It’s summer, 1950. Four men are having a conversation over lunch at the Los Alamos National Laboratory in New Mexico. One of them is an Italian named Enrico Fermi, a man best remembered as the ‘architect of the atomic bomb’. The others are Edward Teller, Emil Konopinksi and Herbert York. They’re all nuclear physicists.
The men are discussing a cartoon in the New Yorker depicting flying saucers stealing garbage bins from the city streets. They start wondering whether the saucers could, in theory, exceed the speed of light.
There are different variations of the conversation that followed, but it went something like this.
‘Edward, what do you think?’ Fermi asked. ‘How probable is it that we’ll have evidence of an object moving faster than light within the next ten years?’
‘One in a million,’ Teller replied.
Fermi didn’t think that was a good answer. After all, there are so many Earth-like planets out there that could theoretically support intelligent space-farers.
‘That’s much too low. The probability is more like ten per cent.’
They paused for a moment. Fermi stared away thoughtfully, then turned back to face them.
‘So where is everyone?’
The simple question, now known as Fermi’s Paradox, has generated a lot of debate. Let’s rephrase it: if life can arise on Earth, then surely it can arise on planets with very similar or identical conditions – and there are so many planets out there that intelligent life must exist elsewhere. It’s basic probability.
So why is there no evidence? Why is the galaxy completely silent?
Renowned scientist David Brin set out to find an answer in an academic article published by the Royal Astronautical Society. He argued that any theory explaining the ‘Mystery of the Great Silence’ must be compatible with a sound philosophical and scientific assumption he calls the ‘principle of non-exclusiveness’.
Now this principle is interesting. It states, ‘diversity will tend to prevail unless there exists a mechanism to enforce conformity.’ In other words, the galaxy should be full of life unless there is a universal, systematic reason why it isn’t. Something must be preventing every single intelligent species from ever talking to any other over the last 13 billion years.
Brin’s article was about the search for aliens, but the principle of non-exclusiveness also applies to us. Humanity, like all other possible civilisations out there, is subject to some kind of glass ceiling over the whole galaxy that determines the fate of every species within.
That means Brin’s principle is a tool we can use to explore what lies in store for us. Whatever outcome is in store for our species must eventually result in the silence we see in space, because that is the natural equilibrium state of the galaxy; and most phenomena, viewed over a long enough time period, are just temporary deviations from equilibrium.
In short, the future looks bleak.
According to Brin, there are only two explanations for the ‘Mystery of the Great Silence’ that are compatible with his principle, systematically preventing all contact over billions of years. I covered the first in my recent article on why inventing the radio may have doomed us all. As the theory goes, we may have accidentally broadcast our location to some kind of xenophobic extra-terrestrial civilisation acting in a classic Prisoner’s Dilemma, blowing everyone else up before they can do the same thing back.
The second is less widely discussed, but to my mind is more plausible. It is modelled on the experience of the most isolated human colony of all – Rapa Nui, or Easter Island, where the inhabitants used all available resources and almost completely died out.
In this theory, humans will colonise other planets, driven by population and resource pressures that are already mounting; Elon Musk has famously argued we need to colonise Mars to ‘preserve our species’. But we’ll take our behaviour with us. New colonies will expand to fill the space available to them, meaning they will eventually use their planet’s resources faster than those resources regenerate - as we are currently doing on Earth.
As we expand outwards in a circle, the inner planets will eventually become unable to support human life and fail. Human civilisation will form a ring, expanding constantly outwards in search of new fuel like a great galactic grass fire.
This could take millions and millions of years – but it cannot continue indefinitely. The galaxy is finite, itself shaped like a ring, and one day human civilisation will hit the edge and burn out.
So why care? Well, this is essentially the story of our own planet writ large. If we can’t figure out how to live sustainably on Earth, we won’t figure out how to live sustainably anywhere. Either climate change and resource exhaustion will render Earth inhospitable to human life, as it has been for most of its history, or we will be forced to live at a technology or population level that uses resources slower than the Earth (or maybe the galaxy) replenishes them.
The story of the last Easter Islanders is a sneak peek of what this looks like – a small population surviving on nothing but chicken meat, surrounded by silent monuments to their past and wondering where everyone went.