https://www.forbes.com/sites/startswitha...48257879c5
EXCERPTS: . . . So why, then, do we have a scientific paper coming out now, using the same set of data and similar techniques, that draws a radical conclusion? Why, then, are we hearing claims that 36 alien civilizations likely exist in our Milky Way right now? Because that new estimate is based on an ill-founded assumption that the authors make: that if you start with an Earth-sized world at an Earth-like distance around a Sun-like star, you will have very good odds of getting a technologically advanced civilization out once 5 billion years have passed. The authors, Tom Westby and Christopher Conselice, state this themselves...
Is this a good assumption? In a scientific sense, absolutely not. As we just discussed, a previous study just demonstrated that it's more likely than not that intelligent life is rare; if you were to rewind the clock and start Earth over again some ~4.5 billion years ago, it appears that you'd be relatively unlikely to have a technologically advanced civilization arise on our planet. [...] After all that, then, how did Westby and Conselice arrive at their conclusion that there are 36 intelligent alien civilizations in the Milky Way right now?
They not only assumed "a reasonable probability" that intelligent life will arise after about 5 billion years on an Earth-like world, but they then imposed a further assumption — what they call the Astrobiological Copernican Strong Condition — that intelligent life must form between 4.5 billion and 5.5 billion years after an Earth-like planet forms in an Earth-like orbit around a Sun-like star. They they further go on to assume that such a civilization should exist for 100 years in its actively-communicating phase [...] and then they do their statistical analysis. In the end, based on these assumptions, they conclude that there should be 36 alien civilizations within our galaxy, right now, with some uncertainty.
[...] Here's how you know these numbers are meaningless: the uncertainties are so large that they do not exclude "0" as a reasonable possibility. Even if their (arguably ill-motivated) assumptions about intelligent life were true, the uncertainties are so large that conclusions about the number of alien civilizations present within the Milky Way cannot be reasonably drawn. [...] If we're willing to make assumptions ... we can indeed draw conclusions about the likelihood of intelligent life throughout the galaxy. The only problems are that our conclusions are only as good as our assumptions, which we have no reason to believe are very good... (MORE - details)
EXCERPTS: . . . So why, then, do we have a scientific paper coming out now, using the same set of data and similar techniques, that draws a radical conclusion? Why, then, are we hearing claims that 36 alien civilizations likely exist in our Milky Way right now? Because that new estimate is based on an ill-founded assumption that the authors make: that if you start with an Earth-sized world at an Earth-like distance around a Sun-like star, you will have very good odds of getting a technologically advanced civilization out once 5 billion years have passed. The authors, Tom Westby and Christopher Conselice, state this themselves...
Is this a good assumption? In a scientific sense, absolutely not. As we just discussed, a previous study just demonstrated that it's more likely than not that intelligent life is rare; if you were to rewind the clock and start Earth over again some ~4.5 billion years ago, it appears that you'd be relatively unlikely to have a technologically advanced civilization arise on our planet. [...] After all that, then, how did Westby and Conselice arrive at their conclusion that there are 36 intelligent alien civilizations in the Milky Way right now?
They not only assumed "a reasonable probability" that intelligent life will arise after about 5 billion years on an Earth-like world, but they then imposed a further assumption — what they call the Astrobiological Copernican Strong Condition — that intelligent life must form between 4.5 billion and 5.5 billion years after an Earth-like planet forms in an Earth-like orbit around a Sun-like star. They they further go on to assume that such a civilization should exist for 100 years in its actively-communicating phase [...] and then they do their statistical analysis. In the end, based on these assumptions, they conclude that there should be 36 alien civilizations within our galaxy, right now, with some uncertainty.
[...] Here's how you know these numbers are meaningless: the uncertainties are so large that they do not exclude "0" as a reasonable possibility. Even if their (arguably ill-motivated) assumptions about intelligent life were true, the uncertainties are so large that conclusions about the number of alien civilizations present within the Milky Way cannot be reasonably drawn. [...] If we're willing to make assumptions ... we can indeed draw conclusions about the likelihood of intelligent life throughout the galaxy. The only problems are that our conclusions are only as good as our assumptions, which we have no reason to believe are very good... (MORE - details)