies, separated by huge voids. I'd go with the later, showing that the CC is false. AG * On Monday, 17 February 2025 at 18:05:20 UTC+13 Alan Grayson wrote: On Sunday, February 16, 2025 at 1:57:39 AM UTC-7 Quentin Anciaux wrote: AG, your argument assumes a false dichotomy between "nothing" and "something" Why a false dichotomy? No transition from finite to infinite if it was alway infinite, but was it? AG 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. Quentin Le dim. 16 févr. 2025, 09:44, Alan Grayson <[email protected]> a écrit : On Saturday, February 15, 2025 at 9:20:55 PM UTC-7 Alan Grayson wrote: On Saturday, February 15, 2025 at 9:11:22 PM UTC-7 Brent Meeker wrote: On 2/15/2025 7:03 PM, Alan Grayson wrote: On Saturday, February 15, 2025 at 1:56:14 PM UTC-7 Brent Meeker wrote: On 2/14/2025 11:36 PM, Alan Grayson wrote: On Friday, February 14, 2025 at 11:06:42 PM UTC-7 Brent Meeker wrote: On 2/14/2025 3:23 PM, Alan Grayson wrote: On Wednesday, February 12, 2025 at 12:36:38 PM UTC-7 Brent Meeker wrote: On 2/12/2025 12:55 AM, Alan Grayson wrote: If the age of the universe is finite, which is generally believed, then no matter how fast it expands, it can never become spatially infinite, So,* IF* it is spatially infinite, this must have been its initial condition at or around he time of the Big Bang (BB). But this contradicts the assumption that it was at a super high temperature at or around the time of the BB. No it doesn't. I can be infinite and high temperature. What gave you idea it couldn't? IOW, if we run the clock backward, the universe seems to get incredibly small, If the universe is infinite, then it is only the Observable Universe that gets incredibly small. *Is there any principle you are aware of, which prevents an infinite universe from becoming incredible small? * *It would have to undergo an infinite change in size in a finite time, which would require infinite relative velocities. Brent* *I can't imagine a universe starting as infinite in spatial extent -- can you? -- * As well as I can imagine any infinite thing. Imagination can be trained. My supervising professor, Englebert Schucking, could visualize four dimensional objects and draw their projection on the blackboard. If you can't do that, you just have to suppress some dimensions; then in the (t,r) plane there's an infinite line, the t-axis, and to the right of this line is the (t,r) plane and in that plane everything is moving apart. Just look at Ned Wright's cosmology tutorial: https://www.astro.ucla.edu/~wright/cosmolog.htm Brent The problem is this; how does one imagine a universe which suddenly comes into being, initially resumably with zero spatial extent, and when it does, it's infinite in spatial extent? IMO, this would be a singularity implying infinite spatial expansion instantaneously. I have no alternative but to reject this model for a finite one, starting small and hot, and expanding, since I have no idea what it means to begin infinitely. I am open to suggestions. AG Expand your imagination. Remember "infinite" just means without bound. You don't have to imagine the whole infinite line, just imagine a line without imagining it's ends. Not saying I believe it, but the best bet at this point in time, is that the universe began as a quantum fluctuation, thus small, very small! AG BTW, since a finite volume such as the observable universe, can originate from a point, those pictorial models of the evolution of the universe, starting from a point, aka the BB, are apparently accurate in their descriptions. That is, they're not necessarily simplifications of the evolution. AG Probably they are since they don't take account of quantum mechanics; but we don't know exactly how they are wrong. Brent 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 -- 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/2ecdf7ed-88dc-4e07-b870-541003d3ed7bn%40googlegroups.com <https://groups.google.com/d/msgid/everything-list/2ecdf7ed-88dc-4e07-b870-541003d3ed7bn%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/b2d1a9a2-0170-4529-81ee-d2167665a05en%40googlegroups.com.
