The Lifespan of Civilizations

Some years ago, a lively debate sprang up on the letters page of Astronomy magazine over whether humans should try to contact intelligent beings outside our solar system.

While many readers seemed genuinely excited by the possibility of discovering intelligent life elsewhere in the universe, a few expressed serious reservations at the prospect. They reasoned that any contact with technologically advanced extraterrestrials could prove devastating for Earth's inhabitants, comparable to the shock visited on the indigenous peoples of the Americas by the arrival of Columbus.


I was reminded of those skeptics during this year's quincentennial observance of Columbus Day, when NASA officially launched the High Resolution Microwave Survey on its giant radio-telescopes at Goldstone, near Barstow, California, and at the Arecibo Observatory in Puerto Rico.

Over the next decade, powerful instruments like these will scan the sky continuously to carry out the largest systematic search ever conducted for signals from intelligent civilizations on other planets.


The project had been kicking around for years as SETI, or Search for Extraterrestrial Intelligence. NASA changed the name to High Resolution Microwave Survey earlier this year in deference to nervous lawmakers who wondered how they could justify spending $100 million over the next decade on what critics deride as a frivolous search for "little green men."

Still, the question of whether we are alone in the universe has long fascinated scientists and laymen alike. Certainly evidence of intelligent civilizations on planets orbitting distant stars would be an epochal event in human history. The scientific, political and religious implications would be profound.

Even if no such evidence were found, important discoveries are likely to result from NASA's survey. Columbus, after all, was looking for a new route to the Indies when he discovered America. It's not unreasonable to think SETI may turn up something equally unexpected.

Yet there's also a dark side to our attempts to communicate with life elsewhere in the cosmos, though it has nothing to do with little green men or UFOs.

It is simply that so magnificent a concept forces us to confront the tenuousness of our own hold on the universe as an intelligent species and the fragility of the civilization that makes such a project possible.

It is a relatively straightforward task, for example, to estimate the likelihood of intelligent species existing elsewhere in our galaxy. One first needs to consider the number of stars similar to our Sun, then the proportion of those stars that have planetary systems, then the number of those systems likely to have planets similar to Earth, etc.

When all these calculations have been performed, it appears likely there are many millions of other places where the physical conditions for life are just as suitable as they are on Earth. Further investigation suggests that intelligent life should have evolved on about 1 million planets since the universe began some 15 billion years ago.

The probable existence of a million planets inhabited by intelligent creatures might at first seem cause for optimism. But then one must consider the likelihood of any two intelligent civilizations existing at the same time, making communication possible between them.


When the calculation is performed it turns out that such communication is likely only among civilizations that have an ZTC average lifespan of about 15,000 years. Industrial civilization on Earth, by contrast, is barely a century old.

This might be fine if we could be assured of a dozen or so more millenniums of uninterrupted development. Unfortunately, we may not have such a grace period.

When one considers the huge growth in human populations, the accelerating pressure on natural resources, the menace of nuclear proliferation, one may well wonder whether our technical civilization can survive beyond a few more decades. Devastating crises, one fears, must shortly overtake us, leading inevitably to a lapse into barbarism.

Is this is too pessimistic a view? Perhaps. Yet we can be certain that the scientists who first proposed SETI were well aware that humanity's capacity to carry out such a project might not last indefinitely.

I would like to believe the human species will find a way to overcome the stupendous problems that threaten it today, and that SETI may one day realize its astounding potential. If we fail, however, the fault will not have been in our stars, as the poet said, but in ourselves.

Glenn McNatt writes editorials for The Baltimore Sun.