The flood of responses to the question of how many civilizations are out there in the cosmos continues, and I thank each and every one of you who took the time to assemble your thoughts and send them to me. Not all will appear in these blogs or in print, but I read and appreciated every one of them. The article that prompted them was in the January 2013 Astronomy, p. 9, “Civilizations in the universe.”

The sampling of opinions continues:

From Surrey, British Columbia, Cameron McLeod writes, “Those stats you listed in January’s issue — with odds like those, I have no doubt we’ll find countless galactic civilizations and empires. This is where science fiction gets in the way. We need to educate people with statistics like this, which will get them to wonder about the possibilities of the universe and our future.”

On the contrary, George Mancuso of San Diego writes that we should be cautious about believing that with big numbers, anything is possible. “Without understanding the basic processes that created life, it’s mere speculation to think that other civilizations exist,” he asserts.

Tom Brewer states that we should keep in mind the words of NASA Administrator Dan Goldin from a few years ago: “I don’t know what I don’t know” and “You can’t perform meaningful statistics on a sample size of one.”

“I think it’s highly probable that there are microbial life-forms on many planets,” writes Theedrich Yeat. “We know that vast clouds of organic molecules float through the galaxy. It’s impossible to make serious mathematical conjectures on the probability of ET civilizations. But if such a civilization emerged and rose to our level once every million galaxies, that would still be an amazing thing.”

Glenn Cooperman believes that “carbon-based life as we know it on Earth is probably incredibly abundant throughout the cosmos. However, intelligent life is probably incredibly rare. We humans may have been an evolutionary accident.” Cooperman asserts that because microbial life can exist in the harshest environments on Earth, it would be egocentric and foolhardy to believe it doesn’t exist elsewhere on planets and moons. But he also thinks “the series of events that enabled mammalian life to evolve to Homo sapiens is probably incredibly rare.” Mass extinctions play a significant role, he says. Earth’s Moon also plays a role in the existence of life here.

“Because of these factors,” says Cooperman, “I believe the evolutionary course that transpired on Earth is incredibly rare. Therefore, I believe only a handful of intelligent civilizations exist in our Milky Way Galaxy despite the billions of planets that might be out there.”

Errol Gautreau of Baton Rouge, Louisiana, believes that observing humanity affords some of the answer. “I am amazed at human intelligence, dexterity, creativity, and complexity of thought, as expressed in science, math, music, and art,” he says. “I lean toward the idea that humans are the only intelligent life in the universe. If my recollection is correct, the ‘Rare Earth’ theory sums up my position quite well.”

“I hope that life exists on a quarter of all planets in the universe,” says Kathy Kudravi. “I would find it incredibly wasteful for all the beauty and the chaos of the universe to be seen by just one intelligent life form — us.”

Andy Haley of Plattsville, Ontario, states: “Statistical analysis can come up with a number from one to a very large number. I can imagine that the conditions to set up a habitable planet that forms a civilization might be slim enough to permit only one per galaxy. Even so, this puts civilizations at a possible 125 billion. However, in what seems to be a bad cosmic joke, the rules have been created such that we would never know of any of these other civilizations because of the vast distances between them and our short life/civilization span.”

The accompanying photo was taken by Scott Tully from Marble Valley Farm in Kent, Connecticut. Scott was reminded of this image, which he titles “Life Circles Life” by the current discussion of possible civilizations in the cosmos. During his exposure, a moth went after his light and appeared, in the image, to circle the Milky Way.