When we are going to talk about alien life, we have to presume some assumptions. Circumstantial evidence indicates alien civilisations are very few and far flung in the universe. I have pointed out that the easiest way to explore the universe is send out self-replicating space probes . Within a cosmologically short period of co-moving time (ie millions of years) we could colonise the Milky Way and the rest of the Local Group. The arrival of such a probe at a star system would preclude and supersede local biological evolution. Since life on Earth has evolved over billions of years then we can’t expect (statistically speaking) to find civilisations within our local group. Where are the aliens, asked Fermi. Many megaparsecs away!!