More and more, the future of humanity seems to lie away from planet Earth in the long run. No matter what we do, the Earth will eventually become unfriendly to life – even without us hurrying it along at such an incredible pace with pollution and a general disregard for the environment.
Of course, we’re talking millions, if not billions, of years before things become completely untenable. But there are plenty of reasons to go searching for a new home out among the stars that don’t give us such a generous timeline.
For one thing, having all of humanity on one planet is the very definition of having all your eggs in one basket. Well, apart from literally having all your eggs in one basket, I guess. One little global disaster and we’ll be as dead as the dinosaurs. While such events are very, very rare, it’s almost inevitable that a huge chunk of rock and iron will eventually hit us head-on rather than just passing us by.
That’s just one doomsday scenario for humans, but we can easily be taken out by a virus or by pollinators like honey bees dying off.
Dividing the human population between different worlds that don’t share the same local fate is one way to help us survive. We’re the only intelligent species we know of so far in the universe, which means we’re pretty valuable, as far as we know. So, giving space colonization a try is worth it in the long run.
A planet like Earth is a rare find. In fact, Earth is the only planet we know of that has life on it. That’s not just compared to the other planets in our own solar system either. Thanks to better technology, we are seeing further and further into the universe – well enough to know things about planets outside our own solar system that give us clues as to their nature.
Some of these exoplanets are very promising in terms of their ability to sustain life. We can’t know with 100% certainty, but some exoplanets seem to be the right size and have atmospheres that could be an indication of life. One of these Earth-like exoplanets could one day be a new home for a colony of human beings. If we can ever get there.
It’s Too Far Out, Man
The problem is that these exoplanets are very, very far away. For example, Gliese 581c was the first exoplanet discovered that promised potential habitability. Further study threw cold water on that idea, but even if Gliese 581c was habitable, it’s 20.37 light years away.
In case you don’t know what a light year is, it’s a measure of distance. It’s how far a particle of light will travel in a vacuum. So 20.37 light years is a staggering 192 trillion kilometers or (for Americans) 119 trillion miles. So even if your mode of transport were moving at the speed of light, it would still take 20 years to reach Gliese 581c. It would also have all sorts of crazy effects on the passage of time. For the people on Earth, the lightspeed ship would take 20 years to reach Gliese 581c and then the transmission would take another 20 years to get here. For the people on the ship in transit, it would feel much less. The closer to the speed of light you get, the slower time passes for them, relative from our point of view on the Earth.
Universal Speed Limits
The problem is that it seems nothing in the universe can accelerate to a speed beyond that of light. Also, the closer you get to that speed, the more energy you need in order to go a little faster. So it’s not even likely that we will have ships, in all practicality, that can be accelerated up to light speed.
Traveling faster than light, at least in the conventional sense, is impossible as far as scientists can tell. Yet science-fiction stories are filled with ships that have seemingly magical engines that can drive them past the speed of light. The fact is that writers had to invent such engines for their stories or they wouldn’t have any stories to tell. Still, having relatively (no pun intended) fast space travel has obvious benefits. So serious scientists have been thinking about ways of moving through space; methods more advanced than huge rockets that have to carry tons of fuel.
The rocket has served us very well. It’s taken us to the moon and back and sent many a probe into the far reaches of the solar system. The problem is that rockets are pretty inefficient. They need tons of propellant, which has to be brought into orbit with yet more rocket fuel at an immense cost. It also limits how far you can go.
This makes NASA’s Ion drive pretty darn cool. Ion thrusters still need propellant, but they need very little of it. The NEXT drive from NASA uses Xenon particles as propellant. Of course, having so little reaction mass means you can’t go very far at all. But if you don’t have mass, then you need speed. These drives use electricity generated from solar panels to accelerate the xenon particles to incredible speeds. This produces enough thrust to accelerate the craft. The acceleration is painfully slow, but you can just keep accelerating until you reach the speed you want. The NEXT thruster, in particular, can generate 6.9 kW of thruster power. It can do it for years and without any real degradation of the engine.
In practice, an Ion thruster will cut the travel time from Earth to Mars from a tough 6 months to about five weeks. That’s important for a lot of reasons. It means you don’t have to carry as much food and other life support, and, important for their health, your astronauts spend much less time in microgravity and radiation. Currently, the theoretical speed limit for an Ion drive is 321,000 kilometers per hour, or about 200,000 miles per hour. That’s fast, but still way off the more or less billion kilometers per hour at which light travels.
If rockets are not crazy enough for you, why not travel by way of controlled nuclear explosion? That’s exactly the idea behind the nuclear pulse propulsion engine. It’s a spaceship engine that only exists on paper so far, but it’s an interesting idea.
Back in the 50s and 60s General Atomics started design work on such an engine. This was done in part to try and solve the issue of mass and weight for spacecraft made with materials from that era. We get away with a lot more these days simply because modern materials are lighter and stronger, which means we don’t have to put so much mass in orbit. Inside this engine a small nuclear explosion would go off, thrusting against a steel pusher plate. The math behind nuclear pulse engines is fine and several tests confirmed the basics. The project was stopped mainly because of nuclear bans.
It remains to be seen if the idea of a nuclear spaceship engine gets resurrected, but think about this: theoretically, a nuclear pulse engine cuts down the travel time to Saturn’s moons from nine years to seven months.
Antimatter drives are another sci-fi concept that’s being seriously considered by the big space agencies. Antimatter is matter that consists of antiparticles. When matter and antimatter come into contact, both will cancel each other out, or “annihilate”, releasing a tremendous amount of energy.
One antimatter-drive solution is a variation of the nuclear pulse engine we just discussed. It provides a way to initiate nuclear fission or fusion using much less space and nuclear material that would otherwise not be useful. You can also use antimatter fuel to heat another propellant or to generate electricity to power your Ion or other electric drives.
The problem is that making antimatter is super hard and storing it is even harder. The best efforts so far have succeeded in trapping antimatter for about fifteen minutes.
So don’t hold your breath that antimatter drives will be powering our space exploration in the near future.
I’m Sailing Away
The last sublight drive I want to talk about is the solar sail. It may seem a little weird, but light can exert physical force. It’s so little that you could never feel it yourself. But if you have a huge, thin, and reflective material, you can use solar radiation to push your spacecraft in a way similar to how wind is used to propel boats.
It’s not a perfect analogy. Newton’s law comes into play when a light particle reflects off the sail. There’s an equal and opposite reaction and the tiny mass of the photon makes an almost imperceptible change in the momentum of the craft. Shoot enough photons at that sucker, and soon you’ll be cruising along at quite a clip. One issue is that the farther you get from the sun, the fewer photons make it to your sail. One idea is to use massive lasers from the moon or even Earth to push spacecraft around the solar system.
All of the other sub-light drives I mention above have one thing in common: they use reaction mass. In other words, they comply with Newton’s third law that states for every action there is an equal and opposite reaction. Without reaction mass, you can’t move anywhere. There have, however, been a few claims of “reactionless” drives over the years, which all inevitably turn out to be bunk.
Obviously, a reactionless drive would be amazing. You’d need no reaction mass on your ship; just a power source such as the sun or a nuclear power generator. As long as you have electricity, you can move.
While claims for reactionless drives are usually destroyed under testing pretty quickly, one such drive has demonstrated a stubborn tendency to resist debunking under experimental conditions. The RF resonant cavity thruster is in dire need of a cooler name, but if it actually works it will not just revolutionize space travel, it will also make us rethink physics.
So now we get to the really sticky stuff: faster than light travel. This is the holy grail and currently does not exist as a technology. It’s also perfectly possible that it will never exist, simply because traveling at faster than light is a flat-out impossibility. However, physicists have had some tantalizing ideas about how the laws of physics could be bent into shape in order to cheat when it comes to that speed limit. So how might we one day overcome the big stop sign in the universe?
You have to give Star Trek credit for this one. The ships on that show have “warp drives” that use a matter-antimatter hreaction to generate exotic matter and create a “warp bubble” around the ship.This expands and contracts space in front of and behind the ship so that the bubble of space gets carried along the wavefront like a surfer at speeds that appear faster than light to us on the outside.
Inside the warp bubble the ship isn’t really moving at all, which doesn’t break the lightspeed limit.
It may all sound like sci-fi gobbledygook and when Gene Roddenberry came up with the idea for his show it may well have been, but thanks to the work of Einstein and those that came after him it isn’t all that far fetched.
Miguel Alcubierre came up with the idea for a real-life warp drive in 1994. He did the math and on paper it should work.
The big problem with this theory was that the required energy to generate a warp bubble was insane. It was more than we could ever hope to make, but further work by harold Sonny White has shown that the warp bubble doesn’t even have to be a bubble. You could get away with a warp ring, which would uses orders of magnitude less energy.
Yes the needs are still monumental, but not outside of the realms of possibility.
Another theoretical possibility is the use of “wormholes” which are hypothetical, but don’t violate anything within the special theory of relativity.
A wormhole tunnels through spacetime to connect two points regardless of their distance. We’ve never observed a wormhole in the real world and really have no idea how to make one, but theoretically you could use a wormhole to jump between any two points in the universe without the speed of light being exceeded locally.
Lightspeed? Maybe Sublight
The bad news is that right now there’s no realistic pathway to faster-than-light travel or even lightspeed travel. So we may have to resort to sublight travel but use technologies such as mind uploading, life extension or suspended animation to make it feasible.
For example, you may send a tiny probe at or near lightspeed to another world. Onboard could be some nanobots and the mind of a few humans. When the probe lands on a distant world the nanobots start to build infrastructure from the local raw materials. This includes making suitable artificial bodies for the stored minds. In this way humans may colonise the universe in a more effective way.
Right now though, we can only look longingly at the countless worlds out there and hope for a day we may visit them.