Something I've always wondered: If a universe spontaneously forms & inflates inside a parent universe, what would happen to anything or anyone who's already inside the parent universe, say within 100 million light years away? Seems to me that would be quite destructive, as in pretty much completely destroying the whole parent universe.
The other scenario, I guess, would be that the new universe could always look like a tiny patch of space inside the parent universe. The baby universe simply gets more & more complex, even as it looks from the inside like it's expanding rapidly in size. This way the new universe wouldn't harm anything in the parent universe - but that strikes me as totally ad-hoc.
It depends on the nature of space, I guess. What happens to the parent universe while there's this enormous spatial expansion going on within it? I can imagine two possibilities:
1. The space of the parent is swept outward, pushed by the inflating space within it. That seems to require some kind of "substance" to space -- at least for this purpose -- which I don't understand, but I guess it's possible. The parent universe would end up surrounding the new universe. The most distant stars (if they existed in the parent) would appear far too old. This hasn't been observed.2. The inflating space simply "blows by" the existing parent universe and goes on expanding. The result is that the new universe ends up surrounding the parent. The parent region might be observable as a discrete portion of the visible universe, and (if it had stars) it would have older stars than we might otherwise expect -- but only if it were at the horizon of the visible universe, which it probably wouldn't be. If the parent universe were made of dark matter, it wouldn't be observed anyway.
Something I've always wondered: If a universe spontaneously forms & inflates inside a parent universe, what would happen to anything or anyone who's already inside the parent universe, say within 100 million light years away? Seems to me that would be quite destructive, as in pretty much completely destroying the whole parent universe.
The following paragraph from page 3 of Anthony Aguirre & Steve Gratton, "Inflation Without a Beginning: a null boundary proposal" (2003, PDF format) is somewhat relevant, I think (my red fonting):
"An observer within a bubble can never leave, but will eventually be encountered by an encroaching bubble wall after a typical time τcoll, where τcoll-1 is related to the r-integral of Eq. (5) by some transformation between the bubble observer's proper time τ and cosmic time t. Since this rate depends on t−t0, a patient and very sturdy oberver could in principle discover the global time at which it formed by counting the frequency of incoming bubbles."
"A patient and very sturdy observer"...nice turn of phrase...