In 2012 NASA and DARPA jointly funded a "100-Year Starship" program, the goal of which was to achieve human interstellar flight within the next one hundred years. On September 13, 2012, the 100-Year Starship (100YSS) project held the first of its planned annual public symposiums, in Houston, Texas. Here, about a hundred scientists, social scientists, educators, journalists, and miscellaneous others gathered to witness a series of scientific presentations outlining schemes by which human beings could, just possibly, leave planet Earth behind, travel to the stars, and establish a new "Earth 2.0" in another solar system, all within a century.
Traveling to the stars, say many of its advocates, is our preordained destiny as a species. As proponent Cameron Smith puts it in "Starship Humanity" (Scientific American, January 2013): "the concept of a Space Ark, a giant craft carrying thousands of space colonists on a one-way, multigenerational voyage far from Earth" is "technologically inevitable."
Far from being technologically "inevitable," the fact is that such a voyage is not even known to be technologically possible. For one thing, the distances to even the "closest" extrasolar stars are unimaginably vast. The nearest star, Proxima Centauri, is 4.22 light years (24,800,000,000,000 miles), away from Earth. Even if we were to travel as fast as the Voyager I spacecraft, which is now receding from us at 38,698 mph, it would take an interstellar craft more than 73,000 years to reach that destination.
But traveling at significantly faster speeds requires prohibitive amounts of energy. If the starship were propelled by conventional chemical fuels at even ten percent of the speed of light, it would need for the voyage a quantity of propellant equivalent in mass to the planet Jupiter. To overcome this limitation, champions of interstellar travel have proposed "exotic" propulsion systems such as antimatter, pi meson, and space warp propulsion devices. Each of these schemes faces substantial difficulties of its own: for example, since matter and antimatter annihilate each other, an antimatter propulsion system must solve the problem of confining the antimatter and directing the antimatter nozzle in the required direction. Both pi meson and space warp propulsion systems are so very exotic that neither is known to be scientifically feasible.
Indeed, these and other such schemes are really just mathematical abstractions, not working systems: they are major extrapolations from states of matter that exist today only at nano levels (antimatter, for instance, requires huge accelerators to make even tiny amounts of, at stupendous costs). Still other systems depend on wild possibilities such as making use of extra dimensions that are not known to exist, physical forces or influences that are not known to be real, or are sheer flights of the imagination (such as altering the value of Hubble's constant to make the universe smaller).
Even if by some miracle suitable propulsion systems became available, a starship traveling at relativistic speeds would have to be equipped with sophisticated collision detection and avoidance systems, given that a high-speed collision with something as small as a grain of salt would be like encountering an H-bomb. Star voyagers face further existential threats in the form of prolonged exposure to ionizing radiation, boredom, alienation from the natural environment, the possible occurrence of a mass epidemic, the rise of a charismatic leader who might derail the whole project, crew mutiny, religious factionalism, and so on. It is far more likely, therefore, that an interstellar voyage will mean not the survival but rather the death of its crew.
Apart from all of these difficulties, the more important point is that there is no good reason to make the trip in the first place. If we need a new "Earth 2.0," then the Moon, Mars, Europa, or other intra-solar-system bodies are far more likely candidates for human colonization than are planets light years away.
So, however romantic and dreamy it might sound, and however much it might appeal to one's youthful hankerings of "going into space," interstellar flight remains a science-fictional concept—and with any luck it always will be.