The Fermi Paradox and fear of the Great Filter

What is the Fermi Paradox?

Sometimes it’s easy to forget how massive the universe is. I don’t mean purely in terms of the distances involved (although this seven-mile scale model of the solar system in the Black Rock Desert demonstrates that point quite well), but in terms of the scale. There are around 100-400 billion stars in our galaxy and around the same number of galaxies in the universe, meaning we’re possibly looking at upwards of 1,000,000,000,000,000,000,000 stars. Try and imagine every grain of sand on Earth. Done it? Right, well there’s more than 100 stars out there for every one of those grains.

Of course, not all of those will be similar to our sun, but even if you go with scientists’ conservative estimates, you’re looking at around 500 quintillion (that’s a five with 20 zeroes) suns that are a bit like ours. Some of these will have planets orbiting them, and some of these will be in their own “Goldilocks zone” – the sweet spot where it’s warm enough for liquid water not to freeze, but cold enough for it not to evaporate.

Naturally, this is speculation because most of these we can’t even see (even what we know about Kepler 452-b is inferred through its shadow), but it could be as high as 50% of these. Halve that, and call it 25%, and you still come up with 125 quintillion Earth-like planets. Hell, call it 1.5%, and there’s still enough Earth-like planets for every human on Earth to adopt one billion Earth 2.0s each, with around 400 billion spares.

These planets are of different ages, and not all of them would have the perfect blend of herbs and spices that has resulted in intelligent life to evolve, but if even 0.1% of them did, that would be around 7,500,000,000,000,000 planets with intelligent life.

Which leads to the puzzling question that physicist Enrico Fermi is said to have asked: where is everybody?

There are a bunch of possible solutions to the Fermi Paradox, but no definitive answer. In broad terms, they come in three flavours:

1. There is no life out there (or isn’t anymore)

2. There is life out there and they haven’t made contact

3. There is life out there and they have made contact. We just didn’t notice

For each of the theories, there are plenty of subsets – some creepier than others. Strap in.

Images: Tom Hall, Alexander Kaufhold, JD Hancock, Damien Phillips, Moyan Brenn, Maxwell Hamilton and Chris Moore used under Creative Commons

1. Fermi Paradox solutions: There is no intelligent life out there (or isn’t anymore)

Given the sheer volume of Earth-like planets I mentioned on the previous page, surely the chances of this are pretty low? Well, maybe, but we’re basing this on what we know about Earth’s evolution. What if we’re just a quintillion-to-one shot that came good? Afterall, it’s now believed that Earth as we know it was formed by the collision of two planets 4.5 billion years ago, which is nothing if not down to chance. So there’s a possibility we’re the most intelligent lifeforms in the galaxy, and hey, if we haven’t cracked it then who can?

But that seems pretty conceited to me, especially considering the raw numbers involved (do I need to hammer my zero key again?). We know the likely numbers and plenty of those planets will have had the conditions ripe for life for far longer than Earth. We’re around 4.5 billion years old, and humans have only been around for 0.004% of that time. If other planets have been around for (say) seven billion years and followed roughly the same time scale, they’d have a whopping 2.5 billion years of evolution on us. Enough to have this whole galaxy travel thing licked.

Or would they? This is where the Great Filter theory comes into play.

The Great Filter theory

One of the theories about why we’re yet to see any aliens is that all life reaches a point where it hits a wall where it’s vanishingly unlikely that it’ll evolve any further. If you’re an optimist, you’d say that we’re special and we’ve passed this. If you’re a pessimist, you’ll say we’re yet to hit it. If you’re really pessimistic, you’ll say that we’re yet to hit it and, when we do, it’ll wipe out all of mankind.

Yep, the seriously hardcore pessimists reckon that the reason there are no aliens popping in for a chat is because any civilisation that gets advanced enough to travel through space destroys itself before it can get there. Elon Musk has his concerns about this, pointing out that we should really head to Mars in case World War III occurs and the world is wiped out by nukes.

 So if the Great Filter theory is right, we’re either virtually unique or yet to hit total catastrophe. We don’t really know what the filter is, but we can rule out a few things: it’s not moving from single-cell to multi-cell life, for example, because we know that’s happened many times on Earth, so is nowhere near rare enough. If we were to find fossilised alien life on Mars when we eventually pay it a visit, we’re in trouble because it rules out a number of potential Great Filters if two planets have managed to harbour advanced life. It would suggest the Great Filter is ahead of us, and given the sheer odds involved, you wouldn’t bet on our chances of passing the test at Ladbrokes.

Of course, it could just be that there are aliens out there, but they’re ignoring us. Why would they do that, then?

Images: Tom Hall, Alexander Kaufhold, JD Hancock, Damien Phillips, Moyan Brenn, Maxwell Hamilton and Chris Moore used under Creative Commons

2. Fermi Paradox solutions: There is life out there and it deliberately hasn’t made contact

If there are intelligent aliens out there, why the hell wouldn’t they try to make small talk with us? Plenty of reasons, some of them just as sinister as the Fermi Paradox, but I’ll get to those in a moment. There are some perfectly innocuous reasons to cover first of all.

For starters, it’s possible that covering the distances involved in reaching us just isn’t possible. A kind of Great Filter for mechanics, you can only get so far, and our Milky Way might just really be in the sticks as far as the universe goes.

Another possibility is that not every other species in the universe has evolved with the same priorities as us. Perhaps space travel just holds no appeal to other life forms and we’re oddballs for finding the idea interesting.

A third possibility is that we’re so underdeveloped or foreign-seeming that we’re of no interest to passing aliens. After all, our ancestors colonising continents for the first time probably didn’t pay much attention to the ants and flies. Or maybe it’s the opposite – maybe we look too warmongering and threatening to risk greeting. You wouldn’t be able to blame an alien for reaching that conclusion, given our history on the ground.

Okay! Those are the nice possibilities, now here’s some more sinister ones for the radio silence:

Intelligent life knows to stay quiet

We’ve seen no evidence of life beyond Earth, but what if that’s because everyone else knows better than to broadcast their whereabouts? Maybe the universe isn’t the super-friendly jamboree we hope it is, and there’s some absolute tool of a civilisation going around destroying everything it knows about. In that instance, wouldn’t it be better to stay quiet and hide? As we’ve already established, the universe is a pretty big place to hide in if you’re smart enough to shut up.

We’re not advanced enough to appear a threat… yet

There could be one other civilisation in the universe that is significantly more advanced than every other life form out there, but doesn’t bother attacking others until they reach a certain point of development where they’re considered a threat. That would explain why you don’t hear anything, and an unpleasant answer to where the Great Filter might be located…

Or maybe, of course, they’re already here.

Images: Tom Hall, Alexander Kaufhold, JD Hancock, Damien Phillips, Moyan Brenn, Maxwell Hamilton and Chris Moore used under Creative Commons

3.Fermi Paradox solutions: There is life out there and they have made contact. We just didn’t notice

If all of this is a little paranoid for you, there is another option which is simultaneously both more mundane and more exciting than everything else I’ve covered: they have made contact and we didn’t notice.

How could we have missed something so important? Well, there are a number of possible suggestions:

They don’t speak the same language as us

The most obvious possible reason we’ve missed signs of alien life is because we’re looking for the wrong things. There’s no reason other civilisations would necessarily adopt radio waves as their communication method of choice. Maybe they’re trying to use Skype while we’re stuck with semaphores, singing telegrams and Yahoo Messenger.

Or, as this brilliant cartoon from XKCD puts it…

They dropped by before we evolved to document them

As I mentioned back on page two, human life has only existed on Earth for around 0.004% of the planet’s lifespan. Civilisation as we’d recognise it is an even slimmer segment of our planet’s history, accounting for around 6,000 years or 0.0001% of our planet’s story. If our planet’s story were the 587,0287 words of

War and Peace, our civilisation would account for just over half a word. And probably not a very meaningful one.

With that in mind, it’s possible – likely even – that aliens called, but we were out. Even if they called and we were in, it’s possible we weren’t advanced enough to document the experience for future generations – or even if we understood what the hell was happening.

There’s another possibility that they’re here right now and we still don’t understand what’s happening, of course. Don’t want to get too conceited on behalf of my dumb species.

We are the aliens

Ready for a plot twist? Maybe we are the aliens. Or, in other words, we’re a colony of aliens left to grow on Earth, while the rest of our species got dropped off on other planets to go about their business, just as clueless about their role in the universe as we are. In that scenario, it’s possible our forefathers will be back to check in on us eventually, and they could end up looking an awful lot like us (although maybe not not much of a resemblance, given the timescale involved.)

Then there are a handful of other oddball suggestions, which don’t quite fit into any of the other categories…

Images: Tom Hall, Alexander Kaufhold, JD Hancock, Damien Phillips, Moyan Brenn, Maxwell Hamilton and Chris Moore used under Creative Commons 

4. Fermi Paradox solutions: Other, stranger ideas

While the majority of the solutions to the Fermi Paradox neatly fit into the last three categories, there are a handful of wildcards. Here’s an additional page devoted to them.

It’s all a simulation

None of this is real and we’re all living inside a computer simulation. Trouble is, it’s a multiplayer map and whatever is in charge has forgotten to include any AI players to meet.

Or maybe the distant stars are all just an illusion, as part of the computer simulation. You know how in, say,

Fallout 4,  you can see mountains beyond the edge of the world map, but never reach them? That could be the case for the stars and distant galaxies we think we can see. Elon Musk considers this one a possibility, saying: “The absence of any noticeable life may be an argument in favour of us being in a simulation. Like when you’re playing an adventure game, and you can see the stars in the background, but you can’t ever get there.”

We’re in an intergalactic zoo

Maybe we’re of interest to alien life, but only as a curiosity – like zoo animals, kept at arm’s length. They could be studying us from afar, but under strict instructions not to interfere with us in any way. This is another one Musk has considered, adding: “If it’s not a simulation, then maybe we’re in a lab and there’s some advanced alien civilisation that’s just watching how we develop, out of curiosity, like mould in a Petri dish.”

Mould may not be the most flattering analogy for humanity, but at least we’re in an alien’s zoo and not in their circus:

Aliens have made contact, but the government covers it up

Probably not.

We’re just wrong about everything we know

All of the ideas on the previous pages rely on humanity’s collected knowledge of Earth, the universe, physics, biology and culture. What if we’re wrong about some or all of it? Every idea falls down and opens the door for intriguing new ones.

Which theory do you buy?

READ NEXT: Why do people see aliens in these NASA Mars shots?

Images: Tom Hall, Alexander Kaufhold, JD Hancock, Damien Phillips, Moyan Brenn, Maxwell Hamilton and Chris Moore used under Creative Commons