The Drake Equation

N = R* fp ne fl fi fc L

The Drake Equation was proposed by the astrophysicist Dr Frank Drake as a means of estimating the number (N) of alien civilizations that may be sharing the Milky Way galaxy with us.

The equation postulates that N is the product of the following:

  • the average rate of star formation in the galaxy;
  • the fraction of stars with planets;
  • the average number of planets capable of supporting life that orbit these stars;
  • the fraction of those planets on which some form of life evolves;
  • the fraction of those planets on which that life becomes intelligent;
  • the fraction of civilizations the develop and are capable of broadcasting their presence be that intentionally or unintentionally;
  • and finally, the length of time for which those civilizations actually broadcast their presence.

Back in 1961 when the equation was formulated the number calculated for N was 10,000. 50 years later no hint of any alien presence has been found, prompting the BBC to ask the question Why haven’t we found aliens yet? And then trying to answer that question through the medium of a programme called The Search for Life: The Drake Equation.

As you can imagine lots of reasons that we haven’t found alien life have been given – to name but a few:

  • life on Earth is unique and there’s no one else out there;
  • there’s life out there but it’s not as advanced as us;
  • there’s life out there, it’s way more advanced than us and finds us about as interesting and worth contacting as we’d consider the average ant to be;
  • there’s life out there and its so different technologically that we’re just not able to detect it, or;
  • we’re the lone inhabitants of a computer simulation being run by an ultra-intelligent race.

I suspect that there are other forms of life in the galaxy (there certainly are within the wider universe) and the reason we haven’t found any trace of that life is the one offered by Drake himself:

We just haven’t tried enough. We’ve looked carefully at only a few thousand stars and very few channels that are possible on the electromagnetic spectrum and that’s hardly even a start.

If you take reasonable or optimistic values for the [Drake] equation, it suggests that right now, there may be around 10,000 civilisations we can detect in the galaxy. That’s one in 10,000,000 stars. Before we have a good chance of succeeding, we still have a long way to go.


3 thoughts on “The Drake Equation

  1. I was rather disappointed with the programme. Not so much for the content – Frank Drake’s contributions were great, and there was little on the wacky side – but for poor graphic and cinematic quality. “Normal” shots were interpolated with grainy images of the presenter and other objects, juddery shots of the equation (many times), the presenter making meanless lines in the sand, and the camera scanning in lunatic fashion. Compare this with any Brian Cox documentary, and it doesn’t rate. These camera tricks were prominent in programmes on the geography of Britain a couple of years ago, and I thought the gremlin had been excised – but apparently not. Please don’t treat your audience as people who need to have arty camera work to stay awake.

  2. The fatal flaw in the Drake Equation is that is doesn’t account for the five great extinction events during the past 540 million years, each of which allowed the survivors to flourish and further evolve via survival of the fittest, after eliminating the then-dominant species. If it weren’t for each of those events, Earth would not be inhabited by intelligent [?] life. The Permian-Triassic Extinction Event, for example, eliminated 96% of marine species and over half of the land species. The assumption that evolution proceeds from the unicellular to the sentient without intervention is not supported by the evidence.

  3. Henry, your comment leaves out the very likely possiblility that intelligent life would arise despite, not because of, the extinctions.  Just because mammals arose here does not preclude the potential for other species to evolve into higher life forms given time.  For example, had not the Cambrian extinction occurred, who’s to say that the trilobite — or any other marine life form — would not evolve into an intelligent creature?

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