Dr. Frank Drake is famous for concocting an equation in 1961 that explains what we're dealing with when searching for extraterrestrial life.
Specifically, it's meant to generate the number of intelligent civilizations in the Milky Way.
Bear with me here, because this is going to be a little drawn out.
The Drake Equation goes as follows:
N = the number of civilizations in our galaxy capable of communicating the same way we do
R* = the rate of star formation in our galaxy
fp = the fraction of those stars with planets
Ne = the number of planets that could be life-bearing
fl = the number of planets that actually are life-bearing
fi = the fraction of those planets which develop intelligent life
fc = the fraction of those with capabilities for interstellar communication
L = basically the lifetime of a civilization, or time period where they're able to communicate
While the equation is a nice, thought-out process of the odds for finding intelligent extraterrestrial life, it really doesn't help.
Let me explain why:
We don't know anything.
The column could end here, but here's a little explanation.
Stars are being born — and are dying — in our galaxy all the time. That's a fact. Another indisputable fact is that stars across our galaxy are home to millions ... likely billions ... of planets. Of course, the actual number is guesswork, since we'll never be able to find and study every single planet in our galaxy anyway. That would be like studying each grain of sand along the Atlantic in my old home of Satellite Beach, Fla. But based on the fact that we've been able to discover about 4,000 planets in very tiny sectors of our galaxy, that gives us an indication of what we're dealing with. Common sense says planets should be somewhat evenly distributed around the galaxy.
So ... millions or billions of planets. But how many of those are possibly life-bearing? Here's where the guessing comes in.
We just don't know how many life-giving suns there are out in the Milky Way. We can narrow it down by choosing the most likely candidates: F, G, K and M stars are most likely to offer planets with extraterrestrial life. The hotter a star is, the farther out its habitable zone. So, cool M-type stars have a different habitable zone than hotter F and G type stars. But, it's hard to place an estimate on how many of those types of stars there are in the Milky Way. We cannot see the other side of our galaxy. If we were above or below and able to see the entire disk, we could, of course. But not being able to make a definitive observation really hurts our ability to nail this answer down.
From there, you know, it's just more unknowns. How do we know how many of those planets give rise to intelligent life such as our own? We can't really tell. And even if we could, how would we measure it? Is there some sort of universal standard?
In the past, I've written several times about things that could trip up an intelligent civilization. Self-inflicted events, such as wars and nuclear weapons, are a major factor. So, too, are accidental or happenstance events, such as a surprise comet or asteroid impact.
There are yet two other possibilities: civilizations being subdued by a higher echelon of systems or galactic confederacy (good or evil), or, the advent of a new form of life in the old one's wake.
Referring to the latter: What if the natural progression of a civilization is from organic to robotic life? Civilizations completely machine based would not communicate with other civilizations the way we do. Or, they wouldn't communicate with other civilizations at all.
Imagine a billion year-old civilization that has shed off its need for bodies like our own. There could be a planet populated by millions of these beings in a nearby star system and we wouldn't even know about it if they didn't want us to.
It's shortsighted, anyway, to focus on beings that would look just like us. But that's a discussion for another day.
So while the Drake Equation does divide our extraterrestrial search piece by piece, it doesn't give us any real numbers to deal with.