There is no hard scientific evidence that intelligent life
exists anywhere beyond Earth, yet when asked if there's anyone
else out there, most people have a strong opinion one way or
the other. When astronomers answer the
question—typically in the affirmative—they are
playing a numbers game. There are hundreds of billions of
galaxies, each bearing hundreds of billions of stars and
perhaps billions of planets, so even if intelligent life is
rare, we can't be completely alone, the argument often goes.
The Drake Equation, named after its creator, radio astronomer
Frank Drake, is an attempt to frame the question
scientifically by assigning a value to all the relevant terms,
from the number of stars born each year in our galaxy to the
number of stars with planets, and so on. In this interactive
version of the Drake Equation, see what Drake's current
estimates are, then play around with the numbers yourself to
see what you come up with for the value N—the number of
communicating civilizations in the Milky Way. To launch the
interactive, click on
the image at left.—Lauren Aguirre
