Universal flows and automorphisms of P(ω)/fin

We prove that for every countable discrete group G , there is a G -flow on ω * that has every G -flow of weight ≤ ℵ 1 as a quotient. It follows that, under the Continuum Hypothesis, there is a universal G -flow of weight ≤ c . Applying Stone duality, we deduce that, under CH, there is a trivial automorphism τ of P ( ω ) / fin with every other automorphism embedded in it, which means that every other automorphism of P ( ω ) / fin can be written as the restriction of τ to a suitably chosen subalgebra. We give an exact characterization of all trivial automorphisms with this property.