Not necessarily.
Yes. Although it's a bit stronger than an assumption, since models based on the cosmological principle ("everything is the same everywhere") seem to produce accurate descriptions of what we can see. It's possible those models are wrong, but I don't think we have any credible models that don't work like this.
I don't understand what you are trying to ask. As far as we are aware the universe is spatially infinite. You can never reach the edge of your observable universe, so you can't "hop from bubble to bubble", but our current best models say that there is no end to space so you can't get back to where you started.
I think your idea of separate "bubbles" is ill-conceived. The universe on a large scale is homogeneous and isotropic. There are no "bubbles" as such.
Yes, I do not mean that they are separate regions of space, just the vantage points. Thank you for clarifying.
I'm trying, this may be a bit advanced for me - thank you!
But there is nothing special about picking "vantage points" that happen to be separated from each other by the diameter of the observable universe so your concept might be misleading you in some way.
Not quite. The fact that there is no special vantage point is does not make it conclusive that the universe is infinite. A universe could be finite (as the universe we live in could still be) but still have no special vantage points. There are several topologies that allow this.
You picture these horizon circles just touching each other, but basically every point is a vantage point that describes it's own horizon, so they could be overlapping or completely disjoint.
A better analogy than a foggy day is the horizon on the Earth: you can only see bits of the ocean so far away, because the Earth is curved. It's not quite the same because you can see tall things further away, whereas in the case of the universe nothing can be visible beyond the horizon.
If this analogy works, and if the universe is finite yet unbounded, would you eventually come back to the same part of the ocean? Forgive my ignorance.
It's 45 BLY today but the number is always increasing.
Yes, if the universe has a positive curvature, then it is analagous to the surface of a sphere and curves back on itself. If our universe is like this, then it must be very large as there is no evidence of significant curvature even across the extent to the observable universe.
Yes, as @PeroK has said, the analogy is apt, BUT ... "the same part" is somewhat misleading in the case of the universe because, as far as we can tell, if the universe IS finite, it is still HUGE (WAY more than the observable universe), and since you can't go faster than light, by the time you got back to "the same place" (after probably many tens of trillions of years) it would be "the same place" only in the most technical sense and would not look anywhere near the same as when you left.
"the same part" as instantly hopping - this is a thought experiment, no "real" travel required!
Understood. I just wanted to make sure you understood the ramifications of real travel
That analogy doesn't follow, because the curvature of the Earth is spatial curvature, and the curvature of space-time which causes our universe's horizon is in space-time. The analogy only really works locally.
I agree, but the best guess does not prohibit discussion of other possibilities, just a realization that they are less likely.
That's potentially a stretch. The universe being actually flat requires infinite fine tuning. Specifically, it requires an exact balance between the rate of expansion and the average density.
On the other hand consider that out of all of the infinite values it COULD take on, it is very nearly exactly flat. What an amazing coincidence if it isn't actually flat.
Keep in mind that the surface of the Earth is almost flat as well.
Mathematics is even more helpful!
I don't think this follows. There are basically three possibilities:
Excuse this late post. This morning, I was viewing an Alan Guth lecture on Inflationary Cosmology. He touched on this point, and argues that because galaxies formed, Ω must be one to 15 decimal places. That is indeed pretty fine tuning.
That's not how expansion works (as we understand it). Light emitted now from Earth will only ever reach objects that are less than about 16.5bn light years away - inside the cosmic event horizon. So either we can already see what it used to look like "here" (we can see things that are now almost 47bn light years away), or we never will, no matter how fast we travel or for how long.