Hey there. I'm Josh Clark and this is BrainStuff. And this is the BrainStuff where I talk to
you about the Drake Equation.
*Intro Music*
Back in 1950, a very very smart physicist named Enrico Fermi was taking a lunch break
away from making nuclear bombs at Los Alamos National Laboratory, when he posited a question
to his lunch companions: Where are they?
What Fermi meant by this was, considering the age of the universe, and the mind-boggling
number of planets that could possibly sustain life - shouldn't by now the universe be teeming
with life, much of it intelligent, and some significant portion of that able to travel
amongst the stars?
And if you take all these things for granted (which it makes sense to), we should've been
visited by this intelligent life time and time again by now.
And yet we only have anything approaching definitive evidence that we're alone in the
universe. This observation became known as the Fermi Paradox. And ever since 1950, people
have sought to explain it.
Probably the most famous attempt to explain the Fermi Paradox is something called the
Drake Equation.
Back in 1961 an astronomer named Frank Drake convened what would be the first meeting of
the SETI Institute. SETI stands for the "Search for Extraterrestrial Intelligence." And at
this conference, which Carl Sagan was at by the way, Frank Drake debuted his now-famous equation.
The Drake Equation is surprisingly simple, and Drake intended for it to be that way.
It's also a probabilistic formula that uses, at this point, random guesses and wild speculation
as inputs. That's because we don't know a whole lot about our universe, or life at the
moment. But the logic behind it is pretty sound. And it goes like this:
N = R* times f_p times n_e times f_l times f_i times f_c times L
Now, N equals the number of intelligent civilizations out there whose communications we could possibly
detect within the Milky Way. In other words, it's the number of potential alien civilizations
out there in the Milky Way that we could conceivably interact with. This is the point of the Drake
Equation, it's what it seeks to understand.
R* is the rate of star formation. Astrophysicists have determined that, in the Milky Way, about
3 solar masses worth of material forms into stars every year. A solar mass is equal to
the mass of our Sun. 3 times that doesn't necessarily mean that 3 suns are made. It
could be one massive star that's 3 times the mass of our Sun that forms that year. Or it
could be 10 smaller suns, that are .3 times the size of our Sun. It could be any combination
of those. But for our intents and purposes, because our Sun is technically an average-sized
star, we can say '3.'
And we arrive at what is to be a very rare occurrence, where we have a value that we
can put in pretty confidently into the Drake Equation.
F_p stands for the fraction of those stars that have planets orbiting them.
N_e stands for the number of those planets that are capable of supporting life. Planets
that orbit the star within its Goldilocks Zone, where things are not too hot or not
too cold, but just right.
We call these 'exoplanets.' And we've been discovering them like crazy lately. There
could be possibly billions in the Milky Way alone. But so far we are pretty confident
that there's at least 3400 exoplanets, or planets capable of supporting life, within
the Milky Way. And we arrive at the other value that we can fairly confidently put into
the Drake Equation: 3400.
From here on out, though, it gets increasingly murky.
F_l stands for the fraction of those exoplanets where life evolves. So far, we can only say
with absolute certainty that life has evolved once in the universe. And since we're talking
about ourselves, we can't input '1' into the Drake Equation because we're not seeking to
find out whether we can communicate with ourselves or not. Y'know what I mean?
F_i is the fraction of that life that evolves (that develops intelligence).
And f_c is the fraction of that intelligent life that develops communications that transmits
in ways that we can detect. Basically along the electromagnetic spectrum. In other words,
it's kind of like, what kind of chatterboxes are out there using radio waves like we are,
with 'I Love Lucy' blasting through space still?
And finally 'L," the Big L, stands for the longevity of this communicativeness. So, how
long does the average intelligent civilization transmit in some way that we can detect, before
they either go extinct or find a new means of communicating that we couldn't possibly
detect. Like, I don't know, telepathy.
So, as you can see, when you put all this stuff in together, the Drake Equation doesn't
really tell us a whole lot about how probable it is that there's intelligent life out there
in the Milky Way.
But it's not the Drake Equation's fault. Don't blame it! Stop! Stop!
Instead, it's because we don't understand the universe. We don't understand the Milky
Way even. We don't even understand life well enough to really confidently put some good,
educated guesses in there.
The problem with the Drake Equation is that, not only could you prove that there's a really
high certainty (depending on wild guess you put in there); you could also prove that there's
a zero chance. All you have to do is put 0 into any one of those factors, and the possibility
that there's any life out there that we could detect or communicate with, is zero.
It's a problem.
So, astrobiologists and astrophysicists and astronomers will keep searching the universe,
will keep searching the Milky Way. And the data they come back with will be plugged by
some people into the Drake Equation to see if it will eventually spit out a verifiable answer.
But in the meantime, it's serving as a pretty great tool for getting people to think about
the possibility of alien life. And not just that, but about the future of our own human
civilization as well.