Corinnguard
Hero
How did a discussion on whether or not intelligent alien life exists turn into the age, size and fate of our universe?
Because those are factors in considering the potential development of life in the universe.How did a discussion on whether or not intelligent alien life exists turn into the age, size and fate of our universe?
One of many. There is also the issue of that intelligent life being carbon-based or being the result of some alternate biology. Hypothetical types of biochemistry - WikipediaBecause those are factors in considering the potential development of life in the universe.
How did a discussion on whether or not intelligent alien life exists turn into the age, size and fate of our universe?
Because those are factors in considering the potential development of life in the universe.
You might not be able to visit an entire single bubble. Non-observable regions are not reachable, if expansion continues at at least the same rate, since the distance to a non-observable region gets bigger faster than it can be traversed.Ultimately it's semantics, but there are a couple of sensible reasons to say eternal inflation leads to a multiverse.
First of all, there is a boundary of sorts, even if a soft one. The space between two bubbles is still inflating and will do so forever, so you will never be able to travel from one bubble two the other, while in principle you could visit every region within a single bubble if you had infinite time (and no dark energy).
In addition, while the high-energy limit of physical laws will be identical for all the bubbles, we are not guaranteed that symmetries that breaks at energy lower than those of the post-inflation reheating scale (which will itself be different in each bubble) break in the same way in the various bubbles.
You might not be able to visit an entire single bubble. Non-observable regions are not reachable, if expansion continues at at least the same rate, since the distance to a non-observable region gets bigger faster than it can be traversed.
TomB
Current evidence is that the rate of expansion is increasing.I admit I was implicitly assuming that other potential bubbles would be similar in composition to our own, so matter, radiation, and possibly curvature and dark energy. In this case, if there is no dark energy, the expansion rate will always be decreasing and there is no upper limit to the distance light can travel, given enough time.
I guess it's possible to have something that is not dark energy, but nonetheless with an equation of state negative enough so that the expansion rate increases with time, in which case as you said there will be regions within a single bubble that will not be reachable.