Science fiction often contains the idea that the human race will expand until we inhabit many star systems. This of course makes for very interesting stories. But why would we really want to colonize other star systems? We are not cockroaches; there is no need for the human race to use all available space. Nor do we need the resources of other star systems either, the energy of the sun and the raw materials of Jupiter (since hydrogen + energy = anything you like) are more than enough.
One motivation might be survival. In the long run the sun only has a limited lifespan, and so we might need to find a new place to live. But that is insufficient reason to colonize the galaxy. It might, at most, justify picking up civilization and moving to another star, but not spreading out to every star. More importantly, no biological human is likely to ever travel to another star. Interstellar flight takes to long, and biological beings have too many needs. If anyone ever leaves the solar system (with any chance at surviving away from home) it will be a digital human, an intelligence that has no living components. And the needs of a digital human are much simpler. In fact digital humans would probably have no need to leave the solar system in the first place. When the sun expands they could simply move outwards. And even after the sun goes out completely there is enough matter lying around to supply power, assuming some way can be found to convert it to energy.
Ok, so maybe we don’t need to colonize other star systems to survive. But what about curiosity? Surely we will still want to know what is out there, even when we have gotten rid of our biological needs. With this I fully agree. But why colonize other star systems? Unmanned probes, or manned missions, could satisfy that curiosity. And, given that people have gone digital, everyone can enjoy simulations from the comfort of the home that make it just like they were there after the mission returns. After the mission returns because I doubt that faster than light communication or travel will ever be possible. (I swear to god I will hate anyone who says “but quantum physics…” to death. See here for an explanation as to why faster than light travel and communication seems impossible, taking into account all current scientific knowledge.)
The light speed barrier is in fact the best reason to suppose that the human race wouldn’t, and shouldn’t, colonize other star systems. To span multiple star systems is to fracture the human race. Even a nearby colony, say only 10 or 20 years away, will be basically out of touch. While the home civilization and the colony can follow the news about each other they will culturally tend to follow different paths. And the situation will only be worse with colonies farther away. You can imagine what it would be like if we were receiving news of a civilization that was one or two hundred years behind ours. While the news might be interesting from an academic point of view it wouldn’t have any real impact on our lives, it would be like an amazingly detailed story. Thus distant colonies are of little value to the home civilization, and so it has no reason to create them. Moreover a fractured human race seems wasteful, since the same discoveries would have to be made over and over again by each different colony.
Of course there are two scenarios in which this barrier of time and space might be useful. One is if there is the need to artificially create diversity. It is possible that as time goes on humanity might become a monoculture, and that this monoculture might become an impediment to social and scientific progress. The creation of distant colonies would be a way to overcome this. Although they might be hundreds of years out of date technologically, news from them might serve as an important source of diversity, as an inspiration to think differently. The second reason that colonies might be created is if people are still unable to get along. If people still war amongst themselves, or even if some groups of people are just made to feel unwelcome, some may choose to separate themselves from the rest of the human race. And such distance would be a very effective shield against aggression and persecution. In some ways these colonists would be like the Puritans, who left England to form a colony in North America because of persecution. Except that they didn’t quite put as much distance between themselves and the English.
But if we end up colonizing other star systems for such reasons that will be a sign that we are a failure as a species, if we can’t learn to get along by the time we develop interstellar travel. And I am an optimist, I believe that we will have solved our social problems by the time anyone has the ability to move to a different star system because of them. And thus, as an optimist, I do not think that we will have any reason to colonize other star systems, and thus that we probably won’t. Of course I’m also being an optimist about our ability to extract energy from matter, but if we can’t solve a little problem like that then we probably can’t make it to another star system (or do anything interesting when we get there).