How many civilizations are there out there? In 1950 Enrico Fermi noted that the Sun is a typical star, and there are billions of stars in the galaxy that are billions of years older. Some will have Earth-like planets, and some might develop intelligent life. Some might develop interstellar travel. Even without interstellar travel, the Milky Way galaxy could be traversed in a million years (150,000 ly wide by 180,000 ly long). Therefore Earth should already have been visited by extraterrestrial aliens. Fermi saw no convincing evidence of this, nor any signs of alien intelligence anywhere in the observable universe. He asked, "Where is everybody?"
Frank Drake in 1961 penned the Drake Equation to stimulate scientific dialogue concerning this question. I thought I'd take a stab at making an estimate along different lines. I assumed that the Earth is typical of a planet that will foster intelligent life. I then looked at some of the constraints on the development of intelligent life such as where an Earth-like planet might exist in the galaxy, what kind of sun might harbor an Earth-like planet and what the sun's population is in our galaxy, how long it might take before intelligent life might arise, and what kind of disasters might befall an intelligent species (based on our own experience on Earth).
In doing this I encountered the studies that others have made into this same question. Some are simulations of a galaxy and some of habitable planets. Several are studies of the Kepler database of planets. Some of these results will be discussed.
I'm a writer. Two books on Amazon Kindle and another being written. This talk is a development of ideas I presented at Barcamp - Omaha last August. I used a specific number of civilizations in our galaxy in my books - which are fiction. But I needed some basis for this number.
Left the government aerospace business (Northrop Grumman) a few years ago after about 30 years of hardware, software, and system development.
Before that I was in the Air Force: Japan, Korea, and Vietnam.
MS Meteorology, Creighton U.; MS Computer Science, U. of Nebraska - Lincoln.