The words “interstellar travel” seem to have generated some interesting data relevant to human behavior. Specifically, they generate a “good” moral intuition in some, and a “bad” moral intuition in others. There does not appear to be a linear relationship between the nature of the response, and the space occupied by the responder along the left/right political spectrum, or at least not yet. For example, Bill Clinton, who is identified, by conservatives, at least, as a “liberal,” recently gave a boost to DARPA’s 100 Year Starship Program. The similarly liberal editors of the New York Times, on the other hand, have just published a piece in their Op-ed section by astronomer Adam Frank heaping scorn on the very idea of travel to the stars. Perhaps the ideological divide will eventually become more focused, as the reasons given on the “bad” side tend to gravitate to the left. They include for example, the conclusion that only rich people will have the means to leave our home planet, leaving the poor, exploited masses behind on a planet they have polluted and despoiled, the belief that the result of interstellar distractions will be insufficient levels of alarm about problems such as global warming and overpopulation, diminished hopes of a peaceful world if there is some means of escaping the aftermath of the next world war, etc. The “good” reasons for interstellar travel tend to focus on existential threats, such as the possibility of a massive asteroid striking the earth, drastic swings in climate, whether natural or anthropogenic, and depletion of the earth’s resources. It has even been proposed that destructive humans be transplanted to other, less sensitive planets, leaving the earth as a “nature park” in space, presumably to be visited by interstellar tourists from time to time.
My own moral intuitions tend to favor survival as a prime virtue, so I support continued research towards enabling interstellar travel. After all, if we choose not to leave our home planet, our genetic descendants, whether in the long or the short run, are doomed to extinction. That said, I do not underestimate the difficulty of reaching the stars. Human interstellar travel will require massive amounts of energy stored in a much more concentrated form than chemical rocket fuels. The smaller the mass, the easier it is to accelerate to extreme velocities, so it may be that we will need to rely on seed ships to escape our home world. These would carry only eggs and sperm, or genetic material in a similarly compact form. Human beings would be born in artificial wombs, and raised by intelligent robots in prefabricated bases, perhaps constructed by self-replicating nano-robots at the destination planet.
All this, of course, assumes massive technological advances in many areas, and it is impossible to predict when and even if they will occur. In the meantime, I suggest we make a start with the technologies available now. We cannot leave the planet and expect to survive the trip across the vast interstellar voids at the moment, but other life forms, with all of which we share a direct, if distant ancestor, can. The 32,000 year old seed of a complex, flowering plant recovered from the ice was recently germinated by a team of scientists in Siberia. Ancient bacteria, as much as 250 million years old have been recovered from sea salt in New Mexico, and also brought back to life. Tiny animals known as tardigrades have survived when exposed to the harsh environment of outer space. We might choose the species from among such candidates most likely to survive the 50,000 to 100,000 years required to journey to nearby stars with conventional rocket propulsion, and most likely to evolve into complex, land-dwelling life forms in the shortest time, and send them now, instead of waiting 100’s or 1000’s of years for the emergence of the advanced technologies necessary to send humans. Slowing down at the destination star would not pose nearly the problem that it does for objects traveling at significant fractions of the speed of light. The necessary maneuvers to enter orbit around and seed promising planets could be performed by on-board computers with plenty of time to spare. Oceans might be seeded with algae in advance of the arrival of organisms that feed on it.
The travel time could be reduced significantly by using nuclear rockets similar to those which have already been built and tested decades ago. The nuclear reactors would be shut down during most of the journey. They would be activated again as the destination star was approached for deceleration and the necessary final maneuvers. During the journey, the small amounts of energy needed to power timing devices for signaling the nuclear reactors to resume operation when necessary, maintain minimal environmental life support conditions, etc., could be supplied using the same power source used by the Curiosity Rover. However, for such long voyages, plutonium 239 could be used instead of the plutonium 238 used on the rover. With a half life of over 25,000 years, it could supply a small but sufficient amount of energy during the long voyage and, perhaps, contribute power to the propulsion reactors at journey’s end.
Missions using such advanced nuclear technology could probably only be carried out by technologically advanced states. However, seeding of the planets around nearby stars with very simple life forms such as bacteria could be undertaken by private companies such as those now engaged in building rockets for missions such as resupplying the space station. The main problem they would need to solve would be how to bring the seed craft out of hibernation at the end of the voyage without access to a suitable radioactive material. Perhaps they could purchase enough americium 243 or some other radionuclide with a sufficient half-life to do the job. Solar panels would begin to generate electricity as the craft approached the target star, but none currently available are capable of surviving such a long voyage. Still, the amount of energy necessary to signal the propulsion and other systems to resume operation would be tiny, and this does not seem to be an insurmountable problem.
Why would this be “ethical”? Because it would enable the survival of the DNA-based life that has evolved on earth, to all forms of which we humans are related. There cannot be anything more immoral than failure to survive. Anyone who thinks otherwise lacks awareness of why morality exists to begin with.