On Saturday, January 25, 2025 at 10:05:20 PM UTC-7 Jesse Mazer wrote:
On Sat, Jan 25, 2025 at 9:56 PM Alan Grayson <agrays...@gmail.com> wrote: On Saturday, January 25, 2025 at 6:57:31 PM UTC-7 Jesse Mazer wrote: On Sat, Jan 25, 2025 at 8:29 PM Alan Grayson <agrays...@gmail.com> wrote: On Saturday, January 25, 2025 at 12:11:15 PM UTC-7 Jesse Mazer wrote: On Sat, Jan 25, 2025 at 1:57 PM Alan Grayson <agrays...@gmail.com> wrote: On Saturday, January 25, 2025 at 6:57:27 AM UTC-7 John Clark wrote: On Sat, Jan 25, 2025 at 5:11 AM Alan Grayson <agrays...@gmail.com> wrote: *> IIUC,* *According to Google, that means the "International Islamic University Chittagong", but it must not understand correctly.* * > it's based on the assumption that the universe is infinite in spatial and temporal extent, but this is mistaken.* *You're right, that is mistaken, so it's fortunate that Hugh Everett did not make that mistake. By the way, I don't feed trolls so if I hear any of that "Trump physics" crap this conversation is over.* *> Our universe, by which I mean our bubble, is finite.* *In Hugh Everett's Many Worlds theory the word "bubble" has no meaning although that word does have meaning in "Eternal Inflation" and in the "String Theory landscape", but as far as Everett's Many Worlds is concerned they are irrelevant, they may or may not be true.* *i call it a Bubble to suggest an approximately spherical shape, which is implied by the Cosmological Red Shift, which has approximately the same value in every direction. So its shape is like a somewhat distorted sphere. AG * *Max Tegmark has proposed 4 different types of "Many Worlds"* *1) A spatial extension of our observable universe, perhaps by an infinite number of light years or perhaps by just an astronomical number of light years. * *Falsified by the data, the age estimate of the universe. AG * If the universe *were* infinite spatially (or at least much larger than the observable region), but still began in a Big Bang a finite time in the past (or at least we could not receive light signals from before then, even if there was something before as in 'eternal inflation' theories), do you think the observational data would be any different? Assuming a finite speed of light, the observable region would still be a finite size in this scenario, no? Jesse *You pose a compound question, so hard to answer. I am just dealing with our Bubble, nothing to do with Eternal Inflation. And within our Bubble, or any Bubble, I think the observable universe will be finite since the SoL is finite. Also, the unobservable part is estimated to be hugely larger, some estimates are 200 times larger but I'm not sure if that refers to its volume or radius. But with a finite age, it cannot evolve to infinity in spacial extent, no matter how fast it expands. That condition could only exist IMO if that was its initial condition. But as I wrote, that would be imposing another infinity on the BB (aside from infinite density at T=0), which again, IMO, is highly dubious. I'm not sure I answered your question, so you might have to rephrase it. AG* In the math of general relativity the universe could have been spatially infinite at every finite time after the Big Bang, and the Big Bang itself is treated as a singularity so it need not have a well-defined size. But anyway, the argument you are making above about why you think the universe must be finite seems to be a theoretical one, but before that in the post I was responding to, you seemed to be saying an infinite universe was falsified by *empirical* data, not just theoretical arguments--is that right? *Yes. The finite age is empirical evidence that our universe cannot be infinite in spatial extent UNLESS that's its initial condition, which I reject as a type of a singularity. AG* If you were making that claim, you should be ready to defend it even in the case where you grant for the sake of argument that there is no theoretical problem with the GR model of a universe that's infinite in size but began a finite time in the past (or at least agree to put aside all theoretical objections for the time being). Are you saying that even if you do put theoretical objections aside, you still think the empirical data is in conflict with the idea of an infinite universe that began a finite time in the past? *Yes. I don't think I ever made a theoretical argument; just an empirical one that the universe was never spatially infinite, now or in the past. * OK, but what are the specific empirical observations that you think conflict with the theory that it's infinite? *All measurements which support the conclusion that the age of the universe is finite, contradict the conclusion that the universe is infinite in spatial extent. AG* If hypothetically it *was* infinite, but the speed of light was finite and it began a finite time in the past, would you expect in that case there WOULD be an upper limit to the distance we could observe (i.e. the observable universe would be finite, even it the unobserved part beyond that went forever), or that there WOULD NOT be any upper limit? (I would say the answer is obviously that there WOULD still be an upper limit because light can only travel a finite distance in a finite time, but I'm curious if you disagree) *The relavant question IMO is whether or not the universe can BECOME spatially infinite in finite time, and the answer is definitely negative, and assuming this is correct, the unobservable region must have an upper bound. OTOH, if it is now spatially infinite, meaning no upper bound on the unobservable region, that means it was an initial condition which I reject as positing a singularity at T=0. AG* *Cosmologists agree that the universe gets smaller as we go backward in time.* They agree the observable universe gets smaller, and the distance between any pair of landmarks at rest relative to the cosmic background radiation (say, a pair of galaxies) gets smaller. But they do not make any claims about whether the *whole* universe gets smaller, since both of those things could be true even if the universe was infinite in size at all times. *I generally agree. But it's hard to imagine a universe which is spatially infinite and yet expanding, which would mean the average distance between galaxies is increasing. AG * Jesse -- 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. 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