How many alien worlds are out there? Well, it’s probably impossible to know, but if you wanted to arrive at a number you’d probably turn to the Drake Equation. At BBC Futures, they’ve built a tool to manipulate the variables in that equation as you please, to see just how many alien civilizations there could be.
You start with how many habitable planets there might be. That number depends on how many new stars are born each year, the percent of those stars with planets, and the average number of habitable planets per solar system. Fiddling with those computes a number for possible habitable planets.
From there, you have to determine how likely it is that life would develop on those habitable planets. Drake assumed that if a planet was Earth-like, it would inevitably develop life. But we’re not just looking for life, we’re looking for intelligent life. As far as we know, out of billions of species on our planet, just one has become intelligent. What are the chances another life form has, too?
The last step is to go from intelligence to civilizations. What’s the likelihood that life could communicate across space. How long would those civilizations last. Would we be able to hear their signals before they are wiped out?
In the end, the Drake Calculator gives you a number of communicating civilizations in the galaxy. From there, we can extrapolate to the universe. Mathemetician Jill Tarter explained to the Smithsonian just how the Drake Equation works.
The number the Drake Equation arrives at is always bigger than you expect. Millions in our galaxy, billions in our universe. And yet, we still can’t find them. Not that we haven’t tried, it’s just really hard. Smart Planet’s John Rennie sums up the ways we’re looking, and explains the challenges:
In fact, it might be literally true that one piece of evidence for alien types of life has been right in front of mankind all along. Back into prehistory, human beings in desert areas have been scratching glyphs and drawings into rocks that have dark weathered surfaces. Those desert varnishes coating the rocks, however, have often perplexed geologists: good explanations for what causes these mineralized layers to form have been lacking. Biological activity has always seemed like one possibility but the agents responsible haven’t been in evidence.
Maybe we just haven’t known what to look for.
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