Empirically valid, my ass.
N = R* x fp x ne x fe x fi x fc x L
R*: We don’t know. Just recently, astronomers were surprised to see formation where theory said it unlikely. Some regions (the Orion nebula, for instance) are more prone to formation than others. We don’t even know how planetary systems form.
fp: We don’t know. based on those we’ve observed, it appears that roughly 20% of stars have life-zone planets. But again, we don’t understand planetary formation since a lot of those are in binary systems that theory said wouldn’t have planets at all. Planets are being found in orbits that theory says makes no sense. What we’ve spotted is such an infinitesimally tiny fraction of the stars that we don’t have a valid statistical universe of data to draw conclusions.
ne: We don’t know. We haven’t found any suitable for Earth-type life yet.
fe: We know of exactly one life-bearing planet: Earth. And we don’t know how life started here (theological discussion aside). We don’t know if other forms (think Star Trek’s silicon-based Horta) are possible.
fi: We don’t know. We have one planet — again, Earth — on which intelligent life appeared. Maybe. Looking at Americans voters, I wonder if we count. Some people think chimps, gorillas, porpoises, and killer whales are intelligent.
fc: We don’t know. Earth is detectable at close range (astronomically speaking) by someone else with similar technology. But we’ve never detected anyone else. Maybe they’re there, but hiding from interstellar locusts that devour tech civilizations. Maybe they saw I Love Lucy and said, “Holy shit, don’t let those creeps find us.” Maybe they just talk to known neighbors with lasers, and all their local comm is on undetectable fiber optic networks. Maybe they jumped straight from wired telegraphy to quantum paired communications. Maybe they don’t exist.
L: We don’t know. We’ve been radiating sufficiently for maybe 60 years. How long will we last? Since we never heard anyone else, we don’t know how long it’s possible to last.
The Drake Equation is, at best, science fiction. More likely, it’s mere mental masturbation. The Frank and Sullivan equation is worse since it effectively adds in yet another imaginary “archeological” variable.
Care to bet if these guys are operating on fed tax money grants?