No Galactic Civilization for You (Part Three)

If population pressure won't push human beings out of the Solar System, and the pursuit of mineral wealth won't carry us far (before compound interest overtakes us), our concern for species survival might still propel us across the galaxy. Last spring Stephen Hawking made a public statement in favor of interstellar exploration and colonization, arguing that humans should not “keep all our eggs in one fragile basket.” Without extrasolar colonies, all of humanity could succumb to a local extinction-level event like a gamma-ray burst or asteroid collision.

While I agree with Professor Hawking's sentiment, I believe that finding a haven for humans and other terrestrial species – I assume we'll want to save them too – will prove quite difficult, and take much time and expense. Extrasolar planets are more common than we used to think, but terrestrial life forms will need water, Earthlike gravity (too much or too little will fatally stress circulatory and skeletal systems), and a breathable atmosphere, conditions which we will only find on a small minority of planets. The third condition poses the real problem: free oxygen is rare without some sort of indigenous life form, presumably carbon-based, to generate it. Alien life would excite and stimulate us intellectually, but presents colonists with problems. It may generate prions and allergens and other toxins deadly to humans, or to the Earthly creatures we bring. It probably will not be biologically simpatico with terrestrial organisms, products as we are of several billion years of separate evolution under an alien sun, so we will have to replace it with our own imported species, which raises serious ethical questions. If somehow we find alien species which we could safely eat or exploit, they may not want to coexist peacefully – they may want to eat us, and may become quite good at it, as Robert Wilson posited in one of my favorite SF novels.

Building settlements on a lifeless alien world, or terraforming a near-Earthlike one, comprise possible alternatives, but more expensive ones than colonizing a planet with free air and water. Of course such worlds already exist relatively nearby, in our own Solar System.

The question with which I started this series is “Will humans colonize the galaxy?” and while I obviously can't provide a definite answer, I still don't think we will have a motive to do so. Finding a single extrasolar biosphere haven for humans and dolphins and penguins and brine shrimp and other Earthly creatures is a worthy and even necessary goal, and in the longer term we will probably need two or three of them as extinction insurance. I don't think we'll need a galaxy full of them, and since we'll have to travel a long distance and spend a lot of resources to find and colonize a suitable New Earth, limited need and high expense will keep the number of them small.