[ExI] Drake Equation Musings

[Anders Sandberg]

My understanding of the story is like this: we start with a spacetime 
manifold which is curled up in a complex way, on which various fields 
slosh around. One of them undergoes a false vaccum phase transition that 
makes some of the directions of the manifold unfold a lot very fast, 
producing a big spacetime. However, this unfolding happens differently 
in different patches, producing big spacetimes separated from each other 
and potentially with different dimensionality or physics (due to local 
symmetry breaking of what dimensions unfolded or the values of the 
parameters set by the fields).

Note that spacetime expansion is allowed to be arbitrary, but fields on 
it can only change with signals moving at the speed of light on the 
spacetime. So vacuum decay can only spread at lightspeed in the 
surrounding manifold, although the internal spacetime metric of the 
decyed region might have turned all weird.


On 2016-05-19 22:03, Rafal Smigrodzki wrote:


    Superluminal? I though all vacuum decay models had it spreading
    merely at lightspeed?


### This is one (of many) things I don't quite get: Inflation was 
superluminal and occurred after the false vacuum decay that generated 
our spacetime, so you would think the change would propagate superluminally.

Now that I think about it, maybe it went like this: vacuum decay 
generated new dimensions and inflation occurred in these new dimensions, 
not in the parent universe. Linde's eternal inflation does not blow up 
the non-inflating domains, it keeps happening between them.




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