Universe Today summarizes a study that concludes that we are probably the only “advanced” civilization in our galaxy.
The result is reached under assumptions of materialism: intelligence is an emergent quality of large brains. Large brains arise from biological evolution, which requires certain chemical conditions on the host planet (water, minerals and carbon in narrow proportions) and stability of the star about which it revolves.
Of course, what I propose here is that intelligence is the play of ideas between souls, and the brain is only an interface. On vastly larger scales, galaxies are civilizations. They just evolve new forms more slowly than we do – which makes us incredibly dangerous.
But galaxies “think”, and store experience. I trust that we’ll know whether we’re alone when we’re mature enough to receive the answer.