Is anybody out there?

If we’re looking at the numbers right, we should be swimming in alien communication. So why aren’t we?

Back in the 1960s, when SETI and all of these other alien signal-spotting agencies were really getting into the swing of things, someone though it might be a good idea to do some serious scientific thought about if aliens might actually exist in the first place. So an astronomer by the name of Francis Drake designed an equation. Because if in doubt, design an equation.

N = R_{\ast} \cdot f_p \cdot n_e \cdot f_{\ell} \cdot f_i \cdot f_c \cdot L

The N is the number of intelligent alien radio waves that we should be able to pick up. R is the rate of star birth in our galaxy. Fp is the percentage of those stars that have planets, Ne is the fraction of those planets that can potentially support life. These numbers we can estimate with a decent level of accuracy. Then things get sketchy. Fl is the fraction of life-supporting planets on which life does develop, Fi is the fraction of those that becomes intelligent, Fc is the fraction of those that begin transmitting radio waves into space and L is how long they do it for.

Now, if we substitute some fairly optimistic but still reasonable numbers into the Drake equation, we can get a decent estimate for the number of intelligent, data-transmitting civilizations in the galaxy. And that number is 36 million.

Now obviously, if there are 36 million civilizations in the galaxy, it would stand to reason that we would have noticed at least one by now. Which…we haven’t.

There are, of course, quite a few reasons why this could happen.

We could be overestimating the value for Fl, the occurrence of life on life-supporting planets. But based on the massive amounts of basic organic compounds that we see all over the solar system (on comets, on Mars, all over the outer moons of the Solar system) this seems pretty unlikely.

We could be overestimating the number of intelligent life forms in space. After all, we only know of a few intelligent species in the history of the Earth (if you count Neanderthals and some other primates).

We could be overestimating the number of species that develop the capacity for interstellar communication. We only know of one. Speaking.

Or we could be overestimating L. We have absolutely no idea how long civilizations hang around for in the grand scheme of things. Given how close we got to total annihilation in the Cold War, it could be not the longest time. But hopefully, we will survive as a species for a while at least.


This is the Fermi Paradox – even if we use conservative estimates, we should have almost definitely found alien communications right now. But we aren’t. So enter a new theory. The Great Filter.

The Great Filter is a hypothetical hurdle that every developing civilisation will have to face, regardless of species or location. We have, at the moment, no idea what that is. It could be the destruction of the host planet’s ecosystems by massive overpopulation. It could be the inevitability of meteorite strike. It could be the death of the host star. It could be a gamma ray burst.

Whatever it is, it is something that will, in all likeliness, obliterate the species long before it colonises other star systems. All of these events drastically reduce L, the time during which a civilisation has the capacity for interstellar communication. And that certainly solves the Fermi Paradox. The vast majority of the aliens were killed by the Great Filter and thus are no longer broadcasting. Great.

But where does that put us?

In the Great Filter universe, there are three possible places we could be, unable to detect alien life.

  1. We could be the first species, chronologically, to pass the Filter in the history of the galaxy. Gold medals to us, but the galaxy is both very big and very old. Not likely. And also that would make us very, very alone.
  2. We could be one of a few species, out of potentially millions, to pass the Filter. By wiping out well over 90% of the potential Drake equation civilisations, the idea of ‘we just haven’t found the aliens yet’ becomes a lot more likely.
  3. We have’t got to the Filter yet. Which means we are, scientifically speaking, mostly f**ked. Sometime in the future, many things will go kablooey and our species will likely be wiped out. And that is why finding primitive life on Mars would be, in one sense, awful news. The statistical odds of two species passing the Filter in the same star system in the same few millennia are virtually nil – it implies that the Filter is yet to come.

So, we are all doomed. The inevitability of life in the universe means that we will, at some point, be wiped out before we find anyone else. Ready your apocalypse bunkers, my friends.

Or that isn’t actually what happens. The Great Filter is, of course, only a theory. Here are a few other possible explanations (with help from, who is a great research source).

  1. Aliens have visited Earth, but in the period before the 5.5 thousand years of recorded history and decided we were too boring and left.
  2. There is life in the galaxy, but not in our bit.
  3. To a super-advanced species, the idea of trying to communicate with aliens is stupid.
  4. There are evil aliens out there, and the other aliens are scared of talking too loud in case the monsters come and get them.
  5. There is only one superintelligent civilisation and it keeps killing anything that gets close to it. Which is effectively just an artificial Great Filter.
  6. We aren’t listening hard enough, or we’re using primitive equipment by alien standards. What if they are yelling at us with their subspace communicators and we just can’t detect it?
  7. The government is hiding the aliens.
  8. There are alien civilisations aware of us, and they are studying us. The ‘Zoo hypothesis’
  9. There are alien civilisations near us, but we are too primitive to even perceive them.
  10. We’re completely wrong about the entire universe and maybe reality itself.

Great. So we are all either doomed, completely alone or living in a hologram.



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