The Washington Post

Sorry ‘Prometheus’ fans: No interstellar travel for five more centuries

In Ridley Scott’s new movie “Prometheus,” a group of humans travel to another star on a trillion-dollar spaceship. The year is 2093. And that got me wondering: Could humans really travel to another solar system that soon?

When do we get one? (AP)

Here’s Millis’s reasoning: Imagine we merely wanted to launch a small, 11-ton probe that took 75 years to get to our closest star, Alpha Centauri. That’s only about four light-years away. A fairly modest goal. Regardless of what type of propulsion technology is used, that probe would need a jaw-dropping amount of power just to accelerate out to Alpha Centauri and then decelerate once it gets there. (This is based on the kinetic energy of the probe — by Millis’s calculations it would take, at absolute minimum, 8.1 x 10^16 Watts of power.)

And humans don’t exactly have that energy just lying around. For the past three decades, the total energy produced by the world has grown at a modest pace — around 1.9 percent per year. And humans have devoted just a tiny fraction of that to spaceflight. Unless either of those trends changes radically, Millis calculates, we won’t have the energy needed to launch an Alpha Centauri probe until sometime around the year 2463, at the earliest.

The good news, Millis notes, is that we could probably have a small colony ship that contained a bunch of humans ready even sooner, by the year 2200 or so. This ship couldn’t necessarily travel to other stars — it wouldn’t be nearly as fast as the Alpha Centauri probe — but it could pack about 500 people in, with supplies. This might be a good backup plan in case we end up trashing the Earth beyond repair and need to ensure the survival of the species.

Below is a graph showing how soon different future spaceships might arrive depending on how fast the world’s energy supply grows. If some genius invents cold fusion, then maybe the energy supply will grow more rapidly and we’ll be able to squeeze out an interstellar probe by 2250 or so. (On the other hand, if we get all this energy by burning more and more fossil fuels and cooking the planet, this whole discussion might be moot.)

Millis, who’s now at the Tau Zero Foundation, also raises an interesting paradox. No matter when we launch the first interstellar probe, it’ll take a long time to reach its destination. Which means it’s quite plausible that we’ll later invent a newer, faster interstellar probe that gets to the star even sooner, with more modern equipment. Which raises the question of why we even bothered to launch that first probe.

Anyway, there are more numbers in Millis’s paper (pdf), which is available on Arxiv. Nor is this paper the last word on the subject. But bottom line: Any sci-fi movie that suggests we’ll go explore other solar systems by the end of the 21st century is probably way too optimistic!


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