We now know that most stars have planets, meaning there are 100+ BILLION planets in our own galaxy, the Milky Way. If even one-in-a-million planets has life, there should be MILLIONS of planets with life in them! Where are all the aliens?
This question is called the Fermi Paradox.
The drake equation merely lists those probabilities affecting how many intelligent civilizations there are in the galaxy. Since we don’t know most of the variables — like the chance of life arising on a given “habitable” planet — it’s mostly useful for discussing what goes into the calculation.
Think about communication. In the 4+ BILLION years of earth, we’ve only been transmitting signals to space for about 70. That’s 70 light years ***IF*** you could detect those signals. Radio strength falls off to the square of the distance. So twice the distance means the signal strength is FOUR times weaker. We can’t even detect our strongest radio signal from a measly ONE light year. And those strongish signals have faded as we humans have invented better ways to get information around the globe without tossing so much energy into space.
The upshot is that, unless an alien civilization is trying to signal, we’re not likely to “see” anything. We’d have a lot better luck in the light spectrum but who’d be blowing out lasers in all directions? Not us. At least one prominent thinker, Stephen Hawking, worried that such attempts may be a bad idea since not all aliens will be benign. We’ve seen the movies.
The Drake Equation
The equation is (from Wikipedia):
- N = the number of civilizations in our galaxy with which communication might be possible
- R∗ = the average rate of star formation in our galaxy
- fp = the fraction of those stars that have planets
- ne = the average number of planets that can potentially support life per star that has planets
- fl = the fraction of planets that could support life that actually develop life at some point
- fi = the fraction of planets with life that actually go on to develop intelligent life (civilizations)
- fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
- L = the length of time for which such civilizations release detectable signals into space