Were There Alien Civilizations?

This is not a new question in the world, or even this show. 55 years ago astronomer Frank Drake came up with an equation that weighed the odds for aliens. This is equation is something we explore in episode 022. But what's happened in-between now and then? Now two astronomers have tweaked the formula to come up with a slightly different spin. NASA’s planet-hunting Kepler space telescope is helping, too. link

Woody Sullivan (University of Washington) and Adam Frank )University of Rochester) published their complicated findings recently in the May 2016 issue of Astrobiology. They slightly alter the question - not if they exist, but if they did. They say:

“While we do not know if any advanced extraterrestrial civilizations currently exist in our galaxy, we now have enough information that they almost certainly existed at some point in cosmic history,” (Adam Frank)

According to them, there’s an astronomically high chance that other technological civilizations have risen and fallen elsewhere in the universe at some point in its 13.8 billion-year history.

How did they arrive at this conclusion? Well, by deconstructing the Drake equation. Here's how they use the equation:

  • They start out with an estimate of 20 sextillion stars in the observable universe (2 x 1022).
  • There appears to be at least one planet for every star (1.0).
  • And about one-fifth of those planets appear to orbit in habitable zones (0.2).

That gives you an estimate of habitable planets in the universe: 4 sextillion, or 4 x 1021

hen the astronomers add a bit of a twist to the equation:

How low do you have to set the chances that a habitable planet gives rise to a signal-beaming civilization, in order to reduce what you get when you do the multiplication (planets times probability) to just one world? The number would have to be one chance in 4 sextillion, or 2.5 x 10-22. Pretty low contact rates, huh?

In a press release after their explosive conclusion, Frank says: “To me, this implies that other intelligent, technology-producing species very likely have evolved before us, Think of it this way: Before our result you’d be considered a pessimist if you imagined the probability of evolving a civilization on a habitable planet were, say, one in a trillion. But even that guess, one chance in a trillion, implies that what has happened here on Earth with humanity has in fact happened about 10 billion other times over cosmic history!”

Is it just a numbers game, or is this a breakthrough?


The above image is from Flickr User Kevin Gill and is licensed under Creative Commons.