Answering Fermi

In a post last year, I talked about the Drake Equation (for predicting the number of intelligent species in the galaxy). In that post, I also mentioned the Fermi paradox, which begs the question, if there are as many intelligent species in the galaxy as the Drake Equation seems to predict, then where are they all?

Theoretical answers to the question have been proposed and, in many cases, explored through science fiction, and I'm going to discuss them further here. Really, the possible answers to the Fermi paradox fall into one of two categories:

1. There is no other intelligent life in the universe
2. They're out there, but we haven't found them yet

Each of these two categories has several sub-examples that might be applicable. In the first case, the most obvious answer might be that we are, in fact, the only intelligent life in the universe. Scientifically this answer is both unplausible and unpalatable. We know that conditions in our universe are right for the formation of life, and for that life to reach intelligence. After all, we exist (though some might argue about our "intelligence"). The scale of the universe is so incredibly vast that it's impossible to believe that intelligent life would form in one and only one location.

But maybe intelligent life develops and doesn't flourish, for one reason or another. Perhaps it gets wiped out by some natural catastrophe, such as asteroid impacts, gamma ray bursts, supernovae, or other natural disaster. Or maybe it wipes itself out through catastrophic climate change, nuclear war, engineered pathogens, self-replicating nano-machines, or through other means we haven't been clever enough to come up with yet ourselves.

Maybe they are out there, though, and we just haven't found them yet. Maybe they have such advanced technology that they could be watching us silently right now. Or maybe we're so beneath their notice that they don't attempt to communicate with us anymore than we attempt to communicate with cockroaches. It's likely that they're communication systems are so advanced that we would not detect their signals.

The final possibility I'm going to mention falls under the first category, but I saved it for last: maybe the first intelligent species to expand out into the universe has gone on a rampage and destroyed every other species that has attempted to expand off its home planet. This possibility has been thoroughly explored in science fiction, from swarms of self-replicating nanites to ginormous robotic destroyers to swarms of human-eating critters. And maybe they just haven't gotten here yet, or maybe they sweep through each sector of space every ten thousand years or so, and they'll be returning soon.

Which of these do I believe? Lacking any scientific evidence, I have to remain skeptical. The one that seems most likely to me is that they're out there, but we're not smart enough to notice. Maybe they're waiting for us to find them.

What do you think?

We're Here... Where are They?

If, as some science-fiction novels and movies would have us believe, the universe is teeming with intelligent aliens, that begs the question: where are they? If they're out there, why haven't they come to visit us yet (and please, for the love of God, don't refer me to stories of alien abductions and UFOs)?

That question has been pondered many times over the years (most famously by Enrico Fermi in 1950), by many scientists far smarter than a lowly computer geek like me. The heart of the matter comes down to one question: just how common is intelligent life?

In 1960, Dr. Frank Drake proposed a method for estimating the number of intelligent species present in the galaxy by use of a mathematical equation, as follows:

N = R^* x f_p x n_e x f_l x f_i x f_c x L

Okay, you're saying, but what the heck does that mean?

Well, N is the number of intelligent alien species currently in our galaxy with which we might hope to be able to communicate.

R^* is the average rate of star formation in our galaxy.

f_p is the fraction of those stars that have planets.

n_e is the average number of earth-like planets that are capable of supporting life per star that has planets.

f_l is the fraction of the above that actually go on to develop life at some point.

f_i is the fraction of the above that actually go on to develop intelligent life.

f_c is the fraction of civilizations that develop advanced enough technology to release detectable signs of their existence into space.

L is the length of time such civilizations release detectable signals into space.

By multiplying out the values you think are probably correct for those variables, you can get an estimate of the number of intelligent, advanced civilizations currently present in our galaxy. And the best part is, our knowledge of the universe is growing all the time, so we can refine the values used in this model as time goes on.

Drake and his colleagues used the following values in 1961:

R^* = 10/year (10 stars formed per year, on the average over the life of the galaxy)
f_p = 0.5 (half of all stars formed will have planets)
n_e = 2 (2 planets per star will be able to develop life)
f_l = 1 (100% of the planets will develop life)
f_i = 0.01 (1% of which will be intelligent life)
f_c = 0.01 (1% of which will be able to communicate)
L = 10,000 years (which will last 10,000 years)

If you work out the math, you'll find that Drake and his team estimated that there are 10 intelligent civilizations in the galaxy capable of producing advanced communication signals that we should be able to detect.

In the past 46 years, however, we've already learned enough to refine the model somewhat. For example, Drake estimated star formation (R^*) at 10 stars per year, but studies by NASA and the ESA show that the number is closer to 6.

Drake himself wrote an article for Wired Magazine in 2004 about revising the information for his model as new data became available. Drake now believes that there are far more intelligent species in the galaxy than he did fifty years ago.

But if Drake is right, then Fermi's original question stands: Where is everybody?