Reasons

Survival of human civilizationedit

The primary argument calling for space colonization is the long-term survival of human civilization. By developing alternative locations off Earth, the planet's species, including humans, could live on in the event of natural or man-made disasters on our own planet.

On two occasions, theoretical physicist and cosmologist Stephen Hawking argued for space colonization as a means of saving humanity. In 2001, Hawking predicted that the human race would become extinct within the next thousand years, unless colonies could be established in space. In 2010, he stated that humanity faces two options: either we colonize space within the next two hundred years, or we will face the prospect of long-term extinction.

In 2005, then NASA Administrator Michael Griffin identified space colonization as the ultimate goal of current spaceflight programs, saying:

... the goal isn't just scientific exploration ... it's also about extending the range of human habitat out from Earth into the solar system as we go forward in time ... In the long run a single-planet species will not survive ... If we humans want to survive for hundreds of thousands of millions of years, we must ultimately populate other planets. Now, today the technology is such that this is barely conceivable. We're in the infancy of it. ... I'm talking about that one day, I don't know when that day is, but there will be more human beings who live off the Earth than on it. We may well have people living on the Moon. We may have people living on the moons of Jupiter and other planets. We may have people making habitats on asteroids ... I know that humans will colonize the solar system and one day go beyond.

Louis J. Halle, formerly of the United States Department of State, wrote in Foreign Affairs (Summer 1980) that the colonization of space will protect humanity in the event of global nuclear warfare. The physicist Paul Davies also supports the view that if a planetary catastrophe threatens the survival of the human species on Earth, a self-sufficient colony could "reverse-colonize" Earth and restore human civilization. The author and journalist William E. Burrows and the biochemist Robert Shapiro proposed a private project, the Alliance to Rescue Civilization, with the goal of establishing an off-Earth "backup" of human civilization.

Based on his Copernican principle, J. Richard Gott has estimated that the human race could survive for another 7.8 million years, but it is not likely to ever colonize other planets. However, he expressed a hope to be proven wrong, because "colonizing other worlds is our best chance to hedge our bets and improve the survival prospects of our species".

In a theoretical study from 2019, a group of researchers have pondered the long-term trajectory of human civilization. It is argued that due to Earth's finitude as well as the limited duration of the Solar System, mankind's survival into the far future will very likely require extensive space colonization.:8, 22f This 'astronomical trajectory' of mankind, as it is termed, could come about in four steps: First step, plenty of space colonies could be established at various habitable locations — be it in outer space or on celestial bodies away from planet earth — and allowed to remain dependent on support from earth for a start. Second step, these colonies could gradually become self-sufficient, enabling them to survive if or when the mother civilization on earth fails or dies. Third step, the colonies could develop and expand their habitation by themselves on their space stations or celestial bodies, for example via terraforming. Fourth step, the colonies could self-replicate and establish new colonies further into space, a process that could then repeat itself and continue at an exponential rate throughout cosmos. However, this astronomical trajectory may not be a lasting one, as it will most likely be interrupted and eventually decline due to resource depletion or straining competition between various human factions, bringing about some 'star wars' scenario.:23–25 In the very far future, mankind is expected to become extinct in any case, as no civilization — whether human or alien — will ever outlive the limited duration of cosmos itself.:24f

Vast resources in spaceedit

Resources in space, both in materials and energy, are enormous. The Solar System alone has, according to different estimates, enough material and energy to support anywhere from several thousand to over a billion times that of the current Earth-based human population. Outside the Solar System, several hundred billion other planets in the Milky Way alone provide opportunities for both colonization and resource collection, though travel to any of them is impossible on any practical time-scale without interstellar travel by use of generation ships or revolutionary new methods of travel, such as faster-than-light (FTL).

Asteroid mining will also be a key player in space colonization. Water and materials to make structures and shielding can be easily found in asteroids. Instead of resupplying on Earth, mining and fuel stations need to be established on asteroids to facilitate better space travel. Optical mining is the term NASA uses to describe extracting materials from asteroids. NASA believes by using propellant derived from asteroids for exploration to the moon, Mars, and beyond will save $100 billion. If funding and technology come sooner than estimated, asteroid mining might be possible within a decade.

All these planets and other bodies offer a virtually endless supply of resources providing limitless growth potential. Harnessing these resources can lead to much economic development.

Expansion with fewer negative consequencesedit

Expansion of humans and technological progress has usually resulted in some form of environmental devastation, and destruction of ecosystems and their accompanying wildlife. In the past, expansion has often come at the expense of displacing many indigenous peoples, the resulting treatment of these peoples ranging anywhere from encroachment to genocide. Because space has no known life, this need not be a consequence, as some space settlement advocates have pointed out.

Alleviating overpopulation and resource demandedit

Another argument for space colonization is to mitigate the negative effects of overpopulation.clarification needed If the resources of space were opened to use and viable life-supporting habitats were built, Earth would no longer define the limitations of growth. Although many of Earth's resources are non-renewable, off-planet colonies could satisfy the majority of the planet's resource requirements. With the availability of extraterrestrial resources, demand on terrestrial ones would decline.

Other argumentsedit

Additional goals cite the innate human drive to explore and discover, a quality recognized at the core of progress and thriving civilizations.

Nick Bostrom has argued that from a utilitarian perspective, space colonization should be a chief goal as it would enable a very large population to live for a very long period of time (possibly billions of years), which would produce an enormous amount of utility (or happiness). He claims that it is more important to reduce existential risks to increase the probability of eventual colonization than to accelerate technological development so that space colonization could happen sooner. In his paper, he assumes that the created lives will have positive ethical value despite the problem of suffering.

In a 2001 interview with Freeman Dyson, J. Richard Gott and Sid Goldstein, they were asked for reasons why some humans should live in space. Their answers were:

• Spread life and beauty throughout the universe
• Ensure the survival of our species
• Make money through new forms of space commercialization such as solar-power satellites, asteroid mining, and space manufacturing
• Save the environment of Earth by moving people and industry into space