We now know, says futurist Peter Schwartz, that nearly all of the billions of stars in our galaxy have planets. If we can master interstellar travel, “there’s someplace to go.” Our own solar system is pretty boring---one planet is habitable, the rest are “like Antarctica without ice” or worse.
The energy required can be thought of in three ways. 1) Impossible---what most scientists think. 2) Slow. 3) Faster than light (FTL). Chemical rockets won’t do at all. Nuclear fission rockets may suffice for visiting local planets, but it would take at least fusion to get to the planets of other stars. Schwartz showed Adam Crowl’s scheme for a Bussard Ramjet using interstellar ions for a fusion drive. James Benford (co-author of the book on all this, Starship Century) makes the case for sail ships powered by lasers based in our Solar System.
As for faster-than-light, that requires “reinventing physics.” Physics does keep doing that (as with the recent discovery of “dark energy). NASA has one researcher, John Cramer, investigating the potential of microscopic wormholes for superluminar travel.
Standard-physics travel will require extremely long voyages, much longer than a human lifetime. Schwartz suggested four options. 1) Generational ships---whole mini-societies commit to voyages that only their descendents will complete. 2) Sleep ships---like in the movie “Avatar,” travelers go into hibernation. 3) Relativistic ships---a near the speed of light, time compresses, so that travelers may experience only 10 years while 100 years pass back on Earth. 4) Download ships---“Suppose we learn how to copy human consciousness into some machine-like device. Such ‘iPersons’ would be able to control an avatar that could function in environments inhospitable to biological humans. They would not be limited to Earthlike planets.”
Freeman Dyson has added an important idea, that interstellar space may be full of objects---comets and planets and other things unattached to stars. They could be used for fuel, water, even food. “Some of the objects may be alive.” Dyson notes that, thanks to island-hopping, Polynesians explored the Pacific long before Europeans crossed the Atlantic. We might get to the stars by steps.
Futurist Schwartz laid out four scenarios of the potential for star travel in the next 300 years, building on three population scenarios. By 2300 there could be 36 billion people, if religious faith drives large families. Or, vast wealth might make small families and long life so much the norm that there are only 2.3 billion people on Earth. One harsh scenario has 9 billion people using up the Earth.
Thus his four starship scenarios... 1) “Stuck in the Mud”---we can’t or won’t muster the ability to travel far. 2) “God’s Galaxy”---the faithful deploy their discipline to mount interstellar missions to carry the Word to the stars; they could handle generational ships. 3) “Escape from a Dying Planet”---to get lots of people to new worlds and new hope would probably require sleep ships. 4) “Trillionaires in Space”---the future likes of Elon Musk, Jeff Bezos, and Richard Branson will have the means and desire to push the envelope all the way, employing relativistic and download ships or even faster-than-light travel.
Schwartz concluded that there are apparently many paths that can get us to the stars. In other words, “Galactic civilization is almost inevitable."