A few years ago, I wrote about the Drake Equation, one attempt at guesstimating whether we are all alone in the Universe or if there are intelligent beings out beyond the solar system with whom we could converse. I wouldn't be much of a dialogue because the nearest star is Alpha Centauri and that's 4.2 light years [same as radio-wave years] away. Ask a question like "Have you discovered Thorium?" or "Is DNA at all relevant to your lifestyle?" and, even having sorted out the language of communications, it's going to be 8.4 years before you get an answer back. It is evens probable that there's a planet orbiting one of the suns of the Alpha Centauri system and that the planet is in the Goldiloxian 'habitable zone': not too close and torrid or so far as to be frigid.
I was tooling about The Déise yesterday and caught Newstalk FM with Sean Moncrieff interviewing one of the team from Nottingham who have re-jigged the Drake Equation to come up with their best guess about the likelihood of Intelligent Life "out there". Despite repeating the name of the interviewee, I was unable to recall it 30 minutes later when I'd stopped driving and was able to pick up a pencil. I did, however, remember their number of habitable planets with intelligent life that hadn't yet blown itself to buggery or asset-stripped their home to an uninhabitable cinder. So I googled "Nottingham 36" and found a) Bus #36 serves the Queen's Medical Centre, whither my boss decamped in 1993 leaving me i/c bioinformatics infrastructure Ireland at INCBI b) the authors of the habitable planets paper "The Astrobiological Copernican Weak and Strong Limits for Intelligent Life" were Tom Westby and Christopher Conselice. What a crappy, keep the proles at bay, title for a paper of such galaxial importance. The Copernican Principle is the idea of human non-exceptionalism: just because we are the only speaking, dancing, technologically capable species we know doesn't mean that we are specially created by a [beneficent] god. It's much more likely [regression to the mean etc.] that we are just about average
What Westby & Conselice [and Drake] are trying to do is have a punt at the number Communicating Extra-Terrestrial Intelligent civilizations (CETI) to establish a) whether it's worth looking for them b) whether any of them pose a threat, so we should worry about them. The answer is a clear nada, nix, zonders, furgeddit. Their key problem is trying to extrapolate a distribution of data points from a single case [humans [and dolphins] on Earth]. The media is predictably joyful about the proximity of "36" to Douglas Adams' Hitchhiker's "42" as the answer to the question "life, the universe and everything?".
W&C are much better informed than Drake on one aspect of the necessary conditions for intelligent life. Since the early 1900s, astrobiologists have been looking hard for planets orbiting around stars and now have 4,000-and-rising to choose from; with the discoveries doubling about every two years. The first was evidenced in 1994. And space-hero Sara Seagar has been designing nifty tech to help find more.
Anyway, that 36 comes with error bars: with all their assumptions and extrapolations or best-guesses, there could be as few as four [4!] CETIs in our galaxy or more than 200. But those are, if you pause your rubbish! button for a moment, really confident bounds on the limits of their calculations: only 2 orders of magnitude. As you have been told [I am careful not to use as you know because the numbers involved are waaaaay bigger than a breadbox and effectively incomprehensible] the galaxy has a great many stars but they are spread really thin: loads of space between them. Another view on the W&C numbers is that the average distance between CETI planets is ~17,000 light years. Even if we detect a signal, it will be such old news that we won't be able to respond appropriately. And if we're planning on sending out a signal telling our story, it seems unlikely that there will be anybody intelligent around to process the response. All good fun, though, or at least "Mostly Harmless"