Occam's Machete: Cosmology

How big is the Universe and if there are many, what would happen if they collided? Not a new question and several answers have been proposed (here is one). Another interesting question is why does time move in a single direction? Why does entropy increase? Laura Mersini-Houghton proposes an idea that answers both questions saying that bubble universes form with different arrows of time, eventually adding up to no preferred direction. She even claims to have a way to test this by looking our into the dark for boundaries.

Some have proposed that the Dark Flow may be one of these collisions, and the (now controversial) Great Void may be another. Where bubble universes are pulling and pushing on ours in places. FQXi has given her a grant to pursue the idea.

Entropy is big lately.  A new paper on arxiv (The Entropic Lanscape, Bousso and Harnik) uses entropic principles to derive predictions about such things as the cosmological constant and the nature of entropic radiation.  These predictions match well with observations in our corner of the universe and give a framework that applies to any part of the universe, even in other vacua.  This paper relates to examinations of the vacuum lanscape that usually end up relying on anthropic arguments.  In other words things are the way they are because we wouldn’t be here to observe them if they were different.  Bousso and Harnik replace arguments like that with ones that favor the maximiztion of entropy.

Also in a comment to a previous post here Nisheeth points to his arxiv article (The relativity of theory, Nisheeth) where he describes a framework for deriving physical laws from information-theoretic first principles.  He too relies on the maximiztion of entropy.

Cosmic Inflation states that for a small amount of time near the big bang the universe grew faster than the speed of light.  This inflationary period explains why the universe is so uniform.  But what is so special about this universe?  If the big bang came from a nucleation site (sort of like how the foam in a bottle of coke nucleates on the Mento) then there may be more universes.  So if there are more universes out there what would happen if they collided?  If we saw this happen what would it look like?  This train of thought describes one type of multiple universe theory and in an area that has few theoretically observable effects the collision scenarios are worth thinking about.  Besides the arXiv article by Anthony Aguirre, Matthew C. Johnson has some nice gratuitous graphics and some show-off math.

Spoiler alert:  there may be cases where a collision does not anihilate us all, which means we might see the effects of the smack-down and it might be visible in the CMB as seen through the Planck observatory.  In fact if you look closely in the picture to the right, well no you are probably going to have to wait for more to fill in.