You can start here for info on eternal inflation:
https://en.wikipedia.org/wiki/Eternal_inflation — Pfhorrest
"Alan Guth's 2007 paper, "Eternal inflation and its implications",[3] states that under reasonable assumptions "Although inflation is generically eternal into the future, it is not eternal into the past."" My emphasis. — fishfry
the eternal inflation field which may have caused the start of this universe, which may be eternal into the past, and may or may not be eternal into the future depending on whether it fully and universally collapsed into the vacuum of our universe. — Kenosha Kid
I think the confusion is between the inflation of the universe, which is described above as being eternal into the future but not the past, i.e. the universe had a start but will have no end, and the eternal inflation field which may have caused the start of this universe, which may be eternal into the past, and may or may not be eternal into the future depending on whether it fully and universally collapsed into the vacuum of our universe. Multiverse theory says it did not do so, and continued making new universes before and after ours through quantum superposition and/or local collapse. — Kenosha Kid
Science aside, I don't get the philosophical objection to the possibility of an "actual infinity". As far as we can tell, the universe is consistent with the possibility of it being infinite in spatial extent: it is, at the very least, so big that our current measurements can't distinguish between how big it is and it being infinitely big. Can you elaborate on what would be wrong with supposing that it might be infinitely big (or that it might be infinitely old, etc)? — Pfhorrest
Some inflationary models do still posit a singularity at the beginning of time, in which case the universe had a beginning just as in ordinary non-inflationary big bang models. But there is also a model of eternal inflation, where there wasn't necessarily any start of time, just a local stop of inflation, which is the "big bang" for all intents and purposes as we usually mean it, in such a model. It seems to be in that context of eternal inflation specifically that the term "big bang" is used that way, rather than to mean a singularity.
You can start here for info on eternal inflation:
https://en.wikipedia.org/wiki/Eternal_inflation — Pfhorrest
there is also a model of eternal inflation, where there wasn't necessarily any start of time, just a local stop of inflation, which is the "big bang" for all intents and purposes as we usually mean it, in such a model — Pfhorrest
So far as I understand, theories of eternal inflation don't claim to settle the question either way of whether time had a beginning; they just open the door for the possibility that it didn't, since the thing that we previously thought was the beginning turns out (on such a model) to not have been. We don't yet have evidence one way or another (even counting the limited evidence that supports eternal inflation) to tell, scientifically, whether or not there was any start to the inflating universe; the model is consistent with either option — Pfhorrest
the eternal inflation field which may have caused the start of this universe, which may be eternal into the past — Kenosha Kid
You'll have to provide a link for the absurd (and false) claim that there is a reputable theory of physics positing an infinite past. — fishfry
You can check Guth's 2007 review where he also discusses inflation fields that are past eternal but bounded. — Kenosha Kid
You seemed to think that it would be absurd to even think that it could be infinitely old, and I don't see why that or any other "actual infinity" would be absurd. — Pfhorrest
I'm willing to stipulate that Susskind and others (Penrose for sure) have theories positing and endless sequence of universes before the big bang. — fishfry
"Past eternal but not bounded?" Sorry that doesn't make a lot of sense. — fishfry
It makes as much sense as an infinite but bounded universe, which is hardly a foreign idea in cosmology. — Kenosha Kid
Nobody is claiming anything in science says the past is definitely infinite, just that it's not definitely finite (which, NB, is not the same thing as "definitely not finite").
I don't think it's absurd at all. — fishfry
"Past eternal but not bounded?" Sorry that doesn't make a lot of sense. — fishfry
I'm still confused by where you're coming from. Sometimes you claim an infinite past is a plausible or at least published scientific theory; but recently you said that you aren't talking about science, only philosophy. — fishfry
I said there are scientific theories that don’t rule it out. That doesn’t mean they say it is definite so. — Pfhorrest
So I do have a lot of misgivings whenever I hear physicists talking about infinity. And when I take the trouble to dig deeper into the details, I generally find that they're not using the word the same way mathematicians do.
But these are just impressions, and as I say I don't know much about speculative cosmology. — fishfry
And if we're talking infinities, it is also consistent with a good body of empirical evidence that the universe is geometrically flat and thus (spatially) infinite. Once again, nature/reality not overly interested in our metaphysical prejudices- if it wants to be infinite, that's what its going to be and we can either get hip with it or gtfo. — Enai De A Lukal
↪tilda-psychist
So if the universe had positive curvature, it would be like a sphere- spatially finite/bounded, if you traveled far enough you'd eventually end up back where you started. But if the universe has either zero curvature (flat) or negative curvature (hyperbolic, so like a saddle), it would be spatially infinite- you could travel indefinitely far and would never return to where you started. So far as our best measurements go, the universe appears to be geometrically flat- so spatially infinite. — Enai De A Lukal
if it wants to be 《insert weird shit 》, that's what its going to be and we can either get hip with it or gtfo. — Enai De A Lukal
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