“The universe is a pretty big place,” as Carl Sagan once remarked. “If it’s just us, seems like an awful waste of space.”
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 how many high-tech civilisations there were in the galaxy. It had seven factors, but they were all empty.
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 pretty 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 a hundred 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 around a hundred billion galaxies in the universe. Total number of potentially life-supporting planets? Around 10,000,000,000,000,000,000,000 (ten billion trillion).
Drake’s remaining factors are still unknown quantities. The only two that matter for Adam Frank – because all he wants to know is how many non-human civilisations have ever existed anywhere in the universe – are what fraction of potentially life-supporting planets actually do develop life; and what proportion of those planets go on to develop intelligent life.
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. That’s big enough for a statistical sample, and what Frank really wants to do is to crank the numbers and get a handle on how many of those civilisations would have made it through the bottleneck.
He doesn’t need to know anything specific about those unknown exo-civilisations. He only need to know that all civilisations use large amounts of energy, and that there is a strictly limited number of ways that a technologically ‘young’ civilisation like ours can access energy.
There are fossil fuels, if your planet had a Carboniferous Era, or just 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.
It turns out that most of the models see runaway population growth, followed at a distance by growing pressures on the planet’s environment that lowers 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 percent) 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. Nobody saw that one coming, but it’s what the models are telling us.
There’s still a huge amount of research to be done in this new domain, but 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 the Organisation of Petroleum-Exporting Countries predicts that it will reach 112 mbd in the next 20 years. That’s the wrong direction.
To shorten to 700 words, omit paragraphs 1 and 8. (“The universe…space”; and “Drake’s…life”)