The Fermi Paradox has had a lot of attention over the years. The question is easy to sum up: “If aliens exist, where are they?” The answers to the question are manyfold. The Zoo Solution is one of those answers, and is often considered with some derision. Rightly so – it asks us to accept quite a lot. In short, the Zoo Solution says the reason we have not discovered extraterrestrial intelligence (ETI) is because they don’t want us to see them – for one reason or another, they take deliberate steps to shield us from the truth of their existence.
The fact that the Solution sounds like a plotline from the X-Files doesn’t help its cause. It tends to languish at the bottom of the pile for precisely this reason. How can the Zoo Solution be taken seriously if we know nothing about alien civilisations? We can’t verify the Solution without a good understanding of xenosociology, and we know zip about that. In fact, if we did, then Fermi’s Paradox would no longer exist. Therefore, the Zoo Solution appears doomed to be an argumentum ad ignorantium (like Bertrand Russell’s teapot between Earth and Mars).
It might sound hopeless, but we can think about some closely related variants of the Zoo Solution. Hence my latest paper on the subject, where I study what I refer to as the ‘chain of culture’ variant. For the Zoo Solution to work, all ETIs must share ‘absolute uniformity of purpose’ – i.e., they must all agree not to interfere in Earth’s affairs. Even if only one civilisation decides to break this Prime Directive, then the Zoo Solution fails. So how do you establish this chain? It’s been recently suggested that if the first civilisation in the Galaxy has a long head start, which is possible, then they can establish this initial motive not to interfere in less-developed civilisations, and perpetuate it amongst every civilisation that follows.
I revisited this idea, because I found it somewhat lacking. Requiring the time between the first and second civilisation’s appearances to be large forces us to appeal to the anthropic principle: things are the way they are because that is how we see them. This is a dangerous road to go down, and something of a cop-out. I decided to look at a more rigorous “chain of culture” – one in which every link in the chain keeps the uniformity of motive alive. Instead of demanding that the first civilisation influences all, let each civilisation influence the next one along the chain. That way, we only require that each civilisation can communicate with the next before the next becomes ‘aware’ of other ETIs.
So, I investigated this chain using my simulation methods, both for empty galaxies and crowded galaxies. The result? The chain is broken frequently. It happens all along the chain, at early times and at late times. The uniformity of motive is not established.
So, we can put this version of the Zoo Solution to bed – the Prime Directive gets torn up many times in Galactic history, so non-interference as a reason for no alien contact seems to be a poor solution, and very much improbable. Fermi’s Paradox is over fifty years old – for now, we’re going to have to keep on looking for the right answer.