Interstellar travel and biosphere reboots means there are a lot of aliens in the galaxy
• https://www.nextbigfuture.com, brian wangIn 1961, radio astronomer Frank Drake developed a pedagogy for analyzing the question of the frequency of extraterrestrial civilizations. Robert Zubrin shows a couple of significant mistaken assumptions by Drake. Robert Zubrin wrote this for Centauri
Wrong! From http://ericmetaxas.com/media/articles/science-increasingly-makes-case-god/: "Today there are more than 200 known parameters necessary for a planet to support life—every single one of which must be perfectly met, or the whole thing falls apart. Without a massive planet like Jupiter nearby, whose gravity will draw away asteroids, a thousand times as many would hit Earth’s surface. The odds against life in the universe are simply astonishing. --- In other words, the odds turned against any planet in the universe supporting life, including this one. Probability said that even we shouldn’t be here."