"Even if there is only 1 intelligent civilization per galaxy where you have over 100 billion stars per galaxy with some galaxies sporting nearer to a trillion stars. There are over 100 billion galaxies in the visible universe, maybe more. So even assuming you have only 1 species per galaxy, that's still 100 billion x 100 billion possible life sustaining solar systems. Which is probably a small estimate. We know that the building blocks of life are present more or less everywhere in the universe."