Just what is the Fermi Paradox?  Well, in a nutshell, it asks, if ET really existed, then why do we not see intelligent civilizations everywhere?  In the late 1950s, the noble prize winning physicist Enrico Fermi asked the question, if there are intelligent civilizations elsewhere in the galaxy, then why don’t we see them everywhere by now, as they would have colonized the entire galaxy long ago?  Fermi’s reasoning seems very sound, as it is based on our existing understanding of population growth and the age of the universe.  He believed that we must be alone in the universe, because if we weren’t, then we should see civilizations much older than our own all over the place.

The Fermi Paradox

Fermi argued that a civilizations home planet would eventually get overwhelmed with an exponentially growing population and would be forced to expand outward and colonize other worlds.  Since the universe itself is astronomically old, Fermi theorized that there must be civilizations that began millions of years before ours.  Furthermore, the Drake Equation postulates that there should be thousands of intelligent civilizations in our own galaxy alone.  Therefore, he argued, since there should be thousands of species, many of which have a million year head start on us, in our own galaxy alone, we should look out of our telescopes and see the signs of a bustling galactic metropolis.  Since we see do not see ET everywhere, then he must be nowhere.

Exponential Population Growth

The Malthusian Population Model is an exponential equation that explains the rate at which a population grows.  The equation states that the population of a species over time is found by multiplying the initial population by its growth rate (otherwise known as a population expansion coefficient).  To use humanity as an example, there are currently 6 billion people on the planet and if we make a reasonable guess as to when the first human emerged, say 10 million years ago, we can use the equation to discover that humanity’s population grows at a rate of “e” to the .00000225 power multiplied by time.  The math is not so important so long as you recognize that a civilization’s population grows exponentially.

Running Out of Room

After finding out the rate at which the human population grows, Fermi calculated how long it would take for us to completely overwhelm the useable surface area of the Earth.  Assuming that at a maximum, 500 humans could “comfortably” occupy a square kilometer, which is twice the population density of New York City.  Very crammed indeed.  Fermi than found how much useable space there is on the planet (everything but oceans, seas, etc.) and applied it to the population density assumption and the rate at which the human population increases.  He found that the human race, or any other similar, intelligent ET civilization, would completely cover their home world in about 10 million years.  Once that happened, the civilization would be forced to expand outwards and colonize other planets.

This estimate ignores the obvious possibility that a planet’s natural resources would become unsustainable long before it becomes overcrowded or that “pioneers” might leave the home planet long before it becomes completely filled.  But for now, lets make the conservative estimate that 10 million years is the time it takes for an organic, intelligent civilization to run out of room on their world.

The Age of the Universe

When you saw that it would take about 10 million years for a civilization to fill up a planet, you may have been unimpressed.  Of course we don’t see any huge, galactic empires, because it takes a millions and millions of years to become over populated, let alone to then fly around and start filling up other solar systems!  There is probably a whole bunch of other civilizations out there, they just have not reached the point where they need to expand yet, or if they have, they haven’t reach us yet, right?  Well, maybe.  But consider what ten million years is compared to the age of the universe.  It is a blink of an eye, a tiny, insignificant fraction.

The universe is approximately 16 billion years old.  The Milky Way galaxy?  About 13 billion years old.  Consider that the entire recorded history of the human race is about 5,000 years long.  Compare that to the age of the galaxy and you realize that our entire civilization’s recorded history takes up  about 0.000000384 of the length of time the galaxy has been around.  It would be statistically impossible for us to think that yes, intelligent life can form elsewhere, but only right around the time that we did.  It is much more likely that other civilizations came into existence far earlier than our own.

Exponential Growth Outwards

As the graph illustrates, a population of an intelligent species grows exponentially.  If our own species were to continue growing at its present rate, then Fermi calculated that we should populate over four hundred billion planets in just about 23 million years.  If every star in our Milky Way galaxy had at least one Earth like planet, then in just a few million years we would have colonized the entire galaxy!  Like an ever expanding wave, human colonies would branch out and fill up the entire interstellar neighborhood.

Now Fermi’s paradox becomes apparent.  Why have we not been colonized by a species (or at least even just seen another species) that is geologically only a few millions of years older than our own?  After all, dinosaurs were around over 65 million years ago, if some alien race had become sentient since that time, it should have colonized the entire galaxy already.  Twice!

Was Fermi Right?

So, was Fermi right when he said we must be alone in the galaxy?  Well, there have been many experts on both sides that have argued this point.  One answer is yes, we are the only intelligent species, at least in our galaxy anyways.  However, this answer in itself is rather perplexing.  To say that life could form, but only once, seems counter intuitive.  Science shows us that processes and systems that are capable of happening at all, usually happen many, many times.  Using the numbers 0 or 1 (no more civilizations out there other than ours) to solve a mathematical problem is often misleading.  You may solve the equation, but you get the wrong answer.  Just think of how many high school math tests you took where 0 or 1 seemed to be the answer, yet you knew in your gut it was just because those numbers do a lot of weird things once you plug them in.

So if we say that Fermi was wrong, then how could that be case?  After all, a paradox is a paradox.  A question with no correct answer.  Many people have come up with a number of theories that attempt to solve the paradox, including:

• a Prime Directive exists, prohibiting alien races from interfering with primitive cultures like our own;
• ET has no interest in us;
• no previous civilization so far has had the need or desire to colonize the galaxy;
• we are the first civilization;
• we are already the results of a colonization effort, the fact of which is lost to ancient history;
• colonizing the galaxy is technologically impossible;
• we have been overlooked by ET;
• or perhaps we are being visited regularly, but lack the technology to detect visitors;

Any or all of these possibilities appear to be viable solutions to Fermi’s paradox.  However, there is no overwhelming data to support any of them.  While we may not know the answer to the Fermi paradox right now, one overlooked fact is inescapable…

He used the wrong math.