Via Kevin Drum, a graphic from New Scientist speculates at the number of habitable planets in our galaxy.
They started with the 3,588 planets discovered by the Kepler space telescope and then pared this back to only smallish planets in the “habitable zone”—not too near their star to boil over and not too far away to be iceballs. That got them down to 51 planets. But that only counts the planets we could see because our view from Earth was directly on their ecliptic. Extrapolating to all the rest produces 22,500 Earthlike planets. And since Kepler only covered 0.28 percent of the sky and only looked out 3,000 light years, extrapolating yet again produces a final estimate of 15-30 billion possibly Earthlike planets.
Hello out there.
The estimable John Gribbin, in his book, The Reason Why, presents the contrary case compellingly. I am persuaded by Mr. Gribbin that there is very probably no intelligent life in our galaxy other than on Earth. His argument rests on the fact that there are a number of factors on Earth that are unusual enough individually that the probability of their being found in combination elsewhere in the galaxy is vanishingly small. Read the book, then tell me if you are still shouting Hello…