Physicist Enrico Fermi noticed that given the vastness of space, and the huge amount of time available, the odds are good that some alien species should have figured out interstellar travel and colonized the galaxy by now.  So where are they? It’s a good question and the answer, whatever the answer, comes with profound spiritual implications.

In 1950, Enrico Fermi, the nuclear physicist, asked a very simple, but very profound question.  He asked, “Where are they?”

The “they” in his question is extra-terrestrial intelligent life forms:  intelligent life on some other planet than the earth.  Extra-terrestrial intelligence.

“Where are they?” simply asks, if there are other forms of intelligent life in our galaxy, or beyond our galaxy in the observable universe, why haven’t we detected them?  Why isn’t there evidence for them?  Why haven’t our old episodes of “I Love Lucy”, broadcast out from earth, passed their old episodes of their old TV sitcoms coming in?  Why is it that everywhere we look, using all the different modes of detection that we have available to us, we don’t see evidence, in decades of trying, that we are anything but alone?  “Where are they?”

The universe is a very big place.  Astronomers estimate that there are 100 to 400 billion stars in our Milky Way galaxy.  And there are about 100 billion galaxies in the observable universe.  “Billions and billions” as Carl Sagan used to say, of places where intelligent life could exist.  We know there are planets around some of those stars.  And some of those planets are Earth-like enough that they could support life.  And if life gets started somewhere, it seems likely that eventually intelligent life would evolve, just as it did here.  That might take awhile but the universe is over 13 billion years old so there’s plenty of time.  And then, eventually, it’s only one more small step to assume that at least some of the intelligent life out there would get sufficiently advanced that they would start doing things that we could detect, like inventing televisions and broadcasting sitcoms into space.

Now that’s a long string of probabilities.  But even if all of those probabilities are very small, very rare, almost never happens, when you start with 100 to 400 billion possible stars just in our galaxy alone, and then multiple that by another 100 billion galaxies, and give yourself a 13 billion year timespan, even a very rare event becomes very possible.

We’re here, after all, so we know it’s possible for intelligent life to exist in the universe.  Wouldn’t it seem almost unfathomably unlikely that in all those billions of possibilities we are the only ones?  Indeed, when you put it that way, a lot of people are quick to affirm, “Well of course, we are not alone.  Absolutely intelligent life is out there.  It would be arrogant to assume otherwise.  We can’t possibly be that special.”

But that is Fermi’s Paradox.  Logically, extra-terrestrial intelligent life must exist.  But observationally, we have no evidence for it.  So, as Enrico Fermi asks, “Where are they?”

In 1961, about 10 years after Fermi asked his question, another man, named Frank Drake, attempted to quantify all of the variables that are implicit in assessing the likelihood of extra-terrestrial intelligence.   He came up with a string of variables, multiplied together in the form of an equation, the result being a number that would tell us the probability for the existence of extra-terrestrial intelligence.

Here is what Drake said we would have to know.

First, we would want to know the average rate at which new stars are formed.

Then how many of those stars have planets

Then, how many of those planets are suitable for life.

So far so good.  Because we have pretty good estimates for all of those.  And the trend line since 1961 has actually been getting consistently better for the odds of extra-terrestrial intelligent life.  We used to think that habitable planets were fairly rare.  Better observations in the last few years say that earth-like planets in the habitable zone, meaning the right distance from the parent star to allow for the existence of liquid water, are pretty common.  Astronomers estimate that about 20% of stars are like our sun, and about 20% of those sun-like stars have habitable planets orbiting them.  That gives us a lot of likely planets:  at least 4 billion just in our galaxy.  In fact, the closet habitable planet outside our solar system is only 12 light years away.

Then it gets trickier.

Once you know how many planets you’re talking about, then the Drake equation asks you to fill in the number of planets where life emerges.

Then, the number of planets with life where intelligent life evolves.

And then, the number of planets with intelligent life who are sufficiently intelligent to develop the technology that would make them deliberately or accidentally detectable to interstellar communication.

And finally, you would need to know, given that all the other conditions are happily met and you actually have an intelligent life form capable of interstellar communication – how long are they likely to last in that fortunate state?

The problem with the Drake equation is that the first three elements can be known fairly accurately, but the final 4 elements are fairly unknowable.

How many planets have life?  Well we’re the only one we know about, so far.  So your guess is as good as mine.

How many planets with life have intelligent life?  Well we know exactly one example, so far.  It’s us. How many intelligent life forms are capable of interstellar communication?  Well just one, so far, just us.  So your guess is as good as mine.

And how long do those civilizations last?  Well human beings have been broadcasting radio messages since the early 20th century.  We’ve lasted a little over a hundred years at that level of technological capacity.  How much longer will human beings continue to be around?  Well your guess is as good as mine. 

The problem with the Drake equation is that once you get past the first three elements, which are fairly objective and knowable, your get to four elements that are pretty entirely unknowable and subjective.

So the problem is that what numbers you plug into the Drake equation after the first three elements is pretty much based on your personal bias.  The Drake equation attempts to answer the question, “How likely is extra-terrestrial intelligent life?” by giving you an equation that requires you to plug in guesses based on your pre-conceived answer to the same question.  If you’re optimistic about the likelihood of extraterrestrial intelligence you’ll plug in optimistic numbers; if you’re pessimistic, you’ll plug in pessimistic numbers.  And then, because all the numbers get multiplied together the final answers that people get from the equation can vary by several orders of magnitude.

Frank Drake’s original estimate from 1961 is that there were somewhere between 1000 and 100 million advanced civilizations in the Milky Way galaxy.  Where are they, indeed.

By the way, Frank Drake is a pretty interesting guy.  He worked with Carl Sagan to design the plaques on the Pioneer space probes and the golden records on Voyager I and II that are meant to document life on earth to any space alien who happens to pick them up somewhere out there.

The Fermi Paradox is that it seems, at first thought, that extra-terrestrial intelligence should be common, but our objective evidence so far is that extra-terrestrial intelligence doesn’t exist at all.

So people have spent the last 70 years attempting to resolve the paradox.  That was the interesting question that I wanted to consider in the context of writing a sermon for worship.  They must be out there, we’re looking, so why haven’t we seen them?  Where are they?

One answer, is that they don’t want to be seen.  This is a common theme in science fiction.  The galactic federation has decided that earthlings are not suitable to join the team.  Usually the reason is that we’re too dangerous.  We’re too warlike.  The galactic federation knows we exist, but for their own protection they have set-up some kind of a communication shield around our planet that protects us from knowing about them until such time as they decide we are sufficiently ready to join the peaceful universal community.  We’re like a planetary toddler in a galactic time-out.  We’re being monitored by more advanced civilizations to see whether we’re going to grow up, or destroy ourselves first.

That we might destroy ourselves first is a different, gloomy answer to the Fermi Paradox.  Perhaps, the reason there are no extra-terrestrial intelligent civilizations out there, is that, every time a species develops the technology necessary for interstellar communication, that same level of technological advancement also, always, results in that civilization destroying itself.  Enrico Fermi articulated the Fermi Paradox in 1950, when he was working at Los Alamos to develop the Hydrogen Bomb.  The irony was not lost on him that at the point where our science had advanced to the point where we might start to wonder about interstellar communication we were using that science to develop a hydrogen bomb that might kill us all.

Maybe that’s just the universal rule.  Sufficiently high technology to reach the stars always creates its own demise before a civilization actually does reach the stars.

That answer to the Fermi Paradox is known, generally, as The Great Filter.  The Great Filter assumes that every other element of the Drake Equation makes intelligent life possible:  lots of stars, lots of planets, life getting formed all the time, intelligent life evolving naturally, but, every life form of sufficient intelligence eventually reaches a filter that stops them from evolving any further and either sends them back to the stone age, or wipes them out altogether.

That kind of answer pertains to the last of the variables in the Drake Equation.  How long do sufficiently advanced civilizations last?  We’ve only been deliberately looking for extra-terrestrial intelligence for about 60 years.  Maybe they were around earlier and we missed them.  Or maybe we’re ahead of the game and we need to wait a few years, or a few thousand years, or a few tens of thousands of years, for the next civilization out there to catch up.

But none of these possible solutions to the Fermi Paradox really satisfy.  The problem with all of these solutions is that they all exchange one unlikely scenario, that we are the only intelligent life in the universe, with other unlikely scenarios.

Take the Galactic Federation, for instance.  How likely is it, really, that all the other intelligent civilizations in the universe, found each other, agreed to cooperate with each other, and all agreed that they would develop a perfect communications black out with the Earth?  Well you can say it’s likely or it’s not likely, but in either case you are speculating about alien sociology of which you can have absolutely zero actual knowledge.  That’s good enough for science fiction but not for, you know, actual science.

Or take the early or late developers scenarios.  What’s the likelihood that alien intelligence is common and out of all of those other civilizations we happened to come in dead last, or uncontested first?  Well you might say it’s likely or it’s not likely, but in either case there’s no real reason to accept the improbability of those scenarios as any better than the improbability that we are actually the only intelligence in the universe.

And so, the Fermi Paradox has persisted for about 70 years now, since Enrico Fermi first articulated it.  Resolving the paradox has proved impossible.  Why is it that extra-terrestrial intelligence ought to be common, and yet we don’t see it at all?  Where are they?

And then, last year, a group of scientists from Oxford published a paper that doesn’t resolve the Fermi Paradox, but dissolves the Fermi Paradox, as they say.  They conclude there really isn’t a paradox, at all.

A paradox is when you hold two ideas, both true, but in conflict with each other.  By logic, extra-terrestrial intelligence ought to exist.  By observation, extra-terrestrial intelligence doesn’t exist.  If both of those are true, you have a paradox. 

The Oxford scientists say the paradox is dissolved when we show that actually, extra-terrestrial intelligence is not likely.  Our first-thought, best guess, logic, is wrong.  By their calculations it is entirely plausible that we are the only intelligent species capable of interstellar communication in the galaxy, and even in the entire observable universe.  So when we look up and see nothing there’s no reason to be surprised.  There’s no paradox to solve.  “Where are they?”  Well who are you talking about?  We are it.

What the scientists did is go back to the Drake equation.  They plugged in the current best estimates we have for the first three elements of the equation, the ones that are fairly objective and knowable.  But then, for the next four, they did two things.  First they made their own best guesses, based on research of prior papers on the subject, but they also included a factor that represents the uncertainty of their estimates turning their specific guesses into probability ranges.  Then they did the same thing with no guesses of their own but simply using all of the previous guesses discovered in their research and used that as a probability range.

Then, they subjected the resulting data to a Monte Carlo analysis.  This is a method of computational analysis that runs large numbers of random samples from data sets that contain high amounts of variables.  If you’ve ever followed some of the predictions that Nate Silver does at Five Thirty Eight it’s the same thing.  You pick data points at random from all the probability fields and you keep the computer running until it has done hundreds of thousands of possible combinations.

There’s obviously a lot of math in their paper, but here’s the bottom line.  The authors conclude that there is a 52% probability that we are alone in our galaxy and a 38% probability that we are alone in all the observable universe.  Furthermore, when the authors update their initial run based on the Drake equation, to include the actual observations we have of alien intelligence (which is none, so far) the probability that we are alone expands.  In the galaxy a range of 53% to 99.6% probability that we are alone – almost certainly alone.  In the observable universe a range of 39% to 85% probability that we are alone.

The paradox dissolves.  There is no paradox.  Finding no evidence of alien intelligence is exactly what we would expect, or at least there’s a high probability of that outcome.  So there’s no explanation required.  We seem to be alone because we are in fact, probably, alone.

So no explanation required.  But here, perhaps, some theology is required.

What would it mean for us to be alone in the universe?  What would that cosmic solitude do to our spirits?  What if, “over my head,” there were nothing but stars, and planets, and maybe some kind of life on some of those planets, but probably on none of them anyone looking up with the same wonder and speculation that we Earthlings do?

Sure we come from the stars, but what if, out of all those billions and billions of stars only we swam up from the sea, stood up on the land, and reached back to the sky with longing?

In my twenty-one years of ministry, I’ve never had occasion to sing the hymn that we sang just before my sermon, “Children of the Human Race.”  Now, I question, whether its simple assurance that we aren’t alone in the universe, might just have been proved an unjustified hope?

Most human religions begin from the premise that humanity has a privileged place in the cosmic order.  We are the receivers of God’s special attention, God’s work and God’s love.  We are the chosen people.  Jesus came to us.  Only enlightened humans can escape the cycle of rebirth.  Most religions claim among life on earth only humanity participates in any kind of salvation story and they have nothing to say at all about possible life beyond earth.

That always seemed incredibly arrogant to me.  Unitarian Universalism emphasizes the interdependent web of all existence.  We’re Universalists, after all.  Human existence is merely a part of the system that includes all.  We follow the science that shows us how connected we are to other life forms, not a special creation but fellow-organisms with swallow and snail and whale.  Christianity was struck to its core when Copernicus said the earth wasn’t at the center of creation.  Unitarian Universalists are happy to accept our place as residents of a minor planet, circling a small star, on the outside of a lesser arm, of a run-of the-mill spiral galaxy called the Milky Way, itself just one of a 100 billion galaxies flung across infinite space.  It’s not about us, we’re happy to say.

But what, then, if it is?

What if we do have a privileged place in the cosmos?

Could our religion survive humanity being shoved back in to the center, the way that Christianity survived Copernicus’ shove out of the center?  We’ve learned to be so humble about our common place in the universe.  What if, instead, we need to accept the responsibility of being caretakers of an extremely precious status?

I imagined when I started thinking about the Fermi Paradox that I would wrestle with the idea of the Great Filter, the idea that civilizations that achieve great scientific advancement inevitably risk destroying themselves by their own achievements.  Instead, I face a prospect even more daunting.  At least, if we’re not alone in the universe, if we do end up destroying ourselves, we could imagine that somewhere, sometime, some other civilization might at last be able to avoid the Great Filter and survive.  If not us, someone, maybe.

But if we are the only ones, then the responsibility to get this right becomes not just a wistful hope but a solemn, solemn duty.  Our advanced intelligence becomes not just a pleasant accident, a fun feature of this human life, but a precious birthright we must respect and protect.

That we might be it, alone in the universe, takes every principle of our faith and multiplies its importance by orders of magnitude:  the inherent worth and dignity of every person, compassion in human relations, acceptance of one another, the goal of world community with peace, liberty and justice for all.

If we have failed to recognize the precious worth of every human being before, and the awesome responsibility to protect a planetary environment that supports intelligent life before, surely, surely, we must not fail to recognize it now.