In Brief Answers to the Big Questions, Stephen Hawking outlined what it would take for humans to reach other planets, particularly inhabitable ones. With existing rocket technology – the chemical combustion of fuel – we can reach planets in our solar system in an acceptable time frame: from 130-260 days to get to Mars, for example. But what if Mars isn’t habitable? What if none of the planets in our close vicinity are?
In that case, we’d have to go to another solar system, a group of planets congregating around another star like the sun, the nearest of which is Alpha Centauri. Unfortunately, at a distance of 4.37 light years, with existing rocket tech, it’d take three million years – one-way. Therefore, we’ll need faster rockets, rockets nearing the speed of light.
“Nuclear fusion could provide 1 per cent of the spaceship’s mass energy, which would accelerate it to a tenth of the speed of light,” Hawking wrote. “Beyond that, we would need either matter–antimatter annihilation or some completely new form of energy. In fact, the distance to Alpha Centauri is so great that to reach it in a human lifetime a spacecraft would have to carry fuel with roughly the mass of all the stars in the galaxy.”
And then, in a voice I can only imagine but that sounds so much like Hawking, he said: “In other words, with current technology interstellar travel is utterly impractical.” Impractical. Talking about humans traveling to another solar system, a feat that’d require an absurd amount of fuel, the kind of which we don’t yet have, Hawking used the word “impractical.” Not impossible. Impractical. Meanwhile, we see no chance Stan from accounting will call us back.
Hawking’s relentless hope is a recurring theme throughout the book. “So far, so possible,” Hawking comments on a theoretical, highly complex laser-propulsion of only-centimeter-big, unmanned spacecrafts set to reach Mars in an hour and Alpha Centauri in 20 years. Another phrase he likes to use? “Turning science-fiction into science-fact.” If we used the word “impractical” where we use “impossible,” then broke down what’s so impractical into tiny pieces, maybe we’d turn more fictions into facts too.
If a man confined to a wheelchair for 50 years, forced to communicate using only his cheek muscles, can show that kind of optimism, who are we to use the word “can’t?”