The Drake Equation

Before we discuss those two things, a brief discourse on the Drake Equation.  The Drake Equation is not so much an equation as a means of quantifying ignorance, and adding up the probabilities of intelligent life arising in the galaxy.  You start with the number of stars in the galaxy, and multiply that number by quite a few factors.  The result is your own personal estimate, N, of how many ETs are out there.

N is the number of civilizations in the Milky way that have developed systems which produce electromagnetic emissions detectable from Earth.  It is equal, then, to the rate of star formation times the probability that the star will have planets, times the number of habitable planets per star times the number of those planets that will develop life, times the number of those that will develop intelligent life, times the number of those intelligent species that will develop means of communication times (finally) the length of time those signals are detectable.

The first two numbers, we actually know something about.  The rate of star formation is about 1.5 a year, and we are finding planets everywhere we look, so .9 for that.  Number of habitable planets?  For us in the Solar System, one definitely, and two maybes – Europa and Mars.  Let’s say three.  (It doesn’t matter if they’re not all habitable at the same time.) SETI researchers always use “1” for the number of habitable planets that develop life.  How many develop intelligent life?  Taylor suggests 2/3, fair enough.  How many develop detectable civilizations?  Taylor suggests a quarter.  Run the numbers, and the Drake Equation yields an interesting result. 

New, detectable ET civilizations are arising at a rate of one every three years.

Assume we’re off by an order of magnitude.  That’s two civilizations per lifetime.  A hundred thousand over the tenure of man’s existence on Earth.  Half a billion extant in the galaxy right now. 

Put in smaller numbers, and the results are still invariably stunning.  Assume that only one in a hundred habitable planets develops life, and that only one in a hundred of those develops intelligent life.  You still get an intelligent species arriving on the scene every thousand years.  The galaxy is billions of years old.  150,000 extant in the Galaxy, right now. 

Taylor and company also make some interesting additions to the Drake Equation.  They take into account the size of the Milky Way, and calculate the galactic density of ETs.  Using Taylor’s numbers, it is .064 ETs per square light year.  Or, in a 1000 ly bubble centered on earth, there are 50,000 species.  That’s intelligent, technological ETs.  Even using my several orders of magnitude more conservative numbers, there are still 15 techno-ETs in local space.  right now.

They also add two more factors to the Drake Equation: ft, the number of technological civilizations that go a-traveling, and v, the velocity at which those species can move about the galaxy.  Here we get some even more interesting numbers.  If we assume that all technological civilizations eventually travel, and that their velocity is a tenth the speed of light, then there are 200,000 travelers within range of Earth.  Which means that there is a great likelihood of someone, sometime, visiting Earth.  And maybe soon.  Maybe next Tuesday.  (Taylor provides all the math for this, btw.) You’ll have to read the book to see what his numbers suggest, you won’t believe me.  (you can see a good chunk of the book here.)

The sheer number of stars in the galaxy, and the staggeringly long time it’s been around mean that whenever you plug a non-zero number into any element of the Drake Equation, you get lots of ETs, and an uncomfortable number in close proximity.  Using my numbers but the same assumptions as Taylor, the likelihood of one of 60 nearby species paying a call on earth is about one visit every 166 years.  Now there may be other factors that slow down the rate of visitation – varying galactic geography, randomness of placement, or even that there are even less species than we think.  Another primary reason we’ll discuss next.

The chance of first contact is not so remote as we may believe.

The Fermi Paradox

Fermi’s Paradox comes from the question, “Where are they?” that Enrico Fermi asked back in the fifties after some back of the envelope calculations led him to consider that given a constant rate of expansion, it would only take millions of years for an intelligent species to spread throughout the Galaxy.  And the Galaxy is billions of years old – if, at any time, an intelligent species had arisen, one might assume that they would have gotten here and, presumably, prevented us from existing in the first place.

This always seemed a fairly reasonable supposition, but it does fly in the face of the results of plugging even the most conservative numbers into the Drake Equation.  Taylor and company put the eye on this dilemma and come up with a surprising conclusion.  The Fermi Paradox is a crock.

Over the years, the SETI community has come up with several responses to the Fermi Paradox.  We could be the first intelligent species.  Or there could be any number of insurmountable obstacles to interstellar expansion: it’s too difficult, conceptually alien to other intelligences, or it’s not really a good idea and just not done.  Or, it has been done and there is some sort of Prime Directive that restrains ET from screwing with us.  Or ET is screwing with us and we don’t know it.  Or we’ve simply been overlooked.

Now all of these things are reasonable.  Taylor, however, contests the ground under Fermi’s feet.  Fermi, in his calculations, used a simple population growth model.  However, says Taylor, that isn’t really the best model for imagining intelligent species moving out into the big world.  First, no species on Earth ever follows a simple exponential growth curve.  Second, intelligent species will likely have different needs and goals, and thus will either defend niches or compete over them within a greater sentient galactic ecology.

Now this gets meaty. 

“Nature here on Earth offers many examples where the struggle for existence between two similar species fighting over the same niche (food supply, space, etc.) occurs.  Ultimately, one species wins out by causing the complete extinction of the other species.  This phenomenon is known as the “principle of competitive exclusion” and was proposed by Darwin in 1859 in his Origin of Species.

“There are also cases on Earth where the “principle of competitive exclusion” is in direct contradiction with some well-known natural phenomenon.  An example of one of these natural contradictions is called the “plankton paradox” and is focused on the variability of plankton organisms which all seem to occupy the same niche.  All plankton algae use the same niche, which consists of solar energy and minerals dissolved in their native habitat waters.  There are many plankton algae species, many more than the different types of mineral components in the water habitat of the plankton.”

Now this seems very interesting indeed to me.  A direct analogy, which the authors do not explore – is that plankton are in effect in a space like environment where solar energy is the primary source of energy, and minerals of varying concentrations are available more or less for the taking within their environment.  A spaceborne civilization using asteroids, comets, and solar energy to sustain itself and grow could be likened to plankton.  One could imagine multiple intelligent races sharing this niche – with the vastness of space making contact fairly minimal.  Of course, one might imagine that if plankton were a little more sophisticated, they might hate and attack other plankton that they did run into.

And that leads us to the next bit – a simple exponential growth law would not explain a species expanding into the galaxy and then running into competition.  Other population growth laws – in fact, predator-prey models – might explain how well ETs do in the big galactic arena.

“Therefore, the simple Malthusian or exponential population growth as described previously is a drastic oversimplification.  Perhaps Fermi’s Paradox is not as paradoxical as it seems.  One could imagine that the galaxy is much like Earth with multiple species supporting and competing against each other over various niche resources.  Perhaps the society that is a few million years older than us is not preying on us as often as expected because they are defending themselves from predators a few million years older than them.  The possibilities are limitless.  Let’s hope that we are living in a natural environment, as on Earth, where the coexistence of predator, prey, and other competing species is possible.”

A galactic meta-ecology, composed not of competing organisms as on Earth, but rather of competing intelligent species is possibly the answer to the Fermi Paradox.  No species can expand willy-nilly, because of the presence of other species.  Like early algae, the first species may have run wild, but ever more competent species will have, over time, engaged in competition.  This competition will certainly engage the intelligence and resources of an alert species – which means that in the dark corners, new species will always be coming up to try their hand (or tentacle, flipper, pseudopod, or claw) in the big game.

The reason, therefore, that we haven’t been assimilated may be not that we are the first, or only intelligent life in the galaxy, but that other intelligent life is too busy staying alive to visit every star, or deal with every potential threat.  Other species’ lifespans in the meta-ecology of the galaxy might be rather shorter than they would otherwise be, due to competition with other species.  Possible aspects of this galactic meta-ecology are left unexamined in the book, which was frustrating to me, as it certainly bears directly on the main question the book is meant to answer.  Still and all, a lot to think about, and we’ll be getting back to that in a minute.

Or maybe more than a minute.  We will continue in part two.