alien expansion vs. the fermi paradox
The more spread out an alien species is across the cosmos, the easier it would be to find and contact them. But how widespread could an alien civilization be?
The last time we tackled the Fermi paradox, we talked about what it means to be intelligent and how trying to speak to an intelligent species separated from us by an evolutionary gulf we can barely begin to describe in a meaningful way would probably leave us at a loss for words. This time, we're going to look at a paper which is trying to answer the paradox by refuting the notion that intelligent alien species could be spreading throughout our galaxy at an exponential rate just like humans and should therefore, be easy to detect because they'd be just about everywhere we look and listen. While the paper itself makes very good points about alien efforts to colonize other planets and how selective pressures would apply to their civilizations, we have to note that the idea they're tackling isn't an explicit part of Fermi's question and the paper misses some crucial points.
From a strictly numerical standpoint, human expansion has been exponential. In the last few hundred years, our population soared thanks to better nutrition, medicine, more advanced technology and reduced mortality. Of course, let's note the qualifiers. We're only expanding as fast as we are because we have the means to do it and survive in large enough numbers. And this is exactly what Jacob Haqq-Misra and Seth Baum note. The hypothesis that an advanced alien civilization, even a rare one, would expand at an exponential clip as it gets older and its population grows simply doesn't work.
To support growing populations scattered across worlds separated by light years may not even be necessary. If the society thrives in relatively small numbers and the forces of evolution on the world in question resulted in a slowly procreating intelligent species, there might be no pressure to settle the cosmos and a cultural bias to stay planted firmly where the aliens evolved. But Fermi wasn't proposing the idea that technologically advanced aliens are perpetual expansion machines. He asked why we would expect intelligent aliens to be common occurrence in the universe if it's so hard to find them.
And you may be surprised that alien cultures don't figure in the paper and neither do the complexities of a vast expansionary effort. Galactic scale colonization involves traveling across tens of thousands of light years and claiming billions of solar systems. Just claiming them is somewhat tenuously plausible. But actually living on alien worlds and easily setting up colony after colony is a monumental task that could only be accomplished by an extremely old and technologically advanced species surviving on a very rare combination of luck, know- how and a drive to go out and explore far and wide for millions upon millions of years.
Living on other planets isn't like exploring new continents. It requires radical adaptations and technological feats that compensate for the differences in just about everything, from air pressure, to atmospheric composition, to surface gravity. The odds of an intelligent species living long enough to spread across billions of solar systems while avoiding a potential extinction event or cataclysms like devastating cosmic events and keeping a huge interstellar supply network up and running for trillions and trillions of individuals across thousands of light years are pretty small and we have to take that into account when looking for ET.
Ok, so how do we look for alien empires in light of these facts? Haqq-Misra and Baum quote ideas with which we're already quite familiar. Look for planets that most resemble our own and try to find aliens as close to our culture and conception as possible because we'd be able to recognize them more readily. Nothing really new or groundbreaking here. And to be honestly blunt, neither are their conclusions that sustainability plays a big role in whether an intelligent species can grow and leave the planet on a scale astronomers would notice.
It's also rather disappointing that questions about alien cultures and worldviews don't come into play either since many important decisions that can determine how, or even if, a civilization will advance are based on cultural biases and politics. For example, the number one reason humans are in space today is thanks to the money and resources provided by the militaries of the U.S. and the USSR in their quest to get a drop on each other in a global PR war and with ICBMs. How and why would aliens end up in space and what would they choose to do there? That's the question on which we should be focusing if we want to find space faring intelligent life.
See: Haqq-Misra, J. & Baum, S. (2009). The Sustainability Solution to the Fermi Paradox J. Br. Interplanet. Soc. 62:47–51, 2009 arXiv: 0906.0568v1
