In a casual chat over lunch back in 1950, the Italian-American physicist Enrico Fermi posed a now famous question. If intelligent life has evolved many times in our galaxy and beyond, why do we see no sign of it?

There are a number of standard reposts to this paradox. The first is that life is actually quite rare and humanity is the first species to become advanced enough to contemplate other civilisations.

Another argument is that intelligent species have been common throughout history but end up destroying themselves or their habitat with their own technology, such as with nuclear weapons or fossil fuel burning.

Yet another approach is that advanced civilisations are common and aware of us but keep themselves hidden for fear of disturbing our delicate culture.

Today, Adrian Kent at the Perimeter Institute in Waterloo, Canada, puts forward another possibility. His idea is that civilisations are common, that they have interacted many times in the past but end up competing for scarce resources. When that happens, the process of evolution, operating over vast time scales, ensures that the survivors learn to keep quiet.

That’s not an idea that can be easily dismissed. Kent says that one counter argument might be to point to the way evolution works on Earth. This usually operates on ecosystems in which species become interdependent in complex ways.

Although many species develop ways of camouflaging themselves, they do not end up hiding in isolation. So by this measure, Kent’s fears are unfounded.

But evolution on a cosmic scale would be very different, he says. Cosmic evolution must operate over vast distances and that the scarce resources offered by habitable plants would be very rare.

Kent puts it like this: “If cosmic habitats are widely enough separated that they are very hard to find, by far the best strategy for a typical species to avoid defeat in such competitions may be to avoid entering them, by being inconspicuous enough that no potential adversary identifies its habitat as valuable.”

That raises important questions about whether humanity is wise to advertise its existence. Various attempts to send messages to the stars have already been made and many scientists have pointed out that this could be a serious mistake, even a suicidal one.

Kent says the risk is easy to misconstrue. I’ll leave you with his conclusion:

“One can summarise the essential point simply enough. If there are no aliens out there, any efforts at communication were obviously wasted. Thus we can assume for the sake of discussion that there are aliens out there likely to receive the messages at some point.

“The relevant parameter, then, is not the probability of our messages being received by aliens who might potentially do us harm: it is the conditional probability of the aliens who receive the messages doing us harm, given that the messages are indeed received (and understood to be messages).

“Can we really say that this probability is so negligible, bearing in mind that any such aliens appear to have made no reciprocal attempts to advertise their existence?

“The arguments considered above suggest that we cannot.”

A sobering thought.

Ref: arxiv.org/abs/1104.0624: Too Damned Quiet

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