this post was submitted on 31 Mar 2024
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Showerthoughts
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Given that we can see the CMB it seems unlikely that the universe is older elsewhere.
Interestingly it's possible the universe could be older elsewhere. One of the theories regarding the big bang is that space-time underwent a phase change. The higher level phase had sufficiently different physics to let the energy level equalise despite the speed of light limits.
There is no reason the entire thing collapsed back into its current state at once. 1 theory has it happening as energy density dropped below a critical limit. Others have "bubbles" of "normal" space time forming, and expanding through the unshifted medium. There is no reason bubbles couldn't be massively apart, temporally. The catch is, the bubbles will likely never have any communication, rendering the point abstract at best.
There's also no reason the bubbles collapsed the same way. Other bubbles could have a vastly different flow rate of time, or a different number of spacial dimensions.
This is all head-of-a-pin physics however. As it stands, we couldn't detect even a type 3 civilization out near the edge of our observable universe. That is also before light cone issues.
I'd be interested in reading more about this, if you have any pointers. It seems to me to be an interesting semantic question as to whether other bubbles of spacetime beyond our own, running at a different temporal rate (from the outside? By what universal clock?) count as part of our universe or not. From the description you gave, it seems like maybe even FTL wouldn't be enough to reach them.
Not got anything to particularly hand. It's mostly offhand articles and pub discussions (drunken freeform thinking is remarkably common and useful in physicists, let alone with undergrads). By its nature, it is into the realm of philosophy, rather than science. It is untestable, since there couldn't be any communication with other bubbles.
As for the time flow, it's fairly arbitrary. We perceive ourselves moving through time via indirect means. Those are potentially an illusion, even in our bubble. The rate of entropy, or the speed of light could be vastly different. That would change the perceived "speed of time" (whatever that means!) compared to some arbitrary communal rest frame.
The big issue is that we don't currently understand our own space-time. Speculating on over variances is very much "how many angels can dance on the head of a pin".
If you want something a little more scientific, cosmic bubble theory is the current version of the theory.
Oh, and the same base assumptions basically preclude FTL. In a relativistic universe, FTL is time travel, with all the resultant problems (tachyonic anti-telephone being just the most obvious)
Considering even the modest estimates of the size of the entire universe compared to the tiny sphere we can observe, I think it'd be pretty arrogant to think our spec is getting enough information to say anything about the universe as a whole is unlikely.
This isn't really a counterargument to what he said. The limits of our observable universe is the CMB. It's the beginning of the universe. The farther we see, the more redshifted it is, the farther in the past it is. Hot, dense, and redshifted is the CMB.