Are space colonies an inevitable step in our galaxy's future?
The world's exponential population growth will soon need to flatten out otherwise within a few hundred years every square foot of the Earth's surface will be taken up by a human. (Which reminds me of one of my favorite bumper stickers from a space advocacy group in the 1970s that read: "American Needs Space to Grow.")
With this population growth, mankind's hunger for energy has also increased exponentially. And if this continues, we will soon consume more energy than the Earth receives from the sun. Should they exist, this could be a common problem faced by burgeoning civilizations across the galaxy.
A solution to this energy demand is to become an extra-terrestrial civilization and harvest the resources of a planetary system to colonize space. A daunting yet logical step is to build solar energy-collecting structures in space and live on them.
This concept was taken to its logical extreme by British physicist Freeman Dyson who proposed in 1959 that advanced extraterrestrial civilizations might encase their stars in an artificially constructed sphere, the radius of Earth's orbit.
This so-called Dyson Sphere would provide a virtually infinite living space 600 million times larger than the surface area of the Earth. It would also trap almost all of the sun's energy output -- 400 trillion trillion watts!
Dyson was inspired by descriptions of such mega structures in two science fiction stories: "The Star Maker" by Olaf Stapledon, written in 1937, and "The World, the Flesh, and the Devil," written by scientist John Desmond Bernal in 1929. The later story describes a "Bernal Sphere" space habitat.
A rigid shell of the Dyson sphere might have a thickness of a few feet, depending on the strength of the material fabricated. It would also have to rotate to make artificial gravity. To maintain habitable temperatures the sphere would need to be bigger than Earth's orbit.
To avoid the dynamical stress a solid shell might undergo, a Dyson Sphere might be a constellation of many small independently orbiting structures -- like squares of mirrored glass on a disco ball. The energy-collecting elements would likely be very thin, while habitat segments would be thicker. Their orbital paths would be adjusted by using solar sails or ion engines.
The classic science fiction story "Ringworld" By Larry Niven, meticulously describes a spinning Hula-Hoop type structure, rather than a sphere as imagined by Dyson.
At least a partial Dyson Sphere -- or Niven's ring -- around the sun could be built from dismantling the planet Mercury and reassembling it into shell segments. The problem is that the energy required for destroying a planet is 100 billion times the U.S. annual energy consumption (sheesh! Even the Death Star probably didn't carry those kinds of batteries!).
So where would that energy come from? The sphere would have to be built piecemeal with the energy collected from the first segments being use to fuel further planetary disassembly.
An army of robots would have to do the task. They would need to use resources to build more robots -- like the enchanted brooms in Walt Disney animation of Paul Dukas' symphonic poem "The Sorcerer's Apprentice." Even with this bootstrapping approach, the construction would take centuries because orbiting solar collectors can only capture so much energy over time.
There have already been astronomical database searches for Dyson spheres. The spheres would absorb and re-radiate the star’s energy as infrared light. As seen from Earth, a shell or partial shell would glow at a comparatively cool few hundred degrees Fahrenheit.
Galactic archeology is now being done by scouring infrared all-sky databases for sources in this temperature range. An artificial structure would need some other clues, perhaps an unusual spectral signature not found in a dust-shrouded young stellar object, or a complex, repeating fluctuation in brightness that is hard to explain by normal circumstellar dynamics.
Finding unequivocal evidence for a Dyson Sphere would tell us that there are no practical limits to the capabilities of an intelligent species, given time, perseverance, and a godlike mastery over matter and energy
