COMMENT

The Drake Equation is gradually filling out, and it's looking good for the existence of life, the rise of intelligence, and the likely number of civilisations elsewhere in the universe.

There's even reason to hope that some high-energy technological civilisations successfully pass through the energy-environment bottleneck that our own planetary civilisation is now entering. But not many make it through the bottleneck without suffering major losses, and quite a lot just collapse.

The Drake Equation was written by American radio astronomer Frank Drake in 1961 to estimate the number of high-tech civilisations in the galaxy. It had seven factors, but they were all empty.

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The first three factors, all uncertain in 1961, were: What is the average rate of star formation in our galaxy; how many of those stars have planets; and what proportion of those planets can potentially support life? We know the answers now, and they are encouraging.

There's around one new star annually, most stars have planets, and about one star in five hosts one or more planets with liquid water on the surface. That means that there are probably around 100 billion planets in this galaxy alone that can support life, but that's just a start.

As Douglas Adams pointed out in The Hitch-Hiker's Guide to the Galaxy, "Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is." The Hubble telescope has revealed about 100 billion galaxies in the universe. Potentially life-supporting planets? About 10,000,000,000,000,000,000,000 (10 billion trillion).

What Adam Frank has done, in his recent book, Light of the Stars: Alien Worlds and the Fate of the Earth, is to point out that there must therefore have been a lot of "exo-civilisations". Make your assumptions about first life and then intelligence emerging on any given planet as pessimistic as you like, and there will still be a lot. Maybe not billions or even millions, but even if you assume that only one life-supporting planet in a million trillion ever supported a civilisation, there would have been ten thousand of them.

All civilisations use large amounts of energy. There are fossil fuels, if your planet had a Carboniferous era, or burning biomaterials if it didn't. There's hydro, wind and tides. There's solar, geothermal and nuclear. That's it. Using energy always produces waste, but some of these modes produce far less heat, carbon dioxide, and toxic chemicals than others.

So put different original mixes of these energy sources into your experimental models, put in different planetary conditions as well (some planets closer to their suns, some further away), and run a few thousand of these models through your computer. Most of the models see runaway population growth, followed at a distance by growing pressures on the planet's environment that lower the "population carrying capacity".

At some point the alarmed population switches to lower-impact energy sources. There is still a steep die-back (up to 70 per cent) in the population, but then a steady state emerges and the civilisation survives.

In other models, the planet's people (creatures? beings?) delay switching the energy sources for too long. They all switch in the end, but the laggards still don't make it. The population starts to fall, then appears to stabilise for a while, then rushes downward to extinction.

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It's time to ask where our own planetary civilisation falls on this spectrum of possible behaviours.

I don't know, but this just in. Oil production is at an all-time high of 100 million barrels a day, and Opec predicts it will reach 112 mbd in the next 20 years. That's definitely the wrong direction.

Gwynne Dyer, is a London-based independent Canadian journalist, columnist and military historian.