The galaxy is vast, the number of planets enormous, so how come we never hear from any alien life forms?
Professor Galacticus proposes the following explanation:
There is a lot of life in the galaxy, and he surmises that all of it will be carbon-based and all of it originate in water. As a result, in every planet in which life takes root, deposits of carbon and hydrocarbons will build up over millions of years as organisms die, form sediments, and are subjected to various geological forces.
In a relatively small proportion of living planets, Galacticus suggests, the process of biological evolution will have resulted in symbol- and tool-using intelligence. This in turn brings into being a newer and much faster secondary evolutionary process, corresponding, roughly speaking, to what we call culture.
At a certain level of development, culture stumbles upon the vast reserves of chemical energy that built up millions of years before it came into being. By exploiting these reserves, culture is able to massively accelerate its own evolution – Galacticus speaks of ‘putting on seven-league boots’ – because the enormous increase in the productivity of individual human beings allows large numbers of individuals to cease to be involved in meeting the basic physical needs of the species.
In such a context, highly complex activities such as space travel become possible: activities which require people to devote themselves to doing things with no immediate practical benefit at all. And when cultures embark on the project of space travel, they naturally begin to contemplate the possibility that other cultures, on other planets, are doing likewise, and begin to develop means of searching for, and communicating with, those putative others.
However all this occurs in a very narrow window for, unknown at first to the individuals who make up these cultures, they have set in train a force that will destroy them. This force is not nuclear weapons, as some have surmised it might be, nor poisonous pollution, but something seemingly entirely innocuous: a very common substance, and one that is not merely non-toxic but actually essential to life. Carbon dioxide.
By the time the danger becomes evident, cultures are already so massively committed to fossil fuels that change is difficult. It is not technically impossible – the explosive development of technological knowledge which the ‘seven-league boots’ have made possible means that a switch to some combination of alternative energy sources is entirely feasible in purely engineering terms – but it is psychologically and sociologically very difficult indeed. Almost every one of the intelligent life forms in the galaxy has gone well past the point of no-return – or will do so – before they have fully taken on board the nature of the threat.
And then the physical world takes over, positive feedback loops of various kinds kick in, and, very rapidly, the culture, what is left of it, is reduced to a precarious existence in which the very idea of attempting to communicate with aliens, just for the sheer fun of it, is simply laughable.
‘Hence,’ says Professor Galacticus, ‘the silence from the sky.’
* * *
‘You may think,’ he adds, ‘that I am making far too many assumptions about the psychology and sociology of unknown life forms, but I don’t think I am. You see, their basic psychological equipment is always going to be the product of a biological evolutionary process. We know how creative such a process is, and we know the diversity it has achieved, but it has one deep limitation. It is reactive rather than teleological. It is not aimed at anything, but is simply based on the accumulation of a kind of trial and error knowledge, and this makes it very weak at dealing with an unpredented threat.
‘I would, however, be very pleased to be proved wrong on that count.’