I don't have too much time for non-work-related writing nowadays, but I really feel the need to spread this meme. Earlier this week I got into a little dust-up with a hacker-news user called moonchrome over the sustainability of exponential growth. It was in response to a story about the catastrophic fires in Indonesia that are intentionally set in order to clear farmland for oil palms, i.e. the plants from which coconut oil is produced. Oil palms have become a growth industry (no pun intended) since trans-fats have become unfashionable.
During that exchange I suddenly realized that there's probably a whole segment of the population that thinks that overpopulation is not a problem because — space colonization! When earth gets overcrowded, we'll just move to Mars. And besides, those Malthusians have been crying wolf since forever. No matter what happens, technology will save us.
Sorry to be the one to break it to you, but no, it won't, and if you think it will you don't understand the truly awesome destructive power of exponential growth.
There's a classic puzzle that goes like this: imagine you have a jar filled with growth medium and a single bacterium of a species that divides twice an hour. After a week, the jar is full. At what point was it half-full?
The classical answer is: half an hour before the end of the week. But that is wrong. The real answer is that the problem as posed is not possible. A week's worth of unchecked bi-hourly doubling would result in a bacterial population vastly greater than the number of elementary particles in the universe.
It helps only a little that our doubling time at the moment is running about 60 years rather than 30 minutes. That stretches the week out to a few hundred or a few thousand years depending on whether you take the total biomass of earth or the mass of the universe as your limiting factor. Predicting the future is usually a fool's errand, but I hope I don't have to convince you that before we have converted every last carbon atom on earth into a human body, life will get very, very unpleasant.
Even if we manage to colonize Mars, that will only help a little. Imagine that we are able to completely terraform Mars, and produce a biomass more or less equal to that of earth. For starters, colonizing Mars will only help the situation here on earth if we are able to emigrate en masse, which isn't very realistic. But even if we were able to do that, having one more planet only buys us one more doubling time, that is, 60 years at current growth rates, after which we would be right back where we started. And now to get ourselves out of that mess we need two more planets!
OK, say the optimists, so we'll go to the next solar system. No, we won't. Even sending a robot probe to the nearest star is a pipe dream at the moment. The massive emigration required for interstellar colonization to improve the situation here on earth is a pipe dream N times over for some very large value of N. And even if that were not so, as I mentioned earlier, even if you take the total mass of the universe as your limiting factor you only get out to a few thousand years. That's the blink of an eye in the grand scheme of things.
The simple fact of the matter is that exponential growth is necessarily transient. Always. It is not possible to sustain exponential growth in a finite universe. At some point, any instance of exponential growth will cease. The only question is whether it happens because we decide to stop it, or because we discover the hard way what the limiting factor actually turns out to be.
Personally, I hope we do the former, because dealing with the latter will not be fun. But to achieve that we have to change our collective mindset. We have to start thinking about steady-state as the goal rather than exponential growth, because open-ended growth is simply not an option. If we don't control our growth, then sooner or later the laws of physics (and mathematics) will do it for us.