The Drake Equation and Extraterrestrial Life

The Drake Equation is a thought experiment meant to provoke thoughtful consideration about extraterrestrial life.  It’s an equation containing factors that you multiply together to produce the “number of civilizations” in the galaxy we could communicate with.

  • N* = the number of stars in the Milky Way
  • fp = fraction of stars with planets around them
  • ne = number of planets per star ecologically able to sustain life
  • fl = fraction of those planets where life actually evolves
  • fi = the fraction of fl that evolves intelligent life
  • fc = the fraction of fi that communicates
  • fL = the fraction of the planet’s life during which the communicating civilizations survives

When you make astronomical or universal calculations, you really have to think in orders of magnitude, or “powers of ten”. You may recall that short film of the same name that goes up and down in scale multiplying by 10 or -10, and seeing how quickly things jump when you keep adding zeroes to the beginning or end of a number. Interestingly, this is also true of the Drake Equation, and really gets one thinking about the scale of things above and beyond our single, lonely planet. The factors that make the biggest impact on the equation are the number or stars, and the fraction of stars with planets around them.

Recent estimates have greatly increased the number of stars in the universe, and thus also our own galaxy – lately the number of stars in our own galaxy has grown to about 5 trillion. Trillion is a really, really big number. I decided to play around with the Drake Equation to produce 2 simultaneously communicating civilizations in our galaxy (us and someone else, because we need at least that many for extraterrestrial life to be possible).

  • N* = the number of stars in the Milky Way: 5000000000000
  • fp = fraction of stars with planets around them: 1 in 100000
  • ne = number of planets per star ecologically able to sustain life: 2
  • fl = fraction of those planets where life actually evolves: 1 in 2
  • fi = the fraction of fl that evolves intelligent life: 1 in 5
  • fc = the fraction of fi that communicates: 1 in 5
  • fL = the fraction of the planet’s life during which the communicating civilizations survives: 1 in 1000000 (about 10,000 years)

These numbers give us N = 2. Now the thing is, we could argue all day about all the “f” factors. We have no basis for comparison at all for any of them, seeing as how we’ve only ever found life on our planet. So we guess, and say that there are 2 planets in our system that could support life, and at least one of them has life on it. But here’s the thing. The actual estimate of stars with planets around them is actually around 20 to 50%, not 0.001%. So, plugging new, conservative numbers into the equation:

  • N* = the number of stars in the Milky Way: 5000000000000
  • fp = fraction of stars with planets around them: 1 in 10
  • ne = number of planets per star ecologically able to sustain life: 2
  • fl = fraction of those planets where life actually evolves: 1 in 10
  • fi = the fraction of fl that evolves intelligent life: 1 in 500
  • fc = the fraction of fi that communicates: 1 in 500
  • fL = the fraction of the planet’s life during which the communicating civilizations survives: 1 in 1000000 (about 10,000 years)

This is what gives us N = 2.5 (and we’ll truncate the number to get 2). We have to lower the “f” factors by several orders of magnitude from where we were before to get to extraterrestrial life being possible. But even this needs to be re-evaluated now, with NASA’s current announcement of life based on different biochemistry than anything we have ever found before, ever. To my mind, this means that the “f” factors have to increase, they can’t be as low as 1 in 2.5 million, life’s abundance is greater than we currently know.  If we move the numbers around some more, communicating with extraterrestrials is practically certain, due to the estimates of stars and planets being so damn big. There could be hundreds, or even tens of thousands of other civilizations existing just in our own galaxy.

Makes you think, no?